Advanced Search

Journal Navigation

Journal Home

Subscriptions

Archive

Contact Us

Table of Contents

Click here for more information

Click here to sign up for SAGE Journal Email Alerts today!

Sign In to gain access to subscriptions and/or personal tools.
Journal of Dental Research
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Free Full Text (Free PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to Saved Citations
Right arrow Download to citation manager
Right arrowRequest Permissions
Right arrow Request Reprints
Right arrow Add to My Marked Citations
Citing Articles
Right arrow Citing Articles via Google Scholar
Right arrow Citing Articles via Scopus
Google Scholar
Right arrow Articles by ten Cate, J.M.
Right arrow Articles by de Groot, P.W.J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by ten Cate, J.M.
Right arrow Articles by de Groot, P.W.J.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?

CRITICAL REVIEWS IN ORAL BIOLOGY & MEDICINE

Molecular and Cellular Mechanisms That Lead to Candida Biofilm Formation

J.M. ten Cate1,*, F.M. Klis2, T. Pereira-Cenci1,3, W. Crielaard1 and P.W.J. de Groot2

1 Department of Cariology Endodontology Pedodontology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Free University Amsterdam, Louwesweg 1, 1066 EA Amsterdam, the Netherlands;
2 Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, the Netherlands; and
3 Department of Prosthodontics and Periodontology, Faculty of Dentistry of Piracicaba, UNICAMP, Brazil

Correspondence: j.t.cate{at}acta.nl


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION AND SCOPE
 MORPHOLOGY AND EVOLUTIONARY...
 THE MOLECULAR ARCHITECTURE OF...
 A WIDE ARSENAL OF...
 SUBSTRATUM PROPERTIES
 Candida BIOFILMS AND Candida...
 PERSPECTIVES, RESEARCH...
 REFERENCES
 
Fungal infections in the oral cavity are mainly caused by C. albicans, but other Candida species are also frequently identified. They are increasing in prevalence, especially in denture-wearers and aging people, and may lead to invasive infections, which have a high mortality rate. Attachment to mucosal tissues and to abiotic surfaces and the formation of biofilms are crucial steps for Candida survival and proliferation in the oral cavity. Candida species possess a wide arsenal of glycoproteins located at the exterior side of the cell wall, many of which play a determining role in these steps. In addition, C. albicans secretes signaling molecules that inhibit the yeast-to-hypha transition and biofilm formation. In vivo, Candida species are members of mixed biofilms, and subject to various antagonistic and synergistic interactions, which are beginning to be explored. We believe that these new insights will allow for more efficacious treatments of fungal oral infections. For example, the use of signaling molecules that inhibit biofilm formation should be considered. In addition, cell-wall biosynthetic enzymes, wall cross-linking enzymes, and wall proteins, which include adhesins, proteins involved in biofilm formation, fungal-bacterial interactions, and competition for surface colonization sites, offer a wide range of potential targets for therapeutic intervention.

Key Words: biofilms • Candida • bacteria • antifungals • saliva • cell-wall proteins


   INTRODUCTION AND SCOPE
TOP
 ABSTRACT
 INTRODUCTION AND SCOPE
MORPHOLOGY AND EVOLUTIONARY...
 THE MOLECULAR ARCHITECTURE OF...
 A WIDE ARSENAL OF...
 SUBSTRATUM PROPERTIES
 Candida BIOFILMS AND Candida...
 PERSPECTIVES, RESEARCH...
 REFERENCES
 
Candida albicans and, to a lesser extent, other Candida spp. are commonly found in the oral cavities not only of adults, but also of children, with a reported prevalence between 15 and 75%. They are recovered from the dentition, tongue, cheeks, and palatal mucosa and from restorative materials and prostheses. Candida spp. are also found associated with root caries (Zaremba et al., 2006) and observed in or next to infected gingival crevices (Shen et al., 2002). In healthy, dentulous persons, Candida presence seldomly causes disease. The most prevalent pathology induced by Candida spp. is found in immunocompromised persons or in those with impaired salivary function. In denture-wearing individuals, Candida spp. often cause denture stomatitis, a mucosal infection in the tissue in contact with the prosthesis (Espinoza et al., 2003). Candida is found more often in denture-wearing than non-denture-wearing edentulous persons (Daniluk et al., 2006). Current research now encompasses a dozen Candida species.

Although Candida spp. were already identified in 1936 as a cause for denture-related infections (Cahn, 1936), considerable progress in understanding the etiology and pathogenesis of this disease has only recently been made. Undoubtedly, this is the result of the various molecular biological methodologies that have been developed and the availability of genomic data. Also, it is now acknowledged that Candida spp. colonize surfaces in a biofilm. In the mouth, Candida will typically reside in mixed biofilms, with bacterial-fungal interactions dictating overall properties and survival of the respective species (for review, see Mukherjee et al., 2005).

In contrast to most other Candida spp., C. albicans is able to switch between the yeast and the hyphal mode of growth, thus combining the better dispersal properties of the yeast form with the invasive properties of the hyphal form. This additional virulence factor contributes to the prevalence of C. albicans in fungal infections compared with other Candida spp. To complicate this picture further, it has been observed that the substratum to which fungi adhere may trigger a genetic response leading to this morphological shift. A genetically dictated cascade of events (hyphae formation, quorum sensing) is decisive for biofilm formation and/or penetration into underlying tissue (Nobile and Mitchell, 2006).

Biofilm formation is a survival mechanism to ensure residence in the mouth. In biofilms, the bacteria and fungi are typically encapsulated into a matrix of glycoproteins and polysaccharides produced by the microbial components, and they often reside in a (seemingly ‘dormant’) state of reduced metabolic activity. Biofilm ‘inhabitants,’ fungi and bacteria, are less sensitive or insensitive to antifungal treatments. Candida spp. adhere not only to denture surfaces, but also to other medical devices, such as voice prostheses (Holmes et al., 2006), blood and urinary catheters (Jain et al., 2007), and heart valves (Salamon et al., 2007). Therefore, the study of Candida adherence to surfaces has a much broader scope and relevance than for oral-dental issues. Candida present in the oral cavity serves as a reservoir for inoculation and infections elsewhere in the body. The fact that Candida spp. are present all through the body is reflected in prevalence data in feces (7–34%) (Jobst and Kraft, 2006). When Candida penetrates the epithelium and invades the host tissues, this may lead to bloodstream infections and systemic infections. These are difficult to treat with antifungals and therefore have a high reported mortality (40%) (LaFleur et al., 2006; Pfaller and Diekema, 2007). In total, this explains and justifies the increased attention to Candida spp. in oral ecology. In this review, we focus on surface reactions relevant to biofilm formation, in particular, on the cell-wall proteins of Candida species and on the interactions of bacteria and fungi in mixed biofilms.


   MORPHOLOGY AND EVOLUTIONARY RELATIONSHIPS OF Candida SPECIES
TOP
 ABSTRACT
 INTRODUCTION AND SCOPE
 MORPHOLOGY AND EVOLUTIONARY...
THE MOLECULAR ARCHITECTURE OF...
 A WIDE ARSENAL OF...
 SUBSTRATUM PROPERTIES
 Candida BIOFILMS AND Candida...
 PERSPECTIVES, RESEARCH...
 REFERENCES
 
Although C. albicans is still the main cause of candidiasis, other species—such as C. glabrata, C. dubliniensis, C. parapsilosis, C. krusei, and C. tropicalis—are becoming increasingly prevalent. This may be related to the (prophylactic) use of antimycotics such as azoles. In many epidemiological surveillance studies, C. glabrata is ranked as the second most prevalent species after C. albicans. Remarkably, C. glabrata is phylogenetically closer to common baker’s yeast (Saccharomyces cerevisiae) than to other Candida spp. (Dujon et al., 2004) (Fig. 1Go). C. glabrata’s yet-unexplained resistance to azole medication makes infections caused by C. glabrata difficult to treat. C. dubliniensis is particularly associated with oral candidiasis in HIV-infected individuals, presumably because C. dubliniensis tends to build up resistance against azoles much faster than does C. albicans, resulting in the replacement of C. albicans with C. dubliniensis (Martinez et al., 2002; L Li et al., 2007).


Figure 1
View larger version (8K):
[in this window]
[in a new window]

  		Figure 1. Neighbor-joining phylogenetic tree indicating the evolutionary relationships between sequenced Candida species and S. cerevisiae based on 18S rDNA sequences. 18S rDNA of the species was found with BLAST against databases containing the genomic DNA assemblies, with the S. cerevisiae RDN18-1 gene as the query. S. pombe was used as the outgroup. C. glabrata CBS138 and S. pombe (strain 971) 18S rDNA was retrieved from GenBank. The tree was calculated with ClustalX, with correction for multiple substitutions using the 18S rDNA alignment produced with MUSCLE (Edgar, 2004), and plotted with NJplot (Perrière and Gouy, 1996) with bootstrap values added (1000 bootstraps performed).

 
C. albicans is the species most frequently encountered in infected tissues, including oral mucosal layers. It is also the predominant species found during vaginal and invasive bloodstream infections. In contrast to most other Candida spp., C. albicans is a pleomorphic fungus exhibiting different modes of growth (Figs. 2Go, 3Go, 5Go) (Table 1Go). It can not only proliferate a unicellular budding yeast, but also, when triggered by specific environmental conditions—such as a growth temperature of 37°C, neutral or alkaline pHs, increased CO2 concentrations, or the presence of serum—it may undergo morphological switching, leading to elongated growth forms, termed ‘pseudohyphae’ and ‘hyphae.’ Collectively, these are named "filamentous forms" (Sudbery et al., 2004). Hyphae are characterized as unconstricted filaments with parallel-sided walls. In contrast, pseudohyphae seem to represent a growth form between those of yeast and hyphae, in which the cells remain attached to each other, but can vary in shape, from elongated ellipsoidal cells to forms that superficially closely resemble hyphae. The various growth forms are important for the establishment of Candida infections, with specific roles proposed in adhesion, biofilm formation, tissue penetration, and organ colonization (Fig. 2Go) (Kumamoto and Vinces, 2005). An overview of some important properties of the various Candida spp. is presented in Table 1Go.


Figure 2
View larger version (36K):
[in this window]
[in a new window]

  		Figure 2. Schematic model indicating multi-species biofilm formation and development of Candida infections.

 

Figure 3
View larger version (92K):
[in this window]
[in a new window]

  		Figure 3. The cell wall of Candida albicans. (A) Cryo-scanning electron microscopy of C. albicans yeast and hyphal cells (Tokunaga et al., 1986). Note the fibrillar nature of the outer protein layer. (B) Schematic representation of the cell wall of C. albicans, which consists of an inner skeletal layer composed of the stress-bearing polysaccharides β-1,3-glucan and chitin (black lines), which run parallel to the cell surface. The inner layer is kept together by extensive hydrogen bonding between individual β-1,3-glucan chains and by the β-1,3-glucan cross-linking protein Pir1 (X). This three-dimensional skeletal network acts as a scaffold for a dense outer layer of glycoproteins (grey lines) extending into the environment and linked through their C-terminus to a flexible β-1,6-glucan moiety (grey ovals), which in turn is linked to β-1,3-glucan. The outer layer covers the inner layer and helps the cell to avoid recognition of the β-1,3-glucan chains by the dectin-1 receptor of the innate immune system. The cell wall is flexible and highly extended under normal osmotic conditions. Consequently, fixed cells are smaller than live cells.

 

Figure 5
View larger version (89K):
[in this window]
[in a new window]

  		Figure 5. Confocal laser scanning micrographs of mixed Candida-bacterial biofilms. The pictures show the yeast and hyphal morphological forms of Candida albicans, whose transition is influenced by various factors such as the type of carbon source (sugar), and the presence of saliva and/or other fungi or bacteria. Panels A and B were taken from mixed C. albicans- S. mutans biofilms, either (A) close to the biofilm outer surface, showing merely C. albicans, or (B) in the biofilm close to the lining material, showing mainly S. mutans. Panels C and D are also examples of mixed biofilms of C. albicans-S. mutans, grown on hydroxyapatite, in the presence of (C) sucrose and (D) glucose, respectively, which illustrates differences in morphological forms depending on carbon nutrient source. Square dotted arrows show C. albicans in the yeast form; dashed arrows show C. albicans in the hyphal morphology; dashed and dotted arrows show S. mutans.

 

View this table:
[in this window]
[in a new window]

  		Table 1. Comparison of Properties of Different Pathogenic Candida Species and S. cerevisiae
 

   THE MOLECULAR ARCHITECTURE OF THE CELL WALL OF Candida albicans
TOP
 ABSTRACT
 INTRODUCTION AND SCOPE
 MORPHOLOGY AND EVOLUTIONARY...
 THE MOLECULAR ARCHITECTURE OF...
A WIDE ARSENAL OF...
 SUBSTRATUM PROPERTIES
 Candida BIOFILMS AND Candida...
 PERSPECTIVES, RESEARCH...
 REFERENCES
 
Adherence and aggregation of Candida with abiotic surfaces, bacteria, or other fungi depend on surface reactions. Therefore, it is important to study the cell-wall properties of Candida spp. The cell wall of C. albicans consists of 4 major components: (i) mannoproteins, which account for about 40% of the cell-wall biomass; (ii) β-1,3 -glucan, the major stress-bearing polysaccharide of the wall; (iii) β-1,6-glucan, a water-soluble component without a regular structure that interconnects mannoproteins to β-1,3-glucan and chitin chains; and (iv) a small amount of chitin (a linear stress-bearing polysaccharide consisting of β-1,4-linked N-acetylglucosamine residues). β-1,3-glucan forms a three-dimensional, hydrogen- bond-stabilized, network of fibrils that run parallel to the cell surface. Chitin bound to β-1,3-glucan further strengthens this network. The molecular architectures of the yeast and hyphal wall of C. albicans are similar. However, the composition of its cell wall, particularly its protein composition, is variable and strongly depends on environmental conditions (Nett et al., 2007; Sosinska et al., 2008; Walker et al., 2008; Yin et al., 2008). The cell wall of C. albicans is essentially bi-layered, with an internal skeletal layer that is surrounded by a coat of fibrillar proteins that emanate outward (Tokunaga et al., 1986; Kapteyn et al., 2000) (Fig. 3Go). Most of the cell-wall proteins (CWPs) are GPI-proteins (GPI, glycosylphosphatidylinositol). They generally consist of a cell-surface-exposed amino-terminal effector domain that is supported by a spacer domain; in addition, they have carboxy-terminal features, including a remnant of a GPI-anchor that causes covalent attachment to the cell-wall β-1,3-glucan network (Kapteyn et al., 2000; Klis et al., 2006). The synthesis of β-1,3-glucan is blocked by the new echinocandin class of drugs (anidulafungin, caspofungin, and micafungin). They are fungicidal and active against a wide spectrum of fungi (Cappelletty and Eiselstein-McKitrick, 2007).

Whereas GPI-CWPs are predominantly found at the outside of the cell wall, immunogold labeling has shown that the cell-wall protein CaPir1 (Protein with Internal Repeats) is uniformly distributed throughout the inner skeletal layer (Kapteyn et al., 2000). Pir1 possesses multiple tandem repeats through which it probably cross-links β-1,3-glucan chains, thus being vital for the mechanical strength of the skeletal wall layer (Martínez et al., 2004; Ecker et al., 2006). Because the cross-linking process between β-1,3-glucan chains takes place outside the plasma membrane, this particular reaction provides a rational and promising target for compounds designed to inhibit fungal growth and biofilm formation in the oral cavity. While the original work was done on C. albicans, all available evidence now indicates that the molecular architecture of the walls of Candida spp. is highly similar (Frieman and Cormack, 2003; Weig et al., 2004; De Groot et al., 2005). This would imply that any agent interfering with the cell-wall structure of C. albicans is likely to affect all Candida spp. and probably many other ascomycetous fungi as well.


   A WIDE ARSENAL OF CELL-WALL PROTEINS (CWP) DICTATES Candida albicans’ EXTERNAL REACTIONS
TOP
 ABSTRACT
 INTRODUCTION AND SCOPE
 MORPHOLOGY AND EVOLUTIONARY...
 THE MOLECULAR ARCHITECTURE OF...
 A WIDE ARSENAL OF...
SUBSTRATUM PROPERTIES
 Candida BIOFILMS AND Candida...
 PERSPECTIVES, RESEARCH...
 REFERENCES
 
Mass spectrometric analysis of the cell-wall proteome in combination with immunological analysis has shown that, at any time, there are about 20 or more different covalently linked CWPs in the cell wall of C. albicans, most of them GPI-CWPs. However, the protein composition of the wall can differ considerably, both quantitatively and qualitatively (De Groot et al., 2004; Sosinska et al., 2008). CWPs determine cell-surface properties such as hydrophobicity, immunogenicity, negative charge, and permeability toward large macromolecules (Yin et al., 2008). They also promote endocytosis by endothelial cells, iron acquisition, and coping with oxidative stress (Holmes et al., 2006; Phan et al., 2007; Hoyer et al., 2008; Yin et al., 2008). Other CWPs are involved in binding of saliva proteins, adhesion to epithelial cells and to teeth and dental prostheses, and in biofilm formation. They are also known to interact with bacterial surface proteins, resulting in co-aggregation and the formation of mixed biofilms (Klotz et al., 2007) (Table 2Go). Conceivably, some CWPs are involved in the production of the extracellular matrix that encases biofilm cells. The presence of such a wide arsenal of glycoproteins in the external wall layer offers various opportunities for the development of new drugs counteracting biofilm formation and infection in the oral cavity (see ‘Perspectives,’ below).


View this table:
[in this window]
[in a new window]

  		Table 2. Role of Candida Cell-surface Glycoproteins in Adhesion and Biofilm Formation, and in Cell-wall Cross-linking Steps
 
Adhesins represent a special class of GPI-CWPs that have important functions in fungal colonization of the oral cavity. Two prominent classes of adhesins can be distinguished: first, the immunoglobulin (Ig)-like adhesins such as the Als (Agglutinin-like sequence) family, found in all Candida spp. except C. glabrata (Hoyer et al., 2001); and second, the Epa (Epithelial adhesion) family of lectin-like adhesins, found only in C. glabrata (Kaur et al., 2005). Some other adhesins, such as CaHwp1 and CaEap1, also play an important role in fungal colonization.

The Als and Epa Families of Adhesins
All Als adhesins in C. albicans have a similar modular structure with an amino-terminal, Ig-like domain, a Thr-rich middle part composed of tandem repeats, and a heavily glycosylated serine (Ser)- and threonine (Thr)-rich spacer domain (Dranginis et al., 2007; Hoyer et al., 2008). The lectin-like Epa proteins in C. glabrata, which are involved in adhesion to host cells, have a comparable modular structure. They also have an amino- terminal effector region, including the recently discovered PA14 domain that is responsible for sugar specificity (Zupancic et al., 2008), followed by a Ser- and Thr-rich middle part consisting of a variable number of tandem repeats, and a Ser- and Thr-rich tail without a periodic structure. The number of tandem repeats in adhesion proteins tends to vary considerably among different strains, resulting in allelic variability.

Two Unique C. albicans Adhesins
Another important adhesin is CaEap1, which mediates adhesion to hydrophobic surfaces, such as polystyrene, and, most likely, to polymer materials used in medical devices (Radford et al., 1999; Li and Palecek, 2003). Eap1 is a typical GPI-protein with a modular structure comparable with that of the Als and Epa proteins; however, it seems unique to C. albicans, since no obvious ortholog can be found in other Candida species (Li and Palecek, 2008). Eap1 has also been shown to mediate attachment to kidney epithelial cells and is required for C. albicans biofilm formation (F Li et al., 2007).

The GPI-modified CWP Hwp1 (Hyphal wall protein 1) is strongly, but not exclusively, expressed in hyphal walls of C. albicans and has been found to be required for normal C. albicans biofilm formation (Nobile et al., 2006). Hwp1 offers a unique insight into how C. albicans can survive in the oral cavity and elsewhere in the human body, notwithstanding the fact that it is subject to considerable shearing forces and to continuous flushing of the oral cavity by saliva. The effector domain of Hwp1 is enriched in glutamine residues, but very poor in serine and threonine residues, whereas the reverse holds for the subsequent domain (Fig. 4Go). It has been shown that the amino-terminal effector region, which extends into the environment, is recognized as a suitable substrate for transglutaminase activity associated with the cell surface of oral epithelial cells (Staab et al., 2004). As a result, isopeptide cross-linkages are formed between Hwp1 and extracellular matrix proteins of epithelial cells. This example of molecular mimicry is thus responsible for irreversible binding of Candida cells to the epithelial layer. Hwp1 is found in C. albicans, and a similar (orthologous) protein has been identified in C. dubliniensis, but it seems to be absent from other Candida species. It seems likely that more adhesins will be discovered in the future. The occurrence of so many and such diverse wall-bound adhesins clearly illustrates how well Candida is adapted to living in warm-blooded animals.


Figure 4
View larger version (16K):
[in this window]
[in a new window]

  		Figure 4. The cell-wall protein Hwp1 of Candida albicans: a case of clever molecular mimicry. (A) Schematic representation of CaHwp1 shows that the predicted polypeptide chain consists of an N-terminal signal peptide, which is required for entry into the endoplasmic reticulum. (B) The signal peptide is directly followed by a glutamine (Q)-rich domain. This domain is recognized as a valid substrate by an epithelial cell-associated transglutaminase, which then covalently links C. albicans cells to oral epithelial cells (Staab et al., 2004). (C) The N-terminal effector domain is followed by a region that is rich in the hydroxyamino acids serine (S) and threonine (T) and therefore potentially highly glycosylated with short O-linked side-chains. This region acts as a spacer domain. The polypeptide chain terminates in a GPI anchor addition signal peptide, which, in the endoplasmic region, is replaced by a GPI anchor. The mature protein is linked through a truncated form of its GPI anchor to the skeletal framework (Kapteyn et al., 2000).

 

   SUBSTRATUM PROPERTIES
TOP
 ABSTRACT
 INTRODUCTION AND SCOPE
 MORPHOLOGY AND EVOLUTIONARY...
 THE MOLECULAR ARCHITECTURE OF...
 A WIDE ARSENAL OF...
 SUBSTRATUM PROPERTIES
Candida BIOFILMS AND Candida...
 PERSPECTIVES, RESEARCH...
 REFERENCES
 
The oral cavity consists of a multitude of substrata to which micro-organisms and fungi may adhere. Early in life, there is just the mucosal tissue, and then the dentition emerges. With increasing age, new substrata are placed in the mouth—various restorative materials, gold, porcelain crowns, acrylic dentures, silicon denture liners, and titanium implants—while the mucosal layers undergo an aging process.

Most of the early work on bacterial and fungal adherence was done by characterizing the substratum by its surface free energy, hydrophobicity, and surface roughness. All these parameters are predictive for Candida adherence. Materials with the roughest surface usually exhibit higher adherence (Nevzatoglu et al., 2007), because such surfaces provide an increased chance of microbial retention and protection from shear forces. C. albicans nested in rougher surfaces was also found to be less sensitive to antifungal treatments (Tsang et al., 2007). Since bacteria and fungi have different dimensions, a given roughness may specifically accommodate micro-organisms that fit the provided irregularities (Whitehead et al., 2005). While being necessary to disclose adherence mechanisms, a general shortcoming of experimental studies on well-characterized substrata is that there are often hidden confounding factors—such as, materials being found to release compounds that have antimicrobial properties, as for monomers in acrylic resins, or acquiring scratches during wear that prove to be favorable nesting sites.

Denture liners are of particular relevance for Candida-related stomatitis. Liners are used to overcome sharp ridges of dentures and are often made of silicon material. They typically have a higher roughness than the acrylic denture and show porosities when inspected under the scanning electron microscope (Nevzatoglu et al., 2007; Pereira-Cenci et al., 2008). Aging of acrylic and liner surfaces results in increased roughness, and therefore increased attachment (Nikawa et al., 2001). Liners are sometimes provided with antifungal agents, which leach out. Various observations have indicated that this may add to the aging process. Porous liners also take up endotoxins produced by the denture plaque, providing a slow release base for infection-inducing molecules. A study of biofilm formation on lining materials showed that inhibition of Candida growth, due to the released antifungal, was limited to a thin layer close to the surface (Fig. 5Go) (Pereira-Cenci et al., 2008). With our current knowledge on mixed bacterial fungal biofilms, new research initiatives to develop antifungal liners should lead to better materials.

Candida spp. are isolated from various sites in the mouth, including the oral soft tissues. In an unhygienic oral environment, biomaterials may act as a reservoir of infection for respiratory and systemic opportunistic pathogens (Sumi et al., 2002, 2003; Nikawa et al., 2006), presenting a niche for the development of biofilms containing antibiotic-resistant micro-organisms (Smith et al., 2003), and ultimately resulting in plaque-associated oral diseases. Exogenous acquisition of C. albicans via contaminated biomaterials may also lead to systemic infections.

Candida hyphae are usually found in the keratinized layer and rarely penetrate epithelial cells. However, this may happen in extremely immune-compromised individuals (Neville et al., 2002). C. albicans may also invade the oral mucosa and persist within the epithelium, causing superficial lesions (Fidel, 2006). Additionally, type IV collagen binds to C. albicans and is a candidate for mediating the adherence of this species to the extracellular matrix and basement membranes of endothelial and epithelial cells of the host (Klotz, 1990). This is considered a crucial step in the development of candidiasis (Alonso et al., 2001). Whereas the high turnover rate of the epithelial tissue and the innate defense mechanisms may hinder deep penetration, C. albicans possesses offensive strategies, in particular morphological switching, which may result in oropharyngeal and systemic infections. Currently, attempts are under way to identify genes involved in fungal infections in oral epithelial tissues (Zakikhany et al., 2007; Jayatilake et al., 2008).

Studies dealing with bacterial and fungal initial adherence have traditionally worked with ‘clean’ systems, involving merely micro-organisms and substrata. Obviously, the oral cavity is considerably more complex, with saliva present as fluid and deposited as pellicle. The substratum dictates the composition of the pellicle, and, more importantly, the pellicle masks many of the properties of the underlying substratum (Gocke et al., 2002). Saliva immersion decreases the surface roughness and surface free energy of acrylic resins, and this might explain the general decrease of Candida species in those in vitro studies where specimens were coated with saliva (Sipahi et al., 2001). However, it has also been reported that denture pellicle lacks salivary statherins and histatin, important salivary defense molecules (Edgerton and Levine, 1992).

While C. albicans was for a long time the only fungus studied in adherence studies, recently other Candida spp. have been included. These findings have added considerably to the complexity of the adherence model, because salivary effects also differed among species (Moura et al., 2006; Pereira-Cenci et al., 2007). Examples of the current controversy are multiple: C. dubliniensis adherence has been shown to decrease (Elguezabal et al., 2004), to increase (Ramage et al., 2001), or to be unaffected (Moura et al., 2006) in the presence of saliva, while C. glabrata counts were not influenced by saliva in one study (Moura et al., 2006), but decreased in another report (Pereira-Cenci et al., 2007). This also highlights the importance of studying various Candida spp. in their adherence properties and the risk of extrapolating findings obtained with a particular species to other Candida spp.


   Candida BIOFILMS AND Candida-BACTERIAL INTERACTIONS
TOP
 ABSTRACT
 INTRODUCTION AND SCOPE
 MORPHOLOGY AND EVOLUTIONARY...
 THE MOLECULAR ARCHITECTURE OF...
 A WIDE ARSENAL OF...
 SUBSTRATUM PROPERTIES
 Candida BIOFILMS AND Candida...
PERSPECTIVES, RESEARCH...
 REFERENCES
 
Candida biofilm cells are generally much more resistant to anti-fungal agents than are their planktonic counterparts. Despite its obvious clinical relevance, the molecular mechanisms underlying this phenomenon are not fully understood (Mukherjee et al., 2005; Ramage et al. 2005; d’Enfert, 2006). Apparently, biofilm resistance is a complex multifactorial phenomenon. Multidrug efflux pumps (ABC transporters) have been suggested to contribute to the increased resistance of cells in the early stages of biofilm formation (Ramage et al., 2002a; Mukherjee et al., 2003). Inhibition of diffusion of antifungals by the extracellular biofilm matrix and the presence of ‘antifungal persister’ cells may also be relevant (Al-Fattani and Douglas 2006; LaFleur et al., 2006; Al-Dhaheri and Douglas, 2008). Recently, a possible role for β-1,3-glucan in antifungal resistance was postulated after it was shown that cell walls from biofilm cells could bind (and hence neutralize) antifungals better than planktonic variants, and that exogenous β-1,3-glucan reduced the activity of fluconazole against planktonic C. albicans cells (Nett et al., 2007). Another contributing factor might be the role of cross-resistance. It has been frequently observed that mild forms of stress may prepare cells for subsequent (increased) stress conditions of a different nature (Arguelles, 1997; Kara et al., 2006). Biofilm cells live in a nutrient-poor, hypoxic environment, and it is conceivable that the suboptimal growth conditions in bio-films may result in increased tolerance to various forms of stress, including antimycotics-related cellular stress.

Since C. albicans and other Candida spp. share their (oral) environment with many bacterial species, the question arises whether bacterial-fungal interactions can affect biofilm formation, morphology, and virulence of Candida. This is indeed the case. C. albicans can bind to the oral microbes Streptococcus gordonii, Streptococcus oralis, and Streptococcus sanguinis, resulting in co-aggregation. This interaction is mediated by streptococcal cell-wall polysaccharides and cell-surface proteins and by as-yet-unknown Candida adhesins and is promoted by specific salivary proteins (Holmes et al., 1995, 1996; O’Sullivan et al., 2000). Not only direct physical cell-cell interactions can affect biofilm formation and virulence, but also indirect interactions mediated by secreted metabolic byproducts and by extracellular signaling molecules, such as ‘quorum sensing’ molecules (Wargo and Hogan, 2006).

Interactions between and among different host microbes in the oral cavity may have inhibitory effects on surface colonization and biofilm formation. For example, competition between different Candida species (C. albicans and Candida krusei) and between Candida and bacteria has been reported, with an additional modulating effect by saliva (Thein et al., 2007). A negative correlation between Porphyromonas gingivalis and C. albicans biomass in a biofilm gave rise to speculation on a possible inhibition of Candida colonization exerted by this periodontal pathogen in the gingival crevicular area (Thein et al., 2006). It was further shown that morphological transitions, and thereby virulence, can be influenced by the presence of oral bacteria in a Candida biofilm (Fig. 5Go) (Thein et al., 2006; Pereira-Cenci et al., 2008).

The role of the quorum-sensing molecules secreted by C. albicans has been studied in considerable detail. C. albicans uses at least two quorum-sensing molecules, tyrosol and farnesol. Under conditions permissive for germ-tube formation, tyrosol stimulates hyphal formation in C. albicans, whereas farnesol inhibits the transition from yeast to hyphal growth (Hornby et al., 2001; Chen et al., 2004). Recently, it was found that C. albicans also secretes dodecanol, which also inhibits the yeast-to-hypha transition (Martins et al., 2007). Importantly, culture supernatants from mature C. albicans biofilms inhibit filamentous growth by planktonic C. albicans cells, which may indicate that farnesol and/or dodecanol is produced in situ in biofilms (Ramage et al., 2002b).

Further, farnesol has been shown to interact with the cell membranes of several bacterial species, including those that are present in multispecies oral biofilms. As a result, bacterial growth, metabolism, and polysaccharide formation are affected (Koo et al., 2003). Studies on the effects of farnesol on Staphylococcus aureus (biofilms) substantiated the effect on bacterial cell membranes, but, more importantly, showed sensitization of S. aureus (and Escherichia coli) to various antimicrobials upon pre-exposure to farnesol (Brehm-Stecher and Johnson, 2003; Inoue et al., 2004). The fact that farnesol inhibits biofilm formation by staphylococci (Jabra-Rizk et al., 2006) indicates that it has great potential in the control of mixed Candida-bacteria biofilms.

Candida signals affect bacteria, but likewise bacterial quorum-sensing molecules can have an effect on C. albicans. The bacterial quorum-sensing signals 3-oxo-C12 homoserine lactone and cis-11-methyl-2-dodecanoic acid both modulate filamentation, and thereby virulence, in C. albicans (Hogan et al., 2004; Wang et al., 2004). For example, the signaling molecule homoserine lactone plays a role in the medically important interactions between C. albicans and Pseudomonas aeruginosa, which separately or together form biofilms on medical devices, and increase each other’s resistance toward antimicrobials (see Hogan and Kolter, 2002; Pierce, 2005; Wargo and Hogan, 2006). An example of an even more complex cross-signaling that may occur in a mixed biofilm is the observation that farnesol reduces the production of the (Pseudomonas) signaling molecule quinolone in cultures of P. aeruginosa (Cugini et al., 2007). The quinolone signal in P. aeruginosa regulates virulence factors such as the synthesis of pyocyanin, a redox-active phenazine compound that inhibits growth of C. albicans (Kerr et al., 1999). This complex chemical interaction may promote C. albicans survival.


   PERSPECTIVES, RESEARCH OPPORTUNITIES/NEEDS, CONCLUDING REMARKS
TOP
 ABSTRACT
 INTRODUCTION AND SCOPE
 MORPHOLOGY AND EVOLUTIONARY...
 THE MOLECULAR ARCHITECTURE OF...
 A WIDE ARSENAL OF...
 SUBSTRATUM PROPERTIES
 Candida BIOFILMS AND Candida...
 PERSPECTIVES, RESEARCH...
REFERENCES
 
In attempts to design an experimental model to mimic the oral conditions, it becomes evident how complex such a system should be to account for all the parameters involved. Moreover, many of these parameters have hardly been studied in their effects on fungal growth in an oral biofilm: flow dynamics, (an) aerobicity, and nutrient availability influence on the matrix density and thickness of biofilms (Al-Fattani and Douglas, 2006; Thein et al., 2007), which in turn determines its erosion and hence dissemination of fungi to other sites in the body. Most studies on fungal adherence have been carried out in simple, clean, presumed ‘one-parameter’ experiments with single type strains. It would seem logical to include at least saliva in such studies, as is now often done. However, saliva in itself is a source of variation, since its composition depends on the salivary gland, time of the day, and general health of the donor. In older persons, the use of multiple medications typically affects saliva production, both directly and by affecting the person’s immune system. Therefore, it is important to include well-characterized saliva in model studies, since the mentioned parameters are established risk factors for Candida-induced pathology.

The available literature (in particular the many controversial findings) convincingly shows that adherence of Candida spp. to denture materials should be studied in more complex or multiple models, with findings being confirmed in vivo, for meaningful and relevant conclusions to be reached. To this end, a model was developed where replaceable acrylic disks were placed in cavities in dentures and recovered after various time periods. Duration, acrylic type, and patient variables could then be controlled (Avon et al., 2007).

Given the above description of fungal life and survival in biofilms, the question may be raised, how can (fungal) biofilm formation be prevented? One approach is the use of signaling molecules secreted by C. albicans, such as farnesol and dodecanol, which inhibit the switch from yeast to hyphal cells and biofilm formation (Martins et al., 2007). In addition, several bacterial species living in mixed biofilms are known to inhibit the growth of Candida spp., or to inhibit the switch from yeast to hyphal growth, thus impeding biofilm formation. Identification of the responsible compounds could provide clues for more effective antifungal treatments.

Alternatively, the extracellular cross-linking of β-glucans by Pir1 and other cell-wall cross-linking steps represent attractive targets to prevent biofilm formation and infection in the oral cavity. Extracellular cell-wall construction steps have the advantage (as targets for treatment) that potential inhibitory compounds do not have to pass the plasma membrane, and thus do not have to be hydrophobic. Combination strategies are also worth considering. For example, a β-1,6-glucan oligosaccharide in combination with a membrane-active peptide synergistically inhibits the growth of yeasts (Bom et al., 2001). Conceivably, a derivative of histatin 5 (a histidine-rich, salivary antimicrobial peptide) could be used together with cell-wall inhibitors (Zhu et al., 2006). Other successful combinatorial approaches are based on the use of calcineurin inhibitors, such as the immuno-suppressive drugs FK506 and cyclosporine, in combination with fluconazole, resulting in strong inhibition of Candida albicans biofilm formation and even the killing of C. albicans (Uppuluri et al., 2008). Importantly, genomic libraries of tagged deletion strains allow for the systematic identification of successful drug combinations (Zakrzewska et al., 2007). Another promising development is the design of short antifungal β-peptides. These are composed of synthetic, β-substituted amino acids, which are resistant to proteolytic degradation. In addition, they kill C. albicans cells at concentrations that do not cause lysis of red blood cells and are active under physiological ionic conditions which tend to abrogate the activity of histatins (Karlsson et al., 2006).

Raising antibodies directed against the effector domains of specific CWPs such as CaAls1 and CaAls3, functionally the two most important members of the Als family in C. albicans, or against CaHwp1, or CaEap1, may also be considered. Vaccination with the recombinant effector domains of CaAls1 and CaAls3 has already been shown to protect mice against disseminated and mucosal candidiasis (Spellberg et al., 2006). Furthermore, the CWPs known to be required for biofilm formation can be targeted in this way. Ideally, a multivalent vaccine should be developed that inactivates the most important CWPs involved in biofilm formation (Yin et al., 2008).

In summary, research in recent years has resulted in significant advances in our knowledge of the surface properties of Candida spp. and of (mixed) biofilm formation which, when considered collectively, should lead to progress in the prevention and treatment of Candida-associated oral diseases.


   ACKNOWLEDGMENTS
 
We thank B. Brandt (Free University Amsterdam) for his help with the phylogenetic tree and the protein composition plots.

Received for publication April 30, 2008. Revision received July 10, 2008. Accepted for publication July 23, 2008.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION AND SCOPE
 MORPHOLOGY AND EVOLUTIONARY...
 THE MOLECULAR ARCHITECTURE OF...
 A WIDE ARSENAL OF...
 SUBSTRATUM PROPERTIES
 Candida BIOFILMS AND Candida...
 PERSPECTIVES, RESEARCH...
 REFERENCES
 

  • Al-Dhaheri RS, Douglas LJ (2008). Absence of amphotericin B-tolerant persister cells in biofilms of some Candida species. Antimicrob Agents Chemother 52:1884–1887.[Abstract/Free Full Text]
  • Al-Fattani MA, Douglas LJ (2006). Biofilm matrix of Candida albicans and Candida tropicalis: chemical composition and role in drug resistance. J Med Microbiol 55:999–1008.[Abstract/Free Full Text]
  • Alonso R, Llopis I, Flores C, Murgui A, Timoneda J (2001). Different adhesins for type IV collagen on Candida albicans: identification of a lectin-like adhesin recognizing the 7S(IV) domain. Microbiology 147 (Pt 7):1971–1981.[Abstract/Free Full Text]
  • Arguelles JC (1997). Thermotolerance and trehalose accumulation induced by heat shock in yeast cells of Candida albicans. FEMS Microbiol Lett 146:65–71.[Medline] [Order article via Infotrieve]
  • Avon SL, Goulet JP, Deslauriers N (2007). Removable acrylic resin disk as a sampling system for the study of denture biofilms in vivo. J Prosthet Dent 97:32–38.[CrossRef][Medline] [Order article via Infotrieve]
  • Bom IJ, Klis FM, De Nobel H, Brul S (2001). A new strategy for inhibition of the spoilage yeasts Saccharomyces cerevisiae and Zygosaccharomyces bailii based on combination of a membrane-active peptide with an oligosaccharide that leads to an impaired glycosylphosphatidylinositol (GPI)-dependent yeast wall protein layer. FEMS Yeast Res 1:187–194.[Medline] [Order article via Infotrieve]
  • Brehm-Stecher BF, Johnson EA (2003). Sensitization of Staphylococcus aureus and Escherichia coli to antibiotics by the sesquiterpenoids nerolidol, farnesol, bisabolol, and apritone. Antimicrob Agents Chemother 47:3357–3360.[Abstract/Free Full Text]
  • Cahn LR (1936). The denture sore mouth. Ann Dent 3:33–36.
  • Cappelletty D, Eiselstein-McKitrick K (2007). The echinocandins. Pharmacotherapy 27:369–388.[CrossRef][Medline] [Order article via Infotrieve]
  • Chen H, Fujita M, Feng Q, Clardy J, Fink GR (2004). Tyrosol is a quorum-sensing molecule in Candida albicans. Proc Natl Acad Sci USA 101:5048–5052.[Abstract/Free Full Text]
  • Cugini C, Calfee MW, Farrow JM 3rd, Morales DK, Pesci EC, Hogan DA (2007). Farnesol, a common sesquiterpene, inhibits PQS production in Pseudomonas aeruginosa. Mol Microbiol 65:896–906.[CrossRef][Medline] [Order article via Infotrieve]
  • d’ Enfert C (2006). Biofilms and their role in the resistance of pathogenic Candida to antifungal agents. Curr Drug Targets 7:465–470.[CrossRef][Medline] [Order article via Infotrieve]
  • Daniluk T, Tokajuk G, Stokowska W, Fiedoruk K, Sciepuk M, Zaremba ML, et al. (2006). Occurrence rate of oral Candida albicans in denture wearer patients. Adv Med Sci 51(Suppl 1):77–80.[Medline] [Order article via Infotrieve]
  • De Groot PWJ, De Boer AD, Cunningham J, Dekker HL, De Jong L, Hellingwerf KJ, et al. (2004). Proteomic analysis of Candida albicans cell walls reveals covalently bound carbohydrate-active enzymes and adhesins. Eukaryot Cell 3:955–965.[Abstract/Free Full Text]
  • De Groot PWJ, Ram AFJ, Klis FM (2005). Features and functions of covalently linked proteins in fungal cell walls. Fungal Genet Biol 42:657–675.[CrossRef][Medline] [Order article via Infotrieve]
  • Dranginis AM, Rauceo JM, Coronado JE, Lipke PN (2007). A biochemical guide to yeast adhesins: glycoproteins for social and antisocial occasions. Microbiol Mol Biol Rev 71:282–294.[Abstract/Free Full Text]
  • Dujon B, Sherman D, Fischer G, Durrens P, Casaregola S, Lafontaine I, et al. (2004). Genome evolution in yeasts. Nature 430:35–44.[CrossRef][Medline] [Order article via Infotrieve]
  • Ecker M, Deutzmann R, Lehle L, Mrsa V, Tanner W (2006). PIR-proteins of Saccharomyces cerevisiae are attached to β-1,3-glucan by a new protein-carbohydrate linkage. J Biol Chem 281:11523–11529.[Abstract/Free Full Text]
  • Edgar RC (2004). MUSCLE: multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Res 32:1792–1797.[Abstract/Free Full Text]
  • Edgerton M, Levine MJ (1992). Characterization of acquired denture pellicle from healthy and stomatitis patients. J Prosthet Dent 68:683–691.[CrossRef][Medline] [Order article via Infotrieve]
  • Elguezabal N, Maza JL, Ponton J (2004). Inhibition of adherence of Candida albicans and Candida dubliniensis to a resin composite restorative dental material by salivary secretory IgA and monoclonal antibodies. Oral Dis 10:81–86.[CrossRef][Medline] [Order article via Infotrieve]
  • Espinoza I, Rojas R, Aranda W, Gamonal J (2003). Prevalence of oral mucosal lesions in elderly people in Santiago, Chile. J Oral Pathol Med 32:571–575.[CrossRef][Medline] [Order article via Infotrieve]
  • Fidel PL Jr (2006). Candida-host interactions in HIV disease: relationships in oropharyngeal candidiasis. Adv Dent Res 19:80–84.[Abstract/Free Full Text]
  • Frieman MB, Cormack BP (2003). The omega-site sequence of glycosylphosphatidylinositol-anchored proteins in Saccharomyces cerevisiae can determine distribution between the membrane and the cell wall. Mol Microbiol 50:883–896.[CrossRef][Medline] [Order article via Infotrieve]
  • Gocke R, Gerath F, von Schwanewede H (2002). Quantitative determination of salivary components in the pellicle on PMMA denture base material. Clin Oral Investig 6:227–235.[CrossRef][Medline] [Order article via Infotrieve]
  • Hiller E, Heine S, Brunner H, Rupp S (2007). Candida albicans Sun41p, a putative glycosidase, is involved in morphogenesis, cell wall biogenesis, and biofilm formation. Eukaryot Cell 6:2056–2065.[Abstract/Free Full Text]
  • Hogan DA, Kolter R (2002). Pseudomonas-Candida interactions: an ecological role for virulence factors. Science 296:2229–2232.[Abstract/Free Full Text]
  • Hogan DA, Vik A, Kolter R (2004). A Pseudomonas aeruginosa quorum-sensing molecule influences Candida albicans morphology. Mol Microbiol 54:1212–1223.[CrossRef][Medline] [Order article via Infotrieve]
  • Holmes AR, Gopal PK, Jenkinson HF (1995). Adherence of Candida albicans to a cell surface polysaccharide receptor on Streptococcus gordonii. Infect Immun 63:1827–1834.[Abstract/Free Full Text]
  • Holmes AR, McNab R, Jenkinson HF (1996). Candida albicans binding to the oral bacterium Streptococcus gordonii involves multiple adhesin-receptor interactions. Infect Immun 64:4680–4685.[Abstract/Free Full Text]
  • Holmes AR, van der Wielen P, Cannon RD, Ruske D, Dawes P (2006). Candida albicans binds to saliva proteins selectively adsorbed to silicone. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 102:488–494.[CrossRef][Medline] [Order article via Infotrieve]
  • Hornby JM, Jensen EC, Lisec AD, Tasto JJ, Jahnke B, Shoemaker R, et al. (2001). Quorum sensing in the dimorphic fungus Candida albicans is mediated by farnesol. Appl Environ Microbiol 67:2982–2992.[Abstract/Free Full Text]
  • Hoyer LL, Fundyga R, Hecht JE, Kapteyn JC, Klis FM, Arnold J (2001). Characterization of agglutinin-like sequence genes from non-albicans Candida and phylogenetic analysis of the ALS family. Genetics 157:1555–1567.[Abstract/Free Full Text]
  • Hoyer LL, Green CB, Oh SH, Zhao X (2008). Discovering the secrets of the Candida albicans agglutinin-like sequence (ALS) gene family—a sticky pursuit. Med Mycol 46:1–15.[CrossRef][Medline] [Order article via Infotrieve]
  • Inoue Y, Shiraishi A, Hada T, Hirose K, Hamashima H, Shimada J (2004). The antibacterial effects of terpene alcohols on Staphylococcus aureus and their mode of action. FEMS Microbiol Lett 237:325–331.[Medline] [Order article via Infotrieve]
  • Iraqui I, Garcia-Sanchez S, Aubert S, Dromer F, Ghigo JM, d’Enfert C, et al. (2005). The Yak1p kinase controls expression of adhesins and bio-film formation in Candida glabrata in a Sir4p-dependent pathway. Mol Microbiol 55 :1259–1271.[CrossRef][Medline] [Order article via Infotrieve]
  • Jabra-Rizk MA, Shirtliff M, James C, Meiller T (2006). Effect of farnesol on Candida dubliniensis biofilm formation and fluconazole resistance. FEMS Yeast Res 6:1063–1073.[CrossRef][Medline] [Order article via Infotrieve]
  • Jain N, Kohli R, Cook E, Gialanella P, Chang T, Fries BC (2007). Biofilm formation by and antifungal susceptibility of Candida isolates from urine. Appl Environ Microbiol 73:1697–1703.[Abstract/Free Full Text]
  • Jayatilake JA, Samaranayake YH, Samaranayake LP (2008). A comparative study of candidal invasion in rabbit tongue mucosal explants and reconstituted human oral epithelium. Mycopathologia 165:373–380.[CrossRef][Medline] [Order article via Infotrieve]
  • Jobst D, Kraft K (2006). Candida species in stool, symptoms and complaints in general practice—a cross-sectional study of 308 outpatients. Mycoses 49:415–420.[CrossRef][Medline] [Order article via Infotrieve]
  • Kapteyn JC, Hoyer LL, Hecht JE , Muller WH, Andel A, Verkleij AJ, et al. (2000). The cell wall architecture of Candida albicans wild-type cells and cell wall-defective mutants. Mol Microbiol 35:601–611.[CrossRef][Medline] [Order article via Infotrieve]
  • Kara D, Luppens SB, ten Cate JM (2006). Differences between single- and dual-species biofilms of Streptococcus mutans and Veillonella parvula in growth, acidogenicity and susceptibility to chlorhexidine. Eur J Oral Sci 114:58–63.[CrossRef][Medline] [Order article via Infotrieve]
  • Karlsson AJ, Pomerantz WC, Weisblum B, Gellman SH, Palecek SP (2006). Antifungal activity from 14-helical β-peptides. J Am Chem Soc 128:12630–12631.[CrossRef][Medline] [Order article via Infotrieve]
  • Kaur R, Domergue R, Zupancic ML, Cormack BP (2005). A yeast by any other name: Candida glabrata and its interaction with the host. Curr Opin Microbiol 8:378–384.[CrossRef][Medline] [Order article via Infotrieve]
  • Kerr JR, Taylor GW, Rutman A, Høiby N, Cole PJ, Wilson R (1999). Pseudomonas aeruginosa pyocyanin and 1-hydroxyphenazine inhibit fungal growth. J Clin Pathol 52:385–387.[Abstract]
  • Klis FM, Boorsma A, De Groot PWJ (2006). Cell wall construction in Saccharomyces cerevisiae. Yeast 23:185–202.[CrossRef][Medline] [Order article via Infotrieve]
  • Klotz SA (1990). Adherence of Candida albicans to components of the subendothelial extracellular matrix. FEMS Microbiol Lett 56:249–254.[Medline] [Order article via Infotrieve]
  • Klotz SA, Gaur NK, Lake DF, Chan V, Rauceo J, Lipke PN (2004). Degenerate peptide recognition by Candida albicans adhesins Als5p and Als1p. Infect Immun 72:2029–2034.[Abstract/Free Full Text]
  • Klotz SA, Gaur NK, De Armond R, Sheppard D, Khardori N, Edwards JE Jr, et al. (2007). Candida albicans Als proteins mediate aggregation with bacteria and yeasts. Med Mycol 45:363–370.[CrossRef][Medline] [Order article via Infotrieve]
  • Koo H, Hayacibara MF, Schobel BD, Cury JA, Rosalen PL, Park YK, et al. (2003). Inhibition of Streptococcus mutans biofilm accumulation and polysaccharide production by apigenin and tt-farnesol. J Antimicrob Chemother 52:782–789.[Abstract/Free Full Text]
  • Kumamoto CA, Vinces MD (2005). Alternative Candida albicans lifestyles: growth on surfaces. Annu Rev Microbiol 59:113–133.[CrossRef][Medline] [Order article via Infotrieve]
  • LaFleur MD, Kumamoto CA, Lewis K (2006). Candida albicans biofilms produce antifungal-tolerant persister cells. Antimicrob Agents Chemother 50:3839–3846.[Abstract/Free Full Text]
  • Li F, Palecek SP (2003). EAP1, a Candida albicans gene involved in binding human epithelial cells. Eukaryot Cell 2:1266–1273.[Abstract/Free Full Text]
  • Li F, Palecek SP (2008). Distinct domains of the Candida albicans adhesin Eap1p mediate cell-cell and cell-substrate interactions. Microbiology 154:1193–1203.[Abstract/Free Full Text]
  • Li F, Svarovsky MJ, Karlsson AJ, Wagner JP, Marchillo K, Oshel P, et al. (2007). Eap1p, an adhesin that mediates Candida albicans biofilm formation in vitro and in vivo. Eukaryot Cell 6:931–939.[Abstract/Free Full Text]
  • Li L, Redding S, Dongari-Bagtzoglou A (2007). Candida glabrata: an emerging oral opportunistic pathogen. J Dent Res 86:204–215.[Abstract/Free Full Text]
  • Martínez AI, Castillo L, Garcerá A, Elorza MV, Valentin E, Sentandreu R (2004). Role of Pir1 in the construction of the Candida albicans cell wall. Microbiology 150(Pt 10):3151–3161.[Abstract/Free Full Text]
  • Martinez M, López-Ribot JL, Kirkpatrick WR, Coco BJ, Bachmann SP, PattersonTF (2002). Replacement of Candida albicans with C. dubliniensis in human immunodeficiency virus-infected patients with oropharyngeal candidiasis treated with fluconazole. J Clin Microbiol 40:3135–3139.[Abstract/Free Full Text]
  • Martins M, Henriques M, Azeredo J, Rocha SM, Coimbra MA, Oliveira R (2007). Morphogenesis control in Candida albicans and Candida dubliniensis through signaling molecules produced by planktonic and biofilm cells. Eukaryot Cell 6:2429–2436.[Abstract/Free Full Text]
  • Moura JS, da Silva WJ, Pereira T, Del Bel Cury AA, Rodrigues Garcia RC (2006). Influence of acrylic resin polymerization methods and saliva on the adherence of four Candida species. J Prosthet Dent 96:205–211.[CrossRef][Medline] [Order article via Infotrieve]
  • Mukherjee PK, Chandra J, Kuhn DM, Ghannoum MA (2003). Mechanism of fluconazole resistance in Candida albicans biofilms: phase-specific role of efflux pumps and membrane sterols. Infect Immun 71:4333–4340.[Abstract/Free Full Text]
  • Mukherjee PK, Zhou G, Munyon R, Ghannoum MA (2005). Candida bio-film: a well-designed protected environment. Med Mycol 43:191–208.[Medline] [Order article via Infotrieve]
  • Nett J, Lincoln L, Marchillo K, Massey R, Holoyda K, Hoff B, et al. (2007). Putative role of β-1,3 glucans in Candida albicans biofilm resistance. Antimicrob Agents Chemother 51:510–520.[Abstract/Free Full Text]
  • Neville BW, Damm DD, Allen CM, Bouquot JE (2002). Oral & maxillofacial pathology. 2nd ed. Philadelphia: W.B. Saunders Co.
  • Nevzatoglu EU, Ozcan M, Kulak-Ozkan Y, Kadir T (2007). Adherence of Candida albicans to denture base acrylics and silicone-based resilient liner materials with different surface finishes. Clin Oral Investig 11:231–236.[CrossRef][Medline] [Order article via Infotrieve]
  • Nikawa H, Chen J, Hamada T, Nishimura M, Polyzois G (2001). Candida albicans colonization on thermal cycled maxillofacial polymeric materials in vitro. J Oral Rehabil 28:526–533.[CrossRef][Medline] [Order article via Infotrieve]
  • Nikawa H, Egusa H, Makihira S, Okamoto T, Kurihara H, Shiba H, et al. (2006). An in vitro evaluation of the adhesion of Candida species to oral and lung tissue cells. Mycoses 49:14–17.[Medline] [Order article via Infotrieve]
  • Nobile CJ, Mitchell AP (2006). Genetics and genomics of Candida albicans biofilm formation. Cell Microbiol 8:1382–1391.[CrossRef][Medline] [Order article via Infotrieve]
  • Nobile CJ, Nett JE, Andes DR, Mitchell AP (2006). Function of Candida albicans adhesion Hwp1 in biofilm formation. Eukaryot Cell 5:1604–1610.[Abstract/Free Full Text]
  • O’Sullivan JM, Jenkinson HF, Cannon RD (2000). Adhesion of Candida albicans to oral streptococci is promoted by selective adsorption of salivary proteins to the streptococcal cell surface. Microbiology 146(Pt 1):41–48.[Abstract/Free Full Text]
  • Pardini G, De Groot PWJ, Coste AT, Karababa M, Klis FM, de Koster CG, et al. (2006). The CRH family coding for cell wall glycosylphosphatidylinositol proteins with a predicted transglycosidase domain affects cell wall organization and virulence of Candida albicans. J Biol Chem 281:40399–40411.[Abstract/Free Full Text]
  • Pereira-Cenci T, Cury AA, Cenci MS, Rodrigues-Garcia RC (2007). In vitro Candida colonization on acrylic resins and denture liners: influence of surface free energy, roughness, saliva, and adhering bacteria. Int J Prosthodont 20:308–310.[Medline] [Order article via Infotrieve]
  • Pereira-Cenci T, Deng DM, Kraneveld EA, Manders EM, Del Bel Cury AA, Ten Cate JM, et al. (2008). The effect of Streptococcus mutans and Candida glabrata on Candida albicans biofilms formed on different surfaces. Arch Oral Biol 53:755–764.[CrossRef][Medline] [Order article via Infotrieve]
  • Perrière G, Gouy M (1996). WWW-Query: an on-line retrieval system for biological sequence banks. Biochimie 78:364–369.[CrossRef][Medline] [Order article via Infotrieve]
  • Pfaller MA, Diekema DJ (2007). Epidemiology of invasive candidiasis: a persistent public health problem. Clin Microbiol Rev 20:133–163.[Abstract/Free Full Text]
  • Phan QT, Myers CL, Fu Y, Sheppard DC, Yeaman MR, Welch WH, et al. (2007). Als3 is a Candida albicans invasin that binds to cadherins and induces endocytosis by host cells. PLoS Biol 5:e64.[CrossRef][Medline] [Order article via Infotrieve]
  • Pierce GE (2005). Pseudomonas aeruginosa, Candida albicans, and device-related nosocomial infections: implications, trends, and potential approaches for control. J Ind Microbiol Biotechnol 32:309–318.[CrossRef][Medline] [Order article via Infotrieve]
  • Radford DR, Challacombe SJ, Walter JD (1999). Denture plaque and adherence of Candida albicans to denture-base materials in vivo and in vitro. Crit Rev Oral Biol Med 10:99–116.[Abstract/Free Full Text]
  • Ramage G, Vandewalle K, Wickes BL, Lopez-Ribot JL (2001). Characteristics of biofilm formation by Candida albicans. Rev Iberoam Micol 18:163–170.[Medline] [Order article via Infotrieve]
  • Ramage G, Bachmann S, Patterson TF, Wickes BL, López-Ribot JL (2002a). Investigation of multidrug efflux pumps in relation to fluconazole resistance in Candida albicans biofilms. J Antimicrob Chemother 49:973–980.[Abstract/Free Full Text]
  • Ramage G, Saville SP, Wickes BL, López-Ribot JL (2002b). Inhibition of Candida albicans biofilm formation by farnesol, a quorum-sensing molecule. Appl Environ Microbiol 68:5459–5463.[Abstract/Free Full Text]
  • Ramage G, Saville SP, Thomas DP, López-Ribot JL (2005). Candida bio-films: an update. Eukaryot Cell 4:633–638.[Free Full Text]
  • Salamon SA, Fuursted K, Egeblad H, Petersen E, Ott P (2007). Candida albicans tricuspid and pulmonic valve endocarditis: challenge of relapsing risk and role of combined medical treatment and surgery. Scand J Infect Dis 39:641–644.[CrossRef][Medline] [Order article via Infotrieve]
  • Shen S, Samaranayake LP, Yip HK, Dyson JE (2002). Bacterial and yeast flora of root surface caries in elderly, ethnic Chinese. Oral Dis 8:207–217.[CrossRef][Medline] [Order article via Infotrieve]
  • Sipahi C, Anil N, Bayramli E (2001). The effect of acquired salivary pellicle on the surface free energy and wettability of different denture base materials. J Dent 29:197–204.[CrossRef][Medline] [Order article via Infotrieve]
  • Smith AJ, Brewer A, Kirkpatrick P, Jackson MS, Young J, Watson S, et al. (2003). Staphylococcal species in the oral cavity from patients in a regional burns unit. J Hosp Infect 55:184–189.[CrossRef][Medline] [Order article via Infotrieve]
  • Sosinska GJ, De Groot PWJ, Teixeira de Mattos MJ, Dekker HL, De Koster CG, Hellingwerf KJ, et al. (2008). Hypoxic conditions and iron restriction affect the cell wall proteome of Candida albicans grown under vagina-simulative conditions. Microbiology 154:510–520.[Abstract/Free Full Text]
  • Spellberg BJ, Ibrahim AS, Avanesian V, Fu Y, Myers C, Phan QT, et al. (2006). Efficacy of the anti-Candida rAls3p-N or rAls1p-N vaccines against disseminated and mucosal candidiasis. J Infect Dis 194:256–260.[CrossRef][Medline] [Order article via Infotrieve]
  • Spreghini E, Davis DA, Subaran R, Kim M, Mitchell AP (2003). Roles of Candida albicans Dfg5p and Dcw1p cell surface proteins in growth and hypha formation. Eukaryot Cell 2:746–755.[Abstract/Free Full Text]
  • Staab JF, Bahn YS, Tai CH, Cook PF, Sundstrom P (2004). Expression of transglutaminase substrate activity on Candida albicans germ tubes through a coiled, disulfide-bonded N-terminal domain of Hwp1 requires C-terminal glycosylphosphatidylinositol modification. J Biol Chem 279:40737–40747.[Abstract/Free Full Text]
  • Sudbery P, Gow N, Berman J (2004). The distinct morphogenic states of Candida albicans. Trends Microbiol 12:317–324.[CrossRef][Medline] [Order article via Infotrieve]
  • Sumi Y, Miura H, Sunakawa M, Michiwaki Y, Sakagami N (2002). Colonisation of denture plaque by respiratory pathogens in dependent elderly. Gerodontology 19:25–29.[CrossRef][Medline] [Order article via Infotrieve]
  • Sumi Y, Kagami H, Ohtsuka Y, Kakinoki Y, Haruguchi Y, Miyamoto H (2003). High correlation between the bacterial species in denture plaque and pharyngeal microflora. Gerodontology 20:84–87.[CrossRef][Medline] [Order article via Infotrieve]
  • Thein ZM, Samaranayake YH, Samaranayake LP (2006). Effect of oral bacteria on growth and survival of Candida albicans biofilms. Arch Oral Biol 51:672–680.[CrossRef][Medline] [Order article via Infotrieve]
  • Thein ZM, Samaranayake YH, Samaranayake LP (2007). Characteristics of dual species Candida biofilms on denture acrylic surfaces. Arch Oral Biol 52:1200–1208.[CrossRef][Medline] [Order article via Infotrieve]
  • Tokunaga M, Kusamichi M, Koike H (1986). Ultrastructure of outermost layer of cell wall in Candida albicans observed by rapid-freezing technique. J Electron Microsc (Tokyo) 35:237–246.[Abstract/Free Full Text]
  • Tsang CS, Ng H, McMillan AS (2007). Antifungal susceptibility of Candida albicans biofilms on titanium discs with different surface roughness. Clin Oral Investig 11:361–368.[CrossRef][Medline] [Order article via Infotrieve]
  • Uppuluri P, Nett J, Heitman J, Andes D (2008). Synergistic effect of calcineurin inhibitors and fluconazole against Candida albicans biofilms. Antimicrob Agents Chemother 52:1127–1132.[Abstract/Free Full Text]
  • Walker LA, Munro CA, de Bruijn I, Lenardon MD, McKinnon A, Gow NA (2008). Stimulation of chitin synthesis rescues Candida albicans from echinocandins. PLoS Pathog 4:e1000040.[CrossRef][Medline] [Order article via Infotrieve]
  • Wang LH, He Y, Gao Y, Wu JE, Dong YH, He C, et al. (2004). A bacterial cell-cell communication signal with cross-kingdom structural analogues. Mol Microbiol 51:903–912.[CrossRef][Medline] [Order article via Infotrieve]
  • Wargo MJ, Hogan DA (2006). Fungal-bacterial interactions: a mixed bag of mingling microbes. Curr Opin Microbiol 9:359–364.[CrossRef][Medline] [Order article via Infotrieve]
  • Weig M, Jansch L, Gross U, De Koster CG, Klis FM, De Groot PWJ (2004). Systematic identification in silico of covalently bound cell wall proteins and analysis of protein-polysaccharide linkages of the human pathogen Candida glabrata. Microbiology 150(Pt 10):3129–3144.[Abstract/Free Full Text]
  • Whitehead KA, Colligon J, Verran J (2005). Retention of microbial cells in substratum surface features of micrometer and sub-micrometer dimensions. Colloids Surf B Biointerfaces 41:129–138.[CrossRef][Medline] [Order article via Infotrieve]
  • Yin QY, De Groot PWJ, De Koster CG, Klis FM (2008). Mass spectrometry-based proteomics of fungal wall glycoproteins. Trends Microbiol 16:20–26.[CrossRef][Medline] [Order article via Infotrieve]
  • Zakikhany K, Naglik JR, Schmidt-Westhausen A, Holland G, Schaller M, Hube B (2007). In vivo transcript profiling of Candida albicans identifies a gene essential for interepithelial dissemination. Cell Microbiol 9:2938–2954.[CrossRef][Medline] [Order article via Infotrieve]
  • Zakrzewska A, Boorsma A, Delneri D, Brul S, Oliver SG, Klis FM (2007). Cellular processes and pathways that protect Saccharomyces cerevisiae cells against the plasma membrane-perturbing compound chitosan. Eukaryot Cell 6:600–608.[Abstract/Free Full Text]
  • Zaremba ML, Daniluk T, Rozkiewicz D, Cylwik-Rokicka D, Kierklo A, Tokajuk G, et al. (2006). Microorganisms in root carious lesions in adults. Adv Med Sci 5 (Suppl 1):237–240.
  • Zhu J, Luther PW, Leng Q, Mixson AJ (2006). Synthetic histidine-rich peptides inhibit Candida species and other fungi in vitro: role of endocytosis and treatment implications. Antimicrob Agents Chemother 50:2797–2805.[Abstract/Free Full Text]
  • Zupancic ML, Frieman M, Smith D, Alvarez RA, Cummings RD, Cormack BP (2008). Glycan microarray analysis of Candida glabrata adhesin ligand specificity. Mol Microbiol 68:547–559.[CrossRef][Medline] [Order article via Infotrieve]

Journal of Dental Research, Vol. 88, No. 2, 105-115 (2009)
DOI: 10.1177/0022034508329273
Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?



This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Free Full Text (Free PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to Saved Citations
Right arrow Download to citation manager
Right arrowRequest Permissions
Right arrow Request Reprints
Right arrow Add to My Marked Citations
Citing Articles
Right arrow Citing Articles via Google Scholar
Right arrow Citing Articles via Scopus
Google Scholar
Right arrow Articles by ten Cate, J.M.
Right arrow Articles by de Groot, P.W.J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by ten Cate, J.M.
Right arrow Articles by de Groot, P.W.J.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?