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The VicRK System of Streptococcus mutans Responds to Oxidative Stress

¹ Department of Cariology Endodontology and Pedodontology, Academic Centre for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA Amsterdam, The Netherlands; and
² Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, The Netherlands

View larger version (25K): [in this window] [in a new window]   Figure 1. Representative fluorescence histogram of flow cytometry measurements of 3 S. mutans strains: S. mutans UA159 (with pVA838) light grey line; S. mutans UA159 (with pMJ9) grey line; and S. mutans UA159 (with pDM15) dark line. The culture in exponential phase (OD600 = 0.2–0.4) was analyzed by flow cytometry before the addition of stresses. We analyzed 10,000 particles (cells) for fluorescence intensity, using a Coulter Epics XL-MCL flow cytometer. Fluorescence intensity distribution of the culture is expressed as arbitrary fluorescence intensity units (AU).

View larger version (12K): [in this window] [in a new window]   Figure 2. Fluorescence and pH changes of different S. mutans strains during growth. S. mutans UA159 (pDM15) was grown in Todd-Hewitt broth. OD600 (diamonds), pH (open squares), and average fluorescence intensity (open circles) were measured simultaneously over time. Subsequently, the pH of samples from each time-point were also adjusted to 7.5. pH (filled squares) and average fluorescent intensity (filled circles) of the samples were measured after the pH adjustment.

View larger version (16K): [in this window] [in a new window]   Figure 3. Responses of S. mutans UA159 (with pMJ9) to various types of stress (A) and to gradients of H2O2 (B). In (A), cells in exponential phase (OD600 = 0.2) were subjected to 0.005% H2O2 (), agitation (), or 0.000625% chlorhexidine (*), or were without any additions (). In (B), cells in exponential phase were subjected to various concentrations of H2O2: 0 (), 0.0025% (•), 0.005% (), and 0.01% (). The results were averaged from 3 independent experiments and were presented as the means with standard deviations. We used a two-way analysis of variance to compare the increase of fluorescence intensity in time among stresses or concentrations (*p < 0.05).

View larger version (9K): [in this window] [in a new window]   Figure 4. Inhibition of different S. mutans strains by H2O2. S. mutans UA159 () and vicK mutant () were grown in the presence of various bactericidal concentrations of H2O2. Cells in exponential phase (OD600 = 0.6) were plated evenly on Todd-Hewitt (with 0.3% yeast extract) agar with the use of a spiral plater. Paper discs containing 40 µL of H2O2 in concentrations as indicated were placed on the surface of the agar. The inhibition zone was measured after 24 hrs. The results were averaged from 3 independent experiments and are presented as the means with standard deviations. We used a two-way analysis of variance to indicate significant increases in zone-diameters (*p < 0.01).

Journal of Dental Research, Vol. 86, No. 7, 606-610 (2007)
DOI: 10.1177/154405910708600705


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