Effects of sub-minimum inhibitory concentrations of antimicrobial agents on Streptococcus mutans biofilm formation.

Department of Operative Dentistry & Endodontics, School of Stomatology, Fourth Military Medical University, 145 Changle West Road, Xi'an 710032, Shaanxi, China.
International journal of antimicrobial agents (Impact Factor: 3.03). 03/2012; 39(5):390-5. DOI: 10.1016/j.ijantimicag.2012.01.009
Source: PubMed

ABSTRACT Many studies have demonstrated that sub-minimum inhibitory concentrations (sub-MICs) of antimicrobial agents can inhibit bacterial biofilm formation. However, the mechanisms by which antimicrobial agents at sub-MICs inhibit biofilm formation remain unclear. At present, most studies are focused on Gram-negative bacteria; however, the effects of sub-MICs of antimicrobial agents on Gram-positive bacteria may be more complex. Streptococcus mutans is a major cariogenic bacterium. In this study, the S. mutans growth curve as well as the expression of genes related to S. mutans biofilm formation were evaluated following treatment with 0.5× MIC of chlorhexidine (CHX), tea polyphenols and sodium fluoride (NaF), which are common anticaries agents. The BioFlux system was employed to generate a biofilm under a controlled flow. Morphological changes of the S. mutans biofilm were observed and analysed using field emission scanning electron microscopy and confocal laser scanning microscopy. The results indicated that these three common anticaries agents could significantly upregulate expression of the genes related to S. mutans biofilm formation, and S. mutans exhibited a dense biofilm with an extensive extracellular matrix following treatment with sub-MICs of NaF and CHX. These findings suggest that sub-MICs of anticaries agents favour S. mutans biofilm formation, which might encourage dental caries progression.

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    ABSTRACT: Objectives The aim of this study was to evaluate Streptococcus mutans adhesion to fluoride varnishes and subsequent change in biofilm accumulation and acidogenicity. Methods After producing fluoride varnish-coated hydroxyapatite discs using Fluor Protector (FP), Bifluorid 12 (BIF), Cavity Shield (CASH), or Flor-Opal Varnish White (FO), S. mutans biofilms were formed on the discs. To assess S. mutans adhesion to the discs, 4-hour-old biofilms were analyzed. To investigate the change in biofilm accumulation during subsequent biofilm formation, the biomass, colony forming units (CFU), and water-insoluble extracellular polysaccharides (EP) of 46-, 70-, and 94-hour-old biofilms were analyzed. To investigate the change in acidogenicity, pH values of the culture medium were determined during the experimental period. The amount of fluoride in the culture medium was also determined during the experimental period. Results BIF, CASH, and FO affected S. mutans adhesion (67–98% reduction) and subsequent biofilm accumulation in 46-, 70-, and 94-hour-old biofilms. However, the reducing effect of the fluoride varnishes on the biomass, CFU count, water-insoluble EP amount, and acid production rate of the biofilms decreased as the biofilm age increased. These results may be related to the fluoride-release pattern of the fluoride varnishes. Of the fluoride varnishes tested, FO showed the highest reducing effect against the bacterial adhesion and subsequent biofilm accumulation. Conclusions Our findings suggest that if the results of these experiments are extrapolable to the in vivo situation, then reduced clinical benefit of using fluoride varnishes to inhibit bacterial adherence may occur with time.
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Jun 20, 2014