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: 4.3). 03/2012; 39(5):390-5. DOI: 10.1016/j.ijantimicag.2012.01.009
Source: PubMed


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.

    • "Reverse transcription and real-time PCR were performed using a Top script TM cDNA synthesis kit (Enzynomics, Daejeon, Korea) and a Power SYBR ® Green PCR Master Mix (Life Technologies, Warrington, UK), respectively, according to the manufacturers' instructions. The gene-specific sequences (gtfB, gtfC, and gtfD) in the primers used in this study were the same as those described previously (Lu et al. 2008; Dong et al. 2012). Relative expression was calculated by normalizing each test gene of the treated biofilms to the 16sRNA gene, which served as the reference gene (Shemesh et al. 2008). "
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    • "The primers used for the quantitative RT-PCR were purchased from Life Technologies Inc. (Burlington, ON, Canada) and are listed in Table 1. The sequences of primers were obtained from a previous study [19] while the primers for atlA were designed in this study. Triplicate reactions were prepared with 25 µl of PCR mixture containing 12.5 µl of IQ SYBR Green Supermix, 5 µl of cDNA, 1 µl of gene-specific primer, and 6.5 µl of RNase- and DNase-free water. "
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    • "Values having different letters are significantly different from each other according to Fisher's least significant difference test (p < 0.05). findings are not surprising, since similar results were also found for Streptococcus mutans with respect to subminimal inhibitory concentrations of anticaries agents (Dong et al. 2012 "
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