Abstract

  Background and Aim: Streptococcus mutans are the most important factors of dental cavity in the mortal because the mutans have the ability to synthesize the extracellular polymers and biofilm formation. Biofilm formation from clinical Streptococcus mutans strains from dental plaque in vitro and our purpose was to study the resistance to antimicrobial agents.

  Materials and Methods: In this study, one strain was selected with prevalent ability in biofilm formation for testing antimicrobial agents from among the isolated Streptococcus mutans strains from dental plaque. Biofilms of Streptococcus mutans were constituted on polyacetiren micro plates. The efficacy scale of common antimicrobial agents such as Penicillin, Erythromycin, Tetracycline and Chlorhexidine was evaluated on the number of live biofilm cells in different occasions. MIC for planktonic cells of Streptococcus mutans was determined.

  Results: It was observed that chlorhexidine 0.2 % with 0.09 mg/ml MIC has the most bactericidal effects within a five-minute treatment on biofilm and Tetracycline with 0.3mg/ml MIC has the lowest effect. The OD a ratio of the untreated biofilm to OD of the biofilm containing biocide in the same strain (OD_r) shows that untreated biofilm forms thicker biofilms than that of treated biofilm with effective microbial agents. A constant reduction was observed in the number of living biofilm cells within treatment by Erythromycin and Penicillin.

  Conclusion: This research demonstrated that to eradicatet the living biofilm cells, a density of over 5 MIC of antimicrobial agents is needed.

  Keywords: Antimicrobial agents, biofilms, Streptococcus mutans