Antimicrobial efficacy of Nisin against Streptococcus mutans

Objectives: Dental caries is multifactorial chronic disease and the resulting acid production is known to cause cavities in the diseased tooth. The presence of Streptococcus mutans in saliva and plaque are known to correlate with caries and progression of the caries lesion has been correlated with increased colony counts of S.mutans. Nisin is an antimicrobial polypeptide produced by strains of Lactococcus lactis subsp lactis. It is an effective bactericidal agent against gram-positive bacteria. It belongs to a group of bactericidal peptides called Type A lantibiotics. The objective of this study was to evaluate the anti-bacterial property of Nisin by Minimal Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) tests against three species of viridans group streptococci (VGS).
Methods: A total of 13 viridans group streptococci S.mitis(7), S.mutans (5)and S.salivarius(1) isolated from patients with dental caries were included in the study. Pure Nisin from Lactococcus lactis (Sigma) was dissolved in sterile distilled water (100 mg/ml). Gentamycin was used as an experimental control. All the isolates were screened for MIC and MBC using micro dilution method in Brain heart infusion broth.
Results: The MIC and MBC of nisin against S.mitis range from 0.62 to 10mg/mL, S.mutans from 0.13 to 1.25mg/mL and S.salivarius ≥ 10 mg/mL.
Conclusions: S.mutans which is known to be a predominant cause of dental caries was found to be significantly inhibited by Nisin.