Susceptibility of Streptococcus mutans to Antimicrobial Agents

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Abstract
Fifty strains of Streptococcus mutans, including defined strains and clinical isolates, were tested for susceptibility to 20 different antimicrobial agents. Minimal inhibitory concentrations were determined by a liquid microtiter procedure. Antibiotics that were most effective in concentrations below 0.1 μg/ml included penicillin, ampicillin, erythromycin, cephalothin, and methicillin. Antibiotics effective in concentrations between 0.1 μg and 10 μg/ml included rifampin, lincomycin, thiostrepton, spiromycin, vancomycin, streptolydigan, novobiocin, tetracycline, chloramphenicol, spectinomycin, and gentamicin. Antibiotics effective at higher concentrations ranging from 10 μg/ml to 400 μg/ml included the aminoglycosides kanamycin, neomycin, streptomycin, and kasugamycin. Although most antibiotics exhibited inhibitory effects in a narrow range of concentrations, antibiotics such as tetracycline, thiostrepton, and spiromycin had a 1,000-fold range from the lowest to highest concentrations required for growth inhibition.