Bacteriocin Production and Susceptibility Among Strains

Whereas the bacteriocin activity of eight strains of Streptococcus mutans was unaffected by growth in the presence of sucrose, such a medium rendered five S. mutans and one S. salivarius indicator strains unsusceptible to the bacteriocins. In contrast, the susceptibility of three S. faecalis and one S. pyogenes strains was unaltered when these indicators were grown in the presence of sucrose. Since the S. mutans and S. salivarius strains produced extracellular polysaccharides from sucrose whereas the S. faecalis and S. pyogenes strains did not, it was concluded that a coating of extracellular polysaccharides rendered normally susceptible organisms unsusceptible to bacteriocin action. This supports previous suggestions that such bacteriocins are not active in vivo and therefore play no role in regulating the microbial ecology in dental plaque.