Suppression of opportunistic infectious bacteria by lactic acid bacteria and antibacterial drugs

Purpose: The objective of this study was to investigate inhibitory effect of lactic acid bacteria and antibiotics on the growth of Streptococcus pneumoniae ATCC 33400.Materials and Methods: Antibiotic activities of five oral probiotic candidate bacteria including two strains of Lactobacillus crispatus, Lactobacillus fermentum, Lactobacillus gasseri and Streptococcus mitis and several antibiotics against S. pneumoniae were investigated using radial diffusion assay and competition assay. The biofilm formation of S. pneumoniae in the presence of 50% saturated ammonium sulfate precipitation fraction from L. gasseri and several concentrations of gentamicin were monitored by real time cell analyzer, xCELLigence. Results: The growth of S. pneumoniae was inhibited by two strains of Lactobacillus crispatus, Lactobacillus fermentum and Lactobacillus gasseri. The saturated ammonium sulfate precipitation fraction (0-30% and 30-50%) from L. gasseri effectively inhibited growth of S. pneumoniae. The biofilm formation of S. pneumoniae monitored by real time cell analyzer (xCELLigence) was suppressed by gentamicin in dose dependent manner. Antibacterial substance from L. gasseri against S. pneumoniae was suggested to be small molecular weight substance.Conclusion: L. gasseri inhibited the growth of S. pneumoniae suggesting that L. gasseri will be a candidate of probiotics.