Bacteriocins from human and rodent streptococci

Abstract

Thirteen strains of streptococci, representing cariogenic and non-cariogenic isolates from humans and rodents were examined for synthesis of bacteriocins. Six strains were found to produce bacteriocins that were active against other streptococci, including strains of Strep. pyogenes and enterococci, but not against unrelated bacteria. There was no correlation between production of bacteriocins and the cariogenicity of the organisms. Several types of bacteriocins could be delineated on the basis of their activity spectrum, the morphology of inhibition zones, and their sensitivity to heat, ether, chloroform, and various enzymes. Several organisms appeared to form more than one type of bacteriocin. All bacteriocins were affected by proteolytic enzymes and some by lipase, suggesting they contain peptide and lipid moieties. They were of low molecular weight, as indicated by their ability to diffuse through a dialysis membrane. Bacteriocin activity was readily demonstrated in agar agarose or starch plate assays, but activity could not be demonstrated in broth cultures. This indicated that the bacteriocins were extremely labile in liquid media, but they were found to be stabilized by low concentrations of agar, starch, glycerol or dextran.