Partial characterisation of the inhibitory substances produced by Streptococcus oralis and related species

The production of inhibitory substances was sought by deferred antagonism. Streptococcus oralis, Streptococcus mitis and Streptococcus sanguis produced bactericidal concentrations of hydrogen peroxide, but no detectable bacteriocin. Actinomycetes and Neisseria pharyngis were particularly susceptible to the lethal action of hydrogen peroxide. Streptococcus milleri produced bactericidal concentrations of hydrogen peroxide and bacteriocin-like substances. S. oralis strains were inhibited by the bacteriocin-like products of strains of Streptococcus bovis, Streptococcus faecalis, Streptococcus mutans and Streptococcus salivarius. Inhibition was due neither to complete bacteriophage nor to fermentation end-products. Extracellular polysaccharides formed during growth could not protect sensitive strains from the effect of hydrogen peroxide or bacteriocin-like substances.