In vitro inhibition of some gram-positive bacteria by Staphylococci and Aerococcus viridans of porcine origin

Nine coagulase-negative Staphylococci and Aerococcus viridans were tested for bacterial antagonism. Seven of the nine of the coagulase-negative Staphylococci and Aerococcus viridans inhibited the growth of four Staph. hyicus, three Staph. aureus strains and some other Gram-positive bacteria, including Streptococcus group A and D, Corynebacteria, but none of the Gram-negative and yeast was inhibited on agar media. There was also production of inhibitory substances in different types of liquid media but no antagonistic activity was observed on Millipore membrane. The inhibition was not due to the pH change of media in which the producers were grown, but due to production of inhibitory substances tentatively classed as antibiotics.