Repression of Staphylococcus aureus by food bacteria. II. Causes of inhibition.

Two food bacteria, Serratia marcescens and Pseudomonas sp. CS-1, inhibited an enterotoxigenic strain of Staphylococcus aureus, apparently by out-competing it for nutrients. Five others, Bacillus cereus, Proteus vulgaris, Escherichia coli H-52, Aerobacter aerogenes, and Achromobacter sp., inhibited by means of antibiotic substances which were Seitz-filterable, dialyzable, and stable at 90 C for 10 min. Inhibition was not caused by changes in pH, oxidation-reduction potential, or production of peroxide or fatty acids. The concentrated antibiotic material from E. coli H-52 contained amino acids but not peptides and was especially effective against staphylococci and micrococci.