Effect of Variations in Conditions of Incubation upon Inhibition of Staphylococcus aureus by Pediococcus cerevisiae and Streptococcus lactis1

Abstract

The effects of pH, temperature, proportion of Staphylococcus aureus in the inoculum, various strains of effector organism, and various strains of S. aureus were examined for their influence on interactions between staphylococci and effector organisms in associative culture. In general, small changes in pH had little effect upon either growth of S. aureus or production of enterotoxin in associative culture. Inhibition of growth of S. aureus caused by effector organisms was much greater at 25 than at 30 C. Proportion of S. aureus in the inoculum greatly affected both growth of the staphylococci and production of enterotoxin. Only slight differences were found between strains of either effector organism or S. aureus which affected the interactions in associative culture. Previous work in this laboratory has shown that several species of lactic acid bacteria, particularly Streptococcus lactis and Pediococcus cerevisiae, were inhibitory to growth and enterotoxin production by Staphylococcus aureus when grown in association with S. aureus at temperatures favorable to the organisms concerned. Several reports (2-8) have indicated that certain conditions of incubation may significantly affect the influence of the competing organisms upon growth of S. aureus, but none report any effect on enterotoxin production. The investigation reported herein was conducted to determine the effect of variations in some conditions upon the ability of S. lactis and P. cerevisiae to inhibit growth and production of enterotoxin by S. aureus. MATERIALS AND METHODS Cultures. S. lactis strains A62, A64, A254, and G18 and P. cerevisiae strains FBB39 and FBB63 used as effector organisms were from the stock cultures in the Food Microbiology Laboratory at Michigan State University. S. Iactis W was obtained from E. H. Marth of the University of Wisconsin. P. cerevisiae 10791 was obtained from the American Type Culture Collection, Rockville, Md. P. cerevisiae "Accel" is a commercial starter culture from Merck and Co.,

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Antimicrobial Activity of a Phage Mixture and a Lactic Acid Bacterium against Staphylococcus aureus from Bovine Mastitis

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