Pseudomonas and Achromobacteraceae cultures, mostly from foods, were tested for their effect on the growth of Staphylococcus aureus 196E in Trypticase Soy Broth at different temperatures (10 to 30 C) and with different ratios of effectors to staphylococci in inocula. Most cultures inhibited the staphylococcus, with inhibition becoming greater with decreasing proportions of S. aureus in the inoculum and decreasing temperatures of incubation, but inhibition usually was not as great as had been found with most coliform and lactic acid bacteria. Only a few of the Pseudomonas cultures could keep numbers of S. aureus below 5 × 106 cells per ml, even with an initial ratio of effectors to staphylococci of 100 : 1 and a low incubation temperature, although most cultures of Pseudomonas and Achromobacteraceae delayed the attainment of these numbers. Especially effective in inhibition of S. aureus were strains of Pseudomonas striata and P. mildenbergii or convexa, and a culture of Alcaligenes viscolactis.
At 15 C Pseudomonas fluorescens, Alcaligenes faecalis, and Achromobacter xerosis stimulated S. aureus enough during early growth to hasten the attainment of hazardous numbers of staphylococci by several hours. At 15, 25 and 30 C most cultures, however, delayed the growth of S. aureus, and all kept maximal numbers of staphylococci below those reached by the coccus growing alone, although numbers usually were less by only about one- to two-thirds.
Most strains of two Pseudomonas species affected S. aureus similarly, and the effects of eight species of effectors on two strains of S. aureus were, for the most part, similar.
1Published with approval of the Director of the Wisconsin Agricultural Experiment Station.
2This investigation was supported in part by Public Health Service Research Grant EF-00282 from the Division of Environmental Engineering and Food Protection.
3Present address: Department of Soils, College of Agriculture, College, Laguna, Philippines.