Staphylococcus aureus growth and enterotoxin a production in an anaerobic environment

Abstract

The effects of strict anaerobic conditions on the growth of Staphylococcus aureus and the production of staphylococcal enterotoxin A (SEA) were studied. The growth of S. aureus, a facultative anaerobic bacterium, is slower anaerobically than aerobically. When grown on brain heart infusion broth at 37°C, the anaerobic generation time at mid-log phase was 80 min, compared with 35 min for the aerobic control. In contrast to previous studies demonstrating that staphylococcal cell density was 9- to 17-fold greater in aerobic than in anaerobic cultures, data for a staphylococcal strain implicated in food poisoning showed that the cell density was only two to three times as great in aerobic cultures. Production of SEA was monitored by Western immunoblotting and shown to be growth dependent. With slower anaerobic growth, relatively less toxin was produced than under aerobic conditions, but in both cases SEA was detected after 120 min of incubation. The combined effects of temperature and aeration on S. aureus were also studied. Growth and toxin production of aerobic and anaerobic cultures at temperatures ranging from 14 to 37°C were analyzed. Growth was still observed at low temperatures in both environments. A linear model for S. aureus aerobic or anaerobic growth as a function of incubation temperature was developed from these studies. The model was tested from 17 to 35.5°C, and the results suggest that the model can accurately predict the S. aureus growth rate in this temperature range. The data suggest that anaerobic conditions are not an effective barrier against S. aureus growth.