The effect of Bacillus subtilis and Streptococcus faecalis var. liquefaciens on staphylococcal enterotoxin A activity

The effect of growing Bacillus subtilis and Streptococcus faecalis var. liquefaciens on staphylococcal growth, thermonuclease (TNase) activity and enterotoxin A (SEA) activity was investigated in liquid media and in foods. Abundant growth of B. subtilis or S. faecalis var. liquefaciens decreased purified SEA concentrations during a 2-day incubation in brain heart infusion broth (BHI) and supernatant fluid by 89 and 67%, respectively. Both staphylococcal TNase activity and SEA concentrations decreased when S. aureus was cultivated in the presence of B. subtilis or S. faecalis var. liquefaciens. Staphylococcal TNase activity decreased by 75 and 78% in the presence of B. subtilis and S. faecalis var. liquefaciens, respectively, while SEA activity decreased by 95 and 65%, respectively, in the presence of those test strains. The results obtained with artificially contaminated sterile chicken or beef samples were similar to those obtained with BHI broth. S. aureus grew very well in heated vegetables. TNase was undetectable, although SEA could be detected. In the presence of B. subtilis or S. faecalis var. liquefaciens, SEA activity was decreased to a non-detectable concentration.