RESUMO
The effect of magnesium and iron on the growth, cellular morphology, deoxyribonuclease, coagulase, and enterotoxin B (SEB) production of Staphylococcus aureus strain S-6 in a pancreatic digest of casein (NAK) which had been treated with alumina to remove mineral ions was determined. Growth of S. aureus in the treated NAK medium (NAKSA) was minimal; the morphology of the cells was heterogenous with many large cells as well as some that were gram negative. The cells gradually reverted towards normal as the Mg2+ concentration was increased to 1.1 µg/ml. Cell dry weight increased from 0.36 ± 0.27 mg/ml to 1.16 ± 0.41 mg/ml, DNase activity increased from 7.6 units/mg dry weight to 77.0 units/mg dry weight, and SEB production increased from 12.2 to 54.3 µg/mg cell dry weight when the Mg2+ content was increased to 1.1 µg/ml. Increasing the Fe2+ content above the 0.4 µg/ml in the NAKSA medium containing 1.1 µg/Mg2+ resulted in decreases in dry weight and DNase activity, a slight increase in SEB production, and a relatively large increase in coagulase production.
RESUMO
The change in pH, growth of mesophilic bacteria and growth, thermonuclease (TNase) and enterotoxin A (SEA) production by Staphylococcus aureus in artificially inoculated cream pies were investigated. The mesophilic count varied from 104 CFU/g at 20°C to 4.0 × 107 CFU/g at 37°C after 12 h of incubation and from 2 × 106 CFU/g at 20°C to 7 × 108 CFU/g at 37°C after 35 h of incubation. The S. aureus count varied from <10 2 at 20°C to 1.6 × 104 CFU/g at 37°C after 12 h of incubation and from 8 × 102 at 20°C to 5.4 × 106 at 37°C after 35 h of incubation. TNase was detectable after incubation for: 35 h at 20°C (2.9 ng/g), 12 h at 30°C (9.4 ng/g), and 12 h at 37°C (72 ng/g). SEA was detectable after incubation for: 35 h at 20°C (3.9 ng/g), 18 h at 25°C (3.9 ng/g) and 14 h at 30°C (4.8 ng/g).
