Intracellular retention of staphylococcal enterotoxin A during the growth of Staphylococcus aureus and its release under simulated gastric conditions

This study aimed to clarify the relationship between intracellular retention of staphylococcal enterotoxin A (SEA) and the growth of Staphylococcus aureus , as well as the effects of low incubation temperatures on intracellular SEA levels and its release into a model gastric juice. Eleven S . aureus strains were cultured at 10°C, 15°C, and 37°C, and both intracellular and extracellular SEA amounts were measured. At all incubation temperatures, intracellular SEA was not detected during the early logarithmic phase of growth, indicating that SEA was quickly released after being synthesized in the cells while the bacteria were actively dividing. Intracellular retention of SEA began during the late logarithmic phase of growth. At 37°C, several strains retained intracellular SEA at levels comparable to those secreted into the medium. At 10°C and 15°C, SEA was produced more slowly in all strains, and intracellular SEA amounts were lower than extracellular levels. To determine whether intracellular SEA could be released under gastric conditions, bacterial cells were exposed to a model gastric juice. Approximately 80% of intracellular SEA was released at pH 1.5-2.0, with minimal release above pH 3.5. These findings suggest that SEA retained within S. aureus cells can be released into the stomach.