Enhanced production and thermal stability of staphylococcal enterotoxin A in the presence of chitin

The link between the only outbreaks of staphylococcal food poisoning involving canned foods, mushrooms, and lobster bisque soup may be the presence of chitin in these foods. This study was undertaken to evaluate the influence of chitin on production and heat stability of staphylococcal enterotoxin A (SEA). Staphylococcus aureus 743 was cultured in brain heart infusion (BHI) broth with and without 0.5% crude chitin for 20 h at 30°C. The S. aureus CFU were enumerated in tryptic soy agar cultures. The concentration of SEA produced was estimated with an enzyme-linked immunosorbent assay kit and compared to a standard curve constructed with purified SEA. The concentration of SEA in the broths was adjusted to 100 or 50 ng/ml by dilution. The diluted broths were thermally processed in 211 X 212 cans in a still retort at 121°C for 16.5 or 28 min. Postprocess SEA concentrations were determined. The effect of crude chitin concentration on SEA production was determined by adjusting the chitin level from 0 to 2.0% in BHI broth. The presence of 0.5% crude chitin in BHI broth increased SEA production by an average of 52%. Numbers of S. aureus 743 cells were not affected. Chitin significantly increased the thermal stability of SEA to the 16.5 and 28 min thermal processes, with 10.5% and 7.3% average increases in recovery, respectively. A crude chitin concentration as low as 0.1% enhanced SEA formation. Production of SEA increased at higher concentrations of chitin. Purified chitin powders had similar stimulatory effects on SEA production. These results indicate that chitin-containing canned foods may be prone to cause staphylococcal food poisoning outbreaks due to increased production and postprocess persistence of active enterotoxin.