ENHANCED PRODUCTION AND THERMAL-STABILITY OF STAPHYLOCOCCAL-ENTEROTOXIN-A IN THE PRESENCE OF CHITIN

The link between the only outbreaks of staphylococcal food poisoning i nvolving canned foods, mushrooms, and lobster bisque soup may be the p resence of chitin in these foods. This study was undertaken to evaluat e the influence of chitin on production and heat stability of staphylo coccal enterotoxin A (SEA). Staphylococcus aureus 743 was cultured in brain heart infusion (BHI) broth with and without 0.5% crude chitin fo r 20 h at 30 degrees C. The S. aureus CFU were enumerated in tryptic s oy agar cultures. The concentration of SEA produced was estimated with an enzyme-linked immunosorbent assay kit and compared to a standard c urve constructed with purified SEA. The concentration of SEA in the br oths was adjusted to 100 or 50 ng/ml by dilution. The diluted broths w ere thermally processed in 211 X 212 cans in a still retort at 121 deg rees C for 16.5 or 28 min. Postprocess SEA concentrations were determi ned. The effect of crude chitin concentration on SEA production was de termined by adjusting the chitin level from 0 to 2.0% in BHI broth. Th e 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 1 6.5 and 28 min thermal processes, with 10.5% and 7.3% average increase s in recovery, respectively. A crude chitin concentration as low as 0. 1% enhanced SEA formation. Production of SEA increased at higher conce ntrations of chitin. Purified chitin powders had similar stimulatory e ffects on SEA production. These results indicate that chitin-containin g canned foods may be prone to cause staphylococcal food poisoning out breaks due to increased production and postprocess persistence of acti ve enterotoxin.