PERSISTENCE OF SEROLOGICAL AND BIOLOGICAL-ACTIVITIES OF STAPHYLOCOCCAL-ENTEROTOXIN-A IN CANNED MUSHROOMS

Outbreaks in 1989 of staphylococcal food poisoning linked to the consu mption of imported canned mushrooms indicated that staphylococcal ente rotoxins (SE) may survive a commercial retort process. To examine this possibility, fresh mushrooms were blanched in boiling water for 5 min and cooled 5 min in sterile water inoculated with enterotoxigenic typ e A Staphylococcus aureus strain 743, to yield approximately 1.3 X 10( 3) staphylococci per g. Inoculated mushrooms were incubated 20 h at 30 degrees C to simulate time-temperature abuse prior to canning. Mushro oms were sealed in 211 x 212 cans and thermally processed in a still r etort to F values of 7, 12, and 18 min at 121 and 127 degrees C. Pre- and post-thermal process staphylococcal enterotoxin A (SEA) serologica l activity was estimated from a standard curve with purified SEA using a commercial enzyme-linked immunosorbent assay (ELISA) kit. SEA was c hromatographically separated from 4-can composite extracts of each F v alue and temperature. A feline emetic assay was used to determine the biological activity. The dose, administered on a body-weight basis, wa s equivalent to approximately 0.5 servings of mushrooms and brine for humans. The presence of SEA in the samples was confirmed by Western bl otting using anti-SEA immunoglobulin G (IgG). The pre-thermal-process concentration of SEA was about 58 ng/g of mushrooms. Serological and b iological activities were detected after all sterilizing values tested at 121 and 127 degrees C. The inactivation of serological activity oc curred in two phases, with a rapid initial rate and a distinctly slowe r rate at higher F values. Attenuation of biological activity, noted b y a reduction in the number of emetic episodes and an increase in time to an emetic response, was observed with increasing F values of the p rocesses.