Abstract
Abstract A microbiological method for estimating population levels of Clostridium perfringens in food, based on the presence of α-toxin, was studied collaboratively in 15 laboratories. The collaborators extracted α-toxin from identical samples of roast beef and quantitatively determined it in hemolysin indicator plates. The titer of a-toxin found was utilized to estimate the population level of C. perfringens in the roast beef by correlating the titer of α-toxin present in the beef with experimental data on the relationship of viable counts and α-toxin production supplied to the collaborators. Forty-five of 52 samples examined were found to contain α-toxin at a dilution of 1+63 to 1+127 as measured in hemolysin indicator plates. The remainder had α-toxin titers one 2-fold dilution higher or lower. The estimated population levels obtained by the various laboratories ranged from 7.3 α 107 to 17.8 α 107/g. The standard deviation among replicate determinations within collaborators was 3.5 × 107/g. These results indicate that the precision of the α-toxin method makes it useful for estimating the maximum population of C. perfringens in a suspect outbreak food.
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