Predicted and observed growth and toxigenesis by Clostridium botulinum type E in vacuum-packaged fishery product challenge tests

The observed growth and toxigenesis by Clostridium botulinum type E in vacu um-packaged unprocessed, raw pickled and cold-smoked rainbow trout stored a t slightly abusive temperatures were compared to predictions generated by t wo currently available predictive microbiological programs, Food MicroModel and Pathogen Modelling Program. In unprocessed fish there was only a 2 log increase in type E cell count at the time the toxicity first occurred afte r 2 weeks storage at 8 degrees C. Neither growth or toxin production was ob served in raw pickled fish with a NaCl concentration of 6.7% (w/v) during 6 weeks storage at 6 degrees C. In cold-smoked fish with a NaCl level of 3.2 % (w/v) toxic samples were detected after 3 and 4 weeks storage at 8 degree s C and 4 degrees C, respectively, without any increase in type E count. Bo th models were hampered by limitations to controlling environmental factors set by the programs which also had an adverse effect on the reliability of predictions. Most predictions generated by the models were inconsistent wi th the results observed in the challenge studies. In certain situations, th e models seemed to be 'fail-safe', in that, the growth rate predicted from the model was faster or a predicted time to toxicity shorter than that whic h actually occurred in the food. In other situations, the predictions showe d the product to be safe when it was not. The results demonstrate the need for further development and rigorous validation of the models before they a re accepted for wider use by inspecting officials and the food industry. (C ) 1999 Elsevier Science B.V. All rights reserved.