GROWTH OF LISTERIA-MONOCYTOGENES, AEROMONAS-HYDROPHILA AND YERSINIA-ENTEROCOLITICA IN PATE AND A COMPARISON WITH PREDICTIVE MODELS

A reference or type strain and a food derived-strain of the cold-toler ant pathogens Listeria monocytogenes, Aeromonas hydrophila and Yersini a enterocolitica were individually inoculated into samples of commerci al pate and incubated at 4 and 10-degrees-C. The organisms were period ically estimated by presumpitive counts, then values for the lag and g eneration times were calculated. Both strains of L. monocytogenes grew at both temperatures. The food strain of A. hydrophila grew only at 1 0-degrees-C, and the type strain did not grow at either temperature. S imilarly, the type strain of Y. enterocolitica did not grow at either temperature, whereas the food strain grew at both 4 and 10-degrees-C. In some cases growth of non-test organisms may have inhibited the grow th of these latter two species. The measured values of lag and generat ion times did not, in general, correlate well with those predicted by response surface models, taken from the literature and produced in thi s laboratory. It may be that the pate contained an inhibitor that affe cted the growth of the organisms. The two strains of A. hydrophila and Y. enterocolitica showed significantly different growth characteristi cs, reinforcing the value of using a 'cocktail' of strains in growth e xperiments. Differences in predicted kinetic values from the models in dicate that a model for any particular Strain may not reflect the grow th of naturally occurring contaminants of the same species.