Growth of psychrotrophic foodborne pathogens in a solid surface model system under the influence of carbon dioxide and oxygen

A solid surface model system was developed to study the effect of gas atmosphere composition on the growth of Aeromonas hydrophila, Yersinia enterocolitica, Listeria monocytogenes, and a cold tolerant strain of Bacillus cereus. The organisms were incubated on an agar surface at 8 degrees C under either 1.5 or 21% O-2, combined with 0, 5, 20 or 50% CO2. The remainder of each atmosphere was made up to 100% with N-2. Growth was evaluated on the basis of three parameters, namely maximum specific growth rate, maximum population density and lag time. These parameters were derived from growth data by fitting with a modified Gompertz equation. In all instances the maximum specific growth rate decreased significantly with increasing CO2 concentration. A strong reduction in the maximum population density was noted only for B. cereus at the highest level of CO2. The O-2 concentrations tested did not significantly affect maximum specific growth rates nor maximum population densities in any case. Prolonged lag times were observed only for Y. enterocolitica under 50% Co-2/21% O-2/29% N-2. The results indicate that the model system may be a suitable means of estimating the growth of bacteria on minimally processed produce, packaged under modified atmospheres. Extrapolation of our results to modified atmosphere packaged (MAP) fruits and vegetables using typical O-2 concentrations of 1-5% and CO2 concentrations of 5-10%, suggest that growth of the above pathogens may occur at 8 degrees C, thereby imposing a safety hazard for these products. (C) 1995 Academic Press Limited