No abstract

Morganella morganii was subjected to cold shock treatment at 10C for 2 h or heat shock treatment at 42C for 45 min. The effect of these shock treatments on the viability of M. morganii under adverse conditions was investigated. Viability of M. morganii cells during storage at 4C was slightly affected by cold shock treatment under the conditions tested (P > 0.05). However, a significant increase in the viable population of the cold-shocked cells was found in the subsequent challenge of -18C, as compared with the nonshocked cells (P < 0.05). In addition, coldshocked cells became more susceptible to high incubation temperature (P < 0.05). Nevertheless, cold shock treatment did not alter the susceptibility of this bacterium to 1.0 mM H2O2, 20% NaCl and low pH (pH, 3.5). On the contrary, heat shock treatment increased the susceptibility of M. morganii to low incubation temperatures and H2O2, while made the cells more resistant to high temperature. As in the cold shock treatment, heat shock treatment under the conditions tested did not affect the susceptibility of M. morganii to NaCl and low pH. PRACTICAL APPLICATIONSThese findings may be of significant importance with regard to food safety because cooling chains and heating regimes do exist in the food industry, which could potentially induce a cold or heat shock phenomenon.