Heat adaptation and survival of Cronobacter spp. (formerly Enterobacter sakazakii)

Adaptation to sublethal stress can confer increased survival capability on foodborne pathogens. In this article, we report on the adaptive response of Cronobacter spp. to heat and compare the survival of heat adapted to unadapted Cronobacter spp. Five different isolates, representing at least three different Cronobacter spp., were adapted at 46°C for 30 min and subjected to a lethal stress at 52°C. All showed increased survival upon adaptation. Survival was greater in milk-grown cells, but broth-grown cells showed a higher degree of adaptation. The survival potential acquired following adaptation was not transferred to survival in a dry environment or to survival during reconstitution of artificially contaminated milk powder by conventional or microwave heat. The ratio of membrane unsaturated to saturated fatty acids decreased, possibly resulting in a more rigid membrane in adapted cells. Heat-adapted cells showed increased survival potential to lethal heat stress, but not to dry stress. Alterations in the ratio of fatty acids in the membrane may explain this adaptation.