Influence of temperature on alkali stress adaptation in Listeria monocytogenes

Listeria monocytogenes cells may induce alkali stress adaptation when exposed to sublethal concentrations of alkaline cleaners and sanitizers that may be frequently used in the food processing environment. In the present study, the effect of temperature on the induction and the stability of such alkali stress adaptation in L. monocytogenes were investigated. Our results demonstrate that temperature plays a critical role in the induction of alkali stress adaptation in L monocytogenes under sublethal alkaline conditions. Pre-exposure to pH 9.0 tryptic soy broth supplemented with 0.6% yeast extract (TSB-YE) at 37 degrees C induced pronounced alkali stress adaptation whereas sublethal alkaline pre-exposure at 4 degrees C failed to induce any alkali stress adaptation. Furthermore, this pattern of alkali stress adaptation in L. monogtogenes was not dependent on the length of pre-exposure time, the concentration of sublethal alkali, the types of alkaline agents and the growth phases of cells. In addition, alkali stress adaptation induced at 37 degrees C was completely reversed in pH 7.2 TSB-YE within 2 h at 37 degrees C or within 4 h at 22 degrees C. However, once it was induced at a higher temperature, alkali stress adaptation in L. monocytogenes remained stable at 4 degrees C for at least 4 h. Our findings suggest that even though cold temperatures do not induce alkali stress adapted phenotypes, but it can maintain the previously acquired alkali stress adaptation much longer in L. monocytogenes. (C) 2015 Elsevier Ltd. All rights reserved.