Influence of temperature on alkali stress adaptation in Listeria monocytogenes

Authors: SHEN, Q - Mississippi State University; PANDARE, P - Mississippi State University; SONI, K - Mississippi State University; NANNAPANENI, R - Mississippi State University; MAHMOUD, B - Mississippi State University; SHARMA, C - Mississippi State University

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2015
Publication Date: 4/1/2016
Citation: Shen, Q., Pandare, P., Soni, K., Nannapaneni, R., Mahmoud, B., Sharma, C.S. 2016. Influence of temperature on alkali stress adaptation in Listeria monocytogenes. Food Control. 62:74-80.

Interpretive Summary: Alkali stress is still one of the most important stresses that L. monocytogenes may encounter due to the wide spread use of alkaline agents to clean and sanitize the food contact surfaces. During the sanitation process, L. monocytogenes may be exposed to sublethal concentrations of the alkaline agents, thus triggering the alkali stress adaptation. Sublethal alkali stress adaptation in L. monocytogenes may also provide cross protection against other antimicrobial treatments. In some situations, instead of being exposed to a lethal inactivation treatment immediately after adaptation, it is possible that alkali stress adapted L. monocytogenes cells remaining on the surface may come in contact with the next batch of raw food materials. Under those conditions, the stability of alkali stress adaptation in L. monocytogenes may play a critical role in escaping the further inactivation treatments such as pasteurization. Our findings show that he induction of alkali stress adaptation in L. monocytogenes under sublethal alkaline conditions is temperature dependent. Such induction that typically occurs under 37ºC or 22ºC does not take place at 4ºC. In addition, upon induction, the alkali stress adaptation is more stable at 4ºC than at 37ºC or 22ºC under neutral conditions. This study suggests that the alkaline cleaning agents should be used at recommended concentrations and temperatures so that they effectively clean all the surfaces and a repeated cleaning process may be required on the previously cleaned surfaces to inactivate all the remaining alkali adapted L. monocytogenes cells.

Technical Abstract: 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 °C induced pronounced alkali stress adaptation whereas sublethal alkaline pre-exposure at 4 °C failed to induce any alkali stress adaptation. Furthermore, this pattern of alkali stress adaptation in L. monocytogenes 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 °C was completely reversed in pH 7.2 TSB-YE within 2 h at 37 °C or within 4 h at 22 °C. However, once it was induced at a higher temperature, alkali stress adaptation in L. monocytogenes remained stable at 4 °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.