Influence of temperature on acid-stress adaptation in Listeria monocytogenes

Authors: QIAN, SHEN - Mississippi State University; KAMLESH, SONI - Mississippi State University; RAMAKRISHNA, NANNAPANENI - Mississippi State University

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2013
Publication Date: 1/1/2014
Citation: Qian, S., Kamlesh, S., Ramakrishna, N. 2014. Influence of temperature on acid-stress adaptation in Listeria monocytogenes. Foodborne Pathogens and Disease. 11:43-49.

Interpretive Summary: In the industrialized countries, foodborne listeriosis is responsible for nearly 25-30% mortality rate among infected individuals. These outbreaks are frequently associated with contamination of Listeria monocytogenes in ready-to-eat (RTE) food products such as deli meat, Mexican-style cheese, cold smoked fish, salads and fresh fruits. Food and drug administration (FDA) and U.S. Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) have a “zero tolerance” policy for L. monocytogenes in RTE food products. Listeria monocytogenes exhibits sophisticated adaptive mechanisms to counteract higher levels of lethal acid, heat, salt or oxidative stresses after pre-exposure to sublethal concentrations of the same stress or different stress environments. Of all the stress adaptations, acid-stress adaptation in L. monocytogenes has received extensive attention. Under food processing conditions, L. monocytogenes cells may be exposed to suboptimal temperatures (4°C to 22°C) which are much lower than that of laboratory conditions. The effect of refrigeration temperatures on acid-stress adaptation in L. monocytogenes is not known. Our findings show that temperature plays a significant role in the induction of acid-stress adaptation in Listeria monocytogenes and two distinct patterns were observed. Our findings suggest that cold temperature can prevent the risk of acid-stress adaptation in L. monocytogenes and our risk analysis may contribute to the critical control point practice of the pathogens in the food industry.

Technical Abstract: Several factors play critical roles in controlling the induction of acid-stress adaptation in L. monocytogenes. Our findings show that temperature plays a significant role in the induction of acid-stress adaptation in Listeria monocytogenes and two distinct patterns were observed: (I) Presence of sublethal acid at 37°C or 22°C significantly induced acid-stress adaptation; and (II) Presence of sublethal acid at 4°C did not induce any acid-stress adaptation. Both patterns were confirmed by two experimental models: (1) L. monocytogenes cells were first grown at 37°C and then exposed to sublethal acid at 37°C, 22°C and 4°C prior to lethal acid challenge; (2) Alternatively, L. monocytogenes cells were first grown at 4°C for 20 days before pre-exposure to sublethal acid and then challenged with lethal acid. Regardless of whether L. monocytogenes cells were simultaneously exposed with both cold stress and sublethal acid stress, or subjected to cold growth first before exposure to sublethal acid, no acid-stress adaptation was induced at 4°C. We also found that acid-stress adaptation in L. monocytogenes did not occur in acidic whey at 4ºC. Bead beating treatment prior to mild acid pre-exposure at 4°C partially induced acid adaptation in L. monocytogenes. Our findings suggest that cold temperature can prevent the risk of acid-stress adaptation in L. monocytogenes.