Stability of sublethal acid stress adaptaion and induced cross protection against lauric arginate in Listeria monocytogenes

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

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2015
Publication Date: 6/1/2015
Citation: Qian, S., Kamlesh, S., Ramakrishna, N. 2015. Stability of sublethal acid stress adaptaion and induced cross protection against lauric arginate in Listeria monocytogenes. International Journal of Food Microbiology. 203:49-54.

Interpretive Summary: Majority of previous studies focused on how L. monocytogenes cells respond to lethal acid or other lethal inactivation treatments immediately after acid adaptation. However, these are not the typical scenarios that occur under food processing conditions where formation of acid-adapted phenotypes is not immediately followed by lethal inactivation treatments. The stability of acid adaptation and its induced cross protection effect, which is defined as the capacity to maintain its acquired acid adaptation and cross protection effect after the induction of acid adaptation, has never been investigated before. It is an important aspect to understand the real impact of acid adaptation in L. monocytogenes on the food processing conditions. In addition, this information is critical for conducting a comprehensive risk analysis during food processing under which the use of acidulants is highly frequent. Our study demonstrated that acid adaptation in L. monocytogenes is stable at 4°C not at 37°C or 22°C in the absence of sublethal acid stress. These findings show that acid stress adaptation can protect the L. monocytogenes cells from other antimicrobial inactivation treatments if acid adaptation was immediately followed by lethal inactivation treatments.

Technical Abstract: The stability of acid stress adaptation in Listeria monocytogenes and its induced cross protection effect against GRAS (generally recognized as safe) antimicrobial compounds has never been investigated before. In the present study, the acid stress adaptation in L. monocytogenes was initially induced in pH 5.0 tryptic soy broth supplemented with 0.6% yeast extract (TSB-YE) at 37°C. Subsequently, the stability of acid stress adaptation, which was defined as the capacity to maintain its acquired acid adaptation after induction in the absence of sublethal acid stress, was determined at 37°C, 22°C or 4°C in broth and in different food substrates. Then, the acid stress adaptation induced cross protection against lauric arginate (LAE) and its stability was investigated in TSB-YE, milk and carrot juice. Our findings show that the acid stress adaptation was stable at 4°C up to 24 h but was reversed at 37°C or 22°C within 2 h. In the cross protection assay with LAE, the acid stress adapted cells had approximately 2 log CFU/ml greater survival than non-adapted cells in broth at 22°C or in milk and carrot juice at 4°C. The acid adaptation induced cross protection against LAE in L. monocytogenes was reversible within 1 h at 4°C in the absence of sublethal acid stress. Our findings suggest that the stability of acid adaptation in L. monocytogenes under cold conditions should be taken into account when the risk analysis is performed during food processing.