Survival of acid stress adapted cells of Listeria monocytogenes serotypes 1/2a and 4b in commonly used disinfectants in broth and water models

Authors: DHOWLAGHAR, N - Mississippi State University; SHEN, Q - Mississippi State University; NANNAPANENI, R - Mississippi State University; SCHILLING, W - Mississippi State University; SAMALA, A - Mississippi State University

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2019
Publication Date: 7/1/2019
Citation: Dhowlaghar, N., Shen, Q., Nannapaneni, R., Schilling, W., Samala, A. 2019. Survival of acid stress adapted cells of Listeria monocytogenes serotypes 1/2a and 4b in commonly used disinfectants in broth and water models. LWT - Food Science and Technology. 109:201-206.

Interpretive Summary: Controlling Listeria monocytogenes in the food-manufacturing environment is difficult despite it is sensitive to commonly used chemical disinfectants. L. monocytogenes acid stress adaptation can induce cross resistance to other physiological stresses and antimicrobials, which increases the possibility of its persistence in various food products or on food contact surfaces. Despite the extensive knowledge on the cross-protection effect from L. monocytogenes acid stress adaptation, few studies have comprehensively investigated the impact of acid stress adaptation on the survival of L. monocytogenes in several types of commonly used disinfectants. Moreover, most of the previous studies compared the survival of acid stress adapted and non-adapted L. monocytogenes cells by performing lethal acidic challenges in rich media (i.e. BHI or TSBYE). Water is typically used as a solvent during the cleaning process in food processing plant. The acid stress adaptation induced cross protection effect in broth might not truly predict the survival pattern in water. Therefore, the objective of this study was to determine the survival of acid stress adapted cells of L. monocytogenes 1/2a (Scott A) and 4b (Bug 600) in various classes of disinfectants which included acids, bases, chlorine, alcohols, oxidative agents and quaternary ammonium compounds (QACs) in both broth (TSBYE) and non-broth (deionized water) model. Planktonic cells of L. monocytogenes when pre-exposed to sublethal acid-stress significantly survived in both models tested (broth and water) when exposed in lethal concentrations of acid, quaternary ammonium and alcohol-based disinfectants for 2 h or to alkaline-based disinfectants for 7 h. Our findings suggest that oxidation-based agents such as H2O2 and chlorine are the best choices to clean and sanitize the food contact surfaces when acid stress adapted L. monocytogenes cells may reside.

Technical Abstract: The purpose of this study was to determine the survival of acid stress adapted Listeria monocytogenes Bug600 and ScottA cells in various lethal concentrations of disinfectants in broth and water models. Acid stress adapted cells had significantly greater survival than the non-adapted cells in lethal concentrations of hydrochloric acid, lactic acid, and acetic acid in tryptic soy broth containing yeast extract (TSBYE). Also, acid stress adaptation protected L. monocytogenes cells against lethal sodium hydroxide (NaOH), potassium hydroxide (KOH) and ammonium hydroxide (NH4OH). Increased tolerance to lethal concentrations of ethanol and isopropanol was also observed after acid stress adaptation. Acid stress adapted cells also exhibited higher survival in two quaternary ammonium compounds (QAC-1 and QAC-2). Acid stress adapted cells were more susceptible to hydrogen peroxide (H2O2) inactivation. Similar survival patterns were observed for the acid stress adapted and non-adapted cells in both water and broth models, suggesting that the impact of acid adaptation on L. monocytogenes survival in disinfectants was not altered due to the presence of nutrients. Overall, these findings indicate that oxidation-based agents are the best choices to decontaminate the food contact surface where acid stress adapted L. monocytogenes cells may be present.