Unravelling the Molecular Mechanisms Underlying the Protective Effect of Lactate on the High-Pressure Resistance of Listeria monocytogenes

Abstract

Formulations with lactate as an antimicrobial and high-pressure processing (HPP) as a lethal treatment are combined strategies used to control L. monocytogenes in cooked meat products. Previous studies have shown that when HPP is applied in products with lactate, the inactivation of L. monocytogenes is lower than that without lactate. The purpose of the present work was to identify the molecular mechanisms underlying the piezo-protection effect of lactate. Two L. monocytogenes strains (CTC1034 and EGDe) were independently inoculated in a cooked ham model medium without and with 2.8% potassium lactate. Samples were pressurized at 400 MPa for 10 min at 10 °C. Samples were subjected to RNA extraction, and a shotgun transcriptome sequencing was performed. The short exposure of L. monocytogenes cells to lactate through its inoculation in a cooked ham model with lactate 1h before HPP promoted a shift in the pathogen’s central metabolism, favoring the metabolism of propanediol and ethanolamine together with the synthesis of the B12 cofactor. Moreover, the results suggest an activated methyl cycle that would promote modifications in membrane properties resulting in an enhanced resistance of the pathogen to HPP. This study provides insights on the mechanisms developed by L. monocytogenes in response to lactate and/or HPP and sheds light on the understanding of the piezo-protective effect of lactate.

The efficacy and safety of high‐pressure processing of food

“…The effect of preservatives (additives, such as organic acids) on HPP microbial inactivation can vary: some studies reported enhanced inactivation of Salmonella in a raw meat matrix when lactic acid was added (Serra‐Castello et al., 2019), while when used as a salt (i.e. lactate) they show a dose‐dependent piezo‐protective effect on L. monocytogenes in laboratory media (Serra‐Castello et al., 2021a) and in different types of meat products (Marcos et al., 2008b; Lerasle et al., 2014; Stollewerk et al., 2014; Serra‐Castello et al., 2021b).…”

“…2.8% (Serra‐Castello et al., 2021b). Though the effect might be partially related to the a w lowering effects of lactate, other mechanisms might be involved as the protection has been found even without changing the physico‐chemical characteristics of the product (Marcos et al., 2008a; Lerasle et al., 2014; Serra‐Castello et al., 2021a,b). Other organic acids in the form of salt, that can be used in RTE foods include acetate/diacetate (alone or in combination with lactate).…”