Proteins of the Cold Shock Domain Family (Csps) Contribute to Nisin and Benzalkonium Chloride Stress Tolerance in Listeria monocytogenes

Introduction: Listeria monocytogenes causes rare but serious foodborne illness (Listeriosis) and high mortality in those with diminished immunity. Cold shock domain family proteins (Csps) are global gene expression regulators that promote stress adaptation responses in bacteria. Nisin and Benzalkonium chloride (BC) are widely used antimicrobials in preservation of food and disinfection of food processing environments, respectively.

Purpose: To investigate the functional contribution of Csps to the innate resistance of L. monocytogenes against stress associated with nisin and BC.

Methods: L. monocytogenes EGDe wild type and csp deletion mutant strains were phenotypically compared under nisin and BC stress using growth assays and gene expression analysis by quantitative reverse transcription PCR (RT-qPCR).

Results: In absence of Csp functions the sensitivity of L. monocytogenes EGDe to nisin and BC stress exposure was increased. Growth and survival capacity of the L. monocytogenes EGDe under nisin and BC stress is significantly (P < 0.05) diminished without Csps compared to the wild type strain. In addition, Csp loss also increases the susceptibility of L. monocytogenes to cell envelope-targeting antibiotics including ampicillin and polymixin B. The induction of csp gene transcripts in response to nisin but not BC exposure was detected. Finally a comparative gene expression analysis revealed an altered expression in genes encoding peptidoglycan-binding proteins (PBPs) in absence of Csp functions.

Significance: Our results suggest that Csp mediated gene expression regulation events contribute to the optimal execution of intrinsic nisin and BC resistance mechanisms in L. monocytogenes.