Purpose: The specific purpose of the study was to identify L. monocytogenes two-component system response regulators that modulate resistance to food antimicrobial compounds.
Methods: L. monocytogenes two-component system response regulators (i.e., liaR, lisR, virR, cesR) that have previously been determined to have a role in responding to cell envelope stress were deleted via allelic exchange method and screened for antimicrobial sensitivity using a minimum inhibitory concentration (MIC) assay in brain heart infusion (BHI) broth. In addition, we assessed the viability of the wild type (WT) and response regulator mutants following exposure to the antimicrobial stress using the Live/Dead staining procedure.
Results: The data from the MIC assay indicated that DvirR was 16-, 4-, and 4-fold more sensitive to NIS, EPL, and CHI, respectively, compared to the WT. A significantly higher proportion of ‘dead’ populations as indicated by the nucleic acid stain ratio (SYTO-9 to propidium iodide) was observed for DvirR compared to the WT under NIS, EPL, and CHI stress (P < 0.05), indicating that VirR contributes to overcoming the antimicrobial stress.
Significance: Identifying regulators involved in antimicrobial stress response is critical for elucidating potential resistance mechanisms. The mechanistic understanding of the resistance mechanisms can then foster opportunities for further improvement in food antimicrobial intervention strategies as these regulatory feature(s) can be exploited using combination treatments that have knowledge-based rationale.