1 Investigating the σB Stress Response System in Two Lineage IIIA Strains of Listeria monocytogenes

Strains of Listeria monocytogenes, an intracellular foodborne pathogen, classify into three genetic lineages. Lineage III strains, associated most commonly with animal disease, have not been extensively studied. σB, a transcription factor encoded by sigB, has been shown to contribute to stress survival and virulence in L. monocytogenes. Recent studies have revealed that σB regulons have varied among strains, and that σB did not contribute to stress survival in one representative lineage IIIA strain. The purpose of this study was to determine if σB significantly contributes to acid and oxidative stress survival in two additional lineage IIIA strains of different serotypes. Two lineage IIIA strains, FSL F2-695 and FSL F2-525, had isogenic ∆sigB mutants made using allelic exchange mutagenesis. Those strains and a control lineage II lab strain, 10403S, with its ∆sigB mutant were subjected to acid stress at pH 2.5 and oxidative stress with 13 mM cumene hydroperoxide for 15 minutes. All three isogenic ∆sigB mutants had significantly higher acid stress death rates (p < 0.001) and oxidative stress death (p < 0.01) than their corresponding wild-type strains. FSL F2-525 exhibited a significantly higher acid stress death rate than the other wild-type strains. 10403S had significantly higher oxidative stress death than FSL F2-695 (p < 0.0006). Consistent with strains in other lineages, σB is a significant factor in acid and oxidative stress survival in most lineage IIIA strains of L. monocytogenes.