Listeria monocytogenes strain F2365 has reduced ability to survive stress while maintaining virulence characteristics

Listeria monocytogenes strain F2365 was the first strain representative of serotype 4b (lineage I) to be sequenced in 2004, suggesting it could become the model organism for this serotype, which is associated with most human outbreaks of listeriosis worldwide to date. F2365 itself is an outbreak strain involved in the Mexican-style soft cheese outbreak in California in 1985. In this study we show through phenotypic and transcriptomic analysis that L. monocytogenes strain F2365 has reduced ability to respond to stress due to the absence of a functional σB-dependent stress response system. F2365 shows no B-dependent ability to survive acid or oxidative stress nor B-dependent ability to infect Caco-2 epithelial cell in vitro or guinea pigs in vivo. Therefore, there is substantial evidence that F2365 is an atypical strain and is not a suitable representative of outbreak-associated serotype 4b strains. Independent RNA isolations were performed for F2365 and ΔsigB strains from cells grown to early stationary phase. Three biological replicates were used in competitive whole-genome microarray experiments. For each set of hybridizations, RNA from a L. monocytogenes wildtype strain was hybridized with RNA from its isogenic ΔsigB null mutant.