σB Plays a Limited Role in the Ability of Listeria monocytogenes Strain F2365 To Survive Oxidative and Acid Stress and in Its Virulence Characteristics

Listeria monocyto genes 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 that was involved in the listeriosis outbreak associated with Mexican-style soft cheese 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 acid and oxidative stress. F2365 has neither the sigma(B)-dependent ability to survive acid or oxidative stress nor the sigma(B)-dependent ability to infect Caco-2 epithelial cells in vitro or guinea pigs in vivo. More studies are needed to determine whether the atypical sigma(B)-independent response to stress observed in F2365 is strain specific, serotype specific, or even lineage specific.