Role of ς^Bin Heat, Ethanol, Acid, and Oxidative Stress Resistance and during Carbon Starvation inListeria monocytogenes

Abstract

To determine the contribution of sigma B ( B ) to survival of stationary-phase Listeria monocytogenes cells following exposure to environmental stresses, we compared the viability of strain 10403S with that of an isogenic nonpolar sigB null mutant strain after exposure to heat (50°C), ethanol (16.5%), or acid (pH 2.5). Strain viabilities were also determined under the same conditions in cultures that had been previously exposed to sublethal levels of the same stresses (45°C, 5% ethanol, or pH 4.5). The ⌬sigB and wild-type strains had similar viabilities following exposure to ethanol and heat, but the ⌬sigB strain was almost 10,000-fold more susceptible to lethal acid stress than its parent strain. However, a 1-h preexposure to pH 4.5 yielded a 1,000-fold improvement in viability for the ⌬sigB strain. These results suggest the existence in L. monocytogenes of both a B -dependent mechanism and a pH-dependent mechanism for acid resistance in the stationary phase.B contributed to resistance to both oxidative stress and carbon starvation in L. monocytogenes. The ⌬sigB strain was 100-fold more sensitive to 13.8 mM cumene hydroperoxide than the wild-type strain. Following glucose depletion, the ⌬sigB strain lost viability more rapidly than the parent strain.B contributions to viability during carbon starvation and to acid resistance and oxidative stress resistance support the hypothesis that B plays a role in protecting L. monocytogenes against environmental adversities.

Contributions of Listeria monocytogenes σ B and PrfA to expression of virulence and stress response genes during extra- and intracellular growth

“…While these results may seem surprising, considering the well-documented occurrence in the vacuole of the types of stressful conditions that have been shown to activate s B or to affect survival of a DsigB mutant (e.g. low pH, oxidative stress) (Chaturongakul & Boor, 2004;Ferreira et al, 2001;Maul et al, 1995;Sue et al, 2004), virulence gene expression has been shown to differ between L. monocytogenes present in professional and nonprofessional phagocytes (Bubert et al, 1999). Hence, it is possible that the intravacuolar environment of professional phagocytes is a more stressful environment for intracellular bacterial pathogens than that in other cell types, which may Table 2) detects transcripts covering the plcA coding region; probe 2 ('plcA-readthrough') detects plcA readthrough transcription; probe 3 ('prfA-P1') detects P1prfA transcript including plcA readthrough transcripts; probe 4 ('prfA-CDS') detects all prfA coding region transcripts.…”

“…haemolysin production (Freitag & Portnoy, 1994;Nadon et al, 2002), it does not affect L. monocytogenes invasion capabilities in human intestinal epithelial cell lines (Kim et al, 2004(Kim et al, , 2005. In L. monocytogenes, s B also contributes to survival under a variety of lethal environmental stresses (Ferreira et al, 2001), including acidic conditions mimicking mammalian gastric fluid (Chaturongakul & Boor, 2004;Cotter et al, 2001;Wiedmann et al, 1998).…”

σ B-dependent gene induction and expression in Listeria monocytogenes during osmotic and acid stress conditions simulating the intestinal environment

“…Overnight broth cultures were diluted 1 : 1000 into 10 ml BHI broth and incubated at 30 uC. When these cultures reached OD 600 =0?4, they were each diluted again (1 : 200) into 120 ml BHI and incubated until each culture reached OD 600 =0?4, as previously described (Ferreira et al, 2001(Ferreira et al, , 2003.…”

Recent Advances in the Study of the Genotypic Diversity and Ecology of Listeria monocytogenes

“…In L. monocytogenes, the gene encoding σ B (sigB) was identified based on its homology to the sigB gene from Bacillus subtilis. Phenotypic characterization of L. monocytogenes strains lacking sigB has shown that σ B plays a role in resistance to various forms of environmental stress, including osmotic, oxidative, and acid stress [16][17][18] . Also, a broad role for σ B -dependent genes in virulence has recently been sug- gested for Gram-positive bacteria.…”