Novel Strategies For Characterizing And Controlling The Stress Response Of Listeria Spp.

Abstract

The genus Listeria includes nine species, including the foodborne pathogen Listeria monocytogenes, which can cause serious illness in humans. Listeria spp. exist in urban and natural environments and are able to survive a diverse range of physiological conditions, to which the general stress response contributes. In Listeria spp. and other Gram-positive organisms, the general stress response is regulated by the alternative sigma factor sigma B (!B). In these studies, we explored several novel methods of controlling and characterizing Listeria spp. in areas relevant to food safety, ranging from inactivation technologies to newly identified compounds for controlling the bacterial stress response. Specifically, the work presented here investigated: i) the use of Pulsed Light (PL), a nonthermal method, to inactivate Listeria innocua (a surrogate organism for L. monocytogenes) on packaging materials, ii) the transcriptional responses to stress of persistent and non-persistent strains of L. monocytogenes isolated from food processing environments as a possible mechanism of persistence, and iii) a novel small molecule inhibitor of !B activity in L. monocytogenes and related Bacillus subtilis. We found that PL was able to achieve inactivation of L. innocua up to 7.2 log CFU on low density polyethylene, and that inactivation was associated with the reflectance properties of the packaging materials that we tested. We found that L. monocytogenes strains from food processing plants classified as persistent did not induce higher transcript levels of four stress genes regulated by the transcriptional factors CtsR and !B in response to salt stress compared to non-persistent strains. Finally, we determined that fluoro-phenyl-styrene-sulfonamide (FPSS), a novel inhibitor of !B activity, inhibits the activation of !B in response to environmental and energy stresses in B. subtilis, and we conclude FPSS does not exert its inhibitory effect by interactions with the phosphatases RsbP or RsbU, or the members of the RsbV/RsbW/!B partner switching model that is central to the regulation of !B. FPSS inhibits !B activity by a yet unknown mechanism, and determining its mechanism of action will further our understanding of the regulation of !B.