Growth Temperature-Dependent Contributions of Response Regulators, σB, PrfA, and Motility Factors to Listeria monocytogenes Invasion of Caco-2 Cells

Foodborne pathogens encounter rapidly changing environmental conditions during transmission, including exposure to temperatures below 37 degrees C. The goal of this study was to develop a better understanding of the effects of growth temperatures and temperature shifts on regulation of invasion phenotypes and invasion-associated genes in Listeria monocytogenes. We specifically characterized the effects of L. monocytogenes growth at different temperatures (30 degrees C vs. 37 degrees C) on (i) the contributions to Caco-2 invasion of different regulators (including sigma(B), PrfA, and 14 response regulators [RRs]) and invasion proteins (i. e., InlA and FlaA), and on (ii) gadA, plcA, inlA, and flaA transcript levels and their regulation. Overall, Caco-2 invasion efficiency was higher for L. monocytogenes grown at 30 degrees C than for bacteria grown at 37 degrees C (p = 0.0051 for the effect of temperature on invasion efficiency; analysis of variance); the increased invasion efficiency of the parent strain 10403S (serotype 1/2a) observed after growth at 30 degrees C persisted for 2.5 h exposure to 37 degrees C. For L. monocytogenes grown at 30 degrees C, the motility RRs DegU and CheY and sigma(B), but not PrfA, significantly contributed to Caco-2 invasion efficiency. For L. monocytogenes grown at 37 degrees C, none of the 14 RRs tested significantly contributed to Caco-2 invasion, whereas sigma(B) and PrfA contributed synergistically to invasion efficiency. At both growth temperatures there was significant synergism between the contributions to invasion of FlaA and InlA; this synergism was more pronounced after growth at 30 degrees C than at 37 degrees C. Our data show that growth temperature affects invasion efficiency and regulation of virulence-associated genes in L. monocytogenes. These data support increasing evidence that a number of environmental conditions can modulate virulence-associated phenotypes of foodborne bacterial pathogens, including L. monocytogenes.