Effect of sublethal heat stress on Salmonella Typhimurium virulence

Abstract

Aims: To determine the virulence gene expression of Salmonella Typhimurium in response to sublethal heat stress and determine the adhesion and invasion pattern of heat‐stressed Salmonella in Caco‐2 intestinal epithelial cells. Methods and Results: Transcriptional profiling was employed to capture the virulence gene response of Salm. Typhimurium at 42°C sublethal heat stress. Data indicated an induction of SPI‐2 and SPI‐5 genes and a repression of SPI‐1‐encoded genes due to heat stress. Gene expression pattern also showed induced transcription of fimbriae genes and genes present within the stress‐associated Rpo regulon. Changes in adhesion and invasion pattern of heat‐stressed Salm. Typhimurium were tested in Caco‐2 cells. Heat‐stressed Salm. Typhimurium showed greater adhesion to Caco‐2 cells compared with nonstressed control cells. Conclusions: Salmonella Typhimurium exposed to sublethal heat stress responds by altered virulence gene expression, which further enhances the adhesion of bacterial cells to intestinal Caco‐2 cells. Results indicate a role of physiological stress in Salm. Typhimurium in promoting microbial virulence and host cell vulnerability to infection. Significance and Impact of the Study: Studying the Salmonella virulence genes expression in response to sublethal heat stress is crucial for the understanding of the virulence status of Salmonella in temperature‐abused foods. Results of this study provide information about the gene response and virulence status of Salmonella pathogenicity factors in response to sublethal heat stress towards host cells.

Salmonella Pathogenicity and Host Adaptation in Chicken-Associated Serovars

“…Conversely, genes related to attachment and/or motility functions were induced, which has been observed previously for S. Typhimurium attachment genes after exposure to 42°C (351). There was also a repression of several heat shock response genes, which, in conjunction with cell membrane damage, indicates that membrane integrity is an important component for Salmonella cells to accurately assess their extracellular environmental conditions and respond accordingly (351). Clearly, more in-depth genetic analysis is needed to sort out the interactions that occur among different stresses in Salmonella versus its collective virulence response capabilities as well as how these may shift over time after initial encounters with the cell's surrounding environment.…”

“…When Milillo et al compared S. Typhimurium transcriptome responses to sodium acetate and sodium propionate exposure after 1 min (55°C at pH 4.0), the respective gene expression patterns were similar, with no increases in expression levels of rpoS, phoPQ, or virulence factors despite their established roles in organic and inorganic acid stress (35,327,328,338). Conversely, genes related to attachment and/or motility functions were induced, which has been observed previously for S. Typhimurium attachment genes after exposure to 42°C (351). There was also a repression of several heat shock response genes, which, in conjunction with cell membrane damage, indicates that membrane integrity is an important component for Salmonella cells to accurately assess their extracellular environmental conditions and respond accordingly (351).…”

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“…The association of Salmonella virulence plasmids with both antibiotic and stress resistance genes as reported in some studies (Dione et al, 2011;Sirsat et al, 2011), could play a major role in the persistence and spread of both resistance and virulence genes in Salmonella and other related pathogens. This may constitute a serious public health challenge in resource poor rural African settings…”

Molecular analysis of the adaptive response in Salmonella Typhimurium after starvation in salty conditions

“…Typhimurium responds to various stimuli such as oxidative stress, extreme pH, heat shock, osmotic conditions, and starvation by changing the expression of groups of genes termed "stimulons" [9]. Genes that contribute to the fitness of the pathogen within the host have been classified as virulence factors [10,11]. Several virulence factors are involved in the adaptive response to environmental conditions because pathogens are exposed to a variety of stresses [10].…”

“…Genes that contribute to the fitness of the pathogen within the host have been classified as virulence factors [10,11]. Several virulence factors are involved in the adaptive response to environmental conditions because pathogens are exposed to a variety of stresses [10]. Studies using mice, together with in vitro models such as cultured eukaryotic cells, have yielded details about the molecular and genetic events that underpin some aspects of Salmonella virulence [12,13].…”