MOLECULAR ANALYSIS OF SALMONELLA VIRULENCE, ANTIBIOTIC RESISTANCE, AND HOST RESPONSE
Location: Food Safety and Enteric Pathogens Research Unit
Title: A Mutation in the PoxA Gene of Salmonella enterica Serovar Typhimurium Results in Altered Protein Production, Elevated Susceptibility to Environmental Challenges, and Decreased Swine Colonization
Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 17, 2010
Publication Date: February 24, 2011
Citation: Bearson, S.M., Bearson, B.L., Brunelle, B.W., Sharma, V.K., Lee, I. 2011. A mutation in the poxA gene of Salmonella enterica serovar Typhimurium results in altered protein production, elevated susceptibility to environmental challenges, and decreased swine colonization. Foodborne Pathogens and Disease. 8(6):725-732.
Interpretive Summary: Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) is a human foodborne pathogen. Salmonella Typhimurium is also one of the most prominent Salmonella serovars isolated from swine production farms. Unfortunately, Salmonella Typhimurium can undetectably reside in pigs without causing noticeable infection. These Salmonella-carrier pigs are a food safety problem for humans, contaminating naïve pigs, the environment, and slaughter plants that process pork for consumption. This study was performed to investigate a mutation in a specific gene of Salmonella Typhimurium (poxA); mutation of the poxA gene reduced the ability of the bacterium to survive numerous stress conditions and chemical exposures. Furthermore, the poxA gene mutation decreased the ability of Salmonella Typhimurium to colonize the pig. Therefore, we have identified an important gene of Salmonella Typhimurium that is required for environmental stress survival and pig colonization. A potential intervention strategy could target the function of this gene in Salmonella Typhimurium, causing the bacterium to be more susceptible to host defenses and environmental stress. Industry, university and government researchers investigating host-pathogen interactions should find this research interesting, especially those investigating control strategies of Salmonella in food production animals.
Using signature-tagged mutagenesis of Salmonella enterica serovar Typhimurium (S. Typhimurium), a mutation in the poxA gene (STM4344; yjeA; poxR), encoding a putative lysyl-tRNA synthetase, was previously identified by our research group which caused decreased survival in an ex vivo swine stomach content assay. In this study, complementation with a plasmid-encoded poxA gene restored survival of the poxA mutant to the level of the parental, wild-type strain. To determine if the mutation in poxA affects colonization of the swine gastrointestinal tract, eight week old pigs were intranasally inoculated with either the wild-type S. Typhimurium strain or the poxA mutant (n=5 for each group). Fecal shedding of the poxA mutant was significantly reduced throughout the 7-day study compared to the wild-type strain, as was the presence of the mutant in the cecal contents of the pigs and colonization of the tonsils at 7 dpi (P < 0.05). Body temperature (fever) of the pigs inoculated with wild-type S. Typhimurium was significantly higher than pigs inoculated with the poxA mutant (P < 0.05). Two-dimensional protein gel analysis revealed characteristic differences in the protein profile of the poxA mutant relative to the wild-type strain. In addition, Biolog’s phenotypic microarray analysis of the poxA mutant showed elevated respiration due to enhanced utilization of metabolic pathways and increased sensitivity to an assortment of chemical and stress conditions. As a member of the class-II aminoacyl-tRNA synthetase family, these findings suggest that eliminating poxA in S. Typhimurium may alter which mRNA transcripts are translated, thereby changing the protein profile of the pathogen and affecting a variety of bacterial processes including stress survival and colonization of the natural swine host.