Novel Mechanisms Used by Salmonella Typhimurium to Colonize the Intestine
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Non-typhoidal salmonellae are zoonotic pathogens that cause the largest number of cases of bacterial foodborne gastroenteritis in the United States annually. Food products of animal origin contaminated with Salmonella are major sources for human infection in the United States with food products of bovine origin responsible for up to 30% of all outbreaks of human disease. Salmonellae are heavily studied pathogens due to the ease of genetic manipulation and rapid growth rate. However, despite thorough investigation of Salmonella virulence mechanisms over the past three decades, few studies have used relevant animal models to study the gastrointestinal phase of infection. In addition, the vast majority of inquiry has focused on few virulence loci, leaving approximately half of the genome poorly explored. We used the calf, a natural host of Salmonella and model that most closely recapitulates early enteric infection, to identify new Salmonella genes needed for infection and further characterized a subset of these genes. We identified more than 20 genes never previously implicated in enteric infection and confirmed the necessity of two genes, STM3846 (retron reverse transcriptase) and STM3602 (transcriptional regulator), during infection of the calf. Additional exploration using both mouse models and in vitro experiments showed that the STM3846 reverse transcriptase produces a RNA-DNA hybrid molecule called multicopy single-stranded DNA. This molecule regulates protein abundance during anaerobiosis, leading to poor colonization of mutants unable to produce this molecule. Further characterization of STM3602 showed that this putative transcriptional regulator is involved in regulating multiple processes that are necessary for Salmonella to thrive within the complex microbial community of the intestine. Thus, through the use of a carefully orchestrated genetic screen in a relevant animal host, novel genes were identified and their functions for colonization characterized. These genes and the processes in which they participate are potential targets for development of novel therapeutics to combat this increasingly antibiotic resistant pathogen.
Elfenbein, Johanna R (2014). Novel Mechanisms Used by Salmonella Typhimurium to Colonize the Intestine. Doctoral dissertation, Texas A & M University. Available electronically from