Investigation of pathogenicity, competitive fitness, and novel methods for rapid diagnosis of Salmonella 4,[5],12:i:- in swine

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Naberhaus, Samantha
Major Professor
Amanda J. Kreuder
Adam C. Krull
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Veterinary Microbiology and Preventive Medicine
Our faculty promote the understanding of causes of infectious disease in animals and the mechanisms by which diseases develop at the organismal, cellular and molecular levels. Veterinary microbiology also includes research on the interaction of pathogenic and symbiotic microbes with their hosts and the host response to infection.
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Salmonella enterica subsp. enterica serovar 4,[5],12:i:- is widely accepted to be a monophasic variant of Salmonella Typhimurium. Salmonella 4,[5],12:i:- has been increasing significantly in prevalence worldwide over the past decade while S. Typhimurium has been subsequently decreasing. Both Salmonella serovars 4,[5],12:i:- and Typhimurium are contained in Salmonella serogroup B, which is currently the predominant serogroup in swine in the United States. However, this serogroup contains serovars of a wide range of pathogenic potential, with Typhimurium generally being associated with enterocolitis and Agona and Derby generally being considered to be of lesser pathogenicity. The pathogenic potential for S. 4,[5],12:i:- in swine is largely unknown but is hypothesized to be similar to S. Typhimurium based on genetic similarities. Current diagnostic procedures for the detection and identification of Salmonella have a wide range of sensitivities, and culture-based protocols have a prolonged turn-around time to serovar-level identification due to the complex serotyping process. To facilitate more rapid detection and serovar-level identification, the work conducted within this thesis validated a multiplex real-time PCR capable of detecting Salmonella spp. in general and differentiating S. 4,[5],12:i:- and S. Typhimurium from other lesser-pathogenic serovars. Further work was focused on determining the level of clinical disease, colonization of tissues, and persistence of infections to be expected with the S. 4,[5],12:i:- in swine. For this study, pigs were experimentally infected with S. 4,[5],12:i:-, S. Typhimurium, or S. Derby to compare S. 4,[5],12:i:- to the pathogenic S. Typhimurium and less-pathogenic S. Derby. This work demonstrated that S. 4,[5],12:i:- induces similar levels of clinical disease, tissue colonization, and persistent infections to that of S. Typhimurium, both of which were more severe than that of S. Derby. Simultaneous infection of swine with equal amounts of S. 4,[5],12:i:- and S. Typhimurium revealed S. 4,[5],12:i:- is detected in higher levels in the feces, tonsils and ileocecal lymph nodes than S. Typhimurium, indicating a potential increased competitive fitness of the monophasic variant. The collective results of these studies provide improved diagnostics and needed insight into the disease causing ability of an increasingly prevalent serovar of Salmonella that is capable of infecting swine, humans, and other species.

Thu Aug 01 00:00:00 UTC 2019