Detection and Fate of Salmonellae in Bovine Feces

Konkin-Garcia, Tamira K.
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High densities of domestic animals in human settings can result in potential human health concerns because many animals harbor and thus be vector for human pathogens. Salmonella sp. belong to a group of pathogens enter farming operations through infected feed, farm equipment, and trading infected animals. In the USA, one-third of all farming operations own animals that are carriers of Salmonella sp. Salmonella cause salmonellosis, a gastrointestinal disease mainly producing symptoms like diarrhea in mild cases, though death can occur in severe cases with immuno-compromised patients. Salmonellosis costs billions of dollars in medical care. Salmonella transmission to humans occurs from cross-contamination of meat or ready-to-eat products, or from vegetables watered or washed with contaminated water. Contamination of water is generally believed to occur through runoff from terrestrial sites, with feces from animals carrying salmonellae being washed into the aquatic system. Since feces are meant to be the original source of contamination with salmonellae, I was interested to explore the presence of salmonellae in feces, with emphasis on cattle feces, and study the fate of salmonellae after defecation as a function of changes in environmental conditions in time. In this thesis, I am addressing three hypotheses: Salmonellae can be detected regularly in fresh feces of cattle, though likely in low numbers and without noticeable impact on animal health; Salmonella populations persist in these feces more likely better under moist conditions, compared to dryer conditions (i.e. drying out in time); Salmonellae can stay viable in feces over time, though numbers might be reduced to below the detection limit of molecular tools; We detected Salmonella in fresh cattle feces in densities of up to 106 cells [g feces {dry wt.}] -1] using in situ hybridization, and were interested in their fate as a function of changes in environmental conditions in time. Population dynamics of indigenous populations of salmonellae as well as of an inoculated strain (107 cells [g feces {dry wt.}]-1) were monitored daily for 10 days in treatments with or without water evaporation, and contrasted to changes in abundance of all bacteria. Reduction in abundance of bacteria was obtained in all treatments though more pronounced at lower water availability. Populations of salmonellae followed the same pattern, however, with higher reduction rates in time in all treatments. At day 10, populations of Salmonella were below the detection limit of the in situ hybridization technique, however, still present and alive. Isolates obtained at that time represented 2 strains of Salmonella as demonstrated by rep-PCR, with one indigenous strain being most prominently isolated even from inoculated treatments. These results demonstrate that salmonellae remain viable for at least 10 days in cattle feces even though their abundance is reduced in time, with specific indigenous populations being highly competitive.
Water, PCR, In situ hybridization, Salmonella
Konkin-Garcia, T. K. (2012). <i>Detection and fate of salmonellae in bovine feces</i> (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.