UC Riverside

The fate of pathogens upon excretion to natural environments from initial hosts is not fully understood. Often overlooked is the fact that pathogens either cannot survive or lose their virulent characteristics upon exposure to environmental stress. However, problematic pathogens such as Salmonella are very resilient and acclimate well in secondary habitats; therefore requiring comprehensive studies to understand the mechanisms of fitness and survival in external environments. Additionally, despite the widespread knowledge of Salmonella and its interaction with targeted hosts, the deposition and transport behavior of this important food- and waterborne pathogen is not commonly studied. The objective of this research was to understand the fate and transport of Salmonella under a framework of environmentally relevant groundwater conditions. Therefore several Salmonella enterica serovars with different phenotypes were selected and the depositions of these pathogens onto solid surfaces were examined over a range of solution chemistries. Packed bed column and radial stagnation point flow (RSPF) systems were utilized for the transport experiments. Several batch experiments were designed to simulate the stress conditions in aquatic environments to understand the fate of Salmonella in terms of fitness, survival and virulence. These experiments were complemented by a wide range of cellular characterization techniques. Transport experiments of Salmonella in comparison to another important pathogen, E. coli O157:H7 has shown that Salmonella can be transported further than E. coli in saturated packed bed column systems. Additionally, this transport behavior was shown to be affected by different solution chemistries and cell injection concentrations. Deposition and transport behavior of three Salmonella enterica serovars with different motility phenotypes were studied in packed bed column and RSPF systems. Results have shown that flagellated strains deposit more than nonflagellated strains, concluding that nonmotile cells can be transported further than motile cells.

Several batch experiments were designed to simulate a wide range of groundwater conditions to study the fate of Salmonella upon short and long term exposure to environmental stress. Both phenotypical (antibiotic resistance, in vitro and in vivo virulence) and genotypical (gene screening in silico) evaluations of Salmonella fitness, survival, and pathogenicity were conducted. The findings of this research suggest that Salmonella successfully remains viable and virulent under a wide range of groundwater environments.