Modulation of cell yields and genetic responses of Salmonella fermentation and colonization in the gastrointestinal ecology of avian species
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In these studies we evaluated specific environmental stimuli relevant to Salmonella virulence and physiology in the gastrointestinal tract of chickens. Results from Salmonella growth in steady state, glucose-limiting continuous culture (CC) indicated that the optimal growth condition was observed between 0.05 h-1 and 0.27 h-1 dilution rates (D). Cell protein concentrations increased proportionally with an increase in D at each steady state, but after D 0.27 h-1 there was a reduction in the cell protein concentrations as the D increased. Genetic responses generally indicated that the lowest D exhibited highest hilA relative expression. Relatively higher expression of hilA was largely observed at low D (low glucose) (0.0125 h-1, 0.025 h-1, 0.05 h-1). Salmonella incubated in CC at different pH shifts demonstrated that cell protein concentration, glucose utilization, Yield ATP and Acetate:Propionate ratios were influenced by an increase in pH (6.14 to 7.41). These parameters increased and decreased consistently with a corresponding increase and decrease in pH. Polymerase chain reaction-based denaturant gradient gel electrophoresis showed that the overall amplicon band patterns of microbial similarity have demonstrated that hens molted with Alfalfa (ALC+) diet were similar to the Full-Fed (FF+) treatment group. Additional, FF+ and ALC+ treatment groups exhibited a higher percentage similarity coefficient (>90%) than the feed deprived treatment group. Fermentation response from cecal inocula on feed substrates revealed that alfalfa based samples yielded consistently higher short chain fatty acid levels when compared to other feed substrates. Salmonella Enteritidis (SE) colonization in liver, spleen and ovaries was significantly (P < 0.05) higher in FW+ hens compared to ALC+ and FF+ treatments groups. A 4-fold (log10 1.29) reduction in SE colonization for ALC+ hens compared to feed withdrawal hens (FW+) (log10 5.12) SE colonization was observed. Relative expression of hilA in all treatment groups was significantly (P < 0.05) higher in FW+ compared to FF+ and ALC+ groups. hilA expression in FW+ hens was 3.2-, 4.2-, and 1.9-fold higher for Days 6, 11 and 12 respectively, when compared with to ALC+ hens. These results suggest that Salmonella virulence in the gastrointestinal ecology of chickens could be impacted by a combination of low nutrients availability and pH shifts.
Dunkley, Kingsley Delroy (2006). Modulation of cell yields and genetic responses of Salmonella fermentation and colonization in the gastrointestinal ecology of avian species. Doctoral dissertation, Texas A&M University. Available electronically from