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Title: Growth and genetic responses of Salmonella Typhimurium to pH-shifts in an anaerobic continuous culture

item Callaway, Todd
item CHALOVA, V - Texas A&M University
item Anderson, Robin
item KUNDINGER, M - Texas A&M University
item DUNKLEY, C - Texas A&M University
item Nisbet, David

Submitted to: Anaerobe
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2008
Publication Date: 5/7/2008
Citation: Dunkley, K.D., Callaway, T.R., Chalova, V.I., Anderson, R.C., Kundinger, M.M., Dunkley, C.S., Nisbet, D.J., Ricke, S.C. 2008. Growth and genetic responses of Salmonella Typhimurium to pH-shifts in an anaerobic continuous culture. Anaerobe. 14:35-42.

Interpretive Summary: Salmonella is a pathogenic bacteria commonly found in the gut of chickens and is frequently the cause of human foodborne illnesses related to consumption of poultry products. The gut of birds contains regions of different pH values (i.e., level of acidity), and by changing the pH we can affect the virulence and survivability of pathogens such as Salmonella. In our study, we evaluated the effects of shifting the environmental pH in a gut simulation model and we determined the expression of virulence genes by Salmonella. Gene expression was altered by pH changes and were different at each pH. These results indicate that pH changes can be a determining factor in survival of Salmonella in the gut of animals, and is an exploitable mechanism to help reduce the virulence of these pathogens.

Technical Abstract: Salmonella infection of chickens that leads to potential human foodborne salmonellosis continues to be a concern. Changes in the pH of poultry gastrointestinal tract could influence Salmonella growth and virulence response. In the current study, growth responses of a chicken isolate Salmonella enterica serovar Typhimurium (ST) to three incremental pH-shifts (6.17 to 7.35) in continuous cultures (CC) were evaluated. The expression of rpoS and hilA was determined by Real Time-Polymerase Chain Reaction (RT-PCR) as well. Increases in pH resulted in higher cell protein concentrations, glucose disappearance, and glucose and ATP yields. Although with some inconsistency between the two trials, the data indicated that the ammonia release into media was favored by low pH. The pH shifts did not significantly affect acetate biosynthesis. No consistent trends of pH influence on propionate and butyrate production could be detected. In all three pH shifts, relative expression of hilA was dominant at 0 h which represented CC steady state. In pH shift 7.35 to 6.86 (Trial 1), the relative expression of rpoS at time 0 and 1 h were over 5-fold higher than after 3 and 6 h of growth. Overall, the results suggest that ST activities including growth and gene expression are altered by changes in pH, which could be a determinant factor in ST survival in gastrointestinal ecosystems of food animals. .