Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2017
Publication Date: 11/27/2017
Citation: Richardson, K.E., Cox Jr, N.A., Cosby, D.E., Berrang, M.E. 2018. Impact of desiccation and heat exposure stress on Salmonella tolerance to acidic conditions. Journal of Environmental Science and Health. Part B, 53:2:141-144. 10.1080/03601234.2017.1397467.
Interpretive Summary: Naturally occurring Salmonella in feed samples can be in either a stressed or non-stressed state. Therefore stressed and non-stressed cultures of important feed isolates of Salmonella serotypes were subjected to the acidic conditions that can occur in the firs step (pre-enrichment) in the laboratory cultural procedures. This study demonstrated how the condition of the salmonella (stressed or non-stressed) along with the acidity of the pre-enrichment medium may influence which Salmonella serotypes are isolated from feed samples.
Technical Abstract: In a recent study, the pH of commonly used Salmonella pre-enrichment media became acidic (pH 4.0 to 5.0) when feed or feed ingredients were incubated for 24 hrs. Acidic conditions have been reported to injure or kill Salmonella. In this study, cultures of four known feed isolates (S. Montevideo, S. Senftenberg, S. Tennessee and S. Schwarzengrund) and four important processing plant isolates (S. Typhimurium, S. Enteritidis, S. Infantis, and S. Heidelberg) were grown on meat and bone meal and later subjected to desiccation and heat exposure to stress the microorganism. The impact of stress on the isolates ability to survive in acidic conditions ranging from pH 4.0 to 7.0 were compared to the non-stressed isolate. Cell injury was determined on xylose lysine tergitol 4 (XLT4) and cell death determined on nutrient agar (NA). When measured by cell death in non-stressed Salmonella, S. Typhimurium was the most acid tolerant and S. Heidelberg was the most acid sensitive whereas in stressed Salmonella, S. Senftenberg was the most acid tolerant and S. Tennessee was the most acid sensitive. The pH required to cause cell injury varied among isolates. With some isolates, the pH required for 50% cell death and 50% cell injury were similar. In other isolates, cell injury occurred at a more neutral pH. These findings suggest that the pH of pre-enrichment media may influence the recovery and bias the serotype of Salmonella recovered from feed during pre-enrichment.