|Cook, Kimberly - Kim|
Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2013
Publication Date: 5/28/2013
Publication URL: http://handle.nal.usda.gov/10113/57158
Citation: Cook, K.L., Flis, S.A., Ballard, C.S. 2013. Sensitivity of mycobacterium avium subsp paratuberculosis, escherichia coli and salmonella enterica serotype typhimurium to low pH, high organic acids and ensiling. Journal of Applied Microbiology. 115:334-345. doi:10.1111/jam.12243. Interpretive Summary: Pathogens responsible for Johne’s disease and gastroenteritis are surprisingly resistant to ensiling process. Mycobacterium avium subsp paratuberculosis (M. paratuberculosis) and Salmonella enterica serotype Typhimurium (S. Typhimurium) are two pathogens that are a concern to food and animal safety due to their ability to withstand harsh conditions encountered in the natural environment and within the host during pathogenesis. Acid tolerance is one mechanism by which pathogens survive adverse conditions and acid adaptation may even increase the organisms’ virulence. ARS scientists in the AWMRU Lab at Bowling Green, KY in collaboration with scientists from the Miner Institute in Chazy, NY evaluated the ability of these pathogens to survive the low pH and high organic acid concentrations encountered as part of the ensiling process. Researchers found that E.coli, S. Typhimurium and M. paratuberculosis exhibit marked differences in response to silage and silage exudates. M. paratuberculosis, the cause of Johne’s disease in cattle, was especially resistant suggesting that when present in manure and applied to forage grasses M. paratuberculosis may survive exposure to low pH’s and high organic acids during the ensilaging process and could, therefore, be a potential route of infection if ingested by a susceptible animal. This information is important for farmers using silage for food preservation and researchers evaluating of potential risks associated with contamination of livestock feed and the environment with manure-borne pathogens.
Technical Abstract: The ability of Mycobacterium avium subsp paratuberculosis (M. paratuberculosis), Salmonella enterica serotype Typhimurium (S. Typhimurium) and a commensal Escherichia coli (E. coli) isolate to persist under low pH and high organic acid conditions was determined. Die-off rates were calculated following (1) exposure to buffered organic acid (OA) (2) exposure to silage exudates and (3) survival through the ensiling process. S. Typhimurium had higher decay rates in silage exudates (-0.5601 day-1) than in the buffered OA (-0.1556 day-1). E. coli had similar rates of decay in silage exudates (-0.1285 day-1) as in buffered OA (-0.164 day-1). Decay rates for M. paratuberculosis exposed to silage exudates were almost 7 times lower than when exposed to buffered OA. All three organisms had significantly lower die-off rates in silage than in buffered OA or silage exudates. E.coli, S. Typhimurium and M. paratuberculosis exhibit marked differences in response to acidity. This information is important for silage preservation and evaluation of potential risks associated with contamination of livestock feed and the environment with manure-borne pathogens but also contributes to the understanding of survival of these organisms in any low pH environment.