Sensitivity ofMycobacterium aviumsubspparatuberculosis,Escherichia coliandSalmonella entericaserotype Typhimurium to low pH, high organic acids and ensiling

Abstract

To evaluate the persistence of Mycobacterium avium subsp paratuberculosis (Myco. paratuberculosis), Salmonella enterica serotype Typhimurium (Salm.Typhimurium) and a commensal Escherichia coli (E. coli) isolate under the low pH and high organic acid (OA) conditions of ensiling of forages. Decay rates and the time required to obtain a 90% reduction in cell concentration were calculated following (i) exposure to buffered OA (pH 4.0, 5.0, 6.0 or 7.0) (ii) exposure to silage exudates and (iii) survival through ensiling of forage materials. Salm. Typhimurium had higher decay rates in silage exudates (-0.5601 day(-1) ) than did E. coli (-0.1265 day(-1) ), but both exhibited lower decay rates in silage than in OA or silage exudates. Myco. paratuberculosis showed no decrease in silage and decay rates in silage exudates were significantly lower (2-12 times) than for the other two organisms. Escherichia coli, Salm. Typhimurium and Myco. paratuberculosis exhibit marked differences in response to acidity. All three organisms show acid resistance, but Myco. paratuberculosis in particular, if present in manure and applied to forage grasses, may survive the low pH and high OA of the ensilaging process; silage may therefore be a potential route of infection if ingested by a susceptible animal. This information contributes to the understanding of potential risks associated with silage preservation and contamination of livestock feed with manure-borne pathogens.