Stress and E. coli O157 shedding in cattle

Purpose: Cattle are a major reservoir of E. coli O157 and source of food-borne disease outbreaks worldwide. Individual animals exhibit significant variation in faecal shedding of E. coli O157 despite known environmental exposure to the bacteria. The host factors that predispose ruminants to E. coli O157 colonisation and the variation in individual animal shedding remain poorly understood. The aim of this study was to explore the relationship between physiological stress and the presence and concentration of E. coli O157 shedding in cattle.
Methods: Faecal samples were collected from 24 beef cows daily over 14 days in summer. The concentration of faecal glucocorticoid metabolites (FGMs) was measured using the previously validated corticosterone I125 radioimmunoassay kit. The faecal samples were also analysed for E. coli O157 using standard techniques. Statistical analyses were performed using a mixed model approach to determine associations between FGMs, numerous environmental variables and a) presence and b) concentration of E.coli O157.
Results: Associations were identified between FGMs and presence (P = 0.018) and concentration (P = 0.012) of E. coli O157 in bovine faeces. Both probability of shedding and quantity of pathogen shed increased with increasing FGMs and changes in FGMs were found to precede changes in shedding. Interactions were also identified between humidity and FGMs, for both models (P = 0.030 and P = 0.028 respectively).
Conclusions: The findings of the present study are the first to show an association between the concentration of FGMs, as a measure of physiological stress, and the presence and concentration of E. coli O157 in bovine faeces.
Relevance: Despite extensive research and increased implementation of intervention strategies to minimise shedding and carcase contamination, foodborne outbreaks of E. coli O157 continue to occur. This study identifies a link between a marker of physiological stress and the occurrence and quantity of pathogen shed that warrants further investigation in order to elucidate the precise nature of the link and potentially facilitate the development of targeted mitigation strategies.