Influence of Exogenous Melatonin on Horizontal Transfer of Escherichia coli O157:H7 in Experimentally Infected Sheep

Abstract

The objective of the current research was to determine if exogenous melatonin would exert a "protective" effect on the gastrointestinal tract of sheep and prevent or reduce the horizontal transfer of Escherichia coli O157:H7 from experimentally infected to noninfected or "naïve" sheep. Sixteen cross-bred ewes were housed indoors and adapted to a high concentrate ration. Ewes were randomly assigned to one of four rooms and treatment (three ewes/room, six ewes/treatment) and received either control (gelatin capsule only) or melatonin (5.0 mg/kg body weight [BW]/d). Four additional ewes served as "carrier" sheep (one/room) and were experimentally infected via oral gavage with E. coli O157:H7. Three days post-challenge, carrier ewes were housed with naïve sheep and remained with them for the remainder of the experimental period. Treatments were administered to the naïve sheep 1 day prior to introduction of the carrier sheep and on each of the remaining 7 days of the experimental period. Fecal samples were collected via rectal palpation from the carrier sheep daily throughout experiment and from the naïve sheep daily for 5 days, starting 2 days following introduction of the carriers. On day 8 of the experiment, all ewes were euthanized and tissues from the rumen, ileum, cecum, colon, and rectum as well as their respective lumen contents collected. The carrier sheep quickly infected the naïve ewes, which had similar fecal concentrations as the carrier animals throughout the 5-day sampling period. Melatonin treatment had no effect (p > 0.10) on daily fecal shedding, luminal content concentrations, or in the percentage of gastrointestinal tract tissue positive for the inoculated strain of E. coli O157:H7.

Comparison of recto-anal mucosal swab and faecal culture for the detection ofEscherichia coliO157 and identification of super-shedding in a mob of Merino sheep

“…Numerous factors are likely to have contributed to this outcome, particularly the type of housing used in the present study, as our findings are consistent with surveys of sheep housed in confined environments such as feedlots and holding yards [27]. Such environments promote faecal-oral transmission and increase the rate of contact between infected and naive individuals, favouring horizontal transmission of enteric pathogens [28]. The dietary change that occurred when moving the mob into indoor pens may also have influenced the concentration and duration of faecal shedding reported here.…”

Utilizing melatonin to combat bacterial infections and septic injury

“…No differences were observed in the percentage of E. coli O157:H7 positive faecal samples in steers receiving 0.5 mg·kg −1 body weight melatonin; however, 5.0 mg·kg −1 body weight melatonin significantly reduced the percentage of faecal samples containing E. coli O157:H7 (Edrington et al , ). In another study, 5.0 mg·kg −1 body weight melatonin treatment was without effect on daily faecal shedding, on luminal content concentrations or on the percentage of gastrointestinal tract tissue positive for the inoculated strain of E. coli O157:H7 (Edrington et al , ). Although melatonin did not influence the shedding patterns or gastrointestinal populations of E. coli O157:H7, the tendency for melatonin‐treated sheep to shed fewer E. coli O157:H7 as the study progressed warrants further examination (Schultz et al , ).…”