|Hallford, Dennis - NEW MEXICO ST. UNIV., NM|
|Chen, Liang - NEW MEXICO ST. UNIV., NM|
Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 29, 2007
Publication Date: September 15, 2007
Citation: Edrington, T.S., Callaway, T.R., Hallford, D.M., Chen, L., Anderson, R.C., Nisbet, D.J. 2007. Effects of exogenous melatonin and tryptophan on fecal shedding of E. Coli O157:H7 in cattle. Microbial Ecology. 55(3):553-560. Technical Abstract: Fecal prevalence of Escherichia coli O157 in ruminants is highest in the summer decreasing to very low levels in the winter. We hypothesize that this seasonal variation is a result of physiological responses within the host animal to changing day-length. To determine the effects of melatonin (MEL) on fecal shedding of E. coli O157:H7 in cattle, eight crossbred beef steers identified as shedding E. coli O157:H7, were allotted to treatment: control or MEL (0.5 mg/kg body weight (BW); 1×) administered orally daily for 7 days. After a 5-day period of no treatment, a second MEL dose (5.0 mg/kg BW; 10×) was administered daily for 4 days. Fecal samples were collected daily for qualification of E. coli O157:H7. No differences (P great than 0.10) were observed in the percentage of E. coli O157:H7 positive fecal samples in steers receiving the 1× MEL dose, however the 10× dose decreased (P=0.05) the percentage of fecal samples E. coli O157:H7 positive. Serum MEL concentrations were higher in the 1×, but not 10×, treated animals compared to control animals. Al¬though it is difficult to explain, this may be a result of decreasing day-length increasing serum melatonin concen¬trations that may have masked any treatment effect on serum melatonin. In a second similar experiment, a second group of cattle (heifers and steers) were administered tryptophan (TRP) over a 17-day experimental period (5 g/head/day for 10 days followed by 10 g/head/day for 7 days). Tryptophan had no effect (P greater than 0.20) on the percentage of fecal samples positive for E. coli O157. Serum TRP (P less than 0.05), but not MEL (P greater than 0.20), concen¬trations were elevated in TRP-treated animals. The decrease in the number of positive fecal samples observed in the first experiment may be related to gastrointestinal MEL, affected by the 10×, but not 1× MEL dose.