Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2007
Publication Date: 2/1/2008
Citation: Edrington, T.S., Callaway, T.R., Haliford, D.M., Anderson, R.C., Nisbet, D.J. 2008. Effects of exogenous melatonin and tryptophan on fecal shedding of E. coli 0157:H7 in cattle. Microbial Ecology. 55:553-560. Interpretive Summary: Cattle and sheep are naturally infected with E. coli O157:H7, a bacteria that causes food sickness in humans. This bacteria is more common in cattle in the summer months than in the winter but nobody knows the reason for this seasonality. We hypothesize that hormones produced by the animal and known to respond to changing day-length may be responsible for the seasonal changes in E. coli O157:H7 prevalence. We conducted research with beef cattle and demonstrated that administration of oral melatonin decreased the incidence of fecal shedding of E. coli O157:H7. However, dosing the amino acid tryptophan, a precursor for melatonin, had no effect on E. coli O157:H7 shedding in cattle. Understanding the biology of E. coli O157:H7 will enable the design of effective strategies to control this bacteria.
Technical Abstract: Fecal prevalence of E. 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 BW; 1X) administered orally daily for seven days. Following a five day period of no treatment, a second MEL dose (5.0 mg/kg BW; 10X) was administered daily for four days. Fecal samples were collected daily for qualification of E. coli O157:H7. No differences (P > 0.10) were observed in fecal shedding of E. coli O157:H7 in steers receiving the 1X MEL dose, however the 10X dose decreased (P = 0.05) the number of cattle shedding E. coli O157:H7. Serum MEL concentrations were higher in the 1X, but not 10X, treated animals. In a second similar experiment, cattle were administered tryptophan (TRP) over a 17-d experimental period (5 g/head/day for 10 days followed by 10 g/head/day for 7 days). Tryptophan had no effect (P > 0.20) on fecal shedding of E. coli O157. Serum TRP (P < 0.05), but not MEL (P > 0.20), concentrations were elevated in TRP-treated animals. The decrease in fecal shedding observed in the first experiment, may be related to gastro-intestinal MEL, affected by the 10X, but not 1X MEL dose.