Effects of exogenous melatonin and tryptophan on fecal shedding of "E. Coli" O157:H7 in cattle

• Tom S. Edrington ; Todd R. Callaway ; Dennis M. Hallford ^[1] ; Liang Chen ^[1] ; Robin C. Anderson ; David J. Nisbet
  1. [1] New Mexico State University

     New Mexico State University

     Estados Unidos

     
• Localización: Microbial ecology, ISSN-e 1432-184X, ISSN 0095-3628, Vol. 55, Nº. 3, 2008, págs. 553-560
• Idioma: inglés
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• Resumen

  • 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 > 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. Although it is difficult to explain, this may be a result of decreasing day-length increasing serum melatonin concentrations 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 > 0.20) on the percentage of fecal samples positive for E. coli O157. Serum TRP (P < 0.05), but not MEL (P > 0.20), concentrations 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.