title: The influence of melatonin on growth of E. coli O157:H7 in pure culture and exogenous melatonin on faecal shedding of E. coli O157:H7 in experimentally infected wethers.
abstract: OBJECTIVE
  To determine if exogenous melatonin (MEL) influences growth of Escherichia coli O157:H7 in pure culture and if MEL affects faecal shedding patterns of E. coli O157:H7 or total leucocyte counts in sheep.
  
  
  RESULTS
  Two strains of E. coli O157:H7 were cultured in the presence of varying concentrations of MEL. Maximal specific growth rates of E.coli O157:H7 strains were not affected by MEL addition in pure culture. Wethers (n = 16) received either 0 (CONT) or 25 mg MEL hd(-1) day(-1) for 21 days. Daily shedding patterns of E. coli O157:H7 were not different (P > 0.10) between groups with faecal populations of E. coli O157:H7 decreasing daily (P < 0.01) in both groups. However, shedding tended to differ between the control and treated group by the end of the experiment. Total WBC and differential leucocyte counts were not affected by treatment.
  
  
  CONCLUSIONS
  Melatonin had no affect on specific growth rates in pure culture nor did the administration of exogenous MEL alter bacterial shedding patterns or immune response indicators in experimentally infected wethers exposed to a long photoperiod.
  
  
  CONCLUSIONS
  Although MEL did not affect shedding patterns or gastrointestinal populations of E. coli O157:H7, the tendency for MEL-treated sheep to shed less E. coli O157:H7 towards the end of the experiment warrants further research. Providing MEL for a longer period of time, or at greater concentrations, may elucidate a potential role that MEL plays in the seasonal shedding patterns of E. coli O157:H7 in livestock.
authors.affiliation: Land O' Lakes, Purina Feed, LLC, St Louis, MO, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Schultz
authors.forename: T S
authors.initials: TS
authors.lastname: Edrington
authors.forename: T R
authors.initials: TR
authors.lastname: Callaway
authors.forename: S B
authors.initials: SB
authors.lastname: Schroeder
authors.forename: D M
authors.initials: DM
authors.lastname: Hallford
authors.forename: K J
authors.initials: KJ
authors.lastname: Genovese
authors.forename: R C
authors.initials: RC
authors.lastname: Anderson
authors.forename: D J
authors.initials: DJ
authors.lastname: Nisbet
mesh_terms: D000818:Animals; D003470:Culture Media; D004927:Escherichia coli Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000187:drug effects / Q000254:growth & development*; D005243:Feces / Q000382:microbiology*; D007958:Leukocyte Count; D008550:Melatonin / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology / Q000382:microbiology*
chemical_list: D003470:Culture Media; D008550:Melatonin