Effect of antibiotic-supplemented feed on fecal enterohemorrhagic Escherichia coli O157:H7 population in lambs

We studied the efficacy of tetracycline and streptomycin in reducing fecal shedding of Escherichia coli O157:H7 by sheep experimentally infected with the pathogen prior to administration of the antibiotics. Following oral inoculation with 1010 colony-forming units (CFU) of E. coli O157:H7, three groups of six Suffolk ram lambs were fed daily for 5 weeks a basal diet without antibiotics (control) or the basal diet with 11 mg/kg of tetracycline or streptomycin. Fecal samples were collected every 5 days and analyzed for E. coli O157:H7 using modified tryptic soy broth with novobiocin as a pre-enrichment broth and cefixim-tellurite sorbitol MacConkey agar (CT-SMAC) as a selective media. E. coli O157:H7 was confirmed by its reaction with O157 and H7 antisera. E. coli O157:H7 was shed continuously and in varying numbers in the feces throughout the 7-week experimental period by all three groups. However, lambs administered streptomycin shed significantly lower (P < 0.05) total number of E. coli O157:H7 than the control and those fed tetracycline. Tetracycline-supplemented lambs were not different from control lambs. Average daily gain (ADG) and gain to feed ratio (G:F) were significantly improved (P < 0.05) by both antibiotic types. The results indicated that supplementing lambs infected with E. coli O157:H7 with streptomycin in the diet before slaughter can reduce total number of E. coli O157:H7 shed in the feces and improve average daily gain (ADG) and feed efficiency as well. Reduction of fecal shedding of E. coli O157:H7 will reduce subsequent contamination of meat by the pathogen, thereby averting the economic losses associated with this food-borne pathogen.