Animal & Veterinary
Control of EHEC in Cattle by Probiotic Bacteria
Michael P. Doyle, Tong Zhao and Ping Zhao
Center for Food Safety
University of Georgia
Griffin, GA 30223-1797
Cathy Brown, Barry Harmon and Suzana Tkalcic
Department of Pathology
College of Veterinary Medicine
University of Georgia
Athens, GA 30620-7388
Cattle are a principal reservoir of enterohemorrhagic Escherichia coli (EHEC). Recent surveillance data indicate that prevalence rates of E. coli O157:H7 in cattle are much higher than was estimated several years ago. Results of a recent study of cattle at slaughter houses in the U.S. during the summer months revealed E. coli O157:H7 in fecal samples of 28% of animals tested. This high rate of E. coli O157:H7 carriage by cattle substantiates the need for intervention strategies at the point of production to prevent contamination of food and water supplies.
Although E. coli O157:H7 is the most important EHEC serotype associated with human disease in the United States, other serotypes of EHEC strains are emerging as important pathogens in the U.S. and throughout the world. Among them are E. coli of serotypes O26:H11 and O111:NM which are recognized pathogens for both humans and young calves. E. coli O26:H11 and O111:NM reportedly all have the ability to produce in young calves colitis characterized by attachment and effacement of the colonic mucosa. E. coli O157:H7 produced attaching and effacing lesion in neonatal calves.
In previous studies, we reported that several strains of probiotic E. coli could inhibit the growth of E. coli O157:H7 in vitro and reduce or eliminate fecal shedding of E. coli O157:H7 in weaned calves. The purpose of this study was to determine the virulence of E. coli O157:H7, O26:H11 and O111:NM isolates perorally administered to very young calves (<1 week of age), and to evaluate the ability of these strains of probiotic E. coli to reduce fecal shedding of EHEC in calves pretreated with probiotic bacteria.
The pathogenicity and fecal shedding of enterohemorrhagic E. coli (EHEC) O157:H7, O26:H11, and O111:NM were compared in calves (<1 week of age) with or without prior treatment of probiotic bacteria (competitive E. coli). Three groups of 12 to 14 calves were administered perorally 108 CFU of a 5-strain mixture with one of the three EHEC serotypes per calf and 2 days thereafter half the calves in each group were perorally administered 1010 CFU of probiotic bacteria per calf. None of the EHEC caused clinical disease and neither gross nor microscopic lesions attributed to EHEC was detected in control or probiotic-treated calves at necropsy. In calves administered E. coli O157:H7, EHEC fecal shedding ended 8 days after aministration and there was no substantive difference in fecal shedding of E. coli O157:H;7 between probiotic and control groups. In contrast, control calves perorally administered E. coli O111:NM or O26:H11 continued to shed in feces substantial populations (102.1-106 CFU/g of feces and 102.5-104.9 CFU/g of feces, respectively) throughout 7 days post administration of EHEC. In both groups administered E. coli O111:NM or O26:H11, substantially smaller populations of EHEC were isolated at necropsy from the probiotic-treated group compared to the untreated control group. In two probiotic-treated calves receiving E. coli O111:NM, fecal shedding decreased by day 7 to levels detectable only by an enrichment procedure. Similarly, fecal shedding of E. coli O26:H11 decreased by day 7 to less than 101.3 CFU/g in two calves treated with probiotic bacteria.
Treatment with probiotic bacteria in calves following challenge of EHEC (E. coli O111:NM and O26:H11) can reduce the fecal shedding of EHEC when compared with the control animals.
E. coli O157:H7, O111:NM, and O26:H11 did not produce any significant pathological changes in all calves. Neonatal calves shed in feces substantially greater populations of E. coli O111:NM and O26:H11 than E. coli O157:H7 from 1 to 7 days following perorally administration of EHEC. Treatment of calves with probiotic bacteria substantially reduced fecal shedding of E. coli O111:NM and O26:H11 in most calves; however, no differences in fecal shedding were observed between the two groups for E. coli O157:H7.
Published findings based on this FDA supported research:
Zhao, T., S. Tkalcic, M. P. Doyle, B. G. Harmon, C. A. Brown, and P. Zhao. Pathogenicity of enterohemorrhagic Escherichia coli in calves and reduced in fecal shedding by treatment with probiotic E. coli. Submitted for publication.
Zhao, T., S. Tkalcic, M. P. Doyle, B. G. Harmon, C. A. Brown, and P. Zhao. Reduction of enterohemorrhagic E. coli carriage in neonatal calves by treatment with probiotic bacteria. 4th International Symposiuma nd Workshop on "Shiga Toxin (verotoxin)-producing Escherichia coli Infection." Oct. 29-Nov. 2, 2000, Kyoto, Japan. p. 91.
Brown, C. A., B. G. Harmon, T. Zhao, and M. P. Doyle. 1997. Experimental Escherichia coli O157:H7 carriage in calves. Appl. Environ. Microbiol. 63:27-32.
Harmon, B. G., C. A. Brown, S. Tkalcic, P. O. E. Mueller, A. Parks, A. V. Jain, T. Zhao, and M. P. Doyle. 1999. Fecal shedding and rumen growth of Escherichia coli O157:H7 in fasted calves. J. Food Protect. 62:574-579.
Tkalcic, S., C. A. Brown, B. G. Harmon, A. V. Jain, E. P. O. Mueller, A. Parks, K. L. Jacobsen, S. A. Martin, T. Zhao, and M. P. Doyle. 2000. Effects of diet on rumen proliferation and fecal shedding of Escherichia coli