Development of a probiotic colicinogenic mix to inhibit Escherichia coli O157:H7 in cattle

A previously identified set of colicinogenic Escherichia coli inhibitory to E. coli O157:H7 was assessed as a pre-harvest food safety intervention in cattle. Twenty-three colicinogenic E. coli were first characterized for virulence factors, antibiotic resistance, and type of colicin(s) present. Nine strains were eliminated from the collection due to possession of a pathogen gene or antibiotic resistance. The remaining fourteen strains were evaluated for previously identified colicins. Seven colicins (B, E1, E2/E7, E7, Ia/Ib, K, and M) were detected. Eight strains that produced colicin E7 were assessed for their ability to inhibit E. coli O157:H7 in artificially inoculated calves. The cattle experiment consisted of three periods that evaluated two probiotic dose levels, with the treatment animals receiving either 107 or 108 CFU/g of colicinogenic E. coli in their feed daily. The count of E. coli O157:H7 was consistently higher during the three periods in the control groups. One group comparison found an overall difference of 1.1 log10 CFU/g reduction that was observed with a maximum decrease of 1.8 log10 CFU/g. The overall statistical significance was P = 0.001. Serotype O157:H7 was detected in 44% of the treatment group's intestinal tissue samples and in 64% of those from the control group (P < 0.04). Ninety-six strains of E. coli O157:H7 were assessed for their resistance potential against anti-0157 colicinogenic E. coli. Thirteen of the fourteen anti-O157 colicinogenic E. coli strains were able to inhibit all 96 E. coli O157:H7 strains. Thirteen of 96 E. coli O157:H7 strains were found to be colicinogenic and eleven of those had genes that encoded for colicin D. PCR products for colicins B, E-type, Ia/Ib and M were also detected individually or combined with other colicins in four strains. The ability of colicin resistance development against single-colicin producing E. coli was observed under in vitro conditions, however the ability of E. coli O157:H7 to become colicinogenic or colicin resistant under in vivo conditions was not observed. These findings indicate that colicinogenic E. coli may be used to reduce E. coli O157:H7 fecal shedding in cattle.