Submitted to: Pathogenicity and Virulence of Verotoxigenic Escherichia Coli
Publication Type: Proceedings
Publication Acceptance Date: 11/10/1999
Publication Date: N/A
Technical Abstract: Human illness caused by VTEC has been epidemiologically linked to ruminants and cattle are considered to be a reservoir. We hypothesized that VTEC are specifically adapted to colonize and persist in ruminants. To test this hypothesis sheep were inoculated with a cocktail of E. coli strains consisting of 2 VTEC O157:H7, 2 ETEC (F4 or F5), and 1 EPEC. Fecal shedding of the cocktail strains was monitored. Sheep were inoculated with all 5 strains at 10**10 CFU or with the 2 VTEC and the F4 ETEC strain at 10**7 CFU. All strains were recovered 2-4 d postinoculation (PI). At 2 wks PI, 10/12 sheep shed both VTEC strains and 6/12 shed the F4 ETEC strain. At 2 months PI, one VTEC strain was shed by 4/12 sheep and the second strain by 6/12 sheep. The F4 ETEC was recovered only from 3/6 sheep given 10**10 CFU and the other strains were not recovered. In contrast, both VTEC strains were recovered from sheep given either dose. When sheep were given 10**10 CFU of either wild-type VTEC or an isogenic intimin deletion mutant, the mutant was recovered from 1/4 sheep 2 wks PI, whereas the wild type was recovered from 4/4 sheep. At 2 months PI, the mutant was not recovered but 2/4 sheep shed the wild type. In additional studies, the transmission of the E. coli cocktail to naive sheep was examined. When fecal shedding of cocktail strains from donor sheep was = 10**4 CFU/g, transmission to naive sheep was detected for 4/5 strains. Thus, VTEC were no more transmissible than the other strains. The results suggest ruminants are a reservoir of VTEC O157, intimin is needed for persistent colonization, and transmission between sheep occurs readily.