PERSISTENCE OF ESCHERICHIA-COLI O157-H7 IN DAIRY-CATTLE AND THE DAIRYFARM ENVIRONMENT

The persistence of Escherichia coli O157:H7 in cattle and the farm env ironment was investigated on eight Ontario dairy farms positive for E. , coil O157:H7 in a longitudinal study commenced one year previously. Faecal samples from cows, calves, humans, cats, rodents, wild birds, a composite fly sample and numerous composite and individual environmen tal samples were cultured and tested for verotoxin-producing E. coil ( VTEC). VTEC isolates were serotyped and E. coli O157:H7 isolates were phage typed. E. coli O157:H7 phage type 34 was isolated from one calf on each of two farms. The same phage type had been isolated on one of these farms 12 months earlier. Most E. coli O157:H7-positive animals a nd farms became culture-negative within 2 and 3 months, respectively. E. coli O157:H7 was not isolated from any environmental samples, altho ugh evidence of VTEC was found in composite samples from calf feeders (19.1%), calf barn surfaces (18%), cow feeders (14.9%), flies (12.5%), cow barn surfaces (11.3%), and individual milli filters (12.5%). VTEC belonging to 21 non-O157 serotypes were isolated from 24 cows (8.2%), 21 calves (18.3%), 2 cow feeder samples (3.0%), and 1 calf feeder sam ple (4.8%). Shedding of E. coil O157:H7 by infected dairy cattle appea rs to be transient and persistence of E., coli O157:H7 was not demonst rated from the farm environment sites tested.