Materials and methods
Escherichia coli strains
Escherichia coli strains were isolated from the fresh fecal
samples of poultry (chicken, duck and turkey), wild birds
(Canada goose and gull) and humans. The human fecal
sample swabs were obtained from healthy volunteers. The
cloacal swabs and/or the swabs of fresh droppings of
chicken, duck, turkey, Canada goose and gull were collected
by collaborators from different locations of British Columbia
(BC) and were transported on ice to the Water and
Watershed Research Laboratory, University of Victoria,
Victoria, BC. Upon arrival at the laboratory, the swabs were
incubated in Luria–Bertani (LB) broth at 37 1C for 24 h. The
turbid broths were diluted in 10-fold serial increments and
filtered through 47mm white gridded 0.45 mm membrane
filters (Millipore Inc.). The filters were transferred to a
50mm Petri dish containing an absorbent pad soaked with
m-ColiBlue24TM medium (Millipore Inc.) and incubated at
37 1C for 24 h. Three blue color colonies (presumptive
E. coli) per fecal sample were isolated and transferred thrice
onto LB agar to generate the pure isolate. The pure isolates
were confirmed to be E. coli according to standard biochemical
tests (Holt et al., 1994) and also by PCR amplification of
the uspA gene of E. coli (Chen & Griffiths, 1998). The
environmental E. coli isolates used in this study were
obtained from the water samples of a natural pond in
Victoria, BC, where the primary sources of fecal pollution
are Canada geese and to some extent gulls. Forty water
samples were collected from this pond and were processed
by the membrane filtration method to obtain the pure
culture of E. coli as described above. The pure E. coli isolates
were resuspended in a 40% glycerol solution and stored at
80