Temporal shedding patterns and virulence factors of Escherichia coli serogroups O26, O103, O111, O145, and O157 in a cohort of beef calves and their dams.

This study investigated the shedding of Escherichia coli O26, O103, O111, O145, and O157 in a cohort of beef calves from birth over a 5-month period and assessed the relationship between shedding in calves and shedding in their dams, the relationship between shedding and scouring in calves, and the effect of housing on shedding in calves. Fecal samples were tested by immunomagnetic separation and by PCR and DNA hybridization assays. E. coli O26 was shed by 94% of calves. Over 90% of E. coli O26 isolates carried the vtx(1), eae, and ehl genes, 6.5% carried vtx(1) and vtx(2), and one isolate carried vtx(2) only. Serogroup O26 isolates comprised seven pulsed-field gel electrophoresis (PFGE) patterns but were dominated by one pattern which represented 85.7% of isolates. E. coli O103 was shed by 51% of calves. Forty-eight percent of E. coli O103 isolates carried eae and ehl, 2% carried vtx(2), and none carried vtx(1). Serogroup O103 isolates comprised 10 PFGE patterns and were dominated by two patterns representing 62.5% of isolates. Shedding of E. coli O145 and O157 was rare. All serogroup O145 isolates carried eae, but none carried vtx(1) or vtx(2). All but one serogroup O157 isolate carried vtx(2), eae, and ehl. E. coli O111 was not detected. In most calves, the temporal pattern of E. coli O26 and O103 shedding was random. E. coli O26 was detected in three times as many samples as E. coli O103, and the rate at which calves began shedding E. coli O26 for the first time was five times greater than that for E. coli O103. For E. coli O26, O103, and O157, there was no association between shedding by calves and shedding by dams within 1 week of birth. For E. coli O26 and O103, there was no association between shedding and scouring, and there was no significant change in shedding following housing.