Molecular epidemiology of antimicrobial-resistant commensal Escherichia coli strains in a cohort of newborn calves.

Pulsed-field gel electrophoresis (PFGE) was used to investigate the dissemination and diversity of ampicillin-resistant (Amp(r)) and nalidixic acid-resistant (Nal(r)) commensal Escherichia coli strains in a cohort of 48 newborn calves. Calves were sampled weekly from birth for up to 21 weeks and a single resistant isolate selected from positive samples for genotyping and further phenotypic characterization. The Amp(r) population showed the greatest diversity, with a total of 56 different genotype patterns identified, of which 5 predominated, while the Nal(r) population appeared to be largely clonal, with over 97% of isolates belonging to just two different PFGE patterns.

High-level genotypic variation and antibiotic sensitivity among Escherichia coli O157 strains isolated from two Scottish beef cattle farms.

Escherichia coli O157:H7 is a human pathogen that is carried and transmitted by cattle. Scotland is known to have one of the highest rates of E. coli O157 human infections in the world.