Abstract
Antimicrobial resistant (AMR) bacteria are increasing threats for human and veterinary
medicine. Faecal Escherichia coli (E. coli) from preweaned dairy calves is often
resistant to multiple antimicrobials and calves may therefore serve as reservoirs for
these bacteria and their resistance genes. This thesis investigated the prevalence, risk
factors, and spread of resistant E. coli on Swedish dairy farms, with special emphasis
on quinolone resistant E. coli (QREC). Faecal samples from preweaned calves and
post-partum cows were analysed for resistant E. coli and set in relation to potential risk
factors. The farm environment was sampled to study the occurrence and spread of
QREC.