Occurrence of quinolone resistant Escherichia coli in Norwegian dairy cattle

Abstract

This study aimed to obtain further understanding of the occurrence of quinolone-resistant Escherichia coli QREC) from cattle despite negligible quinolone usage in cattle treatment, to identify risk factors for QREC among Norwegian dairy cattle, and to gain more knowledge of QREC dynamics over time. QREC occurrence was investigated according to the intensity of milk production in a cross-sectional study. In parallel with this, a longitudinal study was conducted in which QREC occurrence in cows and their calves was screened during the first three months postpartum. QREC occurrence was more abundant in high-intensive farms. Clinically resistant QREC isolates were detected. The most abundant phenotypic multi-resistance pattern was against ciprofloxacin, nalidixic acid, ampicillin, sulfamethaxazole, trimethoprim, and tetracycline. A co-occurrence of QREC isolated from cows, calves, and the environment at the farm level was found. There was a higher within-sample prevalence of QREC in calves compared to postpartum cows. Both studies found a clonal distribution of QREC isolates within the farms. Sequence type 162 that has been isolated from other farm- and wild animals in Norway, was detected in one farms. The within-sample prevalence of QREC seemed low in terms of total E. coli. Repeated findings of QREC in bovine faecal material could indicate a widespread occurrence of QREC despite Norway's long-term low usage of quinolones.