Antimicrobial resistance in Escherichia coli strains isolated from Swiss weaned pigs and sows

Monitoring programs on the development of resistance in bacteria from livestock are implemented in many countries. The aim of this study was (i) to establish baseline data on the resistance situation of Escherichia coli from 60 Swiss pig-breeding farms, and (ii) to analyze differences between weaned pigs and sows. Susceptibility testing was performed on 429 isolates from weaned pigs and 431 isolates from sows. Overall, 17.7% of the isolates from weaned pigs and 22.5% of the E. coli isolates from sows were susceptible to all antibiotics tested. Low resistance prevalence was found for amoxicillin, amoxicillin/clavulanic acid, ampicillin, gentamicin, florfenicol, ciprofloxacin, and colistin. The most common antibiotic resistances were against streptomycin (60.6% of the isolates from weaners and 64.3% of the isolates from sows), sulfonamide (51.5% and 26.9%), tetracycline (35.2% and 22.0%), and trimethoprim (27.5% and 11.1%). With exception of colistin, most resistances were found for those antibiotics commonly used on the farms. Except for ciprofloxacin and streptomycin, isolates from weaned pigs showed higher resistance prevalence than those from sows. This difference was significant for sulfonamide, tetracycline, trimethoprim, cefquinom, and florfenicol (p<0.05).