Antimicrobial susceptibility in faecal Escherichia coli from pigs after enrofloxacin administration in an experimental environment

The study objective was to evaluate the effect of oral (OT) and parenteral (PT) administration of enrofloxacin to weaners on untreated contact animals. We assessed a) fluoroquinolone occurrence in the blood serum of untreated contact animals (COT, CPT); b) resistance to (fluoro)quinolones in commensal Escherichia coli (E. coli) in OT, PT, COT and CPT compared to the control (CON), and c) resistance to other antimicrobials in E. coli in OT, PT, COT and CPT compared to the initial situation before the treatment in these groups. Five groups of 14 weaners each were housed in three separate rooms (OT with COT, PT with CPT, CON alone). OT and PT were treated with enrofloxacin for five days. Rectal swabs and blood samples were taken before, during and until 51 days after treatment. Enro- and ciprofloxacin were detected in all treated, all COT and half of the CPT pigs. Neither through selective isolation nor by susceptibility testing of one random non-selectively isolated faecal E. coli per sample, resistance to ciprofloxacin (metabolite of enrofloxacin) and nalidixic acid was detected in both treatment and contact groups during and short after treatment. However, a transient increase of E. coli resistant to antimicrobials other than quinolones followed the treatment in isolates from OT and COT (e.g. ampicillin p < 0.05). In conclusion, animals in contact with treated animals are exposed to and can intake antimicrobials. Animals in contact with orally treated animals show occurrence of antibiotic resistant E. coli. Further studies are needed to show whether these preliminary findings can be confirmed under different conditions and with more sensitive detection methods.