CTX-M-producing Escherichia coli in pigs from a Czech farm during production cycle.

We evaluated the prevalence and epidemiology of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli isolates in pigs during production cycle on a Czech farm with the history of previous use of ceftiofur. ESBL-producing E. coli isolates were obtained from rectal swabs from pigs of different age groups (suckling piglets, weaned piglets, growers, and sows). Collected samples were directly cultivated on MacConkey agar with cefotaxime (2 mg/l) whereas intestinal swabs of slaughtered pigs and surface swabs from pig carcasses were also pre-enriched in buffered peptone water without antimicrobials before the cultivation. Clonal relationship of selected isolates was determined by XbaI pulse-field gel electrophoresis and multi-locus sequence typing. The transferability of plasmids carrying blaCTX-M genes was tested by conjugation experiments. From all examined samples, 141 (43.7%, n=323) were positive for ESBL-producing E. coli. All ESBL-producing isolates showed resistance to multiple antimicrobials and were positive for blaCTX-M genes. The blaCTX-M-1 was carried by conjugative IncN/ST1 plasmids (approx. 40-45 kb) while the blaCTX-M-15 was located on conjugative F plasmids with F:18:A5:B1 formula (approx. 165 kb). This study demonstrated the persistence of CTX-M-positive E. coli isolates two months after banner of ceftiofur usage and indicated possible risk of transmission of these isolates to humans via the food chain.