Antimicrobial Resistance and Potential Pathogenicity of Isolates from Healthy Broilers in Québec, Canada.

Antimicrobial resistance (AMR) is a global health issue, particularly when it affects critically important antimicrobials such as third-generation cephalosporins (3GC). The objective of this study was to characterize isolates from healthy chickens in Québec in farms where ceftiofur has been administered to chickens over a long period with regard to their AMR, multidrug resistance (MDR), potential virulence, clonality, and possession of plasmids of the incompatibility groups carrying extended-spectrum beta-lactamases (ESBLs)/AmpC genes. More than 62% of indicator isolates were MDR with resistance observed for each of the nine classes of antimicrobials tested by disk diffusion. 3GC resistance was encoded by the gene (26.7% in indicator isolates), whereas was only detected in isolates selected after supplementation with ceftriaxone (3 isolates). Examination of -positive isolates by pulsed-field gel electrophoresis showed clustering of isolates originating from different floors of the livestock building within farms. The gene was carried on replicon plasmids FIB, I1, K/B, and B/O, whereas gene was located on I1 as demonstrated by transformation experiments; some of these plasmids cotransferred nonsusceptibility against tetracycline or sulfonamides. In addition, six isolates, of which three were AmpC-producers, were defined as potential human extraintestinal pathogenic . In summary, this study showed that ESBLs/AmpC-producing isolates from apparently healthy chickens in Québec, Canada predominantly possess rather than maybe because of the use of ceftiofur to prevent omphalitis and may be spread through clones or plasmids, and that some of these isolates could be capable of infecting humans.