Resistance to last resort antibiotics in bacteria is an emerging threat to human and animal health. It is important to identify the source of these antimicrobial resistant (AMR) bacteria that are resistant to clinically important antibiotics and evaluate their potential transfer among bacteria. The objectives of this study were to (i) detect bacteria resistant to colistin, carbapenems, and β-lactams in commercial poultry farms, (ii) characterize phylogenetic and virulence markers of E. coli
isolates to potentiate virulence risk, and (iii) assess potential transfer of AMR from these isolates via conjugation. Ceca contents from laying hens from conventional cage (CC) and cage-free (CF) farms at three maturity stages were randomly sampled and screened for extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae
, carbapenem-resistant Acinetobacter
(CRA), and colistin resistant Escherichia coli
(CRE) using CHROMagar™ selective media. We found a wide-spread abundance of CRE in both CC and CF hens across all three maturity stages. Extraintestinal pathogenic Escherichia coli
phylogenetic groups B2 and D, as well as plasmidic virulence markers iss
, were widely associated with AMR E. coli
isolates. ESBL-producing Enterobacteriaceae
were uniquely detected in the early lay period of both CC and CF, while multidrug resistant (MDR) Acinetobacter
were found in peak and late lay periods of both CC and CF. CRA was detected in CF hens only. blaCMY
was detected in ESBL-producing E. coli
in CC and CF and MDR Acinetobacter
spp. in CC. Finally, the blaCMY
was shown to be transferrable via an IncK/B plasmid in CC. The presence of MDR to the last-resort antibiotics that are transferable between bacteria in food-producing animals is alarming and warrants studies to develop strategies for their mitigation in the environment.
This is an open access article distributed under the Creative Commons Attribution License
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.