Phenotypic and molecular characterization of β-lactamase and plasmid-mediated quinolone resistance genes in Klebsiella oxytoca isolated from slaughtered pigs in Thailand

Background and Aim: Over recent years, antimicrobial-resistant Klebsiella species in humans, animals, food animals, food products, and agricultural environments have been the center of attention due to its role in the evolution of antimicrobial resistance. The emergence of resistance to fluoroquinolones and cephalosporins of third and higher generations in Klebsiella oxytoca has not received much attention in animal husbandry compared to that in Klebsiella pneumoniae. Reports on K. oxytoca are limited in the study area. Therefore, we investigated the antimicrobial susceptibility and resistance genes in K. oxytoca isolated from slaughtered pigs in Thailand. Materials and Methods: Microbiological examination was conducted on 384 Klebsiella spp. isolates recovered from slaughtered pigs in ten provinces of Thailand. Seventy-two K. oxytoca isolates (18.75%) were examined for antimicrobial-resistant genes (β-lactamase [blaTEM, blaCTX-M, and blaSHV]) and fluoroquinolone-resistant genes (qnrA, qnrB, qnrC, qnrD, qnrS, oqxAB, aac(6')-Ib-cr, and qepA). Results: The most common genotype was blaCTX-M (58/72, 80.55%), followed by blaTEM with blaCTX-M (7/72, 9.72%) and blaTEM (6/72, 8.33%). The most common blaCTX-M group was blaCTX-M-1 (19/58, 32.76%), followed by blaCTX-M-9 (1/58, 1.72%). Plasmid-mediated quinolone resistance genes were identified in 13 (18.05%) isolates: qnrS (16.70%) and qnrB (1.4%). All 13 isolates had qnrS transferable to an Escherichia coli recipient, whereas qnrB was not detected in any transconjugants. Either blaCTX-M or blaTEM harbored by one K. oxytoca strain was transferable to an E. coli recipient. Analysis of antimicrobial susceptibility revealed that more than 90% of the blaCTX-M-carrying K. oxytoca isolates were susceptible to chloramphenicol, trimethoprim, ceftazidime, cefepime, cefotaxime, amoxicillin-clavulanic acid, piperacillin–tazobactam, and fosfomycin. All K. oxytoca isolates (13) harboring qnr were susceptible to carbapenem and ceftriaxone; however, 43 (74.13%) of the K. oxytoca isolates harboring blaCTX-M exhibited extended-spectrum β-lactamase activity. Most of the K. oxytoca isolates from pigs were highly resistant to ampicillin, azithromycin, and gentamicin. Conclusion: To prevent further transmission of Klebsiella spp. between food animals and humans, strict control of antibiotic use in clinical and livestock settings is necessary along with routine disinfection of the livestock environment and efforts to increase awareness of antimicrobial resistance transmission.