Slaughtered pigs as reservoirs of One Health-relevant antimicrobial resistance genes in Klebsiella pneumoniae from Brazil.

INTRODUCTION: Klebsiella pneumoniae is an important opportunistic pathogen and a recognized reservoir of antimicrobial resistance (AMR) determinants. However, information on AMR profiles and genomic characteristics of Klebsiella circulating in Brazilian swine production remains limited. This study investigated the occurrence, antimicrobial susceptibility, resistance determinants, and genomic characteristics of Klebsiella spp. recovered from pigs at slaughter in southeastern Brazil. METHODS: Rectal swabs were collected from 100 pigs at slaughter, and Klebsiella isolates were identified by culture and PCR. Antimicrobial susceptibility was determined by disk diffusion and broth microdilution for colistin. AMR genes were investigated by PCR, and four representative multidrug-resistant (MDR) K. pneumoniae isolates carrying multiple β-lactam, quinolone, and tetracycline resistance genes were further characterized by whole-genome sequencing and comparative genomic analysis. RESULTS: Fifty-three Klebsiella isolates were recovered, including 47 K. pneumoniae, four Klebsiella oxytoca, one Klebsiella quasipneumoniae, and one Klebsiella spp. High frequencies of non-susceptibility were observed for tetracycline (86.8%), ciprofloxacin (77.4%), and amoxicillin-clavulanate (67.9%), while 34 isolates (64.2%) were classified as MDR. Three colistin-resistant isolates carried mcr-1. The most frequently detected AMR genes were bla SHV , bla TEM , tetA, qnrS, and oqxAB. Whole-genome sequencing identified two genomic lineages, ST45 and ST1027, differing in resistance gene content and capsular and O-antigen loci. All sequenced isolates carried the acquired siderophore loci ybt and iuc, indicating the coexistence of acquired virulence-associated loci and multiple AMR genes. DISCUSSION: These findings demonstrate a high occurrence of MDR K. pneumoniae carrying clinically important resistance determinants in pigs at slaughter and reveal the circulation of distinct genomic lineages harboring acquired virulence-associated loci. The results suggest that swine production systems may contribute to the maintenance and potential dissemination of One Health-relevant K. pneumoniae and highlight the importance of integrated genomic surveillance to support antimicrobial stewardship and food safety.