Whole-Genome Insights Into Tigecycline-Resistant Klebsiella Spp. Harboring Colistin Resistance Gene From Food Animals in Türkiye.

Antimicrobial-resistant (AMR) Klebsiella spp., the common agents of nosocomial infections, are on the rise and becoming increasingly dangerous, with tigecycline-resistant strains posing a serious clinical threat. This study aimed to characterize isolated tigecycline-resistant strains from Türkiye by using whole-genome sequencing (WGS). The genomes of 40 strains, recovered from turkey caecum samples (n = 23, K. pneumoniae), chicken caecum samples (n = 8, K. pneumoniae; n = 2, K. oxytoca), and chicken meat samples (n = 7, K. pneumoniae), were determined. Additionally, Oxford Nanopore Sequencing was conducted on subsets (mcr-8-positive, n = 9) to characterize the plasmids responsible for colistin resistance spread. Sequence analysis revealed that all K. pneumoniae harbored the tet(A) gene without detectable mutations, whereas several alterations were detected in the ramR gene. Additionally, other tetracycline-encoding genes were also detected in few isolates, including tet(B), tet(D), tet(J), and tet(M). Genomic analysis revealed various AMR genes, including the plasmid-mediated colistin resistance gene mcr-8, for which hybrid assemblies confirmed the localization on IncF group plasmids associated with IS903B. Conjugation assay showed the transferability of mcr-8 in isolates (8/9) to Escherichia coli recipient strains. WGS analysis also revealed 11 different sequence types (STs), with ST37 appearing as the predominant lineage among both tigecycline- and colistin-resistant isolates. Phylogenetic comparison with previously sequenced isolates showed close genetic relatedness between certain isolates and international clones. To our knowledge, this is the first report of mcr-8 in Klebsiella strains from food animals in Türkiye, highlighting a potential risk for transmission of last-resort antimicrobial resistance genes to humans. Hence, continuous genomic surveillance is urgently needed to monitor the spread of these resistance determinants within the One Health perspective.