Clonal Relatedness and Transferable Resistance in Carbapenem-Resistant Klebsiella pneumoniae: An Integrated Molecular Epidemiological Study

Background: Carbapenem-resistant Klebsiella pneumoniae (CRKP) represents a major global clinical threat driven by both clonal relatedness and horizontal transfer of antimicrobial resistance determinants. This study aimed to characterize CRKP isolates through an integrated analysis of phenotypic resistance, resistance genes, conjugative transferability, plasmid replicon backgrounds, and clonal relatedness. Methods: A total of 62 confirmed CRKP clinical isolates were investigated. Antimicrobial susceptibility profiles were evaluated according to EUCAST criteria. Carbapenemase, β-lactamase, extended-spectrum β-lactamase-associated, and plasmid-mediated quinolone resistance (PMQR) determinants were screened by PCR. Conjugation experiments were performed using Escherichia coli J53 as the recipient strain. Plasmid replicon typing was conducted on transconjugants by PCR-based replicon typing, and clonal relatedness was assessed by pulsed-field gel electrophoresis (PFGE). Results: All isolates were resistant to ciprofloxacin, levofloxacin, imipenem, ertapenem, meropenem and ampicillin. The most prevalent resistance determinants were oqxA and oqxB (100%), blaSHV (96.8%), blaCTX-M-1 (93.5%), blaTEM and aac(6′)-Ib-cr (85.5% each), qnrD (69.4%), and blaOXA-48 (66.1%). Conjugative transfer was detected in 14 of the 62 isolates (22.6%) under the experimental conditions used. blaOXA-48, blaCTX-M-1, blaTEM, and blaSHV were detected in all transconjugants, whereas aac(6′)-Ib-cr was transferred in only one. IncFIB was the predominant replicon among transconjugants (13/14, 92.9%). PFGE analysis of 57 isolates identified 24 groups and 41 pulsotypes, with one predominant group comprising 29/57 isolates; conjugation-positive isolates were distributed across multiple PFGE backgrounds. Conclusions: The CRKP population showed extensive multidrug resistance together with both clonal clustering and horizontally transferable β-lactam resistance. The unusually high prevalence of sequence-confirmed qnrD represents a distinctive finding and, to the best of our knowledge, the first report of qnrD in clinical Klebsiella pneumoniae isolates from Türkiye. The predominance of IncFIB among transconjugants and the distribution of conjugation-positive isolates across different PFGE backgrounds support the coexistence of clonal dissemination and horizontal resistance transfer in the local CRKP population.