Differential Effects of Antibiotics on the Horizontal Transfer of blaKPC Plasmid in Clinical Klebsiella pneumoniae Strain

Horizontal transfer of blaKPC-bearing plasmids contributes significantly to the dissemination of carbapenem resistance among Enterobacterales; however, the influence of mechanistically distinct antibiotics on this process remains incompletely understood. This study investigated the effects of meropenem, gepotidacin, and omadacycline on plasmid-mediated transfer of blaKPC from the carbapenem-resistant K. pneumoniae donor strain CDC120 to the ESBL-producing K. pneumoniae recipient strain DS073. Conjugation assays were performed under sub-inhibitory antibiotic concentrations, and plasmid transfer was confirmed by PCR and antimicrobial susceptibility testing. Expression of the conjugation-associated genes traT, traS, traN, and traG was quantified by quantitative real-time PCR (qRT-PCR). Meropenem produced the highest conjugation frequency (3.07 × 10−7 transconjugants per donor), followed by gepotidacin (4.55 × 10−8) and omadacycline (3.38 × 10−9). These differences were reflected phenotypically, with meropenem-selected transconjugants demonstrating the greatest increase in meropenem minimum inhibitory concentration (MIC), followed by gepotidacin and omadacycline. Gene expression analysis revealed antibiotic-specific regulation of conjugation-associated genes rather than uniform activation of the conjugation machinery. Among the genes examined, traS exhibited the strongest induction across all antibiotic treatments, whereas traT was consistently downregulated and traN and traG displayed treatment-dependent expression patterns. Collectively, these findings demonstrate that antibiotics differentially influence plasmid transfer efficiency and the expression of conjugation-associated genes, thereby affecting the dissemination of blaKPC-mediated carbapenem resistance.