Molecular characterization of two conjugative resistance plasmids from a clinical multidrug-resistant ST15 Klebsiella pneumoniae

The increasing emergence of multidrug-resistant (MDR) Klebsiella pneumoniae strains has become a threat to public health, and it is important to understand the mechanisms underlying adaptive evolution. In this study, we characterized a clinical MDR isolate of K. pneumoniae, designated KPA1, which belongs to sequence type 15 (ST15), along with its two associated resistance plasmids, pKPA1-1 and pKPA1-2. Conjugation assays demonstrated that both plasmids were capable of self-transfer. Notably, pKPA1-1 could be transferred to both K. pneumoniae and Escherichia coli, while pKPA1-2 exhibited a restricted transfer capability, being transferable only to K. pneumoniae. Antimicrobial susceptibility testing, along with plasmid stability assays, indicated that the resistance spectrum of pKPA1-2 similar to that of pKPA1-1, and pKPA1-2 was more stable than pKPA1-1. In addition, virulence assays revealed that the acquisition of either plasmid resulted in a reduction in bacterial pathogenicity. This study elucidates the molecular characterization of conjugative resistance plasmids pKPA1-1 and pKPA1-2. These findings shed light on the adaptive mechanisms underlying multidrug resistance in K. pneumoniae.