Evolution of XDR Pseudomonas aeruginosa ST463 strains with two plasmids harboring multiple antimicrobial resistance genes.

The extensively drug-resistant (XDR) Pseudomonas aeruginosa ST463 strains, which co-harbor plasmid-associated metallo-β-lactamase (MBL) and bla_KPC-2 genes, exhibit significant resistance and virulence, posing great clinical treatment challenges. Here, we report on three XDR P. aeruginosa ST463 strains, PA64, PA3117, and PA30, all carrying two plasmid types. One plasmid was a ~450 kb IncP-2-type megaplasmid named pPA64_1, pPA3117_1, and pPA30_1 in strains PA64, PA3117, and PA30, respectively. The other plasmid was a type I plasmid named pPA64_2, pPA3117_2, and pPA30_2 in strains PA64, PA3117, and PA30, respectively, harboring the bla_KPC-2 gene in the core genetic platform ISKpn27- bla_KPC-2-ISKpn6. The bla_KPC-2 gene copies were associated with IS26-mediated inversion or duplication events. Notably, the IncP-2 megaplasmids pPA64_1, pPA3117_1, and pPA30_1 were associated with a variable ~57.3 kb Tn1403-like transposon named Tn6485g, Tn6485h, and Tn6485f, respectively. Tn6485g carried the MBL gene bla_IMP-45, which was located in the class 1 integron In786, followed by an ISCR1-associated armA module and the IS26-composite transposon Tn6309. On this basis, other ISCR1-associated modules (ISCR1-qnrVC6, ISCR1-bla_PER-1, and ISCR1-bla_AFM-1) were inserted between In786 derivatives and ISCR1-armA, resulting in a novel transposon, Tn6485h, carrying two MBL genes, bla_IMP-45 and bla_AFM-1. In contrast to Tn6485h, Tn6485f had another inserted copy of ISCR1-qnrVC6. We inferred that the evolution of the Tn1403-like transposon might be driven by the recruitment of ISCR1-associated antimicrobial resistance (AMR) modules under antibiotic pressure in a clinical setting.