bA total of 431 Pseudomonas aeruginosa clinical isolates were collected from 29 general hospitals in South Korea in 2015. Antimicrobial susceptibility was tested by the disk diffusion method, and MICs of carbapenems were determined by the agar dilution method. Carbapenemase genes were amplified by PCR and sequenced, and the structures of class 1 integrons surrounding the carbapenemase gene cassettes were analyzed by PCR mapping. Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were performed for strain typing. Whole-genome sequencing was carried out to analyze P. aeruginosa genomic islands (PAGIs) carrying the bla IMP-6 , bla IMP-10 , and bla GES-24 genes. The rates of carbapenem-nonsusceptible and carbapenemase-producing P. aeruginosa isolates were 34.3% (148/431) and 9.5% (41/431), respectively. IMP-6 was the most prevalent carbapenemase type, followed by VIM-2, IMP-10, and GES-24. All carbapenemase genes were located on class 1 integrons of 6 different types on the chromosome. All isolates harboring carbapenemase genes exhibited genetic relatedness by PFGE (similarity > 80%); moreover, all isolates were identified as sequence type 235 (ST235), with the exception of two ST244 isolates by MLST. The bla IMP-6 , bla IMP-10 , and bla GES-24 genes were found to be located on two novel PAGIs, designated PAGI-15 and PAGI-16. Our data support the clonal spread of an IMP-6-producing P. aeruginosa ST235 strain, and the emergence of IMP-10 and GES-24 demonstrates the diversification of carbapenemases in P. aeruginosa in Korea.
Pseudomonas aeruginosa is an opportunistic pathogen that causes various nosocomial infections, including sepsis, pneumonia, and urinary tract infections (1). Treatment of P. aeruginosa infections is often difficult because of the intrinsic drug resistance of P. aeruginosa and the ability of this pathogen to acquire genes for antimicrobial resistance determinants (2). Carbapenems are used as last-resort drugs for the treatment of infections caused by multidrug-resistant P. aeruginosa, due to their high affinity for penicillin-binding proteins, stability to various -lactamases, and ability to easily pass through the bacterial outer membrane. However, the increasing use of carbapenems has resulted in the emerging phenomenon of carbapenem resistance (3).P. aeruginosa can become resistant to carbapenems by reduced permeability of the outer membrane due to loss of substrate-specific outer membrane porin OprD, frequently accompanied by AmpC hyperproduction and overexpression of efflux systems (4), along with acquisition of genes encoding carbapenemases (5). While the molecular mechanism of carbapenem resistance is geographically variable, diverse classes of carbapenemase have been increasingly identified in P. aeruginosa, including class A (KPC and GES variants), class B (IMP, VIM, and NDM metallo--lactamases [MBLs]), and class D (OXA variants) (6). The MBLs, in particular IMP and VIM enzymes, are the most widespread carbapenemases in P. aeruginosa (7), with IMP-6 exclusivel...