Characteristics of carbapenem-resistant Enterobacteriaceae isolates from Korea.

In this study, the characteristics of carbapenem-resistant Enterobacteriaceae (CRE) isolates from Korea was investigated. A total of 22 CRE isolates were investigated, and most were identified as Klebsiella pneumoniae (16 isolates). In vitro antimicrobial susceptibility testing, multilocus sequence typing, and pulsed-field gel electrophoresis were performed. Extended-spectrum β-lactamase (ESBL) and carbapenemase genes were detected using gene amplification and sequencing. Efflux pump activity and inactivating mutations in OmpK35/36 were also investigated. Among 22 CRE isolates, only 5 produced metallo-β-lactamases (3 NDM-1, one VIM-2 and one IMP-1). Four and 2 K. pneumoniae and Serratia marcescens isolates showed resistance to polymyxins, respectively, and 2 CRE isolates (1 K. pneumoniae and C. freundii) were resistant to tigecycline. The prevalent carbapenem resistance mechanism found in K. pneumoniae might be porin defects. The most prevalent clone of carbapenem-resistant K. pneumoniae was ST11 (56.3%), which is the most frequently identified clone among ESBL-producing K. pneumoniae isolates from Korea. Three NDM-1-producing K. pneumoniae isolates belonged to a single clone (ST340) despite their different antimicrobial susceptibilities. In the present study, the clonal dissemination of carbapenem-resistant K. pneumoniae isolates (ST11) and NDM-1-producing K. pneumoniae isolates (ST340) was determined. Polymyxin- and tigecycline-resistant CRE isolates were also identified, which limits treatment options for infections causes by these organisms.