High Prevalence of CTX-M-15-Type Extended-Spectrum β-Lactamase Among AmpC β-Lactamase-Producing Klebsiella pneumoniae Isolates Causing Bacteremia in Korea

We investigated the antimicrobial susceptibility, the genotypic distributions of extended-spectrum β-lactamase (ESBL) and AmpC genes, and the molecular epidemiology of AmpC-producing Klebsiella pneumoniae (AmpC-KP) isolates causing bacteremia. Among 260 K. pneumoniae clinical isolates included in this study, plasmid-mediated AmpC β-lactamases were found in 20.7% (54/260), which included DHA-1 (96.3%, 52/54), CMY-2 (3.7%, 2/54), and CMY-10 (1.9%, 1/54). One isolate also produced DHA-1 along with CMY-2. Of the 54 AmpC-KP isolates, 31 isolates (57.4%) showed ESBL positivity. Of these 31 isolates with coproduction of ESBL and AmpC β-lactamases, 25 isolates (80.6%) produced CTX-M-15 in addition to DHA-1. Nine isolates (29.0%) were nonsusceptible to imipenem. The most prevalent sequence type (ST) was ST11 (n = 31, 57.4%), followed by ST2361 (n = 5, 9.3%), which was newly identified in this study, and ST48 (n = 4, 7.4%). K. pneumoniae isolates coproducing DHA-1 and CTX-M-15 have emerged and disseminated in Korean hospitals, even in blood isolates causing bacteremia. Such infections may become a challenge for clinicians because there is a severely restricted range of available therapeutic options for these pathogens.