Emergence of serotype K1 Klebsiella pneumoniae ST23 strains co-producing the plasmid-mediated AmpC beta-lactamase DHA-1 and an extended-spectrum beta-lactamase in Korea

BACKGROUND: Serotype K1 Klebsiella pneumoniae has emerged as an important community pathogen causing various infections, including liver abscesses. Although serotype K1 K. pneumoniae community isolates have been reported as susceptible to most classes of antimicrobial agents, a few cases of infection caused by extended-spectrum beta-lactamase (ESBL)-producing serotype K1 K. pneumoniae have recently been reported in Asian countries. We identified three ESBL-producing strains of serotype K1 K. pneumoniae and conducted a molecular characterization of their drug resistance. METHODS: Three ESBL-producing serotype K1 K. pneumoniae ST23 strains were identified from strains in the Asian Bacterial Bank. Antimicrobial susceptibility testing was performed using the broth microdilution method, and ESBL production was tested by the double-disk synergy test and a confirmatory test. PCR was performed to detect the genes for plasmid-mediated ESBL and AmpC beta-lactamases. RESULTS: All three strains were resistant to cefotaxime, ceftazidime, and piperacillin/tazobactam, and all were determined to be ESBL-producers. No known ESBL genes, including bla (SHV), bla (TEM), bla (CTX-M), bla (GES), bla (PER), and bla (VEB), were detected among the three strains. Of all plasmid-mediated AmpC beta-lactamase (PAB) genes, including bla (DHA-1), bla (CMY), bla (FOX), and bla (MOX), the bla (DHA-1) gene was detected in two of the strains. The PFGE patterns revealed that the two isolates carrying bla (DHA-1) were closely related (84% similarity). CONCLUSIONS: No ESBL genes were detected among three ESBL-producing serotype K1 K. pneumoniae ST23 strains. Two strains contained the PAB gene bla (DHA-1). The emergence of resistant strains of community-origin serotype K1 K. pneumoniae has important implications for effective treatment and infection control practices.