The OmpK36 porin plays a role in carbapenem resistance and may contribute to bacterial virulence in Klebsiella pneumoniae. This study aimed to investigate the characteristics of different groups of K. pneumoniae separated by ompK36 typing. Among 226 nonduplicate K. pneumoniae bloodstream isolates collected at a Taiwanese hospital in 2011, four ompK36 types, designated types A, B, C, and D, were identified by PCR in 61, 28, 100, and 36 isolates, respectively; 1 isolate was untypeable. Statistical analysis showed significantly higher rates of antimicrobial resistance (all tested antibiotics except meropenem), extended-spectrum -lactamases or DHA-1 (47.5% together), Qnr-type quinolone resistance determinants (50.8%), and IncFIIA-type plasmids (49.2%) in group A than in others. Seventeen isolates were identified as belonging to 3 international high-risk clones (4 sequence type 11 [ST11], 10 ST15, and 3 ST147 isolates); all isolates but 1 ST15 isolate were classified in group A. The significant characteristics of group C were hypermucoviscosity (62.0%) and a higher virulence gene content. This group included all serotype K1 (n ؍ 30), K2 (n ؍ 25), and K5 (n ؍ 3) isolates, 6 of 7 K57 isolates, all isolates of major clones associated with pyogenic liver abscesses (29 ST23, 11 ST65, 5 ST86, 7 ST373, and 1 ST375 isolates), and 16 (94.1%) of 17 isolates causing bacteremic liver abscesses. Twelve (42.9%) of the group B isolates were responsible for bacteremic biliary tract infections. Group D was predominant (83.3%) among 12 K20 isolates. This study suggests that most clinical K. pneumoniae isolates can be allocated into four groups with distinct characteristics based on ompK36 types. K lebsiella pneumoniae is an important human opportunistic pathogen that causes a wide variety of community-acquired and nosocomial infections (1-4). The organism is still one of the leading causes of community-acquired pneumonia (3) and has been described as the major cause of pyogenic liver abscesses (PLA) in some Asia-Pacific countries (2, 4). Serotypes K1 and K2 in K. pneumoniae have been linked to invasive infections (2-9). Using multilocus sequence typing (MLST), Brisse et al. (10) identified two virulent K1 clones of K. pneumoniae, clonal complex (CC) 23 and CC82, which were strongly associated with PLA and respiratory infection, respectively. K. pneumoniae is also an important reservoir of antibiotic resistance determinants (1). Several clones of K. pneumoniae with a high prevalence of carbapenem resistance or extended-spectrum -lactamases (ESBLs) have been distributed worldwide (11-16). The epidemic drug-resistant clones, called "high-risk" clones (11), may play an important role in the dissemination of antimicrobial resistance. The major international high-risk clones identified by MLST belong to sequence type 11 (ST11), ST15, ST147,. ST11 and ST258 were included in clonal group (CG) 258 (11,14), while ST15 and ST147 were grouped in CG15 and CG147 (11, 13, 14), respectively.High-level carbapenem resistance in K. pneumoniae ma...