Molecular typing and virulence analysis of serotype K1 Klebsiella pneumoniae strains isolated from liver abscess patients and stool samples from noninfectious subjects in Hong Kong, Singapore, and Taiwan

[[abstract]]Serotype K1 Klebsiella pneumoniae with multi-locus sequence type, ST23, has been strongly associated with liver abscess in Taiwan. Little data is available regarding strain types and virulence of this serotype from other Asian countries. Serotype K1 K. pneumoniae strains, isolated from liver abscess and stool from subjects hospitalized in Hong Kong, Singapore and Taiwan hospitals were examined. Forty-seven serotype K1 isolates were identified; 26 from liver abscess and 21 from stool carriage respectively. MLST revealed 7 sequence types: 85.1% (40 of 47) belonged to ST23, 1 isolate belonged to ST163 (a single locus variant of ST23), and 2 isolates were ST249 (a 3-locus variant of ST23). New STs, namely ST367, 425, and 426 were allocated to 3 of 4 isolates from stool carriage. The virulence of these strains was determined by neutrophil phagocytosis and mice infection models. Except for two ST23 isolates, all Klebsiella pneumoniae were resistant to phagocytosis. Resistance to serum killing varied in isolates of ST23 while non-ST23 strains were all susceptible to serum killing except one with ST249 from liver abscess. Hyper-virulent isolates with LD(50)