Genotypes and virulence in serotype K2 Klebsiella pneumoniae from liver abscess and non-infectious carriers in Hong Kong, Singapore and Taiwan

In Klebsiella pneumoniae liver abscess (KP-LA), K. pneumoniae K2 is the most frequently isolated serotype after K1, but this serotype has been much less studied. In the present study, the molecular types sequences type (MLST) of serotype K2 isolates from three different regions in Asia were identified and the virulence of these isolates was investigated. Eight different MLSTs were found among 26 isolates (ST 65, 66, 86, 373, 374, 375, 380, and 434). There were two major MLST groups, ST-65-like (42%) and ST86-like (46%). No isolates contained allS while all isolates contained rmpA. The prevalence of aerobactin gene and kfu were 25/26 (96%) and 3/26 (11.5%) respectively. Although liver abscess isolates were generally more resistant (11/15 isolates) to serum killing, there was no specific distribution of serum killing resistant or susceptible ST types between stool carriage and liver abscess isolates. Neutrophil phagocytosis showed that the liver abscess and carriage isolates varied in their susceptibility to phagocytosis. Strains with resistance to both neutrophil phagocytosis and serum killing were generally hypervirulent with lethality at LD50 < 10(3) colony forming units by intraperitoneal injection. In conclusion, Anti-phagocytosis and resistance to serum killing are two parameters that most predict hyperviurlence in serotype K2 isolates. Unlike serotype K1 KP-LA that mainly belong to ST-23, ST-65-like and -86-like are the two major MLST types among serotype K2 isolates from Singapore, Hong Kong and Taiwan.