Clinical and bacteriological characteristics of Klebsiella pneumoniae causing liver abscess with less frequently observed multi-locus sequences type, ST163, from Singapore and Missouri, US.

BACKGROUND Klebsiella pneumoniae is the major cause of liver abscesses in several Asian countries. Differences in the type of circulating Klebsiella strains and/or the genetic make up of the host seem to be plausible explanations for this. METHODS Two recent K. pneumoniae strains isolated from patients with liver abscess, one from Missouri in the US, and a second one from Singapore, were fully characterized by molecular typing, association of virulent genes, neutrophil phagocytosis, susceptibility to serum killing, and lethality in mice. RESULTS Both strains had mucoid colony morphology and were similar in multilocus sequence type (ST-163), drug-susceptibility profile, resistance to phagocytosis and susceptibility to serum killing. Although ST-163 is a single nucleotide variant (SNV) to the major ST-23, which is specific to serotype K1 K. pneumoniae that causes liver abscess in Taiwan, these two isolates differ in capsular serotype. One was serotype K1 and the other K29. Since a serotype K35 with ST163 was reported previously to cause peritonitis, serotype K29 with SNV to ST-23 was not impossible. Pulsed field gel electrophoresis by XbaI digestion showed different restriction patterns. The virulence-associated genes rmpA and aerobactin were only present in the serotype K1 isolate from Singapore and not in the serotype K29 isolate from Missouri. The serotype K1 isolate was also more virulent to mice. CONCLUSION The reasons underlying the high prevalence of ST-23 or its SNV in K. pueumonaie liver abscesses is worth further investigation.