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ABSTRACTCapsular serotypes, magA, and rmpAhave been documented in high prevalence for Klebsiella pneumoniaeliver abscess. To investigate the regional difference and the correlation of capsular serotype, magA, and rmpAwith virulence, 73 isolates were collected in Singapore and Taiwan. Capsular serotypes were determined by countercurrent immunoelectrophoresis, the presence of magAand rmpAwas determined by PCR, and virulence was determined by phagocytosis and mouse inoculation. Isolates from Singapore were similar to those from Taiwan in genomic heterogeneity, prevalence of serotype, and the presence of magAand rmpA.The most common serotype was K1 (34/73; 46.6%), followed by K2 (15/73; 20.5%). magAwas restricted to serotype K1. All K1 or K2 isolates and 66.7% (16/24) of isolates that were neither serotype K1 nor serotype K2 (non-K1/K2) carried rmpA. Serotype K1 or K2 isolates demonstrated significantly more phagocytic resistance and virulence than did rmpA-positive and -negative groups of non-K1/K2 isolates. In the non-K1/K2 group, the virulence profiles of rmpA-positive strains from Taiwan and Singapore were different by phagocytosis assay and in the mouse model, indicating that factors other than rmpAcontributed to virulence. The characteristics of K. pneumoniaeliver abscess in Singapore and Taiwan are similar. Capsular serotype K1 or K2 plays a more important role than magAand rmpAin determining virulence in K. pneumoniaeliver abscess.

ABSTRACTThe number of infections attributable to community-associated methicillin-resistant Staphylococcus aureus(CA-MRSA) in Singapore is progressively increasing. Most cases in the past 2 years were caused by Panton-Valentine leukocidin-positive isolates belonging to sequence type 30, according to multilocus sequence typing. This has clearly become the predominant sequence type among CA-MRSA isolates in Singapore.

ABSTRACTAnalysis of hospital-acquired methicillin-resistant Staphylococcus aureusstrains isolated from a tertiary public hospital in Singapore revealed that multisusceptible strains had gradually started to replace the endemic multiresistant strain (ST239-MRSA-III) since 2002. Molecular typing showed that this was a predominantly clonal outbreak of a UK-EMRSA-15 strain (ST22-MRSA-IV).

ABSTRACTThirty-six isolates of carbapenem-resistant Pseudomonas aeruginosawere studied. Pulsed-field gel electrophoresis revealed the presence of two clones. One clone carried a blaIMP-1gene identical to that first described in Japan. The other clone carried a blaIMP-1variant containing four silent mutations. One isolate with a unique pulsed-field gel electrophoresis pattern contained blaIMP-7.

ABSTRACTNine imipenem-resistant Pseudomonas aeruginosaisolates were found to contain a variety of metallo-ß-lactamase genes, including blaIMP-1, blaIMP-7, blaVIM-2, blaVIM-6, and the novel blaIMP-26. Multilocus sequence typing showed a diversity of sequence types. Comparison with isolates from an earlier study showed that the epidemic clones from 2000 have not become established.