Capsular Serotype K1 or K2, Rather than magA and rmpA , Is a Major Virulence Determinant for Klebsiella pneumoniae Liver Abscess in Singapore and Taiwan

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Abstract
Capsular serotypes, magA, and rmpA have been documented in high prevalence for Klebsiella pneumoniae liver abscess. To investigate the regional difference and the correlation of capsular serotype, magA, and rmpA with virulence, 73 isolates were collected in Singapore and Taiwan. Capsular serotypes were determined by countercurrent immunoelectrophoresis, the presence of magA and rmpA was 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 magA and rmpA. The most common serotype was K1 (34/73; 46.6%), followed by K2 (15/73; 20.5%). magA was 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 rmpA contributed to virulence. The characteristics of K. pneumoniae liver abscess in Singapore and Taiwan are similar. Capsular serotype K1 or K2 plays a more important role than magA and rmpA in determining virulence in K. pneumoniae liver abscess.