Capsular serotype K1 or K2, rather than magA and rmpA, is a major virulence determinant for Klebsiella pneumoniae liver abscess in Singapore and Taiwan

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.

FIG. 1.

Dendrogram of PFGE patterns for 49 isolates of serotype K1 or K2 Klebsiella pneumoniae causing liver abscess.

FIG. 2.

Phagocytosis rates of all of the 73 Klebsiella pneumoniae isolates causing liver abscess from Singapore and Taiwan, classified as four groups: serotype K1 (magA positive and rmpA positive), serotype K2 (magA negative and rmpA positive), rmpA-positive non-K1/K2 (magA negative), and rmpA-negative non-K1/K2 (magA negative). For Singapore, 16, 8, 10, and 6 isolates of the K1, K2, rmpA-positive non-K1/K2, and rmpA-negative non-K1/K2 groups, respectively, were examined; for Taiwan, 18, 7, 6, and 2 isolates of the K1, K2, rmpA-positive non-K1/K2, and rmpA-negative non-K1/K2 groups, respectively, were examined; and totals of 34, 15, 16, and 8 isolates of the K1, K2, rmpA-positive non-K1/K2, and rmpA-negative non-K1/K2 groups, respectively, were examined. The percentage of the neutrophils carrying FITC-stained bacteria after a 10-min incubation was used as the phagocytosis rate. Values are means ± SD. * *, serotype K1 versus rmpA-positive non-K1/K2 isolates (P < 0.0001); *, serotype K2 versus rmpA-positive non-K1/K2 isolates (P < 0.01); #, rmpA-positive non-K1/K2 versus rmpA-negative non-K1/K2 isolates (P < 0.01).

FIG. 3.

Mouse lethality of 16 Klebsiella pneumoniae isolates causing liver abscess. (A) Eight from Singapore. (B) Eight from Taiwan. Both are comprised of two serotype K1 (magA positive and rmpA positive), two serotype K2 (magA negative and rmpA positive), two rmpA-positive non-K1/K2 (magA negative), and two rmpA-negative non-K1/K2 (magA negative). (C) All 16 isolates. Six mice were intraperitoneally injected with each isolate of the inoculum of 2 × 10⁴ to 6 × 10⁴ CFU and were observed for 2 weeks after inoculation.