Molecular epidemiological characteristics of Klebsiella pneumoniae associated with bacteremia among patients with pneumonia

Abstract

Some important virulence factors have been elucidated in Klebsiella pneumoniae infections. We investigated the relationship between virulence factors and multilocus sequence types (STs) and assessed the risk factors for bacteremia in patients with pneumonia due to K. pneumoniae. From April 2004 through April 2012, a total of 120 K. pneumoniae isolates from patients with pneumonia (23 with bacteremia and 97 without bacteremia) were collected from 10 medical institutions in Japan. Additionally, 10 strains of K. pneumoniae serotype K2 that were isolated >30 years ago were included in this study. These isolates were characterized using multilocus sequence typing (MLST), and the characteristics of their virulence factors, such as hypermucoviscosity phenotype and RmpA and aerobactin production between patients with and without bacteremia, were examined. MLST analysis was performed on the 120 isolates from patients with pneumonia, and some sequence type groups were defined as genetic lineages (GLs). GL65 was more prevalent among patients with bacteremia (21.7%) than in those without bacteremia (7.2%). The majority of the strains with serotype K2 were classified into GL14 or GL65, and rmpA and the gene for aerobactin were present in all GL65-K2 strains but absent in all GL14-K2 strains. In a multivariate analysis, the independent risk factors for bacteremia included GL65 (adjusted odds ratio [AOR], 9.46; 95% confidence interval [CI], 1.81 to 49.31), as well as neoplastic disease (AOR, 9.94; 95% CI, 2.61 to 37.92), immunosuppression (AOR, 17.85; 95% CI, 1.49 to 214.17), and hypoalbuminemia (AOR, 4.76; 95% CI, 1.29 to 17.61). GL65 was more prevalent among patients with bacteremia and was associated with the virulence factors of K. pneumoniae.

FIG 1

A population snapshot determined by eBURST analysis (http://eburst.mlst.net) showing the clusters of linked and unlinked STs in the entire K. pneumoniae MLST database (1,612 STs; http://www.pasteur.fr/recherche/genopole/PF8/mlst/), including the 120 isolates in this study. The size of the circles indicates the number of isolates, and large circles indicate predominant types. The color of circles indicates the type of founder (blue, primary founder; yellow, subgroup founder; black, all other STs). The pink halos surround STs that were isolated in this study. There is a large cluster of STs (clonal complex 37; green box), with ST37 as the predicted founder.