Hypervirulent (hypermucoviscous)Klebsiella pneumoniae

Abstract

A new hypervirulent (hypermucoviscous) variant of Klebsiella pneumoniae has emerged. First described in the Asian Pacific Rim, it now increasingly recognized in Western countries. Defining clinical features are the ability to cause serious, life-threatening community-acquired infection in younger healthy hosts, including liver abscess, pneumonia, meningitis and endophthalmitis and the ability to metastatically spread, an unusual feature for enteric Gram-negative bacilli in the non-immunocompromised. Despite infecting a healthier population, significant morbidity and mortality occurs. Although epidemiologic features are still being defined, colonization, particularly intestinal colonization, appears to be a critical step leading to infection. However the route of entry remains unclear. The majority of cases described to date are in Asians, raising the issue of a genetic predisposition vs. geospecific strain acquisition. The traits that enhance its virulence when compared with “classical” K. pneumoniae are the ability to more efficiently acquire iron and perhaps an increase in capsule production, which confers the hypermucoviscous phenotype. An objective diagnostic test suitable for routine use in the clinical microbiology laboratory is needed. If/when these strains become increasingly resistant to antimicrobials, we will be faced with a frightening clinical scenario.

Microbiological characteristics of hypermucoviscous Klebsiella pneumoniae isolates from different body fluids

“…hvKP is more resistant to phagocytosis by polymorphonucleated neutrophils, less sensitive to killing by serum complement, and more virulent in animal studies [14][15][16][17][18]. Previous reports have focused on hvKP infections isolated from abscess and blood fluids.…”

Regulation of bacterial virulence gene expression by cell envelope stress responses

“…118 In addition, copious capsule production, or hypermucoviscosity (HMV), has recently become associated with devastating invasive disease. 119 The HMV strain K. pneumoniae CG43 has a plasmid with 2 homologous genes, rmpA and rmpA2, which encode transcription factors in the same family as RcsA and RcsB. The presence of these rmpA genes has been correlated with the HMV phenotype in K. pneumoniae isolates, and RmpA and RmpA2 regulate capsule production in strain CG43.…”

Genomic analysis of diversity, population structure, virulence, and antimicrobial resistance in Klebsiella pneumoniae , an urgent threat to public health

“…pneumoniae infections are particularly a problem among neonates, the elderly, and the immunocompromised (4) but also cause significant numbers of serious community-acquired (CA) infections, including pyogenic liver abscess, pneumonia, and meningitis (6). Virulence factors thought to be associated with invasive CA infections include various siderophores, specific polysaccharide capsule serotypes, and rmpA genes that are associated with hypermucoidy (7).…”