Klebsiella

Abstract

Klebs.i.el' la . N.L. fem. dim. n. Klebsiella , named after Edwin Klebs (1834–1913), a German bacteriologist. Pseudomonadota / Gammaproteobacteria / Enterobacterales / Enterobacteriaceae / Klebsiella Cells are Gram‐stain‐negative straight rods (0.3–1.0 × 0.6–6.0 μm), mostly nonmotile (except K. aerogenes ), and are capsulated. Grow on a variety of growth media including meat extract media (except K. granulomatis , which has not been cultured). Colonies are smooth, circular, more or less dome shaped, and glistening of varying degrees of stickiness, depending on the strain and the composition of the medium. Klebsiella are cytochrome oxidase‐negative, mesophilic, and facultatively anaerobic, having both a respiratory and a fermentative type of metabolism. The majority of Klebsiella fail to grow at 10 and 45°C, while the type strains of K. oxytoca , K. planticola , K. terrigena , K. ornithinolytica , K. michiganensis , and K. variicola show growth at 10°C. Klebsiella are usually positive for Voges–Proskauer test, except strains of K. spallanzanii , K. indica , and K. huaxiensis . Most Klebsiella members hydrolyze urea. Based on genomic sequence‐based phylogenetic analyses, Klebsiella species form higher‐level groups, called the K. pneumoniae species complex (KpSC), K. oxytoca species complex (KoSC), and K. planticola species complex (KplanSC). Additional species complexes may be defined in the future to accommodate other species such as K. aerogenes , K. terrigena , and K. indica . Some Klebsiella strains fix atmospheric nitrogen. Members of Klebsiella are considered ubiquitous and have been isolated from diverse sources including clinical specimens from humans and animals (e.g., cows, horses, and swine, monkeys), the mammalian gut, household items, soil, water, and plants. All Klebsiella species are considered opportunistic pathogens, except for a few specific pathovars, and may harbor a variety of antimicrobial resistance genes. Some strains of the KpSC, called hypervirulent strains, and some toxigenic strains of the KoSC are considered true pathogens. DNA G + C content (mol%) : 53–58 ( T m ). Type species : Klebsiella pneumoniae Trevisan 1887 AL (basonym: Hyalococcus pneumoniae Schroeter 1886).