Klebsiella

Abstract

Historically, the medical importance of the genus Klebsiella has led to the recognition of three species: Klebsiella pneumoniae, responsible for pneumonia; Klebsiella ozaenae, the cause of ozaenia (chronic atrophic rhinitis); and Klebsiella rhinoscleromatis, the cause of rhinoscleroma (chronic granulomatous disease), as described in extensive reviews. In the latest edition (1984) of Bergey's Manual of Systematic Bacteriology, based on phenotypic characteristics and data derived from DNA–DNA hybridization studies, the genus Klebsiella was classified into five species: K. pneumoniae, Klebsiella oxytoca, Klebsiella terrigena, Klebsiella ornithinolytica, and Klebsiella planticola. K. pneumoniae comprised three subspecies: K. pneumoniae subsp. pneumoniae, K. pneumoniae subsp. ozaenae, and K. pneumoniae subsp. rhinoscleromatis. With increasing use of DNA–DNA hybridization techniques and additional molecular studies, new species have been described and others reclassified or moved to the new genus Raoultella. In the current text, the term Klebsiella refers to Klebsiella and Raoultella species, unless specified differently. Thus, by sequencing of 16S rRNA and phoE genes, Calymmatobacterium granulomatis, the supposed agent of donovanosis, was renamed Klebsiella granulomatis; based on 16S rRNA and rpoB sequence analysis, the new genus Raoultella was proposed to accommodate the three species previously called K. planticola, K. terrigena, and K. ornithinolytica, while K. oxytoca was shown to form a distinct genogroup; two new Klebsiella species were described: Klebsiella variicola, from analysis of rpoB, gyrA, mdh, infB, phoE, and nifH sequences, and Klebsiella singaporensis, based on 16S rRNA genes and rpoB gene sequences; and finally, 16S rRNA gene sequences for two proposed species, Klebsiella milletis and Klebsiella senegalensis, and 16S rRNA and rpoB sequences for the proposed species Klebsiella alba were deposited in the GenBank (http://www.ncbi.nlm.nih.gov) in 2003 and 2007, respectively. However, no data has been published describing these three last species to date. A summary of the current classification of Klebsiella is presented in Table 78.1.