Klebsiella spp.

Abstract

Genomics: Klebsiella pneumoniae strain MGH78578 chromosome: 5,315,120 bp; 4776 predicted ORFs (Lery et al. 2014) Cell morphology: Rod-shaped cells (Fig. 18.1) Nonmotile Capsule: major virulence factor (Fig. 18.1; see below) Lipopolysaccharide (LPS): immunostimulatory; associated with inflammation and endotoxic shock; also functions in immune evasion (see below) Gram stain: Gram negative Growth: Facultative anaerobes; oxidase negative. Urease positive; used to obtain nitrogen from host urea. Reservoirs: contaminated soil and surface water; human hosts (primary). Can colonize human mucosal layers, including the gastrointestinal tract and the nasopharynx. Excellent biofilm formers (see below). Six species and several subspecies: K. pneumoniae is the primary human pathogen; K. oxytoca is next most prevalent: K. pneumoniae strains can be classified as either classical or hypervirulent (HV). K. pneumoniae strains are serotyped by LPS (O) antigens and capsular (K) antigens: 9 O antigen serotypes: O1 (most common) 78 K antigen serotypes: K1--K78 Member of the ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp.) family of antibiotic-resistant nosocomial pathogens. Significant increases worldwide in antibiotic-resistant strains and HV strains: Antibiotic resistance -- two major mechanisms: Expression of carbapenemases; display resistance to all $β$-lactam antibiotics. Isolates can be found worldwide. Antibiotic resistance does not increase the virulence of these strains. HV strains (Paczosa and Mecsas 2016; Patel et al. 2014; Shon et al. 2013): Predominantly O1:K1 (93%) and O1:K2 strains. Exhibit a hypermucoviscous phenotype on agar plates; due to the presence of a hypercapsule with increased production of capsule polysaccharide (CPS). Also increased production and utilization of iron siderophores enterobactin, yersiniabactin, salmochelin, aerobactin. Isolates are found predominantly in Southeast Asia and Taiwan, although incidents are spreading worldwide.