Klebsiella species

MICROBIOLOGY

• Gram-negative, lactose fermenting aerobic bacilli of Enterobacteriaceae family.
  • K. pneumoniae, K. oxytoca and K. granulomatis.
    • K. ozaenae and K. rhinoscleromatis are non-fermenting subspecies.
  • Forms highly mucoid colonies w/polysaccharide capsule, a virulence factor that inhibits phagocytosis. Easily cultured on non-selective media for sterile specimens or MacConkey agar for contaminated specimens.
  • Known to contaminate drains[14] and serve as point source for nosocomial outbreaks, esp. K. pneumoniae, K. oxytoca (as well as E. coli., Pseudomonas and Acinetobacter species).[7]
• Resistance issues:
  • Beta-lactamases are constitutive, usually produced at low levels, and provide resistance against ampicillin, amoxicillin and ticarcillin.
    • Few klebsiellae lack these beta-lactamases.
  • Extended-spectrum beta-lactamases (ESBLs): may be plasmid-mediated or chromosomal, confer multidrug resistance (TEM or SHV types), and are detected by in vitro resistance to ceftazidime and aztreonam.
    
    • CTX-M type ESBLs are the most prevalent ESBL types worldwide and are commonly associated with ST131 E. coli.[19]
  • Carbapenemases:
    
    • Klebsiella pneumoniae carbapenemase, KPC (Ambler Class A): confers broad resistance and is associated with mortality rate >50%.[12]
      • Many isolates in US are sequence type, ST258.
      • Susceptibility limited to gentamicin, tigecycline and colistin.
      • Inhibited by clavulanic acid and tazobactam.
    • Metallo-beta-lactamases (Ambler Class B): types include IMP (imipenemase), VIM (Verona integron-encoded MBL), and NDM-1 (New Delhi MBL).
      • Require zinc ions in the active site for activity.
      • IMP and VIM are not resistant to aztreonam.
      • NDM-1 generally resistant to all antibiotics (including aztreonam and aminoglycosides) except tigecycline and colistin.
    • OXA-type carbapenemases (Ambler Class D): include OXA-48, weakly hydrolyze carbapenems, broad-spectrum cephalosporins, and aztreonam; express resistance or decreased susceptibility to carbapenems.
      • Often associated with Acinetobacter baumannii.