Pseudomonas aeruginosa

Background

Microbiology

• Oxidase-positive, non-fermenting Gram-negative bacillus

Mechanisms of Resistance

• Broad intrinsic and acquired antibiotic resistance
• Membrane impermeability
  • Decreased or absent OprD porin: resistance to carbapenems (imipenem and meropenem)
  • Membrane changes: resistance to polymixins (colistin)
  • Reduced aminoglycoside transport: resistance to aminoglycosides
• Efflux pumps
  • MexAB-OprM: resistance to fluoroquinolones and all β-lactams except imipenem
  • MexCD-OprJ: resistance to fluoroquinolones and most β-lactams (cefoperazone, cefpirome, cefepime, meropenem) but not imipenem
  • MexEF-OprN: resistance to fluoroquinolones and all β-lactams
  • MexXY-OprM: resistance to fluoroquinolones, most β-lactams (but not imipenem), and aminoglycosides
• β-lactamases
  • Derepressed AmpC β-lactamase: resistance to penicillins and cephalosporins (except ceftolozane)
  • Acquired carbapenemases such as NDM-1: resistance to essentially all β-lactam antibiotics
• Aminoglycoside-modifying enzymes: resistance to aminoglycosides
• Target site mutations
  • Topoisomerase II (gyrA) or IV (parC) point mutations: resistance to fluoroquinolones

Epidemiology

• Loves moist and wet environments
• Causes healthcare-associated infections
  • UTI, SSI, bacteremia, HAP, VAP
  • Especially common in cystic fibrosis

Treatment

• Refer to antipseudomonal antibiotics for specific treatment options
• Double coverage (ß-lactam + non-ß-lactam) in cases of severe infection in order to ensure activity against the infection