Pseudomonas aeruginosa

Gram Stain

• Gram negative straight/slightly curved bacilli - nonfermenter (aerobic) 

Clinical Significance

This organism is found in a variety of sources including water, soil, vegetation, and hospital environments.

It can colonize the gastrointestinal tract, the upper respiratory mucosa, and moist skin areas of hospitalized patients who have received broad spectrum antibiotics.  It can cause both community and healthcare associated infections.

Community infections include superficial skin and ear infections, malignant otitis externa, eye infections (often contact lens associated), osteomyelitis, and endocarditis  (intravenous drug users).

Nosocomial infections include pneumonia (especially in neutropenic patients), urinary tract infections, bacteremia, wound infections (especially in burn patients), and CAPD peritonitis.

Mucoid strains (difficult to eradicate)  are often found in patients with cystic fibrosis.

Predictors of P. aeruginosa bacteremia include:
- severe immunodeficiency
- age > 90 years
- receipt of antibiotics in past 30 days, and
- presence of medical device

Usual Susceptibility Pattern

This organism is resistant to TMP/SMX, nitrofurantoin, oral fosfomycin, most penicillins (except piperacillin-tazobactam), most cephalosporins (except ceftazidime, cefepime, ceftolozane-tazobactam, ceftobiprole), and ertapenem.  
Ciprofloxacin has best activity of the quinolones (moxifloxacin has no activity). Tobramycin has better activity than gentamicin.

Carbapenem resistance is increasing often due to multiple mechanisms.

Combination therapy (ideally with anti-pseudomonal beta-lactam and aminoglycoside) is controversial but may be beneficial for serious infections such as endocarditis or if severe immunosuppression.