Pseudomonas and Related Bacteria

Pseudomonas Basics - The Green Menace

• Microscopy & Growth: Gram-negative rod. Strictly aerobic, ensuring growth in oxygen-rich sites.
• Motility & Enzymes: Actively motile (single polar flagellum). Oxidase-positive.
• Culture: Non-lactose fermenter (NLF) on MacConkey agar.
• Ecology: Ubiquitous: found in soil, water, plants, and notably in moist hospital settings.

  ⭐ Produces characteristic blue-green pigment (pyocyanin) and a distinctive grape-like odor.

• 📌 PSEUDOMONAS: Pigment, Sweet odor, Exotoxin A, Ubiquitous, Drug resistance, Opportunistic, Non-fermenter, Aerobe, Sepsis/Swimmer's ear.

P. aeruginosa Virulence - Armed & Dangerous

• Exotoxins & Enzymes:
  • Exotoxin A: Inhibits protein synthesis via ADP-ribosylation of EF-2.

    ⭐ This mechanism is identical to that of Diphtheria toxin.

  • Phospholipase C: Hemolysin; degrades lipids, lecithin, aiding tissue destruction.
  • Elastase, Alkaline Protease: Degrade elastin, collagen, immunoglobulins; cause tissue damage (e.g., ecthyma gangrenosum).
  • Pyocyanin: Blue-green pigment; generates ROS, impairs cilia, pro-inflammatory.
• Iron Acquisition:
  • Pyoverdin: Siderophore; chelates iron for bacterial growth.
• Biofilm & Adherence:
  • Alginate: Exopolysaccharide; key for biofilm formation (esp. in CF patients), resists phagocytosis.
  • Pili, Flagella: For adherence and motility.
• Endotoxin:
  • LPS: Lipid A component triggers fever, shock.

P. aeruginosa Diseases - Clinical Mayhem

A versatile pathogen causing diverse, often severe infections.

• 📌 Mnemonic: BE PSEUDO
  • Burns: Leading cause of burn wound infections.
  • Endocarditis: Esp. in IV drug users.
  • Pneumonia: Hospital-acquired (HAP), Ventilator-Associated (VAP); chronic in Cystic Fibrosis (biofilm).
  • Sepsis: Bacteremia, often with high mortality.
  • Ecthyma gangrenosum: Necrotic skin lesions in neutropenic patients.
  • UTI: Common in catheterized patients.
  • Diabetic Osteomyelitis / Malignant Otitis Externa.
• Other key infections:
  • Hot tub folliculitis.
  • Keratitis (contact lens wearers).
  • Surgical site infections.

⭐ Ecthyma gangrenosum, a necrotic skin lesion, is highly characteristic of P. aeruginosa sepsis in immunocompromised individuals.

Lab ID & Treatment - Catch & Kill

• Lab Identification:
  • Culture: MacConkey (Non-Lactose Fermenter - NLF), Nutrient agar (Pyocyanin: blue-green; Pyoverdin: green-yellow, fluorescent), β-hemolysis on blood agar.
  • Odor: Fruity/grape-like.
  • Key Tests: Oxidase positive, grows at 42°C.

• Treatment: (Combination therapy often vital)
  • Anti-pseudomonal Penicillins: Piperacillin-tazobactam
  • Cephalosporins: Ceftazidime, Cefepime
  • Carbapenems: Imipenem, Meropenem (NB: Ertapenem is INEFFECTIVE)
  • Monobactams: Aztreonam
  • Aminoglycosides: Gentamicin, Tobramycin, Amikacin
  • Fluoroquinolones: Ciprofloxacin, Levofloxacin
  • ⚠️ High rates of resistance (MDR/XDR common).

⭐ P. aeruginosa is notoriously resistant to many antibiotics due to efflux pumps, beta-lactamases, and biofilm formation.

The Relatives - Pseudomonas' Cousins

• Burkholderia cepacia complex: Cystic Fibrosis (CF) patients (cepacia syndrome), nosocomial.
• Burkholderia pseudomallei: Melioidosis (Whitmore’s disease); safety-pin appearance (bipolar staining); endemic SE Asia/N Australia.

  ⭐ Burkholderia pseudomallei, causative agent of melioidosis, can mimic tuberculosis and shows a characteristic "safety pin" appearance on bipolar staining.

• Stenotrophomonas maltophilia: Nosocomial; intrinsically carbapenem-resistant; treat: TMP-SMX.
• Acinetobacter baumannii: "Iraqibacter"; nosocomial (VAP, bloodstream); highly drug-resistant; coccobacillary, oxidase-negative.

High‑Yield Points - ⚡ Biggest Takeaways

• P. aeruginosa: Gram-negative rod, oxidase (+)ve, pyocyanin (blue-green), grape-like odor.
• Key in nosocomial infections, burns, cystic fibrosis (CF), immunocompromised.
• Causes VAP, UTIs, ecthyma gangrenosum, hot tub folliculitis, malignant otitis externa.
• Significant multidrug resistance (MDR) is common.
• Burkholderia cepacia: Severe lung infections in CF (e.g., cepacia syndrome).
• Stenotrophomonas maltophilia: Nosocomial pathogen, intrinsically carbapenem-resistant.
• Acinetobacter baumannii: ICU infections (pneumonia, sepsis); often MDR.