Pseudomonas and Related Non-Fermentative Rods

• Aerobic, non-fermentative, Gram-negative rod

• Oxidase-positive (distinguishes it from Enterobacteriaceae)

Pseudomonas aeruginosa: oxygen requirement, fermentation, Gram, shape, oxidase

• Grows on bile salt-containing media (e.g., MacConkey agar)

• Produces fluorescent pigments:

  • Pyocyanin (blue-green)

  • Pyoverdin (yellow-green, fluorescent)

• Sweet, grape-like odor

Pseudomonas aeruginosa: media, pigments, odor

• Widespread in the environment

  • Found in moist hospital reservoirs: sinks, mops, respiratory therapy equipment, dialysis machines, disinfectant solutions, distilled water.

  • Can colonize the human body: skin, oral cavity, GI tract.

• Minimal nutritional requirements & versatile growth

  • Can survive in a variety of environments, including distilled water and disinfectants.

• Multiple virulence factors

Pseudomonas aeruginosa: why such a serious opportunistic pathogen?

• Pili and flagella → adhesion to host cells.

• Alginate biofilm (important in cystic fibrosis) → resistance to immune clearance.

• Exotoxins (e.g., elastase, pyocyanin, exotoxin A) → tissue destruction, immune evasion.

Pseudomonas aeruginosa: virulence factors

• Skin & Soft Tissue Infections

  • Folliculitis (Hot Tub Dermatitis): caused by contaminated water.

  • Otitis externa (Swimmer’s Ear): external ear canal infection.

  • Invasive Malignant Otitis Externa: spreads to skull base; seen in diabetics.

  • Eye Infections: due to contaminated contact lenses.

• Endocarditis

  • IV drug users at risk.

Pseudomonas aeruginosa: kinds of infections in normal hosts

• Ventilator-Associated Pneumonia (VAP) → most serious pathogen in ICU patients.

• Urinary Tract Infections (UTIs) → especially in catheterized patients.

• IV-line Sepsis (Bacteremia) → life-threatening.

Pseudomonas aeruginosa: hospital acquired infections

Chronic Colonization in Cystic Fibrosis (CF) Patients

Bacteremia in neutropenic patients (≤1000 PMNs/mm³) → high mortality

Burn wound infections → major concern in burn units

Ecthyma gangrenosum:

• Hemorrhagic skin lesions associated with disseminated P. aeruginosa infections.

• Caused by elastase, which destroys blood vessels.

Pseudomonas aeruginosa: infections in immunocompromised hosts

Pathogenesis in CF:

• Early colonization via pili & flagella.

• Persistent infection due to:

  • Loss of highly immunogenic O-antigen, pili, flagella.

  • Biofilm formation (via alginate upregulation) → prevents immune clearance.

  • Chronic neutrophilic inflammation → lung damage, respiratory failure.

Pathogenesis of Pseudomonas aeruginosa in CF patients

Diagnosis

• Culture Identification: Green pigmentation (pyocyanin & pyoverdin), Fruity/grape-like odor, Oxidase-positive.

Treatment: Highly antibiotic-resistant → must perform antibiotic susceptibility testing

Combination therapy recommended:

• Aminoglycoside (e.g., gentamicin, tobramycin) +

• Anti-Pseudomonas β-lactam (e.g., piperacillin-tazobactam, ceftazidime, carbapenems in resistant cases).

Pseudomonas aeruginosa diagnosis and treatment

Opportunistic pathogen primarily associated with healthcare-associated infections, ICU patients particularly affected.

Common infections: wound infections, vent-associated pneumonia

Highly antibiotic resistant

Acinetobacter baumannii: what is it, what kind of infections does it cause?

Nosocomial pathogen, particularly in patients receiving broad-spectrum antibiotics.

Infects:

• Cystic fibrosis (CF) patients → causes severe respiratory infections.

• Chronic granulomatous disease (CGD) patients.

• IV catheter-associated septicemia → second most common infection caused by B. cepacia.

Burkholderia cepacia: what is it, who does it infect and in what way?

• Highly antibiotic-resistant opportunistic pathogen.

• Typically infects immunocompromised patients and those receiving broad-spectrum antibiotics.

• Common nosocomial infections:

  • Pneumonia.

  • Bacteremia (especially in ICU patients).

• Resistant to carbapenems, but usually susceptible to TMP-SMX.

• Often contaminates hospital equipment, including:

  • Disinfectants, respiratory therapy equipment, ice machines

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Key Takeaways

✔ Acinetobacter baumannii → MDR pathogen, serious threat in ICU/VAP patients.
✔ Burkholderia cepacia → Risk for CF and CGD patients, TMP-SMX susceptible.
✔ Stenotrophomonas maltophilia → Nosocomial pneumonia & bacteremia, TMP-SMX effective, carbapenem-resistant.

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Stenotrophomonas maltophilia: what is it, who does it infect, what kind of infections?