Pseudomonas

Epidemiology & Risk Factors

• Microbiology: Gram (-), lactose non-fermenting, oxidase (+), obligate aerobe, motile rod. Produces pyocyanin (blue-green pigment) & pyoverdin, sweet/fruity grape-like odor. Exotoxin A (inhibits EF-2 via ADP-ribosylation).
• Host Risk Factors:
  • Immunocompromised (severe neutropenia [ANC < 500], post-chemo, advanced HIV).
  • Structural lung disease (Cystic Fibrosis [CF], bronchiectasis).
  • ICU / Invasive devices (ventilators [VAP], urinary catheters [CAUTI], central lines).
  • Cutaneous barrier loss (severe burns, IVDU, puncture wounds through sneakers).
  • Environmental exposure (hot tubs, warm moist environments, contact lenses).

Virulence factors and resistances

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• Mucoid polysaccharide capsule → biofilm formation
  • Conversion to a mucoid phenotype that produces an alginate polysaccharide, which strengthens biofilm structure and aids in the inhibition of opsonization and phagocytosis
• Endotoxin → fever, shock
• Exotoxin A: inactivates EF-2 → inhibition of protein synthesis → death of host cells
• Phospholipase C: degrades cell membranes

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Clinical Features

• Pulmonary:
  • VAP / HAP: Fever, purulent sputum, tachypnea, leukocytosis, hypoxemia in intubated/hospitalized pts.
  • CF Exacerbation: Productive cough, worsening dyspnea, decline in FEV1, purulent green sputum.
• Dermatologic & Soft Tissue:
  • Ecthyma Gangrenosum: Rapidly progressive cutaneous necrosis in neutropenic/bacteremic pts. Erythematous macules/bullae $\to$ punched-out ulcer w/ central black eschar. Painless initially. c
  • Hot Tub Folliculitis: Pruritic, papulopustular rash occurring 8-48h after hot tub exposure; self-limiting, concentrated under bathing suits.
  • Burn Wound Infection: Discolored eschar, green discharge, fruity odor, rapid graft loss, systemic sepsis.
• Otologic:
  • Otitis Externa: Pain, pruritus, purulent discharge, tragal tenderness (“swimmer’s ear”).
  • Malignant (Necrotizing) Otitis Externa: Elderly pts w/ poorly controlled DM. Severe, deep otalgia (worse at night), granulation tissue in external auditory canal (EAC), CN VII palsy (facial droop), skull base osteomyelitis.
• Musculoskeletal:
  • Osteomyelitis: Foot/calcaneal osteomyelitis following puncture wound through rubber-soled sneaker; sternoclavicular/vertebral osteomyelitis in IVDU.
• Ophthalmologic:
  • Keratitis / Corneal Ulcer: Severe eye pain, photophobia, ring-shaped corneal ulceration in contact lens wearers.
• Cardiovascular:
  • Endocarditis: Tricuspid valve involvement in IVDU (fever, septic pulmonary emboli).