Gram-Negative, Oxidase-Positive Motile Rods
• P. aeruginosa is the most common clinically significant pseudomonad.
1. Gram-negative, oxidase-positive, aerobic rods with one to three flagella
3. Positive nitrate reduction test
6. Blue-green pigment (pyocyanin) or other diffusible pigments produced by many strains
1. Pili promote adherence to respiratory epithelium.
2. Capsule is antiphagocytic and promotes adherence to tracheal epithelium.
3. Exotoxin A inhibits protein synthesis by adenosine diphosphate (ADP)-ribosylation of elongation factor-2 (EF-2), similar to diphtheria toxin (see Chapter 10, Fig. 10-1C).
4. Biofilm production occurs when sufficient bacteria trigger quorum sensing.
5. Other virulence factors include the endotoxin exoenzyme S, which prevents phagocytic killing; degradative enzymes that damage host tissues; and antibiotic resistance.
• P. aeruginosa causes a wide variety of opportunistic infections, most commonly in hospitalized, immunocompromised, and debilitated individuals.
1. Urinary tract infection (UTI)
• P. aeruginosa is a common cause of UTI, especially in patients with indwelling catheters who are on antimicrobial therapy, which selects for drug-resistant strains.
• Vesicular and pustular lesions; cellulitis, abscesses, and subcutaneous infections
• In cystic fibrosis patients, P. aeruginosa and Staphylococcus aureus are the most common causes of chronic pulmonary infection, which exacerbates the underlying disease and is difficult to eradicate.
• In neutropenic and other immunocompromised individuals, P. aeruginosa acquired from contaminated respiratory therapy equipment can cause diffuse, bilateral bronchopneumonia.
6. Keratitis (fulminating ulceration of the cornea)
• Initial trauma to the eye followed by exposure to P. aeruginosa can lead to eye-threatening panophthalmitis without prompt treatment.
7. Disseminated infections of the immunocompromised host (e.g., transplant patient).
8. P. aeruginosa osteomyelitis
• P. aeruginosa is ubiquitous in the environment and in moist reservoirs (e.g., respiratory and dialysis equipment, cut flowers, sinks, and bars of soap) throughout hospitals and other institutions.
