Pseudomonas
Clinical Manifestations
Pseudomonas aeruginosa and P maltophilia account for 80 percent of opportunistic infections by pseudomonads. Pseudomonas aeruginosa infection is a serious problem in patients hospitalized with cancer, cystic fibrosis, and burns; the case fatality is 50 percent. Other infections caused by Pseudomonas species include endocarditis, pneumonia, and infections of the urinary tract, central nervous system, wounds, eyes, ears, skin, and musculoskeletal system.
Structure, Classification, and Antigenic Types
Pseudomonas species are Gram-negative, aerobic bacilli measuring 0.5 to 0.8, ?m by 1.5 to 3.0 ?m. Motility is by a single polar flagellum. Species are distinguished by biochemical and DNA hybridization tests. Antisera to lipopolysaccharide and outer membrane proteins show cross-reactivity among serovars.
Pathogenesis
Neutropenia in cancer patients and others receiving immunosuppressive drugs contributes to infection. Pseudomonas aeruginosa has several virulence factors, but their roles in pathogenesis are unclear. An alginate is antiphagocytic, and most strains isolated produce toxin A, a diphtheria-toxin-like exotoxin. All strains have endotoxin, which is a major virulence factor in bacteremia and septic shock.
Host Defenses
Phagocytosis by polymorphonuclear leukocytes is important in resistance to Pseudomonas infections. Antibodies to somatic antigens and exotoxins also contribute to recovery. Humoral immunity is normally the primary immune mechanism against Pseudomonas infection but does not seem to resolve infection in cystic fibrosis patients despite high levels of circulating antibodies.Copyright © 1996
The University of Texas Medical Branch at Galveston