Pseudomonas aeruginosa

Pseudomonas aeruginosa

Organism

Pseudomonas aeruginosa is a moderately-sized gram-negative bacillus.
Possess a monotrichous (def) arrangement of flagella.
Pseudomonas is typically aerobic (def) but can grow under select anaerobic conditions (def).
Does not ferment sugars.

Habitat and Source

A ubiquitous bacterium found in soil, water, vegetation, decaying organic matter, throughout the hospital environment, and frequently carried in the respiratory and intestinal tracts of hospitalized patients and immunocompromized hosts.

Epidemiology

Pseudomonas aeruginosa is also an opportunistic pathogen. It is a common cause of nosocomial infections (def) and can be found growing in a large variety of environmental locations. In the hospital environment, for example, it has been isolated from drains, sinks, faucets, water from cut flowers, cleaning solutions, medicines, and even disinfectant soap solutions. It is especially dangerous to the debilitated or immunocompromised patient.
P. aeruginosa is responsible for 12 percent of hospital-acquired urinary tract infections, 16 percent of nosocomial pneumonia cases, and 10 percent of the cases of septicemia.

Clinical Disease

Pseudomonas causes a variety of opportunistic infections including urinary tract infections, wound infections, pneumonia, and septicemia.
P. aeruginosa is a significant cause of burn infections with a 60 percent mortality rate.
P. aeruginosa also colonizes and chronically infects the lungs of people with cystic fibrosis.

Pathogenicity

In the outer membrane of the gram-negative cell wall, the lipopolysaccharide functions as an endotoxin . Endotoxin, especially when in the blood, can lead to inflammation, high fever, hypotension, capillary damage, intravascular coagulation, tissue degradation, and irreversible shock. Death is a result of what is called the shock cascade (see Fig. 1).
Pili (def) and various cell wall adhesins (def) enable the bacterium to initially adhere to host cells.
A polysaccharide capsule enables P. aeruginosa to adhere to host cells and resist phagocytosis.
A green to blue water-soluble pigment caled pyocyanin stimulates an inflammatory response, catalyzes formation of toxic oxygen radicals (def), and impairs ciliary function (def).
Exotoxin A inhibits host cell protein synthesis, produces tissue damage damage, and is immunosuppressive.
Exotoxin S inhibits host cell protein synthesis and is immunosuppressive.
Alkaline protease mediates tissue distruction.
Phospholipase C mediates tissue distruction and stimulates inflammation.
Rhamnolipid inhibits pulmonary ciliary activity and damages lecithin-containing tissue .
Elastase damages elastin-containing tissue such as lung tissue, blood vessels, and the skin. It also destroys collagen (def), immunoglobulins (def), and complement factors (def).
Cytotoxin disrupts eukaryotic cell membranes causing damage to leukocytes (def) and microvascular injury.

Treatment

Usually treated with a combined use of aminoglycosides and beta-lactam antibiotics* (see antibiotic table). In vitro antibiotic susceptibility tests usually guide treatment of more complicated infections.

*Drugs may change with time.

For a more detailed article on Pseudomonas aeruginosa infections, see Pseudomonas aeruginosa Infection, by Samer Qarah, MD, Fellow, Department of Internal Medicine, Division of Pulmonary and Critical Care, The Brooklyn Hospital Center and Cornell University; Burke A Cunha, MD, Professor of Medicine, State University of New York at Stony Brook School of Medicine; Chief, Infectious Disease Division, Vice-Chair, Department of Internal Medicine, Winthrop-University Hospital; Pratibha Dua, MD, Staff Physician, Department of Internal Medicine, The Brooklyn Hospital Center; Klaus-Dieter Lessnau, MD, FCCP, Clinical Assistant Professor of Medicine, New York University School of Medicine; Medical Director, Pulmonary Physiology Laboratory, Department of Medicine, Section of Pulmonary Medicine, Lenox Hill Hospital.