Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Gram-negative rod

Strict aerobes

Do not ferment glucose.

Found free-living in the environment in soil & water.

Most strains produce green diffusible pigments which discolor the agar around colonies.

Grows well on all common agar & produces NLF colonies on MacConkey.

Found on the skin in moist areas & can colonize upper respiratory tract of hospitalized patients.

Ability to grow in simple aqueous solutions has resulted in contamination of respiratory therapy & anesthesia equipment, IV fluids, & distilled water.

An opportunistic pathogen that causes infections in hospitalized patients: those with extensive burns & chronic respiratory disease.

Both endotoxin & exotoxin play a role in pathogenesis.

Exotoxin A inhibits eukaryotic protein synthesis by ADP ribosylation of EF-2.

Diseases:

- urinary tract infections.

- pneumonia.

- wound infections (especially burns).

From these sites, organism can enter blood, causing sepsis with mortality rate of over 50%.

A severe external otitis & other skin lesions occur in users of swimming pools & hot tubs in which chlorination is inadequate.

In patients with diabetes mellitus, malignant otitis externa develops in which the infection spreads rapidly into the tissues of the face & neck & underlying bone.

Common cause of osteochondritis of the foot in those who sustain puncture wounds through the sole of gym shoes.

Corneal infections in contact lens users.

Nosocomial infections:

- local infections: catheter-related UTI, infected ulcers, bed sores, & infection of burns.

- pneumonia leading to septicaemia.

- cystic fibrosis: colonization of lung leading to progressive lung damage.

- immunocompromised patients with neutropenia.

Grows as a non-lactose-fermenting (colorless) colonies on MacConkey’s or EMB agar.

Typical metallic sheen of growth on TSI agar, coupled with blue-green pigment on ordinary nutrient & a fruity aroma suffice to make diagnosis.

Diagnosis confirmed by biochemical reactions.

Resistant to many antibiotics.

Often sensitive to the:

- cephalosporin ceftazidime.

- various aminoglycosides including gentamicin.

- ciprofloxacin.

Prophylaxis:

- pseudomonas septicaemia is so common & dangerous in neutropenic patients that it is usual practice to give them prophylactic antibiotics when their white cell count becomes low.

- ciprofloxacin is commonly used, which prevents other Gram negative rod septicaemias.

Prevention:

- keeping neutrophil counts above 500/mL.

- remove indwelling catheters promptly.

- taking special care of burned skin.

- limit infection in patients with reduced host defences.