Pseudomonas aeruginosa is a gram-negative, oxidase-positive, motile rod, which frequently grows on agar in yellow-green iridescent colonies resulting from two pigments, pyocyanin and fluorescein, diffused in the medium.
Pseudomonas can be found occasionally in the axilla and anogenital areas of normal skin but rarely in the stools of adults unless antibiotics are given. The organism is commonly a contaminant of lesions populated with more virulent organisms but occasionally it causes infection in tissues that are exposed to the external environment.
Pseudomonas infections can develop in many anatomic locations, including skin, subcutaneous tissue, bone, ears, eyes, urinary tract, and heart valves. The site varies with the portal of entry, and the patient's particular vulnerability.
Bacteremia without a detectable urinary focus, especially if due to Pseudomonas species other than aeruginosa, should raise the possibility of contaminated IV fluids, medication, or antiseptics used in placing the IV catheter.
Pseudomonas is a common cause of urinary tract infections and usually is seen in patients who have had urologic manipulation or have obstructive uropathy. Pulmonary infection can occur in hospitalized patients in association with endotracheal intubation, tracheostomy, or IPPB treatment in which Pseudomonas has joined with other gram-negative rods in colonizing the oropharynx.
The most serious infections occur in debilitated patients with diminished resistance resulting from other disease or therapy.
Pseudomonas infections occur most often in hospitals, where the organism is frequently found in moist areas such as sinks, antiseptic solutions, and urine receptacles. Cross infection transmitted from patient to patient via the hands of personnel may occur in outbreaks of urinary tract infections, on burn units and in neonatal intensive care nurseries.
Diagnosis of pseudomonas infection is established by culturing the organism from infection sites.
When infection is localized and external, treatment with 1% acetic acid irrigations or topical agents such as polymyxin B or colistin is effective. Necrotic tissue must be debrided and abscesses must be drained.
When parenteral therapy is required, 5 mg/kg/day in divided doses of the aminoglycoside antibiotic tobramycin or gentamicin inhibits most Pseudomonas.
Other antibiotics used include amikacin, tobramycin and gentamicin. Several penicillins, including carbenicillin, ticarcillin, piperacillin, mezlocillin, and azlocillin, are active against Pseudomonas.
Specific choice of antibiotic must be based upon the history of pseudomonas sensitivity to the particular drug in the community and, if the organism is cultured, its specific sensitivity.