PSEUDOMONAS

Description

Pseudomonas infections are caused by any of several types of the Gram-negative, rod-shaped bacteria. Although there are over 200 species of Pseudomonas only a small number are known to be pathogenic for man. Below are three of the more common pathogenic species:

• aeruginosa - sputum of patients with cystic fibrosis, burns, urinary tract infections. Especially prevalent in nosocomial infections, external ear infections.
• mallei - causes glanders (transmitted from horse to man), nodular, necrotic involvement of mucous membranes of nasal area (lymphatics, lymph nodes and skin).
• pseudomallei - causes melioidosis, a glanders-like disease with clinical manifestations ranging from pulmonary infection to septicemia.

Paeruginosa, primarily a nosocomial pathogen, rarely causes disease in healthy individuals. In most cases of infection, loss of the physical skin or mucous membrane barrier usually occurs or underlying immune weakness usually is present

Pseudomonas, can cause minor skin infection or serious, life-threatening illness. Of the two million nosocomial infections each year, 10% are caused by P. aeruginosa. The bacterium is the second most common cause of nosocomial pneumonia and the most common cause of intensive care unit (ICU) pneumonia.

Risk factors for P. aeruginosa pneumonia include: debilitation; cystic fibrosis; chronic lung disease; immunocompromised condition; being on antibiotic therapy or a respirator; and congestive heart failure. Patients with cystic fibrosis often develop pseudomonas infections as children and suffer recurrent attacks of pneumonia. People with diabetes are particularly prone to Pseudomonas infections. Pseudomonas can also cause infection in the blood, skin, bones, ears, eyes, urinary tract, heart valves, and lungs. Pseudomonas can cause severe pneumonia in hospitalized people, especially those in intensive care. Pseudomonas can also cause urinary tract infections, usually in people who have had urologic procedures or those who have an obstruction of the urinary tract. Pseudomonas aeruginosa is rarely found in stool unless antibiotics are given. Unfortunately, Pseudomonas aeruginosa has become one of the "hospital bugs" that may be multi-drug resistant.

Two minor Pseudomonas infections that can affect otherwise healthy people are swimmer's ear and hot-tub folliculitis. Swimmer's ear (otitis externa) is infection of the external ear canal that produces pain and drainage. Hot-tub folliculitis is an itchy skin rash consisting of tiny pimples, some of which may contain a drop of pus in their center. Pseudomonas can also cause ulcers in the eye after gaining entry through an eye injury, a contaminated contact lens, or contaminated contact lens fluid. The ulcers are painful and may lead to a loss of vision. Pseudomonas can cause infection in deep puncture wounds, especially those occurring in the feet of children. When Pseudomonas infects a wound, growth in the soiled dressings often gives off a characteristic fruity odor.

Where are they found?

Pseudomonas is present throughout the world in soil, water, and on the skin of animals and people. Pseudomonas favors moist areas, such as sinks, toilets, pools, and hot tubs, and usually can withstand standard levels of pool chlorination. The bacteria have even been known to live in weak antiseptic solutions, (e.g. benzelchonium chloride). P. aeruginosa is a resident of the intestinal tract in about 10% of healthy individuals, and it is found sporadically in moist areas of the human skin (axilla, groin) and in the saliva. Its nutritional requirements are simple and it can metabolize a large variety of carbon sources. P. aeruginosa can thus multiply in almost any moist environment containing even trace amounts of organic compounds, e.g., eyedrops, soaps, anesthesia and resuscitation equipment, fuels, humidifiers and even stored distilled water. It has also been reported in kidney dialysis machines.

How do we get infections?

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. 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. In burns, the region below the eschar can become heavily infiltrated with organisms, serving as a focus for subsequent bacteremia (blood stream invasion) - an often lethal complication of burns. 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.

Incubation period

P.aeruginosa infection can be sudden and severe, or slow in onset and cause little pain. As with other infections, symptoms include fever, chills, and the production of purulent matter in infected wounds. Diagnosis of pseudomonas infection is established by culturing the organism from infection sites.

Treatment

Most pseudomonas infections can be successfully treated with antibiotics and surgery. In immunocompromised persons, however, P. aeruginosa infections have a high mortality rate, particularly following bacteremia or infections of the lower lung. Mortality rates range from 15 to 20% of patients with severe ear infections to 89% of patients with infections of the left side of the heart.

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.

Prevention

Hand washing between patient contacts and the use of gloves when appropriate is of paramount importance.

Most hospitals have programs for the prevention of nosocomial infections. Patients with cystic fibrosis may be given periodic doses of antibiotics to prevent episodes of Pseudomonas pneumonia.

In order to be classified as a hospital disinfectant under the Federal EPA's registration guidelines, registered products must possess germicidal efficacy against Pseudomonas with claims also proven against Salmonella and Staphylococcus organisms.

Minor skin infections can be prevented by avoiding hot tubs with cloudy water; avoiding public swimming pools at the end of the day; removing wet swimsuits as soon as possible; bathing after sharing a hot tub or using a public pool; using appropriate amounts of chlorine in the water and cleaning hot tub filters regularly and frequently using an EPA approved disinfectant product.