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Pseudomonas Infections

by Matthew E. Levison, MD

Pseudomonas infections are caused by any of several types of the gram-negative bacteria Pseudomonas, especially Pseudomonas aeruginosa.

  • Infections range from mild external ones (affecting the ear or hair follicles) to serious internal infections (affecting the lungs, bloodstream, or heart valves).

  • Symptoms vary depending on which area of the body is infected.

  • Identifying the bacteria in a sample taken from infected tissue confirms the diagnosis.

  • Antibiotics are applied externally for external infections or given intravenously for more serious, internal infections.

Pseudomonas bacteria, including Pseudomonas aeruginosa, are present throughout the world in soil and water. These bacteria favor moist areas, such as sinks, toilets, inadequately chlorinated swimming pools and hot tubs, and outdated or inactivated antiseptic solutions. These bacteria may temporarily reside in the skin, ears, and intestine of healthy people.

Pseudomonas aeruginosa infections range from minor external infections to serious, life-threatening disorders. Infections occur more often and tend to be more severe in people who

  • Are weakened (debilitated) by certain severe disorders

  • Have diabetes or cystic fibrosis

  • Are hospitalized

  • Have a disorder that weakens the immune system, such as human immunodeficiency virus (HIV) infection

  • Take drugs that suppress the immune system, such as those used to treat cancer or to prevent rejection of transplanted organs

These bacteria can infect the blood, skin, bones, ears, eyes, urinary tract, heart valves, and lungs, as well as wounds (such as burns, injuries, or wounds made during surgery). Use of medical devices, such as catheters inserted into the bladder or a vein, breathing tubes, and mechanical ventilators, increase the risk of Pseudomonas aeruginosa infections. These infections are commonly acquired in hospitals.


Pseudomonas aeruginosa causes several different infections.

Swimmer’s ear (external otitis) is a mild external infection that can occur in otherwise healthy people. Water containing the bacteria can enter the ear during swimming. Swimmer’s ear causes pain and a discharge from the ear (see External Otitis).

Hot-tub folliculitis is another mild external infection. Hair roots (follicles) become infected in people who use hot tubs or whirlpools, particularly if the hot tubs and whirlpools are inadequately chlorinated. Spending a lot of time in the water softens the follicles, making them easier for bacteria to invade. An itchy rash consisting of tiny pimples develops. Pimples may have a drop of pus in their center (see Folliculitis).

Malignant external otitis is a deep ear infection. It is most common among people with diabetes. Tissues become swollen and inflamed, partly or completely closing the ear canal. Symptoms may include fever, loss of hearing, inflammation of tissues around the infected ear, severe ear pain, a foul-smelling discharge from the ear, and nerve damage.

Eye infections due to these bacteria may damage the cornea, often permanently. Enzymes produced by the bacteria can rapidly destroy the eye. Infections may result from contamination of contact lenses or contact lens solution.

Soft-tissue infections include those in muscle, tendons, ligaments, fat, and skin. These infections can occur in deep puncture wounds, especially in the feet of children who are wearing sneakers and step on a nail. These bacteria can also infect pressure sores, burns, and wounds due to injuries or surgery. When these bacteria grow in soiled dressings, the dressings turn green and smell like newly mowed grass.

Severe pneumonia can develop in hospitalized people, especially those who need to use a breathing tube and a mechanical ventilator.

Urinary tract infections usually develop after a procedure involving the urinary tract is done, when the urinary tract is blocked, or when a catheter must remain in the bladder a long time.

Bloodstream infections (bacteremia) often result when the following occur:

  • Bacteria enter the bloodstream from an infected organ (such as the urinary tract).

  • A contaminated illegal drug is injected into a vein.

  • A contaminated needle or syringe is used to inject illegal drugs.

Sometimes the source of the bacteria is unknown, as may occur in people who have too few white blood cells after cancer chemotherapy. Purple-black spots surrounded by a red rim on the skin often develop in the armpits and groin. Without treatment, infection can lead to shock and death.

Bone and joint infections usually occur in the spine and the joint between the collar bone and breastbone. The bacteria usually spread to bones and joints from the bloodstream but may spread from nearby soft tissues that have been infected after an injury or surgery.

Heart valve infections are rare. They usually occur in people who inject intravenous drugs and in people with artificial heart valves. The bacteria usually spread to heart valves from the bloodstream.


Doctors diagnose Pseudomonas aeruginosa infections by taking a sample of blood or other body fluids and growing the bacteria in cultures. Tests to determine which antibiotics are likely to be effective (susceptibility tests) are also done.

Prevention and Treatment

To prevent swimmer’s ear, people who have had it should irrigate their ears with an acetic acid solution before and after swimming. Acetic acid drops with or without corticosteroids are usually effective for treatment.

Hot-tub folliculitis usually resolves without treatment.

Eye infections are treated with highly concentrated antibiotic drops, applied frequently at first. Sometimes antibiotics must be injected directly into the eye.

Serious Pseudomonas aeruginosa infections are difficult to treat. Malignant external otitis, internal infections (such as pneumonia or heart valve infection), and blood infections require weeks of antibiotics given intravenously. Usually, a combination of antibiotics is required because many strains, particularly those acquired in health care facilities, are resistant to many antibiotics. Doctors choose an antibiotic that is usually effective in their geographic area. They may change the antibiotics after test results indicate which antibiotics are likely to be effective.

For heart valve infections, open-heart surgery to replace the valve plus antibiotic therapy is usually needed (see Replacing a Heart Valve).