The Pseudomonas genus of bacteria are common environmental bacteria, and the most important pseudomonas in medical issues, Pseudomonas aeruginosa, lives on about half of the human population. A wide array of Pseudomonas infections affect humans and other animals, such as pneumonia, urinary tract infections, heart infections, ear infections and infections of the joints. Although the genus is ubiquitous in the environment, the bacteria tend to be opportunistic pathogens, which means that they generally become dangerous only in sick people.
Pseudomonas species tend to like living in areas that are moist, such as soil or water. They also survive well in sinks, hot tubs and swimming pools that have low chlorine levels. When they infect people, they live in the intestines, in ears or on skin.
The most medically important species, Pseudomonas aeruginosa, is resistant to salt, some antiseptics and some antibiotics. Pseudomonas aeruginosa also can survive with limited nutrients. All of these characteristics mean that pseudomonas infections are a significant part of hospital-acquired infections.
Pseudomonas aeruginosa infections are the top cause of potentially lethal pneumonia in hospital patients who use a ventilator or who are in intensive care. This type of bacteria also is a major cause of infection in patients who have cystic fibrosis, cancer and burns, with about half of the affected patients dying from the infection. Other hospital-acquired types of pseudomonas infections are urinary tract infections, surgical incision infections and blood poisoning. Sometimes bacteria that have invaded the blood can pass into bone and joints and cause infection. The bacteria might also cause heart infections through intravenous drug use or from heart valve surgery.
Outside of the hospital, pseudomonas infections are the most common cause of ear infections and corneal ulcers. The bacterium can also infect the eyes of contact lens users and is a common cause of urinary tract infections. Pseudomonas aeruginosa can also infect the soft tissue, the joints or the bone of the body when it is introduced through puncture wounds. Bacteria present in inadequately sanitized water can also cause "swimmer's ear" or a disease called folliculitis, which infects hair follicles in skin, usually in people who use hot tubs.
Some bacterial species that were previously included in the Pseudomonas genus have been renamed because of genetic classification systems. These bacteria might still be referred to as pseudomonas but are more correctly known by their new names. For example, the Burkholderia name has replaced Pseudomonas in some medically relevant species such as Burkolderia cepacia and Burkolderia pseudomallei. These bacteria also cause opportunistic infections.