The genus Pseudomonas is made up of Gram-negative, rod-shaped bacteria that inhabit many environments; Pseudomonas species are common in soil, water, and vegetation. The genus is particularly noteworthy because of the tendency of several species to cause infections in people who are already ill, or whose immune systems are not operating properly. Such infections are termed opportunistic infections.

Pseudomonas rarely causes infections in those whose immune systems are fully functional. The disease-causing members of the genus are therefore prevalent where illness abounds. Pseudomonas are one of the major causes of nosocomial (hospital acquired) infections.

Bacteria in this genus not only cause infections in man, but also cause infections in plants and animals (e.g., horses). For example, Pseudomonas mallei causes ganders disease in horses.

The species that comprise the genus Pseudomonas are part of the wider family of bacteria that are classified as Pseudomonadaceae. There are more than...