Pseudomonas aeruginosa is a commonly found microbe of the family of Gram-negative bacteria which can give rise to serious and life threatening infections. Bacteria are classified as Gram-negative or Gram-positive on the basis of how much colour these structures retain when stained with a purple dye; the thicker surface of the Gram-positive bacteria holds more dye. Gram-negative bacteria are characterized by a dense layer of lipopolysaccharide (LPS) molecules on their surface. LPS is also called endotoxin, and it causes fever and many symptoms of sepsis after being shed from the surface of Gram-negative bacteria.
Pseudomonas aeruginosa is ubiquitously found in the environment, in soil, water and even on plants; it grows under aerobic (with oxygen) as well as anaerobic (without oxygen) conditions. Pseudomonas bacteria easily form colonies in any environment and on any type of surface. This colonization is also observed in humans.
Pseudomonas aeruginosa is recognized as an opportunistic pathogen of high clinical relevance because it exploits some deficiencies in the host defense system to initiate an infection. The bacterium almost never infects tissues in uncompromised human beings with an intact immune system, yet there is hardly any tissue that it cannot infect if the tissue defense system is compromised in some way.