2. The liquid product of inflammation composed of albuminous substances, a thin fluid, and leukocytes; generally yellow in color.
It is usually, but not always, caused by infectious microorganisms.
If red, it suggests rupture of small vessels. If blue or green, it indicates the presence of Pseudomonas aeruginosa.
Streptococci, staphylococci, gonococci, pneumococci, and other species of bacteria cause the formation of pus.
An expanded explanation of Pseudomonas aeruginosa
Pseudomonas aeruginosa is the versatile "blue-green pus bacteria" that takes every opportunity to infect people, especially those who are immunocompromised.
Pseudomonas rarely causes infection in healthy individuals but it is a major cause of hospital acquired (nosocomial) infections. It tends to infect people with immunodeficiency or burns and those with indwelling catheters or on respirators.
Infection with pseudomonas can lead to urinary tract infections, sepsis (blood stream infection), pneumonia, pharyngitis, and many other medical problems. Pseudomonas colonizes the lungs of patients with cystic fibrosis (CF) and contributes to the chronic progressive pulmonary disease and death rate in CF.
Pseudomonas normally resides in the soil, marshes, and coastal marine habitats. It can survive under conditions that few other organisms can tolerate, it produces a slime layer that resists phagocytosis (engulfment), and it is resistant to most antibiotics.
Pseudomonas can multiply in an extraordinary assortment of environments including eyedrops, soaps, sinks, anesthesia and resuscitation equipment, fuels, humidifiers, and even stored distilled water. It has also been reported in kidney dialysis machines. The characteristic color of the pus is due to a bluish pigment (pyocyanin) and a greenish pigment produced by pseudomonas.