P. aeruginosa
P. fluorescens
P. fragi
P. putida
P. syringae
etc. The bacterial genus Pseudomonas includes plant pathogenic bacteria such as P. syringae (various pathovars), the opportunistic pathogen P. aeruginosa , the ubiquitous soil bacterium P. putida, and some species that are known to cause problems in dairy products. However, the actions of this group of bacteria are mainly considered neutral to man. They are considered to be metabolically diverse agents of spoilage and degredation. In recent times, members of the Pseudomonas have been used as biocontrol agents.

Members of Pseudomonas are Gram-negative, aerobic (able to consume oxygen) rods or cocci. Most are flagellated so they can move around. Most produce a slime layer that cannot be phagocytosed, and which aids in the production of surface-colonising biofilms P. fluorescens is easily recognised as it secretes large amounts of a fluorescent, yellow-green siderophores under iron-limited conditions. Many "Pseudomonidacea" are capable of producing these flourescent pigments called pyoverdines. The opportunistic pathogen P. aeruginosa similarly secretes bright blue-green metabolites, which turns out to be pyoverdine and pyochelin. Growth of this and other "Pseudomonads" is usually accompanied by a "fruity" odor compared to Escherichia coli.

P. aeruginosa usually causes problems to humans who have already have had their immune systems weakened. This bacteria usually infects the urinary tract, burns, wounds, and also causes other blood infections. One in ten hospital acquired infections is from Pseudomonas. Cystic fibrosis patients are also predisposed to aeruginosa infection of the lungs. This species is also known to be an opportunistic pathogen of plants.

Pseudomonas are able to grow in unexpected places. They have been found in areas where a lot of pharmaceuticals are prepared. Any carbon source, such as soap residue or cap liner adhesives is a suitable place for them to thrive. Other unlikely places where they have been found include antiseptics such as ammonium compounds and bottled mineral water. This ability to thrive in harsh conditions is a result of their hearty cell wall that contains porins. Their resistance to most antibiotics is attributed to their rapid efflux pumps which pump out the antibiotics before they are able to work.

Common hygiene practices should help to ward off any unwanted infections by this bacterium. If a more serious infection occurs, it can be treated with antibiotics such as piperacillin, imipenem, tobramycin, or ciprofloxacin, among others. Most pseudomonads are naturally resistant to penicillin and related beta-lactam antibiotics.