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Pseudomonas is a genus of Gram-negative aerobic gammaproteobacteria, belonging to the family Pseudomonadaceae containing 191 validly described species.
Pseudomonas aeruginosa is increasingly recognized as an emerging opportunistic pathogen of clinical relevance. Several different epidemiological studies indicate antibiotic resistance is increasing in clinical isolates. Phage therapy has been found to be effective in treating P. aeruginosa infections[citation needed].
The members of the genus demonstrate a great deal of metabolic diversity, and consequently are able to colonise a wide range of niches.Their ease of culture in vitro and availability of an increasing number of Pseudomonas strain genome sequences has made the genus an excellent focus for scientific research; the best studied species include P. aeruginosa in its role as an opportunistic human pathogen, the plant pathogen P. syringae, the soil bacterium P. putida, and the plant growth promoting P. fluorescens.
Because of their widespread occurrence in water and in plant seeds such as dicots, the pseudomonads were observed early in the history of microbiology. The generic name Pseudomonas created for these organisms was defined in rather vague terms by Walter Migula in 1894 and 1900 as a genus of Gram-negative, rod-shaped and polar-flagella bacteria with some sporulating species, the latter statement was later proved incorrect and was due to refractive granules of reserve materials. Despite the vague description, the type species, Pseudomonas pyocyanea (basonym of Pseudomonas aeruginosa), proved the best descriptor.

http://en.wikipedia.org/wiki/Pseudomonas