Proteus is a member of the Enterobacteriaceae family. The genus of Proteus consists of motile, aerobic and facultatively anaerobic, Gram-negative rods. Proteus is a member of the tribe Proteeae, which also includes Morganella and Providencia. The genus Proteus currently consists of five named species: P. mirabilis, P. vulgaris, P. penneri, P. myxofaciens and P. hauseri and three unnamed genomospecies: Proteus genomospecies. However, a recent study indicated that P. myxofaciens may represent a separate genus with low similarity to tribe Proteeae, and it has been suggested that this organism be renamed Cosenzaea myxofaciens.

A striking microbiologic characteristic of Proteus species is their swarming activity. Swarming appears macroscopically as concentric rings of growth emanating from a single colony or inoculum. On a cellular level, swarming results from bacterial transformation from "swimmer cells" in broth to "swarmer cells" on a surface such as agar, in a process involving cellular elongation and increased flagellin synthesis. The genus name Proteus originates from the mythological Greek sea god Proteus, who was an attendant to Poseidon. Proteus could change his shape at will. This attribute reminded early microbiologists of the morphologic variability of the Protei on subculture, including their ability to swarm.

Members of the genus Proteus are widespread in the environment and are found in the human gastrointestinal tract. The most common infections caused by Proteus spp. are urinary tract infections (UTIs). Proteus spp. can be found to colonize the vaginal introitus prior to onset of bacteruria. Therefore, like Escherichia coli, Proteus spp. causes urinary tract infections by ascending from the rectum to the periurethra and bladder.

P. mirabilis is by far the most common species identified in clinical specimens. P. mirabilis is a common cause of both community-acquired and catheter-associated UTI, cystitis, pyelonephritis, prostatitis, wound infections, and burn infections, and occasionally causes respiratory tract infections, chronic suppurative otitis media, eye infections (endophthalmitis), meningitis, and meningoencephalitis. It is a common cause of bacteremia following catheter-associated UTI, and in rare cases has been reported to cause cellulitis, endocarditits, mastoiditis, empyema, and osteomyelitis. It has also been suggested that P. mirabilis could have a role in the etiology of rheumatoid arthritis.
P. vulgaris, previously considered biogroup 2, has been reported to cause UTIs, wound infections, burn infections, bloodstream infections, and respiratory tract infections. There has also been one case study of P. vulgaris causing bacteremia and brain abscesses, with the suspected point of entry being the digestive tract.
P. penneri, previously biogroup 1, generally causes UTIs, wound infections, burn infections, bloodstream infections, and respiratory tract infections.There has been one case study ofP. penneri Fournier's gangrene in a child with congenital genitourinary anomalies. There has also been one recent report of P. penneri causing "red body disease" of the Pacific white shrimp Penaeus vannamei. Notably, P. penneri may be incorrectly identified as P. mirabilis due to being indole-negative , and it cannot be clearly resolved from P. vulgaris by 16S sequencing unless using the 16S-23S internal transcribed spacer. Thus, the burden of human infections caused by this organism may be underestimated.>
P. myxofaciens was originally isolated from a gypsy moth and has been isolated from UTIs in India.
P. hauseri, previously considered biogroup 3, has not been associated with infections in humans.


The members of the genus Proteus are Gram negative, motile facultative anaerobic rods. On culture plates, Proteus species are distinguished by their ability to swarm. Proteus spp. have 2-3mm colorless, flat, colonies on MacConkey agar, whereas they swarm in waves to cover blood agar plates and LB agar plates.

Proteus spp. are identified by the following biochemical characteristics: positive methyl-red reaction, negative Voges-Proskauer reaction, phenylalanine deaminase production, growth on KCN and urease production. P. mirabilis and P. penneri are indole-negative, while other Proteus species are indole-positive. The Proteus genomospecies can be distinguished from other Proteus species based on five biochemical characteristics: esculin hydrolysis, salicin fermentation, L-rhamnose fermentation, and elaboration of DNase and lipase.

Proteus Urease Test Positive (Urease Test)