Last updated on June 21st, 2021
Proteus are Gram-negative rod-shaped bacteria of the family Enterobacteriaceae. They are widely distributed in nature and also occur as normal intestinal flora of humans. An opportunistic pathogen, they are one of the common causes of urinary tract infections (UTIs) and are associated with infection-induced renal stones. Other infections caused by Proteus species are pyogenic lesions, infection of ear, respiratory tract infections, and nosocomial infections.
Proteus species have pili (fimbriae). Pili are associated with adhesive properties and, in some cases, are correlated with virulence.
The word ‘Proteus’ was derived from Greek mythology, which described ‘Proteus’ as an early sea-god, noted for being versatile and capable of assuming many different forms.
Plemorphicnature of this organism and its rapid swarming motility might have persuaded its discoverer Gustav Hauser to rename it as Proteus.
The bacilli possess thermostable, ‘O’ (somatic) and thermostable ‘H’ (flagellar) antigens, based upon which several serotypes have been recognized.
Certain strains of Proteus
- Non-spore-forming rods
- Facultative anaerobes
- Urease positive (strong)
- Oxidase test: Negative
arereduced to nitrites
- Ferments glucose but does not ferment lactose
- Deaminates phenylalanine to phenyl pyruvic acid
Urease enzyme produced by Proteus species is thought to play a major role in the production of infection-induced urinary stones. The ammonia
Biochemical Properties of Proteus mirabilis and Proteus vulgaris
Organisms that swarm on 5% sheep blood agar, exhibit a characteristics odor, and are oxidase negative can be presumptively identified as Proteus spp. With further testing by spot indole, the positive isolates may be presumptively reported as Proteus vulgaris and the negative ones as Proteus mirabilis.
|Properties||Proteus mirabilis||Proteus vulgaris|
|Colony characteristics in MacConkey Agar|| |
Pale or colourless (NLF) colonies
Pale or colourless (NLF) colonies
|Motility||Swarming motility||Swarming motility|
Laboratory Diagnosis & Identification
The sample used for the isolation and identification of the Proteus species depends on the nature of the disease/site of infections. For UTI, a
Culture: The choice of the culture media used for the isolation of the etiological agents depends on the nature of the specimen and suspected pathogens. For pus & urine samples, blood agar and MacConkey agar are commonly used. Proteus grow on the Blood agar plate in successive waves to form a thin
Swarming properties of Proteus presents problems in the diagnostic laboratory when mixed growth is present in which Proteus is one of the isolate. Several methods have been used to inhibit swarming. These are
- increasing the concentration of agar in the medium, raising it to 6% instead of 1-2%.
- incorporation of
cholralhydrate (1:500), sodium azide (1:500), boric acid (1:1000) in the medium
- Using cysteine lactose electrolyte deficient (CLED) agar as a sole medium instead of MacConkey agar and blood agar for the processing of urine samples.
Proteus mirabilis is well known for its ability to differentiate into hyperflagellated, motile, and elongated swarmer cells that rapidly spread over a surface.
When two different strains of P. mirabilis swarm on the same agar plate, a visible demarcation line with lower cell density forms at the intersection, and this line is known as a Dienes line (after Louis Dienes, who described the phenomenon in 1946) BUT when two identical isolates meet, the swarming edges merge without formation of a Dienes line.
This phenomenon is of value in differentiating the two strains of Proteus for epidemiological purposes. Find more about Dienes phenomenon in “small things considered blog“
Gram staining, colony characteristics in culture media, and above mentioned bio-chemical tests (indole production, urease production, H2S production and more importantly phenyl pyruvic acid (PPA) etc. ) when used in combination are sufficient to identify an isolate as Proteus species.