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, infections of the 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.
Plemorphic nature of this organism and its rapid swarming motility might have persuaded its discoverer Gustav Hauser to rename it as Proteus.
Table of Contents
Characteristics of Proteus spp
Gram-negative - Non-spore-forming rods
- Facultative anaerobes
- Urease positive (strong)
- Oxidase test: Negative
- Nitrates
are reduced 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 
Antigenic characteristics
The bacilli possess thermostable, ‘O’ (somatic) and thermostable ‘H’ (flagellar) antigens, based upon which several serotypes have been recognized.
Certain strains of P
Biochemical Properties of Proteus mirabilis and Proteus vulgaris
Organisms that swarm on 5% sheep blood agar, exhibit a characteristic 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 Lactose fermentation No No Indole production No Yes Urease production Yes Yes H2S production Yes Yes
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 midstream urine sample is used, and for pyogenic lesions, it is the pus aspirate. The sample should be collected in a sterile container maintaining aseptic conditions and reach the laboratory within an hour of collection.
Culture: The choice of the culture media used to isolate 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 grows on the Blood agar plate in successive waves to form a thin filmy layer of concentric circles ( swarming). Proteus does not swarm in the MacConkey agar medium and forms smooth, pale or colorless (NLF) colonies.
Swarming properties of Proteus present 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
- increase in agar concentration in the medium, raising it to 6% instead of 1-2%.
- incorporation of chloral hydrate (1:500), sodium azide (1:500), and 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 to process urine samples.
Dienes Phenomenon
Proteus mirabilis is well known for its ability to differentiate into hyperflagellated, motile, and elongated swarmer cells rapidly spreading 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.”
Identification:
Gram staining, colony characteristics in culture media, and above mentioned biochemical 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.
References
- Madigan Michael T, Bender, Kelly S, Buckley, Daniel H, Sattley, W. Matthew, & Stahl, David A. (2018). Brock Biology of Microorganisms (15th Edition). Pearson.
- Bailey & Scott’s Diagnostic Microbiology, Forbes, 11th edition
