Proteus: Meaning, Structure and Pathogenicity

In this article we will discuss about Proteus:- 1. Meaning of Proteus 2. Antigenic Structure of Proteus 3. Pathogenicity.

Meaning of Proteus:

Proteus are saprophytic, widely distributed in nature and also occur as commensals in the intestine and on the moist skin. They cause urinary or respiratory tract or ear wound, burn infections, infantile diarrhoea as opportunistic pathogen.

There are five species:

Proteus vulgaris, Pr. mirabilis, Pr. morganii, Pr. rettgeri, and Pr. inconstans. They are Gram-negative pleomorphic motile rods (0.5-1-3 p). They are aerobic and facultative anaerobic.

Their colonies emit a characteristic ‘fishy’ or “seminal” odour. Pr. vulgaris, and Pr. mirabilis produce “swarming” (concentric circles) growth on nutrient agar medium at 37°C as they are motile; but other species do not.

The swarming is inhibited by increasing the concentration of agar (6%) or incorporation of chloral hydrate, sodium azide, alcohol etc. On MacConkey agar, the swarming does not occur, but smooth, pale colonies are formed. The swarming mechanism is yet to be understood.

In broth, an uniform turbidity with a slight powdery deposit is produced by proteus with ammoniacal odour. Proteus transforms phenyl alanine to phenyl pyruvic acid (PPA), other members of the family entero-bacteriaceae do not.

Urea is hydrolysed by all Proteus species as they produce urease (Fig. 30.1) except Pr. inconstans (Providencia). They are MR +ve and VP -ve, ferment glucose with acid and gas production.

They are further classified into species on the basis of Indole and H₂ S, citrate utilisation:

Antigenic Structure of Proteus:

Motile stains of proteus possess thermo-stable ‘O’ (somatic) and thermolabile H (flagellar) antigen and all strains have distinct “O” antigens.

The “O” antigen has got alkali labile and alkali stable fractions. The alkali stable fraction of “O” antigen (polysaccharide) is common to OX19, OXK and OX2 strains with rickettsia prowazeki (causing typhus fever) which are agglutinated by sera of typhus patients (Weil Felix reaction).

Pathogenicity of Proteus:

Proteus are opportunistic pathogens and are responsible for the production of:

1. Urinary tract infection.

2. Pyogenic infection (abscess, bedsore, infection of wound, ear and respiratory tract).

3. Summer diarrhoea in children (mainly caused by Pr. morganii).

4. Exogenous infection in patients having obstructive lesions of urinary tract which may be due to prolonged catheterisation or diagnostic instrumentation.

5. Endogenous infection by their dissemination through blood (haematogenous spread). However the human infection is mostly caused by Pr. mirabilis.

Proteus can be isolated on MacConkey agar, blood agar with 6% agar which inhibit swarming so that other bacteria are not overgrown and identified by biochemical reaction. Many strains are sensitive to nitrofurantoin, tetracycline and kanamycin.