Proteus (bacterium)

Proteus is a genus of Gram-negative Proteobacteria.

Clinical significance
Three species&mdash;P. vulgaris, P. mirabilis, and P. penneri&mdash;are opportunistic human pathogens. Proteus includes pathogens responsible for many human urinary tract infections. P. mirabilis causes wound and urinary tract infections. Most strains of P. mirabilis are sensitive to ampicillin and cephalosporins. P. vulgaris is not sensitive to these antibiotics. However, this organism is isolated less often in the laboratory and usually only targets immunosuppressed individuals. P. vulgaris occurs naturally in the intestines of humans and a wide variety of animals; also manure, soil and polluted waters. P. mirabilis, once attached to urinary tract, infects the kidney more commonly than E. coli. P. mirabilis are often found as free-living organisms in soil and water.

Identification
Proteus species do not usually ferment lactose, but have shown to be capable lactose fermenters depending on the species in a triple sugar iron (TSI) test.

Since it belongs to the family of Enterobacteriaceae, general characters are applied on this genus: It is oxidase-negative, but catalase- and nitrase-positive. Specific tests include positive urease (which is the fundamental test to differentiate Proteus from Salmonella) and phenylalanine deaminase tests.

On the species level, indole is considered reliable, as it is positive for Proteus vulgaris but negative for Proteus mirabilis.

Some species are motile.

It has a characteristic "swarming" pattern.