Proteus (bacterium) - Identification

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 nitrate-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. Most of them, except for some Providencia strains, produce powerful urease, which rapidly hydrolyzes urea to ammonia and carbon monoxide. Proteus bacilli possess somatic O and flagellar H antigens, which are of historical interest. Weil and Felix studying Proteus bacilli observed that the flagellated strains growing on agar formed a thin surface film resembling the mist produced by breathing on glass and named this variety the Hauch. Non-flagellated variants grew as isolated colonies without the surface film and were called Ohne Hauch. These names came to be abbreviated as H and O forms. Proteus bacilli are widely distributed in nature as saprophytes, being found in decomposing animal matter, in sewage, in manure soil, and in human and animal feces. They are opportunistic pathogens, commonly responsible for urinary and septic infections, often nosocomial.