ABSTRACT
The Proteus organisms are motile, gram-negative bacilli that exhibit significant variation in size and shape. Young cultures grown on solid agar are particularly pleomorphic. Short coccobacillary and long filamentous forms may be identified in cultures and exhibit rapid spread over the entire surface of the culture. Such “swarming” is due to the organism’s very high motility. The spread is so rapid that, not infrequently, the presence of a Proteus strain as a component in a specimen may mask the presence of another pathogen. Such specimens should be reisolated by cultivation on relatively dry surfaces of 5% agar or on ordinary 1% to 2% agar containing 0.1% chloral hydrate. Urease production is characteristic of the Proteus group. Experimental evidence suggests that urease production may preferentially enhance bacterial replication within the renal medulla once infection is established. While urease production is a distinguishing metabolic characteristic, functional subdivision of the Proteus group is based on maltose fermentation and indole formation. The maltose-fermenting strains form indole; those that do not ferment maltose are indole negative. The relative ability or inability to form indole is important in antibiotic chemotherapy. Indole-positive strains, such as P. vulgaris, are resistant to ampicillin, whereas most of the indole-negative strains, such as P. mirabilis, are highly susceptible.
