Proteus: Properties of the Bacteria

Properties of the Bacteria

◗ Morphology

Proteus shows following features:

·      Proteeae organisms are Gram-negative and noncapsulated coccobacilli measuring 1–3 0.6 m in size.

·      They are arranged as single, in pairs, or in short chains.

·      Many of them form long, curved, and filamentous forms in young cultures.

·      Most of them, with few exceptions, are motile due to the presence of peritrichous flagella.

·           They are fimbriated.

◗ Culture

Proteeae organisms are aerobic bacteria, which grow well on ordi-nary media, such as nutrient agar. Proteus colonies on the medium emit a characteristic putrefactive (“fishy” or “seminal”) odor.

Swarming: P. mirabilisandP. vulgaristypically spread or swarmon surface of the medium. They spread on the surface of the plate in successive waves to form a thin filmy layer in concen-tric circles. This is known as swarming (Fig. 31-5, Color Photo 33). The exact mechanism responsible for swarming shown by Proteus species is not known. Swarming, shown by Proteus, is aproblem when mixed growth on a solid medium is obtained in which Proteus bacilli are present with other bacteria. Hence, sev-eral methods are available to inhibit swarming; these include the use of increased concentration of agar in the medium from 1–2% to 6%, and the use of chloral hydrate (1:500), sodium azide (1:500), alcohol (56%), sulfonamide, surface active agents, or boric acid (1:1000). Swarming does not occur on MacConkey medium, on which Proteus produces colorless non-lactose-fermenting colonies. It is because bile salts present in the MacConkey medium inhibit the swarming.

◗ Biochemical properties

Proteus shows following reactions:

·           Proteus species ferment glucose with production of acid only.

·           They are urease and PPA positive.

·      They do not ferment lactose, mannitol, mannose, inositol, adonitol, dulcitol, sorbitol, raffinose, and arabinose.

·      They reduce nitrate to nitrite but do not utilize malonate.

·      They do not decarboxylate amino acids, such as lysine or arginine.

·           Proteus species show variable reactions in the production ofhydrogen sulfide and indole. P. mirabilis is indole negative, while P. vulgaris is indole positive.

Biochemical characteristics of Proteus species are summarized in Table 31-11.