Proteus antigen cross react with ?

Ans. is 'b' i.e., Rickettsiae . Proteus antigen cross reacts with rickettsial antigens. The application of this propey is done in the Weil Felix test. PROTEUS . They are gram negative, non capsulated, pleomorphic, motile bacilli. . Proteus bacilli are divided in to three genera. - Proteus --> Proteus vulgaris, Proteus mirabilis - Morganella --> Morganella morganii - Providencia --> Prov. alcalifaciens, Prov stuaii, Prov. rettgeri . Most of them except providencia strains, produce powerful urease. . A characterstic feature of proteus bacilli is "PPA reaction" . It is due to presence of enzyme phenylalanine deaminase which conves phenylalanine to phenyl pyruvic acid. . Culture of proteus bacilli have a characteristic putrefactive odour described as "fishy or seminal". . They produce swarming growth over the surface of agar, except for morganella morganni which does not swarm. . Some non motile proteus strains (OX-2, OX-19 and OX-K) are used in weil-felix agglutination reaction for the diagnosis of rickettsiae infections.