Cell Wall Components and Antigenic Properties - Proteus

Cell Wall Components and Antigenic Properties

Motile Proteus strains possess somatic O and flagellar H anti-gens. Somatic O antigens are heat-stable proteins, which are resistant to heating at 100 °C. They are also resistant to treat-ment with ethanol and dilute hydrochloric acid. Thirty two dif-ferent O antigens are found in P. mirabilis, 22 in P. vulgaris, and five in P. penneri and P. myxofaciens.

      The O antigen contains both alkali-labile and alkali-stable fractions. The alkali-stable component is polysaccharide in nature and shows cross-reactivity with certain rickettsial antigens. The sharing of antigens with rickettsial antigens was first observed by Weil and Felix. They observed that certain nonmotile strains of P. vulgaris called the “X strains” were agglutinated by sera from typhus fever patients. This heterophilic agglutination by certain Proteus strains formed the basis of the Weil–Felix reaction for the diagnosis of some rickettsial infections. Three nonmotile Proteus strains OXl9 (P. vulgaris serotype O1), OX2 (P. vulgaris serotype O2), and OXK (P. mirabilis) are used in the Weil–Felix agglutination test.

        Flagellar antigens are heat-labile proteins sensitive to etha-nol and to dilute hydrochloric acid.

On the basis of their O antigens, P. mirabilis and P. vulgaris have been classified into 54 O groups. These O groups are further subdivided into a large number of O types depending on their flagellar or H antigens.