Enzyme-linked immunosorbent assay for detection of Pseudomonas aeruginosa H (flagellar) antigen

An enzyme-linked immunosorbent assay (ELISA) with goat anti-rabbit IgG conjugated to peroxidase was used to test for the two antigen types of Pseudomonas aeruginosa: b (homogeneous) and a (heterogeneous) which contains the common subantigen (a0) and combinations of subtypes (a, a2 a3 a4). Preparations of b-type flagellar antigen could be distinguished from a-type by using b-adsorbed antisera titers as reciprocals of endpoint dilutions exceeding one million. Extracts from nonflagellated bacteria or purified lipopolysaccharides from the same strain were used as controls, which showed only background activity. Unknown flagellar antigen was determined using both isolated antigen preparations and formalin-killed bacterial cells. The ELISA procedure proved much more sensitive than the slide agglutination procedure: whereas nine of 18 strains tested did not react in the slide agglutination procedure all 18 strains were definitively typed as a or b strains with the ELISA. The ELISA also revealed the presence of a dominant, cross-reacting epitope (a0) in the heterogeneous a-type flagella using either isolated antigen or intact cells.