Homogeneity of lipopolysaccharide antigens in Pseudomonas pseudomallei

An antiserum raised against a single strain of Pseudomonas pseudomallei reacted equally in a whole cell agglutination test, an indirect haemagglutination (IHA) test and an ELISA with a panel of 12 strains of the species which had been isolated from human beings and animals in various parts of the Far East and Australia between 1923 and 1990. Absorption of the serum with either of two strains removed all reactivity of the serum with other strains. Phenol-water extracted lipopolysaccharide (LPS) from a single strain blocked the reactivity of the serum with red cells sensitised with crude extracts of any of the panel of strains, thereby suggesting that the 'common' antigen was LPS. This antigen was not detected in other Pseudomonas species with the exception of Pseudomonas mallei. Protease K-digested extracts of the 12 strains gave highly similar silver-stained LPS banding patterns in gel electrophoresis. Furthermore, immunoblots of LPS with either rabbit or a patient's serum showed identical ladder profiles for each strain. The results suggest that the LPS antigen is highly conserved throughout P. pseudomallei and that this antigen is detected by the IHA test.