Detection of Legionella pneumophila capsular-like envelope antigens by counterimmunoelectrophoresis

Abstract

The capsular-like envelope of Legionella pneumophila strains Togus 1 (serotype 2) and Philadelphia 1 (serotype 1) was isolated and purified by column chromatography on Sepharose 6B. Antibody raised in rabbits to these two antigenic materials did not cross-react in gel diffusion. Upon electrophoresis followed by gel diffusion, the majority of both envelope materials was found to migrate towards the cathode. A minor antigenic component of each envelope only migrated slightly towards the anode. Using the envelope antigens and the two anti-envelope sera in a counterimmunoelectrophoresis (CIE) assay, positive results were only obtained when the antigenic materials were placed in the cathodal well. The Togus 1 and Philadelphia 1 antigens did not cross-react in CIE. The sensitivity of the CIE assay was poor (15.6 μg/ml by carbohydrate content) compared to its sensitivity in other microbial systems. Although CIE may not be a useful diagnostic aid in identifying Legionella species due to its low sensitivity, it may be of value in serotyping the microorganism since we did not see cross-reactivity between the two strains when anti-envelope sera were used.