Cross-reacting lipopolysaccharide antigens in Legionella pneumophila serogroups 1 to 14

Immunological cross-reactions among Legionella species were investigated with sonicated, proteinase K-digested cell lysates. The antigens separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were either analyzed for lipopolysaccharides (LPSs) by silver staining or transferred to nitrocellulose membranes for serological characterization with rabbit antibodies directed against Legionella pneumophila serogroups 1 and 5. When antiserum prepared against serogroup 5 was used to probe the LPSs from L. pneumophila serogroups 1 to 14, the antibodies recognized a common epitope harbored by all L. pneumophila serogroups but not by other Legionella species or by the gram-negative bacteria tested as controls. Hence, the serogroup 5 antiserum correctly identified all serogroups of L. pneumophila tested in the LPS immunoblot assay. Moreover, the silver-stained profiles of the isolated LPSs revealed characteristic patterns allowing the identification of the individual serogroups of L. pneumophila.