Identification of Legionella species by lipopolysaccharide antigen pattern

Electrophoretic analysis of lipopolysaccharide (LPS) extracts from 430 previously serotyped Legionella isolates and 28 American Type Culture Collection (ATCC) non-Legionella pneumophila Legionella reference strains representing different Legionella species and serogroups has been performed. LPS was prepared from Legionella suspensions by sonication and proteinase K digestion. Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis, LPS bands were either stained with silver nitrate or transferred onto a nitrocellulose membrane and detected with rabbit antibodies raised against L. pneumophila serogroup 5, which was known to cross-react with L. pneumophila serogroups 1 to 14. Silver staining revealed that each of the 28 ATCC non-L. pneumophila Legionella strains possessed an individual and characteristic LPS banding pattern. The LPS profile was defined by the molecular weight of the visualized bands and/or the individual ladder-like LPS pattern. It was demonstrated by immunoblotting that non-L. pneumophila Legionella strains did not react with the serogroup 5 antiserum, thus allowing for the differentiation between L. pneumophila and non-L. pneumophila species.