Serogrouping of Legionella pneumophila by double diffusion and counter immunoelectrophoresis.

Ten serogroups of Legionella pneumophila have now been described.' Although the direct fluorescent antibody technique is widely used to identify and serologically differentiate L pneumophila isolates,2 some cross reactivity between serogroups3 and some staining of non-legionella organisms with legionella antisera4 have been reporrea. Several simple alternatives to the direct fluorescent antibody technique have been described which do not require fluorescence microscopes and competent microscopists. These include slide agglutination,2 staphylococcal coagglutination,5 latex agglutination,6 and antiserum-agar plates.' Counter immunoelectrophoresis and double diffusion have been used to detect human antibodies to L pneumophila.89 The studies reported here suggest that both double diffusion and counter immunoelectrophoresis can be used as alternatives to direct fluorescent antibody when serogrouping isolates of L pneumophila.