Identification of 22 Legionella species and 33 serogroups with the slide agglutination test

We used the slide agglutination test to determine the serologic relationships of 22 Legionella spp. representing 33 serogroups. Antisera prepared against 14 of the Legionella spp. contained cross-reactive antibodies (1+ or greater) at their working dilutions. Numerous cross-reactions were observed for the blue-white fluorescing Legionella spp. With only three exceptions in the latter group, cross-reactive antibodies were removed by absorption, thereby producing serogroup-specific antisera. For screening tests or for identification only to the genus level, nine polyvalent antiserum pools were prepared. Routine use of slide agglutination test reagents should expand the number of Legionella spp. that can be identified in the clinical laboratory and, at the same time, provide a simpler, less costly test procedure.