Detection of flagella in 278 Legionella strains by latex reagent sensitized with antiflagellum immunoglobulins.

To determine whether all Legionella species show common flagellum antigen properties, we developed a reagent using latex beads sensitized with flagellin-specific immunoglobulins that could be used in a simple and rapid agglutination reaction to identify Legionella colonies. A total of 278 strains (68 Legionella reference strains and 210 patient and environmental isolates) were tested. The results were compared with those obtained by a direct immunofluorescence assay using an antiflagellum serum and by morphological observations by electron microscopy. The immunological methods based on the use of a flagellum-specific serum have confirmed the presence of a common flagellum antigen for all Legionella species described to date. Flagella were detected for all the legionellae studied except four species: L. oakridgensis, confirmed as a nonflagellate species; L. brunensis; L. cincinnatiensis; and L. longbeachae serogroup 1. However, we noted a remarkable variability in flagellum expression, of greater or lesser degree, according to the species and their origin. A combination of all three methods of flagellum detection revealed that 86.3% of Legionella strains studied were flagellate. The latex test identified 89.6% of these strains, 97.5% of L. pneumophila, and 100% of L. pneumophila serogroup 1.