FLAGELLA ARE A POSITIVE PREDICTOR FOR VIRULENCE IN LEGIONELLA

Pathogenesis of Legionnaires' disease is strictly related to the abili ty of the legionellae to infect phagocytic cells, yet surface markers of virulence in Legionella isolates are currently unknown. Rabbit anti bodies raised against purified flagella of Legionella pneumophila sero group 1 recognized a total of 24 of 30 laboratory-maintained isolates of L. pneumophila serogroups 1-15 and 16 of 24 other Legionella specie s tested by rapid immunoblot and indirect immunofluorescence assay. Al l isolates possessing flagella detectable with these anti-flagella ant ibodies, regardless of species, were capable of infecting Hartmannella vermiformis. Isolates lacking immunologic cross-reactivity were shown to lack purifiable flagella. The majority of aflagellate isolates wer e not motile and failed to multiply intracellularly in co-culture with Hartmannella vermiformis. Some isolates characterized as aflagellate when harvested from BCYE agar were able to multiply in amoebae, and fl agella were subsequently detectable by immunologic methods. These data suggest that lack of immunologic recognition of flagella in laborator y-maintained isolates of Legionella is due to their attenuation and a corresponding loss of expression of flagella. More importantly, the pr esence of flagella can serve as a positive predictive marker for strai n virulence and is useful in determining the virulence status of Legio nella isolates. (C) 1997 Academic Press Limited.