ASSOCIATION OF FLAGELLUM EXPRESSION AND INTRACELLULAR GROWTH OF LEGIONELLA-PNEUMOPHILA

We examined the role of the flagella of Legionella pneumophila in the infection of amoebae and human monocyte-like cells. Insertional mutant s were constructed with mini-Tn10. Ten mutants (F-) which did not reac t with polyclonal L. pneumophila antiflagellar antisera were identifie d. Ten randomly selected mutants (F+) that did react with the polyclon al antiflagellar antiserum were also identified. The infectivity of th ese 20 mutants in Hartmannella vermiformis and human U937 cells was ch aracterized. Seven of the 10 F- mutants were attenuated in their abili ty to multiply in the amoebae during the first 3 days of coincubation and failed to multiply in U937 cells. Three of the 10 F- mutants multi plied as well as the wild-type parent strain did in amoebae and to a l imited degree in U937 cells, None of the 10 F+ mutants were attenuated in either the amoebae or U937 cells. While the flagellar structure is not essential for virulence, the ability of L. pneumophila to infect amoebae and human phagocytic cells appears to be linked to flagellar e xpression. We believe that the attenuated F- mutants contain insertion s in genes critical to both flagellum expression and the infection pro cess.