Antigenic Heterogeneity Among Legionella, Fluoribacter, and Tatlockia Species Analyzed by Crossed Immunoelectrophoresis

Abstract

Crossed immunoelectrophoresis (XIE) reference systems were established for Fluoribacter (Legionella) (containing Fluoribacter bozemanae, Fluoribacter dumoffii, and Fluoribacter gormanii) and for Tatlockia (Legionella) micdadei. The Fluoribacter and Tatlockia XIE reference systems contained 54 and 72 anodemigrating antigens, respectively. These two systems, together with the previously described polyvalent Legionella pneumophila (serogroups 1 through 6) XIE reference system, were used to study the crossreactivities of antigens from organisms comprising the three proposed genera in the family Legionellaceae. Antigenic homology was expressed as the matching coefficient (MC), the ratio of the number of cross-reactive antigens to the total number of antigens. The MCs for individual L. pneumophila serogroups when the polyvalent L. pneumophila antibody was used were 0.98 ± 0.05, which was significantly higher than the MCs determined by using Fluoribacter or Tatlockia antibodies (0.50 ± 0.13) (P ≪ 0.001). The MCs for the three species of Fluoribacter when polyvalent Fluoribacter antibody was used were 0.93 ± 0.10, which was also significantly higher than the MCs when heterologous antibodies were used (0.40 ± 0.04) (P ≪ 0.001). The MCs for T. micdadei with the two heterologous antibody preparations were similar to each other (0.32 and 0.46) and to all other heterologous MCs among members of the Legionellaceae. The MCs for organisms representing three other families of bacteria were 0.16 ± 0.04 in all three XIE reference systems and were significantly lower than the MCs among members of the Legionellaceae (P ≪ 0.001). When a priori criteria for MC interpretation established in previous serotaxonomic studies of other bacterial species by XIE were used, our results from studies on the antigenic relationships among Legionella, Fluoribacter, and Tatlockia supported the proposal that there are multiple genera in the family Legionellaceae.