Misleading serological identification of Legionella anisa as Legionella bozemanii

Identification of six Legionella species, which we previously identified by serological test as Legionella bozemanii (L. bozemanii), was performed by DNA-DNA hybridization using a commercial DNA-DNA hybridization kit (Kobayashi Pharm. Co., Japan) introduced by Ezaki et al. All strains were identified as Legionella anisa (L. anisa), this being the first identification of L. anisa in Japan. Conventional laboratory tests were performed following the DNA-DNA hybridization. In this study the results of biochemical examination obtained, corresponded closely with those described in previous reports, but the oxidase reaction was very weak and varied according to the age of the culture, indicating the unreliability of this test in our case. All strains examined under long wave ultraviolet (UV) light (366 nm) revealed a blue-white fluorescence, the intensity of which ranged from strong to weak. Serological identifications were performed by both the slide agglutination test (SAT) and indirect immunofluorescent assay (IFA). SAT using commercially available antiserum (Denka Seiken., Japan) supposedly specific for L. bozemanii showed cross-reaction between L. bozemanii and L. anisa. Hyperimmune rabbit antisera prepared in this study for both L. bozemanii and L. anisa, from which cross-reactive antibodies were removed by the absorption of each antigen, reacted only with homologous antigens. IFA using a commercially available antiserum and hyperimmune rabbit antiserum previously described, gave positive reactions with each strain.