Comparison of phenol- and heat-killed antigens in the indirect immunofluorescence test for serodiagnosis of Legionella pneumophila group 1 infections.

An antigen prepared with agar-grown Legionella pneumophila group 1 killed by 0.5% phenol and suspended in 0.5% yolk sac was examined for use in the indirect immunofluorescence test for legionellosis and compared with a heat-killed antigen. The serological results of the two antigens for single and paired sera agreed well. Morphological and staining characteristics were better for phenol-treated organisms. Electron microscopy observation showed an apparently well-preserved cell surface. The background antibody level among a healthy control population was very low (3.4% with titers of greater than or equal to 16). Sera of patients with gram-negative bacteria infections (Yersinia enterocolytica, Campylobacter jejuni, Salmonella typhimurium, Escherichia coli, Brucella melitensis, Pseudomonas aeruginosa, Mycoplasma pneumoniae, Coxiella burnetti, and Chlamydia psittaci) showed no cross-reactions with the phenol-killed antigen. The data suggest that phenol-killed antigen is sensitive and specific. This antigen is stable for at least 1 year.