Enzyme-linked immunosorbent assay (ELISA) with bacterial sonicate antigen for IgM, IgA, and IgG antibodies to Francisella tularensis: comparison with bacterial agglutination test and ELISA with lipopolysaccharide antigen.

An enzyme-linked immunosorbent assay (ELISA) with bacterial sonicate (S) as antigen developed for determining the presence of IgM, IgA, and IgG antibodies to Francisella tularensis was compared with the bacterial agglutination (BA) test and a corresponding ELISA using lipopolysaccharide (LPS) antigen. Of the organisms tested, F tularensis was the only one to cause significant inhibition, indicating the specificity of the S-ELISA. BA test titers correlated significantly with antibody levels in all three immunoglobulin classes and most closely with IgM antibodies (r = 0.83). With some minor exceptions, the S-ELISA and the LPS-ELISA gave identical results, and the correlations between the tests were very close (r = 0.94-0.99). The S-ELISA confirmed the tularemia diagnosis with the first serum specimens from 43% of patients with tularemia vs 17% of the BA test. In addition, no seroconversion was observed by the BA test in 4% of the patients, although large increases were observed in S-ELISA titers.