Application and usefulness of enzyme immunoassay for diagnosis of Salmonella typhimurium infection.

An enzyme immunoassay for serogroup specific immunological diagnosis of salmonella infections has been developed. Antigens representing salmonella O-antigens 4 (serogroup B) and 9 (serogroup D) were prepared by periodate oxidation of phenol-water extracted lipopolysaccharides from S. typhimurium and S. enteritidis respectively. Applied for seroepidemiological studies of S. typhimurium infections such chemically modified antigens showed a superior specificity compared to native lipopolysaccharides. The antibody titres against O-antigen 4 measured by the enzyme-linked immunosorbent assay (ELISA) were detectable during the second week and increased during the first 3--4 weeks of S. typhimurium infection. High titres persisted for at least 2--3 months and in some cases for more than 3 years. For reliable serodiagnosis a significant increase of the titre between acute and convalescent samples is necessary . Determination of ratio between IgG and IgM antibody titres against the pathogen may, however, be used on single serum samples to indicate whether the observed antibody titre is of recent or longstanding origin.