Detection of Salmonella infections by polyvalent enzyme-linked immunosorbent assay

Serum immunoglobulin G (IgG) and IgM were measured for individual Salmonella species by the enzyme-linked immunosorbent assay (ELISA). F344 rats were experimentally infected with Salmonella typhimurium (serogroup B), S. enteritidis (serogroup D), and S. rubislaw (serogroup G.) Endotoxin extracted from each serogroup served as the antigen in a classical indirect ELISA. Antibody specific for each Salmonella serogroup was detected by ELISA. Normal gut flora from control animals appeared not to cause cross-reactions in the ELISA. Specificity and sensitivity of the IgG ELISA were determined by statistically evaluating false-positives and false-negatives. Ideal values of 90% or better were achieved in nearly all instances. Each antigen was also tested with heterologous antisera in an effort to develop a polyvalent assay for Salmonella species. No single antigen detected all positive heterologous antisera. Therefore, a polyvalent antigen composed of the three serogroup antigens was tested. The results suggested that Salmonella infections can be detected by measuring serum IgG levels with a polyvalent ELISA 6 to 9 days postinfection.