Comparison of immunofluorescent antibody test and enzyme-linked immunosorbent assay for detection of antibodies to Listeria monocytogenes.

This laboratory has used an immunofluorescent antibody test (IFAT) for the detection of IgG and IgM antibodies to Listeria monocytogenes. This test is performed using whole cells of serotypes 1/2a, 1/2b, and 4b as antigen. Sera are pre-absorbed to remove cross-reacting antibodies. This test can diagnose listeriosis by demonstration of seroconversion in appropriately spaced acute and convalescent sera. The disadvantages of this test are the necessity for pre-absorption, the use of three different test antigens and the need for subjective interpretation. An enzyme-linked immunosorbent assay (ELISA) using sonicated listeria cells as the antigen in a microtitre plate system can theoretically overcome these shortcomings. An ELISA for antilisterial IgG and IgM was compared to the IFAT using sera from bacteriologically confirmed cases as positive controls and sera submitted for routine rubella serology as negative controls. The ELISA method as tested appeared to be less specific than the IFAT. As the serological diagnosis of listeriosis is complicated by the failure of the main antibody response to switch from IgM to IgG after infection, asimilar ELISA system was used to detect anti-listerial IgA antibody. This assay detected IgA in patients with proven listeriosis but not in the control patients. It appears to be sensitive, specific and easy to perform.