Immunofluorescent studies of Listeria monocytogenes and Erysipelothrix insidiosa. Application to clinical diagnosis

Cultural identification of Listeria monocytogenes is made by study of growth and morphologic characteristics and biochemical properties and by serologic testing. These tests require several days or weeks. A study of the fluorescent antibody technique adapted to rapid identification of suspected organisms from cultures or from clinical speciments was undertaken. Serotypes 1, 2, and 3 share a common, thermostable, somatic antigen (factor II), and type 4 organisms have common somatic antigens (factors V and/or VI). Antisera to a type 4b organism and to a type 3 organism were conjugated with fluorescein isothiocyanate. The labeled 4b antiserum gave specific fluorescent staining of type 4b organisms (5 strains tested) and type 4a organisms (2 strains) and did not stain other serotypes or Erysipelothrix insidiosa. The labeled type 3 antiserum stained organisms of type 1 (8 strains), type 2 (2 strains), and type 3 (4 strains) but not types 4a, 4b, or E. insidiosa. The clinical and pathologic features of a fatal case of the meningoseptic form of listeriosis of the newborn are presented. Identification of L. monocytogenes type 4b from the blood and cerebrospinal fluid cultures was made by the fluorescent antibody technique and confirmed by serologic and biochemical methods. A proposal is made to use the fluorescent antibody technique for screening all gram-positive bacilli from blood or cerebrospinal fluid cultures for rapid diagnosis of L. monocytogenes infections.