Fluorescent-Antibody Techniques for the Identification of Group D Streptococci: Direct Staining Method

Fluorescent-antibody (FA) techniques were employed in an attempt to develop a rapid test for the identification of group D streptococci. Fresh isolates were obtained from sewege and feces of sheep, cattle, horses, rabbits, chickens, geese, and rats. Identification to species were made by the conventional physiological, biochemical, and serological tests. Both whole and disrupted cells of representative strains of each species were used for the preparation of the group D streptococcus vaccine. Globulin fractions of individual and pooled antisera were labeled with fluorescein isothiocyanate, and the resulting conjugates were tested with homologous and heterologous antigens. The specificity of the conjugates and staining was assessed by adsorption and inhibition tests utilizing controls with homologous and heterologous antigens. Employing the direct staining method and individual and pooled conjugates, it was possible to obtain 84 and 85% positive FA reactions, respectively, with group D streptococcal strains. Trypsinization of the smears prior to staining eliminated all FA cross-reactions observed with non-group D streptococci and staphylococci. These findings suggest that the direct staining method will be of value in the rapid identification of group D streptococci.