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Identification of Actinomyces israelii and Actinomyces naeslundii by Fluorescent-Antibody and Agar-Gel Diffusion Techniques¹

Department of Parasitology, School of Public Health, University of North Carolina, Chapel Hill, North Carolina 27515
Bureau of Disease Prevention and Environmental Control, National Communicable Disease Center, Atlanta, Georgia 30333

ABSTRACT

This study was an attempt to develop a fluorescent-antibody (FA) test to differentiate Actinomyces israelii and A. naeslundii as an aid in their laboratory identification. Two strains of A. israelii (X522 and A601) and two strains of A. naeslundii (X454 and X600), which had received intensive study by several investigators, were used for the immunization of rabbits. Working titers, based on tests with antigens prepared from the homologous strains and from well-established heterologous strains, were determined for each labeled antibody preparation. These conjugates and their normal serum control conjugates were used separately to stain 85 cultures of Actinomyes species and 23 strains of other species that might be confused with them. Acetone-precipitated soluble antigens from these same strains were tested with different antisera in the agar-gel diffusion test. Results showed that A. israelii (X522 and A601) and A. naeslundii (X454 and X600) labeled antiglobulins, when used at their working titers, stained most strains of their homologous species. Agar-gel diffusion results showed general agreement with those of the FA tests. The two tests appear to be equal in sensitivity, but the FA test is more specific, since several cross-reactions were noted with the agar-gel diffusion test whereas no cross-reactions were obtained with the FA reagents. Agar-gel and FA studies suggest that at least two serotypes of A. israelii may be associated with human disease. Although the majority of strains tested in this study appear to belong to a common serotype, "serotype 1," two strains of an apparent second serotype, "serotype 2," were encountered. FA staining of tissue impression smears from experimentally infected mice was successful when a counterstain, Evans Blue dye, was used.

² Present address: Virginia State Department of Health, Richmond.

¹ A portion of a Dissertation submitted by the senior author to the University of North Carolina in partial fulfillment of the requirements for the degree of Doctor of Public Health in the School of Public Health. Training was provided by the Laboratory Directors' Program which is supported by Training Grant 5 T1 GM 567 from the National Institute of General Medical Sciences, U.S. Public Health Service. The laboratory research was performed at the Laboratory Program, National Communicable Disease Center, Atlanta, Georgia, under the supervision of Lucille K. Georg.