Assignment of Actinomyces viscosus and Actinomyces naeslundii strains to numerical taxonomy clusters by immunofluorescence based on antifibril antisera.

A previous observation, using a few representative laboratory strains, that rabbit antisera raised against isolated surface fibrils might be useful in identifying Actinomyces viscosus and Actinomyces naeslundii isolates to their correct numerical taxonomy clusters was reexamined with a large culture collection, including clinical isolates from three different laboratories. Strains were first identified by a slower standard procedure, including agglutination with anti-whole-cell antisera, catalase test, and gas and paper chromatography as needed. Indirect immunofluorescence tests indicated that antisera raised against fibrils of strains representing the three principal taxonomic clusters could separate most strains into their correct clusters. The antisera were particularly successful in separating two taxonomically distinct groups of A. naeslundii, clusters 3 and 5, but could not separate A. viscosus belonging to the principal cluster (no. 1) and minor clusters (no. 2, 4, 6).