A Comparison of Strains of Bacteria Designated Actinomyces viscosus and Actinomyces naeslundii

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Abstract
The similarity between A. viscosus serotype II and A. naeslundii has been noted by several workers. Apart from many common physiological characteristics, antigenic cross-reactions are known to occur. The increase in the use of these organisms experimentally makes it important to establish the relationships within the type strains, and those of the strains to wild type oral isolates. The results of a total of 65 tests on 43 strains have been subjected to computer analysis and compared to 5 strains of A. israelii. The analysis shows the degree of similarity between A. viscosus serotype II and A. naeslundii to be comparable to that between the two serotypes of A. israelii. Comparisons have also been drawn on the basis of antigenic structure, these have shown that cell wall carbohydrate antigens are shared by strains of both A. naeslundii and A. viscosus although specific antigens do exist. The results of the study indicate that human strains of A. viscosus and strains of A. naeslundii are closely related and that further consideration should be given to the validity of their present separation into 2 species. Within this group of organisms, however, variations do exist which should be considered when selecting strains for experiments relating to the human oral situation. Strains should be selected that are representative of commonly occurring isolates rather than those peripheral to the group.