Actinomyces naeslundii II sequences are essentially identical to A. viscosus. The reference strain for this taxon is that for the type strain of A. viscosus, which is a hamster isolate. Strains from animals are often different than those from humans, however, in this case, there appear to be a human taxon with high sequence similarity to the hamster strain.
The Oral phylotypes 169, 170, 171, 175, 176, and 688 cluster together and all are probably members of the species Actinomyces naeslundii (a fuzzy group). At this time, the Dewhirst laboratory has not examined whether strains classified as A. naeslundii genospecies 1 or 2 fall consistently into particular phylotypes in this cluster. The taxonomy of this group is is discussed in the references [1-3]. Over the next year, we will be sequencing a number of actinomyces strains from the Moores' collection, and should be able to clarify these issues.
There is a vast literature on Actinomyces naeslundii which we will not attempt to review here.