Overview: Bacteria of the genus Actinomyces are abundant in the healthy oral microbiome, making up 5-10% of the cells in dental plaque. In 2018 some species formerly considered to be Actinomyces were reclassified into genus Schaalia, including several species abundant on the tongue (Nouioui et al. 2018). Twelve oral species remain in the genus Actinomyces include A. naeslundii, A. oris, and A. graevenitzii.

Ecological role/importance in health and disease: A. naeslundii and its relatives are early colonizers in the dental plaque biofilm (Diaz et al. 2006, Dige et al. 2009). A. graevenitzii is abundant in the biofilm on the tongue. Some species, particularly A. israelii and A. gerencseriae, are in lower abundance in the healthy microbiome but can cause opportunistic infections known as actinomycosis.