Actinomyces are filamentous, gram-positive, anaerobic bacteria. They were in the past mistakenly classified as fungi, probably because of their filamentous morphology, and sometimes more chronic clinical presentation. The most common commensal and pathogenic human species is Actinomyces israelii .
Actinomyces israelii is a commensal organism of the oral cavity so the rounded aggregates of Actinomyces organisms seen above in tonsillar crypts are not pathogenic. The aggregates can also be seen in the setting of clinical infection, particularly in puralent material (pus) draining from abscesses, where they are large enough to be seen macroscopically and are said to resemble 'sulphur granules'.
Clinical infection with Actinomyces is usually treated with surgical drainage and antibiotics (Penicillin).