Actinomycete bacteria, micrograph and computer illustration. These filamentous Gram positive bacteria form a fungus-like mat or mycelium. Actinomycete bacteria are normally saprophytic, feeding off decaying matter in soil and aquatic habitats. They are also normally present on the gums and can cause infections after dental procedures. Actinomyces israelii is the causative agent of actinomycosis, a granulomatous infection characterized by formation of abscesses.