A microscopic demonstration of beaded, branched, gram-positive bacilli in purulent material or tissue specimens suggests the diagnosis. The specimen should be taken only from a normally sterile site. Acid-fast staining can be used to distinguish Actinomyces species, which are acid-fast negative, from Nocardia species, which are variably acid-fast positive. "Sulfur granules" in drainage or loculations of purulent material usually are yellow and may be visualized microscopically or macroscopically and suggest the diagnosis when present. A Gram stain of sulfur granules discloses a dense reticulum of filaments. Immunofluorescent stains for Actinomyces species are available. Actinomyces species can be identified in tissue specimens using the 16s rRNA sequencing and polymerase chain reaction assay. Although most Actinomyces species are microaerophilic or facultative anaerobic, specimens must be obtained, transported, and cultured anaerobically on semiselective media.