Actinomyces spp and related species

Related species include Gleimia spp, Schaalia, Winkia spp. Some Actinomyces species have been renamed under these species. 

Gram Stain

• Gram positive non-spore forming irregular/branching bacilli (facultative anaerobic)

Clinical Significance

These organisms are part of the normal flora of the gastrointestinal, genitourinary, and upper respiratory tracts. 

They are implicated in polymicrobial infections, especially chronic wounds/abscesses (including brain, lung and breast abscesses) and draining sinus tracts often in association with other anaerobes. They may cause bacteremia, endocarditis/septicemia, bone/joint and medical device related infections, and pelvic infections related to intrauterine contraceptive devices, genitourinary infections, abscesses (including hidradenitis).

Actinomyces spp have recently been implicated in osteoradionecrosis or bisphosphonate related osteonecrosis of the jaw bones.

Actinomycosis (cervicofacial, thoracic, or abdominal) may be caused by several Actinomyces spp. or related species.

Usual Susceptibility Pattern

These organisms are typically susceptible to penicillin, carbapenems, vancomycin, and linezolid.  

Susceptibility to clindamycin, erythromycin, ceftriaxone, and tetracyclines is variable.

Daptomycin is less active than vancomycin and linezolid.

Actinomyces spp are resistant to metronidazole. 

Quinolones do not have reliable activity.