Actinobaculum spp

• A. massiliense
• A. suis

Gram Stain

• Gram positive bacilli (straight to curved) singly or in clusters (facultative anaerobic)

Clinical Significance

A. massiliense - associated with chronic cystitis in elderly females.  It may also be involved in superficial skin infections/abscesses.

A. suis - associated with urinary tract infections and abortion in pigs.

Usual Susceptibility Pattern

These organisms are usually susceptible to penicillin, amoxicillin, ceftriaxone, tetracycline, and nitrofurantoin.  Prolonged therapy with beta-lactam antibiotics is often necessary. 

Susceptibility to clindamycin and macrolides is variable. 

They are resistant to metronidazole and ciprofloxacin (levofloxacin may have better activity).

Susceptibility testing to TMP/SMX is not reliable as it is dependent on the testing medium and urinary folate levels. It is safest to consider as resistant.