Walsh & Hoyt: Propionibacteria

Propionibacteria are obligate anaerobic gram-positive or gram-variable bacilli that are often pleomorphic. These organisms constitute a major component of the normal flora of mucocutaneous surfaces. Propionibacterium acnes is a predominant component of the skin flora and may also be found on mucosal surfaces, including the mouth, intestine, urethra, and vagina. It thus is not surprising that they are responsible for a variety of CNS infections, particularly those in patients who have undergone previous intracranial surgery or placement of an indwelling catheter or shunting device. Postoperative infection with Propionibacterium species can result in a brain abscess, ventriculitis, encephalitis, or a subdural empyema. Typically, the infection becomes evident several weeks after surgery. The process may be polymicrobial, although isolation of P. acnes as a sole organism in brain abscesses has been reported.