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Winning Abstracts from the 2010 Medical Student Abstract Competition: Propionibacterium Acnes: When Will You Grow Up?

Author: Kelly J. McGlaughlin, MS IV, recent graduate of Jefferson Medical College

Introduction:
Propionibacterium acnes (P. acnes) is a gram-positive anaerobe that is normal flora of the mouth, conjunctiva, colon, and skin, predominantly in sebaceous follicles. P. acnes rarely causes serious infections and is often dismissed as a contaminant. However, in certain clinical circumstances, a positive culture deserves more attention. Recent literature has shown that P. acnes is an increasingly important pathogen in post-neurosurgical and prosthetic joint infections.

Case Presentation:
A 67 year old man was admitted to the hospital with confusion and was found to have bilateral subdural hematomas, which were evacuated by craniotomy. During that admission, Factor XI deficiency was discovered. The patient was readmitted four weeks later with fever, frontal headache, confusion, and unsteady gait and a CT scan showed persistence of bilateral subdural hematomas. Single doses of Vancomycin and Cefepime were given. A subsequent MRI suggested a possible subdural empyema on the right side. After consultation between Hematology, Neurosurgery, and Infectious Disease, a decision was made to re-operate. The right subdural fluid appeared to be purulent, but the Gram stain showed few WBCs and no organisms in five different subdural samples. Vancomycin was discontinued four days post-operatively because all cultures remained negative and the patient was asymptomatic. However, on day five, two of five subdural cultures grew P. acnes. The patient was discharged on IV Penicillin G. After four weeks, there has been radiological and clinical improvement.

Discussion:
Propionibacterium acnes is an infrequent but important cause of subdural empyemas following craniotomy. Because this organisms grows very slowly (an average of five to six days after cultures are obtained1), the clinical diagnosis of subdural empyema is occasionally delayed and sometimes even missed. It is standard procedure for microbiology laboratories to hold body fluid cultures for five days. Therefore, it is imperative to inform the laboratory that P. acnes is being considered as a potential pathogen so the cultures can be held for seven to ten days. P. acnes has been reported as pathogenic in 3 to 5% of neurosurgical infections and, recently, up to 31 to 56% of prosthetic shoulder infections 1,2. In previously reported cases, clinical diagnosis of postsurgical infections with P. acnes has been delayed 12 to 1578 days. The characteristics of most of these case reports are similar to this case of subdural empyema, demonstrating slow-growth of the organism and difficulty identifying the pathogen. A clinical suspicion for P. acnes, along with coordination with the laboratory, will allow for more timely and accurate diagnoses.

References:
Levy PY, Fenollar F, et al. Propionibacterium acnes postoperative shoulder arthritis: an emerging clinical entity. Clin Infect Dis. 2008;46(12):1884-1886. Piper KE, Jacobson MJ, et al. Microbiologic Diagnosis of Prosthetic Shoulder Infection using Implant Sonication. J. Clin Microbiol. 2009;47:1878-1884.
1. Nisbet M, Briggs S, et al. Propionibacterium acnes: an under-appreciated cause of post-neurosurgical infection. Journal of Antimicrob Chemoth. 2007;60:1097-1103.

Back to July 2010 Issue of IMpact

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