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.