Propionibacterium acnes are slow growing anaerobic gram positive bacteria. They can be rod shaped or branched—usually found in the skin’s pores. Propionibacterium acnes may colonize in the axilla, especially in males. There is difficulty in obtaining positive cultures from standard labs.
Propionibacterium acnes are generally nonpathogenic but can cause numbers of infection such as acne vulgaris. One of its species (P. freudenreichii) is used in Swiss cheese which produces flavor and the special holes in the cheese.
The Propionibacterium acne infection is the most common cause of rotator cuff infection. It is the most common organism isolated.
Allow up to 14 days for the culture to grow and identify this organism. Ask the lab to hold the culture even longer if you strongly suspect infection. This organism colonizes the shoulder at an increased rate. Mini open cuff repair after arthroscopic surgery may have increased the risk of infection. A second prep and drape of the surgical field may be necessary to reduce the infection. Positive cultures were found also in revision shoulder arthroplasty. Staphylococcus epidermidis loves the prosthesis of the hip and knee. P-acne however, loves shoulder prosthesis. P-acne is skin bacteria responsible for shoulder infection and it usually has a subtle subclinical presentation.
The clinical presentation is insidious and nonspecific. Traditional signs of infection usually include:
-Blood work not consistently elevated
It is a slow growing bacteria and the culture takes from 1 week to 3 weeks to become positive. This creates a diagnostic challenge. If the initial culture is negative, the lab does not usually hold the cultures for a long time unless instructed. If you suspect infection, ask the lab to hold the culture for at least two weeks. Men have a higher bacterial burden than women. P-acne is a common cause of indolent infection and shoulder implant failure. Infection of the shoulder with P-acne should be considered as a cause of persistent unexplained shoulder pain.
Treatment options can be determined after obtaining fluid from the aspiration or a tissue sample (multiple tissue samples are better) and keeping the culture for about two weeks. Once the results are back from the lab you can perform a debridement, administer IV antibiotics—resistance to antibiotics is a challenge, and many may need to remove their prosthesis.
In summary, the Propionibacterium acne infection is an emerging clinical entity. Its harm goes beyond the skin and should not be considered a contaminant. It is becoming an orthopedic pathogen and not just a dermatology pathogen. The infection will probably be resistant to the standard broad spectrum antibiotics. The clinician should be aware that this bacteria loves to infect the shoulder.
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