Saturday, December 20, 2014

Propionibacterium in the shoulder: the Strange Case of Dr Jekyll and Mr Hyde

Presence of Propionibacterium acnes in primary shoulder arthroscopy: results of aspiration and tissue cultures

This is a great study.

These authors collected control, 2 skin swabs, synovial fluid, and 3 tissue samples were obtained from 57 patients (mean age 51 years) undergoing first-time shoulder arthroscopy. None of these patients had prior surgery or antibiotic treatment within the prior month. Demographic data and medical comorbidities were collected.

Patients received pre-arthroscopy cefazolin or clindamycin. The skin was scrubbed with chloroxylenol cleansing solution and then prepared with  2% ChloraPrep. The skin of the anterior deltoid at the site of the anterior arthroscopic portal was then swabbed with a skin swab for culture. The glenohumeral joint was then aspirated for culture. If no fluid was available, the glenohumeral joint was flushed with 5 mL of saline, which was then collected in a sterile specimen container. Three samples of debrided tissue were collected through a cannula. The first tissue sample was collected  from the middle glenohumeral ligament. The second tissue sample came from the rotator interval and the third tissue sample from the bursa. A sample of the cuff was taken instead of the bursa in  patients with torn rotator cuffs. For a patient undergoing a labrum repair, the second tissue sample was collected from the high rotator interval and the third tissue sample from the low rotator interval

All samples were placed on aerobic plates, on anaerobic plates, and in thioglycolate broth and held for 28 days. Two of 39 control air samples cultured positive for Priopionibacterium.

Eighty-one samples (21.8%) were positive for P. acnes when cultures were held 14 days. From 4 to 27 days were required for the cultures to become positive (overall average 8.4).

32 subjects (56%) had at least 1 culture that grew P. acnes. Thirteen patients (22.8%) had more than 3 cultures positive. The rate of positive cultures was not different for those shoulders with prior injections.

Positive skin cultures for P. acnes increased from 15.8% before incision to 40.4% at closure. In men positive skin cultures increased from 31.3% before incision to 63.0% at closure. 

None of the patients in this study have had signs or symptoms to suggest clinical P. acnes infection.

Comment: This is a very well done and important study in that it suggests that surgical wounds - even those without any prior procedure - are commonly culture positive for Priopionibacterium. While the authors opine that these these positive cultures are "a consequence of true positive cultures from imperfect skin preparation and dermal contamination," there is another hypothesis: that Priopionibacterium can inhabit normal shoulders (perhaps in a manner similar to the inhabitance of the normal gut with E Coli). We have previously shown that Priopionibacterium live in normal skin, so it is not a big stretch to imagine their presence in normal shoulders. It may be the case that when the internal environment of the shoulder is disturbed by a procedure that implants prosthetic components (creating an anaerobic niche in a biofilm), an opportunity is created for these bacteria to turn from benign to potentially problematic. 


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