These authors conducted a prospective study aimed to determine the rate of positive P acnes cultures in arthritic shoulders using a strict specimen collection technique and culturing methods specific for Propionibacterium. 32 patients underwent a general anesthetic, with administration of a prophylactic dose of intravenous cephazolin (2 g) on induction. During the surgical procedure, as soon as the glenohumeral joint was opened, 6 capsule/synovium tissue specimens were collected each with a separate sterile surgical blade and forceps. Five specimens were sent in separate sterile specimen containers for microbiology. Tissue samples were ground, and an aliquot of the homogenized suspension was inoculated onto blood agar, prereduced blood agar, and chocolate agar plates. Specimens were incubated at 37C under 5% carbon dioxide aerobic conditions and anaerobic conditions for 14 days. Three of 32 patients had a positive culture for P acnes.
Comment: While the authors attempted to use histology in a sixth specimen to identify 'infection', it is generally recognized that histology is only weakly associated with positive cultures for Propionibacterium.
It is important to recognize that this study included only 14 male patients and three of these had positive growth for Propionibacterium. None of the 18 female patients were culture positive. These results, then, are very similar to those discussed in this post:
Propionibacterium can be isolated from deep cultures obtained at primary arthroplasty despite intravenous antimicrobial prophylaxis.
in which 4 of 10 male patients having primary arthroplasty were culture positive for Propionibacterium. Of the 50 specimens, 7 were positive for Propionibacterium: 3 in each of 2 patients and 1 in 1 patient. The specimen sources having positive anaerobic cultures were the dermis (1 of 10), fascia (2 of 10), synovium (1 of 10), and glenoid tissue (3 of 10). None of these patients had evidence of infection at the time of the arthroplasty.
We can conclude that preoperative antibiotics and skin preparation do not always eliminate Propionibacterium from the surgical field of primary shoulder arthroplasty. The presence of these bacteria in the arthroplasty wound may pose a risk of delayed shoulder arthroplasty failure from the subtle type of periprosthetic infection typically associated with Propionibacterium as discussed in this post.
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