Paper of the week: Cutibacterium acnes and the shoulder microbiome. Qiu B, Al K, Pena-Diaz AM, Athwal GS, Drosdowech D, Faber KJ, Burton JP, O’Gorman DB. J Shoulder Elbow Surg. 2018 Oct;27(10):1734-1739. doi: http://dx.doi.org/10.1016/j.jse.2018.04.019.
The aim of this study is to determine if there is a microbiome in the native shoulder joint and whether Cutibacterium acnes (previously known as Propionibacterium acnes), the most common cause of shoulder infections, is part of this microbiome. The indolent nature of Cutibacerium acnes (C. acne) along with lack of significant biomarker response makes it a difficult bacteria to manage. Also, its presence in culture samples in cases with negative joint infection leads to a theory that this bacterium could be commensal in the native joint.
In this study, researchers collected tissue samples from patients undergoing primary open shoulder arthroplasty with no history of previous infection. Twenty-three patients were included in the study. Researchers collected tissue samples from skin, subcutaneous fat, anterior edge of the supraspinatus tendon, middle glenohumeral ligament, and humeral head. A total of 136 samples were collected. Samples were then analyzed using 16s RNA sequencing to identify operational taxonomic units. After careful removal of contamination, results showed that 53 samples showed positive for microbial genome and most abundant bacterial type was Acinetobacter and Oxalobacteraceae. C. acnes was only identified in one skin sample. Anatomical structure wise 74% of supraspinatus tendon samples and 49% of joint capsule samples were positive for a microbial genome.
This study shows that the native shoulder joint is not completely sterile, and bacteria are present. Interestingly C. acnes is not present in the native shoulder joint. Advances in the genomic analysis are making it easier to identify bacterial species and to characterize the microbial genome. Studies of 16s RNA sequencing remain limited by both the risk of contamination and the risk of identifying dead bacteria [1,2]. Further research is needed on the impact of oral and gut microbial load on tissue microbiome as it is well known that transient bacteremia can occur following activities like oral brushing and can lead to tissue seeding.[3,4]
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 Weiss S, Amir A, Hyde ER, Metcalf JL, Song SJ, Knight R. Tracking down the sources of experimental contamination in microbiome studies. Genome Biology 2014;15:564. doi:10.1186/s13059-014-0564-2.
 Maharaj B, Coovadia Y, Vayej AC. An investigation of the frequency of bacteraemia following dental extraction, tooth brushing and chewing. Cardiovasc J Afr 2012;23:340–4. doi:10.5830/CVJA-2012-016.
 Lockhart Peter B., Brennan Michael T., Sasser Howell C., Fox Philip C., Paster Bruce J., Bahrani-Mougeot Farah K. Bacteremia Associated With Toothbrushing and Dental Extraction. Circulation 2008;117:3118–25. doi:10.1161/CIRCULATIONAHA.107.758524.