These authors remind us that Cutibacterium acnes is the most common bacterium isolated from periprosthetic shoulder infections.
Sequencing of Cutibacterium has been proposed as a method of determining subtypes associated with pathogenicity and antibiotic resistance patterns.
When multiple deep samples from the same surgery are culture positive for the same species, and the isolates show the same appearance on culture, it is typically assumed that these isolates are clonal, i.e. that they are genetically identical. However, it is known that Cutibacterium is not clonal on the skin of most individuals. These authors tested the hypothesis that the Cutibacterium recovered from multiple samples at the time of revision shoulder arthroplasty would often represent more than one subtype as revealed by full genome sequencing and characterized by Single Locus Sequence Type (SLST).
Of 11 patients, five (45%) had different subtypes of Cutibacterium within the deep tissues even though the colony morphologies were similar. One patient had four subtypes in the deep tissues (see table below), while four had two different subtypes.
SLST subtypes C, G, K, and L were more common in the polyclonal isolates, while types D and H were more common in the monoclonal isolates (see below).
Of 11 patients, five (45%) had different subtypes of Cutibacterium within the deep tissues even though the colony morphologies were similar. One patient had four subtypes in the deep tissues (see table below), while four had two different subtypes.
SLST subtypes C, G, K, and L were more common in the polyclonal isolates, while types D and H were more common in the monoclonal isolates (see below).
Comment: This study demonstrates that testing of a single deep sample may be insufficient to properly characterize the Cutibacterium present in the deep tissues of a failed arthroplasty. If multiple subtypes are present within the deep tissues as this study suggests, then it cannot be assumed that one sample would be representative of the whole with respect to virulence and antibiotic sensitivity.
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