Genomics of invasive Cutibacterium acnes from deep-seated infections

Background: Cutibacterium acnes, formerly known as Propionibacterium acnes, is a commensal of the human pilosebaceous unit, but also causes deep-seated infection, especially in the context of orthopaedic and neurosurgical foreign materials. Interestingly, little is known about the role of specific pathogenicity factors for infection establishment.Methods: 86 infection-associated and 103 commensalism-associated isolates of C. acnes were collected from three independent microbiology laboratories. Isolates were whole genome sequenced for genotyping and a genome wide association study (GWAS).Results: C. acnes acnes IA1 was the most significant phylotype in infection isolates (48.3% of all infection isolates, OR=1.98 for infection). In commensal isolates, C. acnes acnes IB was the most significant phylotype (40.8% of all commensal isolates, OR=0.5 for infection). Interestingly, C. acnes elongatum (III) was overall rare and did not occur at all in infection. The ORF-GWAS did not show any loci with a strong signal for infection-association (No p-values |2|).Conclusion: All subspecies and phylotypes of C. acnes, possibly with the exception of C. acnes elongatum, are able to cause deep-seated infection given favourable conditions, most importantly foreign material inserted in the host. Genetic content appears to have a small effect on the likelihood of infection establishment and functional studies will be needed to understand individual factors contributing to deep-seated infections caused by C. acnes.