Cutibacterium Adaptation to Life on Humans Provides a Potential C acnes Infection Biomarker

Propionibacteriaceae appear to have adapted to life on humans during the domestication of cattle. These microbial immigrants formed the genus Cutibacterium, and a descendent of those microbial trailblazers (C acnes) now dominates 25% of human skin. C acnes colonization of human skin requires the protein RoxP. Although all Cutibacteria encode this adaptation to life on humans, nothing like RoxP has been found in any other organism. In this study, we report an extensive assessment of 21 RoxP orthologs, which identified conserved molecular surfaces linked to heme-dependent oligomerization and low pH stability. Our investigation suggests how RoxP helps C acnes dominate sebaceous skin, and it identified an ortholog associated with the emergence of an acne vulgaris-associated, pathobiont subspecies. C acnes is also an emerging pathogen that frequently infects joint prostheses and other medical devices. These infections are often missed, because there is no test to confirm a C acnes infection. To address this clinical need, we developed immunoassays that can assess RoxP in human biofluids commonly infected by C acnes. This study's findings and assays will help shed light on the consequences of Neolithic Age livestock domestication, the evolution of skin commensals into pathogens, and how to identify infections of human "replacement parts."