Cutibacterium acnes as an Opportunistic Pathogen: An Update of Its Virulence-Associated Factors

Abstract

• Cutibacterium acnes (C. acnes): Member of skin microbiota, maintaining healthy skin.
• Recently recognized as an opportunistic pathogen.
• Produces several virulence factors, forming biofilms and triggering immune responses.
• Diversity in virulence factors increases pathogenicity.
• Colonizes various ecological niches, adapts to different environments.

Characteristics of C. acnes

• Classification: Gram-positive, rod-shaped bacterium.
• Morphology: Diphtheroid or coryneform.
• Growth: Aerotolerant anaerobe.
• Historical Classification: Renamed from Propionibacterium acnes to Cutibacterium acnes.
• Cell Wall Composition: Unique compared to other Gram-positive bacteria.
• Resistance: Up to 40% strain resistance to common antibiotics.

C. acnes Classification

• Originally two main types based on carbohydrate content.
• Now classified into types I, II, III based on phylogenetic and phenotypic differences.
• Advanced methods like MLST, SLST, and WGS are used for better resolution.

Skin Microbiota and Acne

• Acne vulgaris: Chronic inflammatory skin disease, common in teenagers.
• Pilosebaceous Unit (PSU): Interaction of PSU and hormones leads to imbalance, causing acne.
• C. acnes plays a role in both commensal skin health and as an acne pathogen.
• Skin Microbiota: C. acnes prevalent in sebaceous sites, imbalance triggers acne.

C. acnes and Other Infections

• Associated with inflammatory diseases and implant infections.
• Common in cerebral and osteoarticular prosthesis infections.
• Diagnosis: Differentiating true infection from contamination is challenging.

C. acnes and Inflammation

• Interacts with various receptors (TLRs, NLRs) triggering immune responses.
• Produces pro-inflammatory molecules and enzymes exacerbating inflammation.
• Involvement of IL-36 in acneiform toxicity.

C. acnes Virulence Factors

• Genome sequenced, identifying potential virulence genes.
• Key Virulence Factors:
  • Lipases: Metabolize sebum, enhancing PSU colonization.
  • Polyunsaturated Fatty Acid Isomerase: Role in CLA isomerization.
  • Hyaluronate Lyase: Degrades skin matrix, facilitating tissue invasion.
  • Glycosidase and Sialidase: Break down host glycoconjugates.
  • RoxP: Antioxidant enzyme, helps survival in oxygen-rich environments.
  • Sortase F: Facilitates protein attachment to cell wall.
  • Porphyrin: Linked to perifollicular inflammation.
  • Biofilm Formation: Increases antibiotic resistance and adherence.
  • Pili/Fimbriae: Aid in adhesion and colonization.
  • CAMP Factors: Cytotoxic proteins, form pores in host membranes.

Conclusion

• C. acnes Adaptability: Colonizes diverse body sites.
• Opportunistic Pathogen: Expresses various virulence factors under environmental changes.

Author Contributions

• Equal contribution by all authors.

Funding & Conflicts of Interest

• No external funding.
• Authors declare no conflict of interest.

These notes summarize the comprehensive article on C. acnes, highlighting its dual role as both a skin commensal and an opportunistic pathogen, detailing its classification, pathogenicity, and associated virulence factors. The notes are structured to provide a clear understanding of C. acnes' interaction with human hosts and its impact on health.