Nonpathogenic Cutibacterium acnes Confers Host Resistance against Staphylococcus aureus

Area of Science:

• Microbiology and Immunology
• Host-Microbe Interactions
• Model Organism Research (C. elegans)

Background:

• Cutibacterium acnes (C. acnes) is a common human skin bacterium with dual roles in health and disease.
• While C. acnes is linked to acne, its beneficial effects and strain-specific impacts on host immunity are less understood.
• Understanding C. acnes strain diversity is crucial for deciphering its role in the skin microbiome.

Purpose of the Study:

• To investigate the differential effects of C. acnes strains on the lifespan of the model organism Caenorhabditis elegans.
• To evaluate the protective role of a nonpathogenic C. acnes strain (HL110PA4) against Staphylococcus aureus infection.
• To elucidate the host immune pathways involved in C. acnes-mediated protection against S. aureus.

Main Methods:

• Assessed the impact of various C. acnes strains on C. elegans lifespan.
• Fed C. elegans with C. acnes HL110PA4 and subsequently infected them with S. aureus to measure survival rates.
• Utilized C. elegans mutants in key immune pathways (daf-16/FoxO, skn-1/Nrf2, tir-1/SARM1, nsy-1/MAPKKK, sek-1/MAPKK, pmk-1/MAPK) to identify mechanisms of protection.

Main Results:

• Certain C. acnes strains shortened C. elegans lifespan, while strain HL110PA4 did not affect it.
• C. elegans fed C. acnes HL110PA4 exhibited significantly increased survival upon S. aureus infection compared to controls.
• Host resistance mediated by C. acnes HL110PA4 against S. aureus required the TIR-1 and p38 MAPK pathways, but not DAF-16/FoxO or SKN-1/Nrf2.

Conclusions:

• C. acnes strains exhibit strain-specific pathogenicity and host interactions.
• Nonpathogenic C. acnes strains can confer significant host resistance against opportunistic bacterial infections.
• The TIR-1 and p38 MAPK signaling pathways are critical for C. acnes-mediated immune defense against S. aureus.