Vitamin A Derivative Boosts Immune Cell Killing of MRSA and Directly Fights Strep Skin Infections

Retinoic acid stimulated human neutrophils to produce LL-37 antimicrobial peptide, reactive oxygen species, and extracellular traps, enhancing MRSA killing in vitro. RA directly inhibited GAS growth and, in a murine skin infection model, topical RA reduced both skin lesion size and bacterial burden.

In vitro experiments using primary human neutrophils treated with retinoic acid, tested against MRSA, E. coli K1, P. aeruginosa, and GAS. Antimicrobial peptide production (LL-37), ROS, and NETs were measured. In vivo murine skin infection models tested topical RA against both MRSA and GAS.

Antimicrobial resistance is a growing crisis, and this research suggests vitamin A derivatives could enhance the body's natural antimicrobial peptide defenses. The finding that retinoic acid boosts cathelicidin (LL-37) production — a key human antimicrobial peptide — while also directly killing certain bacteria opens a potential dual-action therapeutic approach for drug-resistant skin infections.

This work connects vitamin A biology to antimicrobial peptide research, showing that retinoic acid can upregulate cathelicidin (LL-37) — one of the body's most important natural antibiotics. This could inform strategies for boosting innate immunity against antibiotic-resistant bacteria, particularly for skin and soft tissue infections.

In vitro and animal study with no human clinical data. RA failed to reduce MRSA burden in vivo despite in vitro activity, suggesting the in vitro-to-in vivo translation is not straightforward. GAS-specific effects may not generalize to other pathogens. Murine skin immunity differs from human skin immunity.