Abstract
Acne vulgaris, a chronic skin condition, is, in part, caused by the bacteria Cutibacterium acnes (C. acnes). Antibiotics are commonly used for treatment of this condition, but antibiotic resistance poses an increasing challenge for a successful outcome. This study aims to investigate the synergistic antimicrobial activity of tea tree oil (TTO), chamomile oil (CO), with erythromycin against clinical strains of erythromycin-sensitive and erythromycin-resistant strains of C. acnes. Twenty-one clinical samples of C. acnes were used. Minimum inhibitory concentrations (MIC) of TTO, CO, and erythromycin alone and in combination were investigated using microdilution and checkerboard assays. Synergistic interactions were evaluated using the Fraction Inhibitory Concentration Index (FICI). The mixture of TTO and CO combined with erythromycin showed a significant 95.97 % (P<0.05) reduction in MIC of erythromycin (FICI = 0.13), restoring this antibiotic activity on the erythromycin-resistant C. acnes. These results suggest using essential oil combinations simultaneously with conventional topical antimicrobials to treat Acne vulgaris.