Antimicrobial resistance in commensal skin bacteria among individuals without prior exposure to acne therapy

• Although macrolide-resistant S. epidermidis and C. acnes were still isolated from healthy volunteers without a history of antibiotic treatment for acne, resistance rates of skin bacteria were significantly lower in these volunteers than in acne patients. • Compared with acne patient isolates, volunteer isolates showed fewer clade F and more clade K strains, indicating distinct clade distributions of C. acnes between the groups. • The proportion of Clade F among C. acnes isolates increased from 2014 to 2019. Antimicrobial resistance (AMR) in skin bacteria is a salient issue in patients with acne vulgaris. This study aimed to investigate the antimicrobial resistance status of skin bacteria isolated from university student volunteers with no history of treating acne. We evaluated the antimicrobial susceptibility of Staphylococcus epidermidis and Cutibacterium acnes , isolated in 2014 and 2019 from volunteers, and identified macrolide–clindamycin-resistance determinants. C. acnes genotyping was performed by using single-locus sequence typing (SLST). These isolates were compared with isolates obtained from patients with acne. In total, 92 S. epidermidis and 150 C. acnes isolates from 119 volunteers were analyzed. In 2019, the resistance rate of roxithromycin and clindamycin were 27.3% and 25.0% in S. epidermidis , 4.1% and 2.0% in C. acnes , respectively, significantly lower than the rates isolated from patients with acne (P <0.05). The major resistance factors of macrolide–clindamycin in S. epidermidis and C. acnes were erm (C) and 23S rRNA mutation, respectively. SLST analysis of C. acnes isolates in 2019 revealed a statistically significant increase in the population of clade F compared with that in 2014. In addition, the population of clade K among C. acnes isolates was significantly higher in volunteers than in patients with acne. The results of this study suggest that the use of antimicrobials for the treatment of acne may substantially contribute to the development of AMR in skin bacteria. Therefore, it is crucial to use antimicrobial agents appropriately when treating acne to prevent the emergence of AMR in commensal skin bacteria.