Increased frequency of clindamycin-resistant Cutibacterium acnes strains isolated from Japanese patients with acne vulgaris caused by the prevalence of exogenous resistance genes.

Cutibacterium acnes, a resident bacterium of the skin, is a target for antimicrobial treatment of acne vulgaris, because it exacerbates inflammation. Recently, antimicrobial-resistant C. acnes strains have been isolated worldwide, and their prevalence has led to failure of antimicrobial treatment. This study aimed to analyze the antimicrobial resistance of C. acnes strains isolated from Japanese patients with acne vulgaris who visited the hospital and dermatological clinics between 2019 and 2020. Resistance rates to roxithromycin and clindamycin increased during 2019 to 2020 compared with those during 2013 to 2018. Additionally, the proportion of doxycycline-resistant and low-susceptibility strains (minimum inhibitory concentration [MIC] ≥8 μg/mL) increased. No difference in clindamycin resistance rates between patients with and without a history of antimicrobial use was observed during 2019 to 2020, which were significantly higher for patients with a history than for patients without a history during 2016 to 2018. The proportion of high-level clindamycin-resistant strains (MIC ≥256 μg/mL) gradually increased; particularly, the resistance rate was 2.5 times higher in 2020 than that in 2013. The proportion of strains showing high-level clindamycin resistance that also have the exogenous resistance genes erm(X) or erm(50), which confer high resistance, showed a strong positive correlation (r = 0.82). Strains with the multidrug resistance plasmid pTZC1 encoding erm(50) and tet(W) genes were frequent in clinic patients. Notably, most strains with erm(X) or erm(50) were classified as single-locus sequence types A and F (traditional types IA1 and IA2). Our data show that the prevalence of antimicrobial-resistant C. acnes is increasing in patients with acne vulgaris attributable to acquisition of exogenous genes in specific strains. To control the increasing prevalence of antimicrobial-resistant strains, it is important to select the appropriate antimicrobials while taking into consideration the latest information on resistant strains.