Characterisation of Cutibacterium acnes phylotypes in acne and in vivo exploratory evaluation of Myrtacine.

Objective: Our main objective was to compare Cutibacterium acnes (C. acnes) skin colonisation in patients with mild to moderate acne versus healthy controls and secondly, to evaluate a Myrtacine -based cream on C. acnes total population and antibioresistant Cutibacteria in patients with acne.

Methods: In 60 acne patients (Global Acne Severity Scale, GEA grades 2-3), of mean age 20 [15-30] years and in 24 age- and sex- matched healthy controls, forehead strips samplings were performed for microbiological analysis of comedones by colony forming unit (CFU) counts of global C. acnes and erythromycin (EryR) or clindamycin-resistant (ClnR) populations of Cutibacterium and determination of phylotypes by MALTI-TOF. Clinical evaluations of acne patients (GEA, lesion count, porphyrin fluorescence) were performed at baseline and after 56 days of twice-daily application of a Myrtacine -based cream.

Results: We first showed (i) high and similar levels of C. acnes colonisation in superficial pilosebaceous follicles and detection of EryR and ClnR strains in both acne and control groups; (ii) different repartition of phylotypes in acne patients versus healthy control, with a predominance of phylotype IA in acne patients and a link between phylotype IA and erythromycin resistance. Besides, after treatment with the Myrtacine -based cream in acne patients, there was no change in C. acnes total load, but a significant decrease of EryR Cutibacteria, reduced porphyrin production by C. acnes, a decrease in acne severity (GEA), associated with reduced retentional and inflammatory lesions.

Conclusion: Cutibacterium acnes colonisation was not significantly different in acne versus control groups. Phylotype IA was predominant in acne patient and in EryR C. acnes. A Myrtacine -based cream significantly reduced the level of EryR Cutibacteria in vivo and improved acne lesions.