Objective: The aim of the present study is to determine the antibiotic susceptibility patterns of P. acnes strains from acne patients in Thailand.

Material and Method: A cross sectional was used to investigate in this study. Ninety-five acne patients were enrolled. Samples were collected from facial closed comedones using comedone extraction technique and isolated in an anaerobic condition. The strains were identified by phenotypic characteristics and API 20A. Antibiotic susceptibility tests and minimal inhibitory concentration (MIC) of P. acnes strains to five antibiotics that are commonly used in acne treatments in Thailand (erythromycin, clindamycin, tetracycline, doxycycline and amoxicillin), were determined by the Epsilometer test method.

Results: Among 95 samples, P. acnes strains were isolated from 75 patients (78.95%). MIC90 of doxycycline, tetracycline, amoxicillin, clindamycin and erythromycin were 1.7, 16, 0.016, 256 and 256 μg/mL, respectively. By using CLSI breakpoints for resistance, forty-eight (64%) and forty-seven (62.66%) strains resisted to erythromycin and clindamycin, while only one (1.33%) strain resisted to tetracycline. No resistance to doxycycline and amoxicillin was found in this present study. Moreover, there were statistically significant differences among age groups, history of previous antibiotic treatment and macrolide antibiotic resistance.

Conclusion: Among the antibiotics tested in the present study, the most common antibiotic resistance was erythromycin, followed by clindamycin and tetracycline, respectively; whereas, no resistance to doxycycline and amoxicillin was found. The antibiotic-resistant P. acnes strains have been continuously increasing in Thai acne patients from the present study.

Keywords: Acne vulgaris, Antibiotic resistance, Antibiotic susceptibility, Propionibacterium acnes