Abstract: Ma Ying*, Liu Ye, Wang Qianqian, Wu Shi, Yang Yang, Huang Haihui, Xiang Leihong. *Department of Dermatology, Huashan Hospital, Fudan University, Shanghai 200040, China Corresponding authors: Xiang Leihong, Email: flora_xiang@vip.163.com; Huang Haihui, Email: huanghaihui@fudan.edu.cn 【Abstract】 Objective To evaluate the in vitro antibacterial activity of fusidic acid against P. acnes. Methods Fifty strains of P. acnes were clinically isolated from Huashan Hospital, Fudan University from March to September 2013. The minimum inhibitory concentrations （MICs） of several antibacterial agents including fusidic acid against these P. acnes isolates were determined by using the agar dilution method according to the recommendations of Clinical and Laboratory Standards Institute （CLSI）. Data were analyzed using the WHONET 5.4 software. Results Among the 50 P. acnes isolates, 90% were sensitive to fusidic acid, 90% to moxifloxacin, 54% to clindamycin, 46% to erythromycin, but 100% were resistant to metronidazole. The minimum concentration required to inhibit the growth of 50% organisms （MIC50） and 90% organisms （MIC90） were 0.5 and 1.0 mg/L respectively for fusidic acid, whereas clindamycin and erythromycin both showed higher MIC90 values （> 128 mg/L）. At the concentration of 128 mg/L, clindamycin inhibited the growth of 70% of the P. acnes isolates, and erythromycin inhibited the growth of 48% of them, while the growth of all the isolates was inhibited by fusidic acid at 2 mg/L. Conclusion Fusidic acid exhibits excellent antibacterial activity against clinical isolates of P. acnes in vitro.

Key words: Propionibacterium acnes, Fusidic acid, Microbial sensitivity tests