Abstract: Zeng Xianyu*, Jiang Min, Fu Chen, Dong Bilin, Wu Zhuoxuan, Wang Weizhen. *Department of Dermatology, Wuhan First Hospital, Wuhan 430022, China Corresponding author: Wang Weizhen, Email: weizhenwang2007@aliyun.com 【Abstract】 Objective To determine whether erythromycin-resistant propionibacteria isolated from patients with acne in Wuhan city harbor 23S rRNA gene mutations as well as the transposon Tn5432 carrying ermX genes. Methods Twenty-nine Propionibacterium strains isolated from outpatients with acne in Wuhan city were included in this study. The E-test method was used to determine the susceptibility of these strains to erythromycin and clindamycin. PCR was performed to amplify the 23S rRNA, ermX, ermX（cj）, IS1249a and IS1249b genes from resistant strains followed by DNA sequencing and nucleotide alignment. Results Among the 29 Propionibacterium strains, 19 were identified as P. acnes and 10 as P. avidum. All of these Propionibacterium strains were resistant to erythromycin （MIC > 256 μg/ml） and clindamycin （MIC > 256 μg/ml）, except for 3 P. acnes strains sensitive to clindamycin. Seven P. acnes strains resistant to both antibiotics exhibited an A→G transition at a position cognate with Escherichia coli 23S rRNA 2058. An A→G transition at a position cognate with E.coli 23S rRNA 2059 was identified in one clindamycin-resitant and three clindamycin-sensitive P. acnes isolates. The ermX gene was found in the remaining 8 P. acnes isolates and 2 P. avidum isolates, with the sequence 100% identical to the reference sequence of the ermX gene of P. acnes in Genbank. Meanwhile, the ermX （cj） gene was successfully amplified from the other 8 P. avidum isolates, which showed 99% sequence homology with the ermX（cj） gene of Corynebacterium jeikeium, but 94% homology with the ermX gene of P. acnes in Genbank. Both IS1249a and IS1249b genes were amplified in the 10 ermX gene-positive Propionibacterium strains, but not in the other ermX gene-negative strains. Conclusions The erythromycin resistance in Propionibacterium isolates from Wuhan city may be associated with the A→G transition at the E.coli equivalent bases 2058 and 2059 of the 23S rRNA gene, as well as the presence of the erm X （transferred through the transposon Tn5432） and ermX （cj） genes.

Key words: Propionibacterium, Erythromycin, Clindamycin, 23S rRNA, Genes, erm