1Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College, Nanjing, Jiangsu 210042, China. 2Jiangsu Key Laboratory of Molecular Biology for Skin Diseases and STIs, Nanjing, Jiangsu 210042, China.

��Abstract�� Objective Skin and soft tissue infections caused by rapidly growing nontuberculous mycobacteria have become an increasing clinical problem. Here, we confirm a rare case of cutaneous infection caused by Mycobacterium immunogenum from histology and genetics. Methods A biopsy was taken for histological examination and tissue culture. Organisms that grew in L?wenstein-Jensen medium were identified by polymerase chain reaction and sequencing of hsp65 and 16S rRNA genes. In vitro drug susceptibility testing was conducted using the microtiter plate method. Results The tissue culture was mycobacteria-positive. Analysis of hsp65 and 16S rRNA genes confirmed that the organism isolated was Mycobacterium immunogenum. Systemic therapy for the patient was based on the in vitro drug susceptibility results. It involved 6 months of clarithromycin (0.5 g twice per day) and moxifloxacin (0.4 g once per night) combined with 6 months clarithromycin tapering (0.25 g once per day), and completely resolved the skin lesions, leaving only residual scaring. Conclusion Mycobacterium immunogenum, an environmental organism, has emerged as an infection-causing pathogen of immunocompetent individuals.