A 66-year-old Taiwanese woman, who was free from immunocompromised conditions including diabetes mellitus or acquired immunodeficiency syndrome, developed enlarging tender nodules on her left dorsal foot for 2 months. Two months prior to this presentation, her left dorsal foot was traumatized by the spring of a trashed mattress. Physical exam showed reddened, indurated, and confluent nodules with pus discharge. She was afebrile and she denied other constitutional symptoms. She initially tried acupuncture on the left lower leg for but failed. 10 days of empirical oral amoxicillin clavulanate (Augmentin® 1250 mg/day) were administered after the sampling of the pus. Though the culture turned out to be negative, the lesion deteriorated. To exclude atypical infection, we performed skin biopsy for pathology exam, as well as fungal and mycobacterial culture. Microscopically, skin specimen demonstrated dermal suppurative granulomas composed of histiocytes and multinucleated giant cells. A few acid-fast bacilli were identified by Ziehl–Neelsen stain. 14 days after the culture, wheat-colored colonies developed. Using Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS; Bruker’s MALDI Biotyper, Bruker Libraries/Mycobacteria Library V2.0) to compare the extracted proteins from the colony to the reference, we successfully identified the pathogen to be the Mycobacterium farcinogenes–senegalense group (MS score 1.94; MS score 1.800–1.999 for species level for mycobacteria). After confirming the pathogen, the antibacterial regimens, featuring the combination of oral clarithromycin (1000 mg/day) and sulfamethoxazole/trimethoprim (Baktar®, 1960 mg/day), were administered for 2 months. Nevertheless, sulfamethoxazole/trimethoprim was held 2 weeks later due to hyperkalemia. The skin lesion resolved gradually thereafter and the residual lesion was eventually cured by surgical removal.