T he patient's pus stain showed unstained organisms in the Gram stain (see Fig. 1C in the photo quiz), which were positive by acid-fast staining (see Fig. 1D in the photo quiz). Tissue and pus specimens were cultured at 32°C by inoculating the sediment on LJ solid medium and in a mycobacterial growth indicator tube (MGIT) (Becton, Dickinson, Sparks, MD). The cultures grew acid-fast bacilli (AFB) after 4 weeks for the pus specimen and 8 weeks for the tissue specimen. Two groups of mycobacterial colonies were identified. The first group (at 4 weeks) contained colonies that were creamy in color and turned yellow when exposed to light (photochromogenic), while the second group of colonies (at 8 weeks) appeared yellow and rough, with a welldemarcated edge. The organisms were later identified as Mycobacterium marinum and M. ulcerans, respectively (1). DNA extracted from pus and tissue samples were evaluated by PCR targeting the 16S rRNA gene and by the IS2404 insertion elements. PCR targeting the 16S rRNA gene confirmed Mycobacterium species most closely matching M. marinum and/or M. ulcerans. The sequences of the IS2404 amplicon were identical to those from M. ulcerans. Coinfections due to M. marinum and M. ulcerans, thus, were diagnosed based on cultures (M. marinum and M. ulcerans) and PCR primers specific for M. ulcerans. M. marinum and M. ulcerans were subjected to antimicrobial susceptibility testing (AST) using a broth microdilution susceptibility test (2), and both organisms were susceptible to clarithromycin, doxycycline, moxifloxacin, and rifampin. The patient was empirically treated with rifampin, clarithromycin, and streptomycin together with multiple surgical debridements of his left index finger, which resulted in a significant reduction of the inflammation and resolution of the abscess. Nontuberculous mycobacteria (NTM) are widely distributed in the environment, with high isolation rates worldwide. These organisms can be found in soil and water, including both natural and treated water sources. The most common clinical manifestation of NTM disease is lung disease, but lymphatic, skin and soft tissue, and disseminated diseases are also frequently described. M. marinum is the cause of "swimming pool granuloma" or "fish tank granuloma." A systematic search of the literature found that exposure to a fish tank in a household with indoor or outdoor aquariums, death of the tank fishes, and injury from or contact with a fish spine or oysters were commonly identified risk factors (3). Infection is typically acquired from a soft tissue injury to the hand in an aquatic environment, usually without a history of direct contact with fish. M. ulcerans is widely dispersed in geographic areas in the watersheds of tropical rain forests, primarily in Africa, Southeast Asia, Australia, and South and Central America (4, 5). M. ulcerans causes indolent, progressive necrotic lesions of the skin and