Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 5 4 2021 01 16 124 127 Nasim Eftekhari Department of Microbiology, Kerman Branch, Islamic Azad University, Kerman, Iran. Reza Rezaeizadeh Private Clinic, Kerman, Iran. Shayan Shahabinejad Department of Microbiology,School of Medicine, Kerman University of Medical Sciences, Kerman, Iran. 2020 06 27 2020 07 12 The Lowenstein-Jensen is an egg-based microbiology medium that was designed for selective isolation of Mycobacterium spp. The main inhibitory composition in this medium is a synthetic dye called malachite green. Mycobacterium spp. is resistant to the dye by de-colorization and oxidation of it. Some non-tuberculosis organisms may also overcome this inhibitory ingredient by similar enzymatic activity. In the final inspection of the bone TB culture of a teenage patient, the blind smear revealed the Pseudomonas talus osteomyelitis. According to the present and similar experiences, the preparation of 1-2 blind smears from TB culture- negative specimens taken from sterile sites of the body may unmask mycobacteria with the atypical colony and non-tuberculosis microorganisms. https://crcp.tums.ac.ir/index.php/crcp/article/view/370 https://crcp.tums.ac.ir/index.php/crcp/article/download/370/375