Isolation of nontuberculous mycobacteria from soil using Middlebrook 7H10 agar with increased malachite green concentration

• Published in: AMB Express 2017-12, Vol.7 (1), p.69-69, Article 69
• Main Authors: Hu, Yuli, Yu, Xinglong, Zhao, Dun, Li, Runcheng, Liu, Yang, Ge, Meng, Hu, Huican
• Format: Article
• Language: English
• Subjects: Agar; Biomedical and Life Sciences; Biotechnology; Contamination; Decontamination; Life Sciences; Malachite green; Microbial Genetics and Genomics; Microbiology; Mycobacterium; Original; Original Article; Sodium dodecyl sulfate; Sodium lauryl sulfate; Soil contamination
• ISSN: 2191-0855; 2191-0855
• DOI: 10.1186/s13568-017-0373-6

Environmental exposure is considered to be responsible for nontuberculous mycobacterial infections in humans. To facilitate the isolation of mycobacteria from soil, Middlebrook 7H10 agar was optimized as an enhanced selective medium by increasing the concentration of malachite green. A series of modified Middlebrook 7H10 agar media with malachite green concentrations ranging from 2.5 to 2500 mg/L was evaluated using 20 soil samples decontaminated with 3% sodium dodecyl sulfate plus 2% NaOH for 30 min. Among these modified Middlebrook 7H10 media, the medium with malachite green at a concentration of 250 mg/L, i.e., at the same concentration as in Löwenstein–Jensen medium, was the most effective in terms of the number of plates with mycobacterial growth. This medium was further evaluated with 116 soil samples. The results showed that 87.1% (101/116) of the samples produced mycobacterial growth, and 15 samples (12.9%) produced no mycobacterial growth. Of the plates inoculated with the soil samples, each in duplicate, 5.2% (12/232) showed late contamination. In total, 19 mycobacterial species were isolated, including seven (36.8%) rapidly growing mycobacteria and 12 (63.2%) slowly growing mycobacteria. Our results demonstrate that the modified Middlebrook 7H10 agar with 250 mg/L malachite green is useful for the primary isolation of nontuberculous mycobacteria from soil.