Persistence of Mycobacterium tuberculosis in environmental samples

Background Limited evidence showed the persistence of Mycobacterium tuberculosis (MTB) in soil and water of TB sanatoriums or hospitals, but no reports suggest the occurrence of MTB in nature. Here, this study investigates the probability of isolating MTB from the environment with no clear source of contamination. To further highlight the transmission vehicle from human to nature and vice versa, the typing patterns of isolated MTB strains from the environment was compared with clinical MTB isolates. Additionally, the viability of MTB after 3 and 6 months of contamination was investigated. Methods The soil ( n = 700) and water ( n = 800) from different locations of suburban towns of Tehran was examined for the presence of MTB. The digested and decontaminated samples were inoculated in three LJ (Lowenstein Jensen) mediums and incubated at 37 °C, 25 °C and 42 °C for 12 weeks. Spoligotypes and MIRU-VNTR typing methods were performed on DNA extracted from single colonies. Thereafter, the obtained typing patterns were compared with the genotyping of TB patients that were residents of Robat Karim ( n = 25), Firuzkuh ( n = 10), Shahr-e-Ray ( n = 20) and Tehran ( n = 413). Result MTB accounts for 14.4% of total mycobacterium that was isolated from soil and water in suburban towns of Tehran. Based on polymerase chain reaction (PCR) typing methods, T family (56/82; 68%) followed by Delhi/CAS (11/82; 13.4%) were the most frequent MTB super families in both water and soil samples. Overall, 27.7% of isolates in clusters were intra-connected strains, i.e., found in different regions; however, no similar typing pattern between soil, water and clinical isolates was observed. The most frequent super family of MTB in clinical isolates was Delhi/CAS (142; 30.3%) followed by NEW-1 (127; 27.1%). The environment and clinical isolates had a minimum of 2 and a maximum of 10 loci difference (5–7 difference on average). The bacilli in contaminated soil (36%) and damp water (8.4%) remained alive for a considerable period of time, i.e., up to 9 months . Conclusion Persistence of MTB in soil and water highlights the risk of transmission, which needs further investigation. This study was supported by the National Research Institute of Tuberculosis and Lung Disease of Iran, Iran.