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Assessment of soil features on the growth of environmental nontuberculous mycobacterial isolates from Hawai’i


Natural and man -made environments harbor potentially disease -causing species of 71 nontuberculous mycobacteria (NTM) (1). The NTM species responsible for human lung 72 infections are thought to be influenced by the specific environmental source exposures and the 73 NTM species diversity within these environmental niches. While water -associated biofilms 74 contain potentially disease -causing NTM, a variety of NTM species have also been discovered in 75 soil (2 -4). Prior studies have shown that potting soil can be a reservoir for clinically relevant 76 mycobacteria (4). In Japan, residential soil from patients with pulmonary NTM infections were 77 demonstrated to harbor NTM that were genetically related to patients’ respiratory NTM isolates 78 and that soil was a source of the patients’ polyclonal and mixed Mycobacterium avium complex 79 infections (5, 6). In the United States (U.S.), Hawai’i has the highest prevalence of NTM lung 80 infections with almost four times higher NTM infection rates than the national average in a 81 survey among older adults (7). In prior work (8), we reported the presence of clinically relevant 82 slow -growing mycobacteria (SGM) including Mycobacterium chimaera, Mycobacterium 83 marseillense, and Mycobacterium intracellulare in Hawai’i soil samples, in addition to rapid - 84 growing mycobacteria (RGM) including Mycolicibacterium septicum and Mycolicibacterium 85 alvei.


The breadth of NTM species diversity in soil is likely driven by the proportion and composition 88 of minerals and nutrients in that particular soil sample. For example, higher amounts of metals 89 such as copper, and cations such as sodium, have been shown to be significant predictors for 90 NTM infection in the U.S. (9). Prior studies from Queensland, Australia have shown soil on September 1, 2020 by guest Downloaded from 5 91 containing nutrients such as nitrate or having low pH predicted the presence of RGM, including 92 Mycolicibacterium fortuitum and Mycobacteroides chelonae (10). Yet, soil components such as 93 natural rock, sand, or clay may also impact NTM presence and diversity. A study by Lipner et al. 94 reported increasing clay concentrations as protective against NTM, while increasing silt 95 concentrations was associated with NTM infection (11). In this same study and another, higher 96 manganese concentration was associated with disease prevalence (9, 11). Thus, variable soil 97 characteristics and components may either inhibit or promote NTM growth in soil.

In the current study, we performed microbiome and mineral/chemical analyses on a set of 100 Hawai’i soil samples and tested the impact of particular clays and chemicals on the in vitro 101 growth of native NTM species recovered from the Hawai’i environment. Since almost all of the 102 rock underlying Hawai’i ecosystems is oceanic basalt, comprised of volcanic rock with limited 103 variations in composition (12), the characteristics associated with the presence of NTM in 104 Hawai ’i soil may significantly vary from what has been described so far.

Figure 1. Hawai'i soil map. A) Location of soil samples in the Hawaiian Islands, with NTM positive (green stars) and NTM negative soils (black dots) as indicated. B) Map of Oahu indicating NTM positive and negative soils. Blue contours are mean annual rainfall (mm/yr). Red indicates the presence of bedrock at the surface and the other map colors represent various soil orders (USDA, 2019).

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