Assessment of Soil Features on the Growth of Environmental Nontuberculous Mycobacterial Isolates from Hawai'i

Abstract

Environmental nontuberculous mycobacteria (NTM) with the potential to cause opportunistic lung infections can reside in soil. This might be particularly relevant in Hawai'i, a geographic hot spot for NTM infections and whose soil composition differs from many other areas of the world. Soil components are likely to contribute to NTM prevalence in certain niches, as food sources or attachment scaffolds, but the particular types of soils, clays, and minerals that impact NTM growth are not well-defined. Hawai'i soil and chemically weathered rock (a.k.a., saprolite) samples were examined to characterize the microbiome and quantify 11 mineralogical features as well as soil pH. Machine learning methods were applied to identify important soil features influencing the presence of NTM. Next, these features were directly tested in vitro by incubating synthetic clays and minerals in the presence of Mycobacteroides abscessus and Mycobacterium chimaera isolates recovered from the Hawai'i environment and changes in bacterial growth were determined. Of the components examined, synthetic gibbsite, a mineral form of aluminum hydroxide, inhibited the growth of both M. abscessus and M. chimaera, while other minerals tested showed differential effects on each species. For example, M. abscessus (but not M. chimaera) growth was significantly higher in the presence of hematite, an iron oxide mineral. In contrast, M. chimaera (but not M. abscessus) counts were significantly reduced in the presence of birnessite, a manganese containing mineral. These studies shed new light on the mineralogic features that promote or inhibit the presence of Hawai'i NTM in Hawai'i soil. IMPORTANCE Globally and in the United States, the prevalence of nontuberculous mycobacterial (NTM) pulmonary disease - a potentially life-threatening, but under-diagnosed chronic illness – is prominently rising. While NTM are ubiquitous in the environment including soil, the specific soil components that promote or inhibit NTM growth have not been elucidated. We hypothesized that NTM-culture positive soil contains minerals that promote NTM growth in vitro. Because Hawai'i is a hot spot for NTM and a unique geographic archipelago, we examined the composition of Hawai'i soil and identified individual clay, iron, and manganese minerals associated with NTM. Next, individual components were evaluated for their ability to directly modulate NTM growth in culture. In general, gibbsite and some manganese oxides were shown to decrease NTM, whereas iron containing minerals were associated with higher NTM counts. These data provide new information to guide future analyses of soil-associated factors impacting persistence of these soil bacteria.

Lower Recovery of Nontuberculous Mycobacteria from Outdoor Hawai’i Environmental Water Biofilms Compared to Indoor Samples

“…In our prior work, we have elucidated potential factors that modulate M. chimaera growth in vitro. Specifically, incubation of an environmental M. chimaera isolate from Hawai’i with birnessite, a manganese-containing mineral and gibbsite, a mineral form of aluminum hydroxide, both of which are common in Hawai’i soil, significantly reduced M. chimaera growth in vitro [ 30 ]. However, M. chimaera growth remained unchanged in the presence of iron-containing minerals such as hematite, magnetite, and maghemite after 96 h in culture [ 30 ], suggesting particular soil minerals influence M. chimaera in the environment.…”

“…Specifically, incubation of an environmental M. chimaera isolate from Hawai’i with birnessite, a manganese-containing mineral and gibbsite, a mineral form of aluminum hydroxide, both of which are common in Hawai’i soil, significantly reduced M. chimaera growth in vitro [ 30 ]. However, M. chimaera growth remained unchanged in the presence of iron-containing minerals such as hematite, magnetite, and maghemite after 96 h in culture [ 30 ], suggesting particular soil minerals influence M. chimaera in the environment. The water-associated factors that drive the presence or absence of M. chimaera remain to be elucidated, but may include the propensity of M. chimaera to form biofilms in man-made instruments as highlighted by the associated heater-cooler outbreaks or other exogenous surfaces [ 31 , 32 ].…”

Exposure Pathways of Nontuberculous Mycobacteria Through Soil, Streams, and Groundwater, Hawai'i, USA

“…In summary, mycobacteria are a significant, if minor component of Hawai'i aquifer and a major component of soil biomes (Kirs et al., 2020), and cell count and transport studies indicate up to >10 7 cells/ml of bacteria may be expected in fractured basalt. NTM are now known to exist in the riparian environments of Kauai and Oahu where cells may tend to bind with hematite (Glickman et al., 2020). Furthermore, it appears that there are plausible, and possibly likely, pathways for basal aquifers to be continuously inoculated by NTM derived from losing streams and episodically by storm events.…”

“…Depending on rainfall rates, basalt can weather to soil and saprolite comprised of 1:1 clays (kaolinite and/or halloysite), Fe‐oxides/hydroxides (hematite, maghemite, and goethite), and gibbsite. From prior work, NTM have been shown to attach to Fe‐oxides/hydroxides in Hawai'i soil (Glickman, 2020), which may facilitate NTM entry into ground water supplies.…”

Characterization of Biofilm Formation by Mycobacterium chimaera on Medical Device Materials

“…Mycobacterium chimaera is a slow-growing non-tuberculous mycobacterial (NTM) species ubiquitously found in the environment, including tap water ( Falkinham, 2009 ; Wallace et al, 2013 ; Glickman et al, 2020 ). M. chimaera was first identified as a part of the Mycobacterium avium complex (MAC) in 2004 ( Tortoli et al, 2004 ).…”