SCANNING ELECTRON MICROSCOPY TO EVALUATE THE ATTACHMENT OF NONTUBERCULOUS MYCOBACTERIA TO MINERAL SURFACES

The prevalence of nontuberculous mycobacterial (NTM) pulmonary disease – a potentially life-threatening, but under-diagnosed chronic illness – is rising throughout the world. Hawai’i has the highest incidence of NTM pulmonary infections in the United States with four times higher NTM infection rates than the national average. While NTM are ubiquitously found throughout the environment, including soil, it is not clear what soil characteristics contribute to NTM growth. Thus, this study examines the relationship between mineralogy and NTM survival in soil. We hypothesize that NTM-culture positive soil contains minerals that promote NTM growth in vitro.

Scanning electron microscopy (SEM) was used to observe soil mineral-NTM interactions. Crushed kaolinite, gibbsite, birnessite, and hematite readily found in Hawaiian soil, were separately incubated in the presence or absence of clinically-significant NTM including Mycobacterium abscessus and Mycobacterium chimaera in a mineral-free growth media. SEM imaging revealed that neither M. abscessus or M. chimaera bound to the surface of birnessite or gibbsite. However, both M. abscessus and M. chimaera attached to hematite crystalites. Growth of M. abscessus and M. chimaera were not significantly altered by exposure to kaolinite.

NTM is hydrophobic and binds to surfaces. Binding of NTM to soil minerals may have clinical implications. Pure gibbsite could exhibit Al-toxicity. Birnessite and gibbsite mineral faces could be too small for NTM to attach. Soils with hematite, ubiquitous in the Islands, could provide an environment where NTM flourish and may be a major factor as to why Hawai’i has significantly higher infection rates. The binding of NTM to hematite could have greater implications as to how NTM travel through soil and water to infect humans. Overall, this study enables a more accurate prediction of where NTM may be found in the environment and enables future work for mitigation in order to lower infection rates.