Review: Environmental mycobacteria as a cause of human infection

Area of Science:

• Environmental microbiology
• Infectious diseases
• Molecular epidemiology

Background:

• Nontuberculous mycobacteria (NTM) cause pulmonary infections, increasingly seen in older adults without immune defects.
• NTM are ubiquitous in soil and water, but transmission pathways to humans remain largely unknown.
• Current understanding of NTM environmental reservoirs and human transmission is limited, particularly in developing nations.

Purpose of the Study:

• To investigate the environmental sources and transmission routes of pathogenic nontuberculous mycobacteria (NTM).
• To highlight the need for broader environmental sampling across diverse geographical and climatic conditions.
• To address gaps in identifying clinical NTM isolates within tested environments.

Main Methods:

• Molecular analyses including partial sequencing, PCR-restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD) PCR, repetitive element (rep-) PCR, and pulsed field gel electrophoresis (PFGE).
• Comparison of clinical NTM isolates with environmental isolates from patients' local environments.
• Identification of potential NTM sources such as showers, faucets, hot-tubs, and garden soil.

Main Results:

• Molecular techniques enable definitive strain-level differentiation for NTM source tracking.
• Specific environmental niches like domestic water systems and soil have been implicated in NTM transmission.
• Challenges remain in fully identifying the environmental origins of many clinical NTM isolates.

Conclusions:

• Advanced molecular methods are crucial for accurate NTM source attribution and epidemiological studies.
• Understanding NTM transmission requires comprehensive investigation of diverse environmental reservoirs globally.
• Further research is needed to elucidate NTM's environmental ecology and human infection pathways, especially in understudied regions.