Nontuberculous Mycobacteria
One-Sentence Definition
Nontuberculous mycobacteria (NTM) are environmental, acid-fast mycobacteria other than the M. tuberculosis complex and M. leprae that cause chronic lung disease, lymphadenitis, skin/soft-tissue, and disseminated infection in susceptible hosts.
Taxonomy & Morphology
- Acid-fast bacilli; mycolic acid–rich walls (Acid-Fast Stain)
- Major clinical groups: slowly growing (e.g., M. avium complex / MAC, M. kansasii) vs rapidly growing (e.g., M. abscessus, M. fortuitum, M. chelonae)
- Ubiquitous in water and soil — colonization vs infection is a clinical judgment
Virulence Highlights
- Biofilm in plumbing and medical devices (Biofilm)
- Intracellular survival in macrophages (MAC)
- Intrinsic multidrug resistance of cell envelope — especially M. abscessus
- Host susceptibility: COPD/bronchiectasis, CF, immunosuppression, anti-IFN-γ autoantibodies
Clinical Syndromes
- Chronic nodular/bronchiectatic or fibrocavitary lung disease (MAC classic)
- Cervical lymphadenitis in children
- Skin/soft tissue after trauma or cosmetic procedures (RGM)
- Disseminated MAC in advanced HIV (HIV)
- Healthcare-associated outbreaks from water systems
Diagnosis
- AFB smear/culture of sputum or tissue; multiple positive sputa often needed for lung disease criteria
- Species ID: MALDI-TOF MS, HPLC historically, or sequencing (rpoB, 16S, housekeeping genes)
- Distinguish contamination/colonization from disease (ATS/IDSA-style criteria)
- GeneXpert-type TB assays target MTBC — negative does not exclude NTM
Treatment Notes (conceptual)
- Multidrug regimens, long duration; MAC often macrolide + ethambutol ± rifamycin
- M. abscessus: among hardest bacteria to treat — specialty care; surgery sometimes
- Macrolide susceptibility critical for MAC prognosis
- Not every isolate is treated — avoid unnecessary toxic courses (Antimicrobial Stewardship)
AMR
- Intrinsic resistance high (efflux, wall impermeability, inactivating enzymes)
- Inducible macrolide resistance (erm in M. abscessus subspecies) — phenotypic induction testing matters
- Acquired mutations under therapy (e.g., 23S rRNA) → macrolide failure
- Contrast with Mycobacterium tuberculosis drug regimens and TB public-health framing
Genomics & Computational Notes
- WGS for species/subspecies (M. abscessus abscessus vs massiliense vs bolletii) and outbreak tracing in CF clinics
- ANI and Species Delineation / GTDB Taxonomy refine mycobacterial naming flux
- Water-system genomics for nosocomial NTM clusters (Clinical WGS Pipelines)
Related Notes
- Mycobacterium tuberculosis · Acid-Fast Stain · Biofilm · HIV
- MOCs: MOC - Bacteriology · MOC - Clinical Microbiology · MOC - Antimicrobial Resistance (AMR)
Active Recall
- Name one slow grower and one rapid grower of clinical importance.
- Why can a negative MTB/RIF PCR still leave NTM on the differential?
- Why is erm induction testing relevant for M. abscessus?