What this test measures
Mycobacteria Other Than Tuberculosis (MOTT, also called non-tuberculous mycobacteria or NTM) are environmental mycobacteria that can cause lung, lymph node, skin, and disseminated disease, especially in patients with underlying lung disease, bronchiectasis, cystic fibrosis, or immunosuppression. The two largest groups are slow-growing (M. avium complex, M. kansasii) and rapid-growing (M. abscessus, M. fortuitum, M. chelonae) — and they require very different treatment regimens.
MOTT DST tests the cultured isolate against a panel of drugs appropriate to the species, including macrolides (clarithromycin, azithromycin), aminoglycosides (amikacin), rifabutin, ethambutol, doxycycline, linezolid, moxifloxacin, clofazimine, and others. Critical concentrations and clinical correlation differ from M. tuberculosis — ATS/IDSA guidelines provide species-specific recommendations.
Why it matters
NTM lung disease is rising globally, including in India. Many patients are mis-diagnosed as drug-resistant TB initially because their AFB smear and culture are positive but molecular tests for M. tuberculosis are negative. Confirming the species (often by HPLC, MALDI-TOF or sequencing) and tailoring drug susceptibility testing is essential because:
- M. avium complex disease is treated with macrolide-based 3-drug regimens for 12–24 months. - M. abscessus is intrinsically resistant to most TB drugs and needs intravenous antibiotics for months. - Treating NTM as TB does not work and exposes the patient to unnecessary first-line TB drugs.
For patients with bronchiectasis, post-tuberculous lung disease, or persistent symptoms after "failed" TB treatment, MOTT DST can be transformative.
How to prepare
A positive AFB culture identified as NTM is required. The species drives which drug panel is appropriate — confirm species identification before requesting DST. Inform the lab of all antibiotics taken in the past 4 weeks.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Clarithromycin (macrolide) (—)[1] | Sensitive | — | Resistant — macrolide is the keystone drug for M. avium complex. Resistance dramatically worsens prognosis and requires alternative regimen choice. |
| Amikacin (—)[1] | Sensitive | — | Resistant — amikacin (oral or intravenous) is a major drug for M. abscessus. Resistance significantly limits treatment options. |
| Linezolid (—) | Sensitive | — | Resistant — linezolid is a useful oral option, especially for M. abscessus. Resistance is uncommon but limits oral options. |
| Moxifloxacin (—)[1] | Sensitive | — | Resistant — moxifloxacin is a companion drug in many NTM regimens. Resistance limits regimen flexibility. |
NTM species and typical first-line drugs
| Species | Typical regimen | Duration |
|---|---|---|
| M. avium complex (MAC) | Clarithromycin / Azithromycin + Rifampicin + Ethambutol | ≥12 months after culture conversion |
| M. kansasii | Rifampicin + Isoniazid + Ethambutol | 12 months |
| M. abscessus (rapid grower) | Macrolide + Amikacin (IV) + Imipenem / Cefoxitin / Tigecycline | 12+ months, often with surgery |
| M. fortuitum | Amikacin + Cefoxitin + Quinolone | 6–12 months |
Frequently asked questions
How is MOTT different from M. tuberculosis?
MOTT (or NTM) are environmental mycobacteria from soil and water. Unlike TB, they are not contagious person-to-person in most species, but they can cause chronic lung, skin, and disseminated disease — especially in damaged lungs or immunosuppression.
Why is species identification critical before DST?
Each NTM species has its own drug panel and intrinsic resistance pattern. M. avium and M. abscessus need very different drugs. Species ID (by HPLC, MALDI-TOF, or sequencing) must be done before requesting DST.
How long does MOTT DST take?
Slow-growing species (M. avium, M. kansasii) take 1–3 weeks from a positive culture. Rapid growers (M. abscessus) can be quicker. Total time from sample is often 4–8 weeks.
I was treated as TB but did not improve. Could this be NTM?
Yes — this is a common scenario. If your AFB smear / culture stays positive but molecular tests for M. tuberculosis are negative, species ID and MOTT DST should be done.
Is NTM treatment shorter than TB?
No — NTM treatment is usually longer (12–24 months) and often less effective. Some species (M. abscessus) require intravenous therapy and may need surgical resection of affected lung areas.
Is NTM common in India?
Reported NTM disease is rising in India, particularly among patients with bronchiectasis and post-TB lung damage. Many cases remain under-diagnosed because the algorithm is more complex than for TB.
Where can I get this test in Mumbai?
Specialised mycobacteriology labs in major Mumbai and Thane hospitals offer species ID and DST for NTM. Zelnoo can facilitate sample collection and routing to the right reference lab.
Related Tuberculosis / Mycobacterial tests
Tests commonly ordered alongside AFB DRUG SUSCEPTIBILITY - MOTT, or that help interpret an unexpected result.
Sources & references
- ATS / IDSA / ERS NTM Pulmonary Disease Guidelines · accessed 2026-05-30T00:00:00.000Z
- CDC — Nontuberculous Mycobacteria · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Nontuberculous Mycobacteria · accessed 2026-05-30T00:00:00.000Z
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