Atypical Mycobacteria - Study NotesDefinition & Terminology

Atypical mycobacteria are also called:

  • Non-Tuberculous Mycobacteria (NTM)

  • Mycobacteria Other Than Tubercle Bacilli (MOTT)

Key characteristics:

  • Found in birds, animals, soil, and water

  • Opportunistic pathogens in humans

  • Different from Mycobacterium tuberculosis (MTB)

Important ExamplesM. avium-intracellulare complex (MAC)

  • Comprises two related organisms:

    • M. avium (Battey bacillus)

    • M. intracellulare

  • Opportunistic pathogen in HIV patients with CD4 count < 50/μl

M. ulcerans

  • Waterborne skin pathogen

  • Causes Buruli ulcer

Classification Systems1. Based on Growth Rate

Slow Growers:

  • M. avium-intracellulare

  • M. kansasii

  • M. marinum

  • M. ulcerans

Rapid Growers:

  • M. fortuitum

  • M. chelonae

  • M. abscessus

2. Runyon Classification

Groups based on pigment production and growth rate:

  • Group I - Photochromogens

  • Group II - Scotochromogens

  • Group III - Non-chromogens

  • Group IV - Rapid growers

Differentiation from MTB

NTM can be distinguished from MTB by:

Test

NTM

MTB

PNB (paranitrobenzoic acid)

Resistant

Sensitive

TCH (thiophen-2-carboxylic acid hydrazide)

Sensitive

Resistant

Aryl sulfatase

Positive

Negative

Catalase

Strong positive

Weak positive

Guinea pig pathogenicity

Non-pathogenic

Pathogenic

Mouse pathogenicity

Pathogenic

Non-pathogenic

Antitubercular drugs

Resistant

Sensitive

Clinical Significance

  • Opportunistic infections in immunocompromised patients

  • Different treatment approach compared to TB

  • Resistance to standard antitubercular drugs