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Micobactérias

Complexo Mycobacterium avium (MAC)

Acid-fast bacilli

Identification & Growth

Identification

  • Slow-growing, non-chromogenic mycobacterium; identified by molecular probe or MALDI-TOF

Growth Conditions

  • Löwenstein-Jensen or liquid medium, 10–21 days, 37 °C; smooth translucent colonies

Clinical Significance

  • Pulmonary disease in bronchiectasis and COPD; disseminated disease in HIV with low CD4
  • Cervical lymphadenitis in children

Intrinsic Resistance

  • Resistant to classical antituberculosis drugs; treatment is based on a macrolide with ethambutol and a rifamycin

Bench Alerts

  • Test only clarithromycin and amikacin by MIC, per CLSI M24 — EUCAST/BrCAST do not cover mycobacteria
  • A single sputum isolate may represent colonisation: clinical and radiological criteria are required

Clinical Notes

Clinical presentations

  • Chronic pulmonary disease, often in patients with pre-existing bronchiectasis, COPD or other structural lung disease, with a slowly progressive course.
  • Disseminated disease in patients with advanced immunosuppression, particularly HIV with very low CD4 counts, presenting with fever, weight loss, anemia and hepatosplenomegaly.
  • Cervical lymphadenitis in immunocompetent children, usually unilateral and painless.

Specimens and collection

  • Diagnosis of pulmonary disease requires combined clinical, radiologic and microbiologic criteria, with at least two positive sputum cultures or one positive bronchoalveolar lavage culture.
  • Mycobacterial blood culture (dedicated bottle/system) is the method of choice for diagnosing disseminated disease.
  • Lymph node biopsy with mycobacterial culture in the evaluation of lymphadenitis, avoiding fine-needle aspiration alone when complete excision is feasible.

Epidemiology and at-risk populations

  • Nontuberculous, environmental mycobacterium found in water and soil; no documented person-to-person transmission.
  • MAC pulmonary disease is the most common nontuberculous mycobacterial infection, predominating in thin, older women without prior structural lung disease (Lady Windermere syndrome) and in patients with bronchiectasis.
  • Disseminated disease is nearly restricted to severe immunosuppression (advanced HIV without ART, CD4 < 50 cells/µL), having become rare with effective antiretroviral therapy.

Resistance and therapeutic implications

  • Treatment of pulmonary disease relies on a combination regimen with a macrolide (azithromycin or clarithromycin), ethambutol and a rifamycin (rifampicin or rifabutin), given for a prolonged period.
  • Macrolide susceptibility is the test with the strongest validated clinical correlation; macrolide resistance predicts treatment failure and warrants regimen adjustment.
  • Primary prophylaxis with azithromycin was recommended in advanced HIV with very low CD4 before effective ART; today reserved for specific settings with limited antiretroviral access.

Bench and reporting notes

  • Slow-growing acid-fast bacillus; species/complex identification by molecular methods or MALDI-TOF is required to differentiate it from M. tuberculosis complex.
  • An isolated positive sputum culture does not confirm active disease; always interpret using combined diagnostic criteria (clinical + radiologic + microbiologic) before initiating treatment.
  • Unlike tuberculosis, MAC disease is not a notifiable condition in most jurisdictions and does not require respiratory isolation, given the absence of person-to-person transmission.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Complexo Mycobacterium avium (MAC) in the lab?

Complexo Mycobacterium avium (MAC) is identified through slow-growing, non-chromogenic mycobacterium; identified by molecular probe or maldi-tof.

What are the intrinsic resistances of Complexo Mycobacterium avium (MAC)?

This organism is naturally resistant to resistant to classical antituberculosis drugs; treatment is based on a macrolide with ethambutol and a rifamycin. These drugs should not be reported as susceptible.

Where is Complexo Mycobacterium avium (MAC) commonly found?

It is typically associated with pulmonary disease in bronchiectasis and copd; disseminated disease in hiv with low cd4, cervical lymphadenitis in children.

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