Mycobacterium avium-intracellulare complex - MegaMicro

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Mycobacterium avium-intracellulare complex

Microbiology > Bacteriology > Mycobacteria
Otherise known as MAI or MAC - Mycobacterium avium-intracellulare or Mycobacterium avium complex- M. avium and M. intracellulare are similar organisms that are usually grouped together due similarities in clinical presentation and management, adn difficulties in distinguishing them in the microbiology laboratory

I.                    Structure
a.       Stain: Acid fast
b.      Non-tuberculosis mycobacteria
c.       Slender rod with waxy cell wall

II.                  Pathobiology
a.       Physiology: Obligate aerobe, Runyon Group III- Nonphotochromegens (no pigment)
b.      Virulence factors
                                                i.      Much less virulent than M. tuberculosis
                                                ii.      Does not typically infect healthy people
III.                Epidemiology
a.       Widespread in the environment particularly in the southeastern US.
b.      Mode of infection is usually inhalation or ingestion
c.       Should always be considered in a person with HIV infection presenting with diarrhea

IV.                Laboratory diagnosis
a.       Laboratory culture of blood or sputum
b.      Bone marrow culture can often yield an earlier diagnosis

V.                  Disease Manifestations
a.       Systemic Opportunistic infection in immunocompromised
typically seen in AIDS with CD4 count <100
Symptoms: Fever, night sweats, and weight loss, local tissue involvement
Can infiltrate Lymph nodes, bone marrow, liver/spleen, GI tract
b.       Lung disease with productive cough
Usually affects patients with abnormal lungs or bronchi, manifesting as lung disease of the right middle lobe or lingula

VI.            Treatment:
a.  At least two agent treatment, typically with one agent being azithromycin or clarithromycin and the other ethambutol, rifabutin, or ciprofoxacin

VII.            Prevention:
a. Azithromycin prophylaxis for immunocompromised individuals with CD4 count under 75
dosed at 1200 mg once weekly
b. secondary regimens do exist (rifabutin), but are rarely used due to drug-drug interactions
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