BRIEF REVIEW OF ATYPICAL MYCOBACTERIUM
1)
Background: Bacteriology, identification, transmission
2)
Clinical Features
3) ATS Criteria for Diagnosis
4) Treatment: Medical, surgical
5) Adjunctive therapy
6) Prognosis and outcomes
Background
–
Non-motile,
non-spore forming, slender, pleomorphic bacteria with complex cell walls
–
Ubiquitous
bacterium: Found in soil, water, house dust
–
>
50 mycobacterial species, about one half are pathogenic.
Runyon classification; pigment
and speed of growth
–
Most
commonly encountered organisms: M. avium, M intracellulare, M. scrofulaceum
Detection
–
Ziehl-Neilsen
stain methylene blue –
sensitivity
< 50% on sputum and tissue samples in children
–
Fluorochrome
stain, auramine
rhodamine
–
PCR
technique (Haas et al, 1998)
Culture
Identification and caveats
–
~ 10,000 AFB/ml of specimen to be seen on a smear
–
Susceptible to being killed by alkali agents
–
Growth of colonies may take 10 days (rapid growing) up to 6 wks (slow
growing)
–
Rapid growth of MAC may obscure MTB growth
–
Drug susceptibility reports should be interpreted with caution
Mode
of Transmission
–
Probable aerosol transmission, not human-to-human
–
Mechanism of infection: Use complex glycopeptidolipid cell wall to downregulate
macrophage responses and infect cells, then release of cytokines that
recruit and stimulate lymphocytes from innate and acquired immune system.
Defective cytokine production implicated (IL-12), TNF
–
Low
virulence unless immunocompromised (mycobacterium avium complex reported
in men with underlying pulmonary disease, some older women without underlying
disease and disseminated infections in those with HIV)
Clinical
Features and Presentation of atypical mycobacterium pulmonary disease
–
Highly
variable, lung involvement usually adolescents and adults
–
Cervical lymphadenitis (most common presentation in children) (McCabe
et al. JAMA 1984;Gilbert Am Rev Respir Dis 1972)
–
Pneumonia
–
Mediastinal lymphadenopathy
–
Significant extrinsic bronchial compression
–
Endobronchitis
–
Invasive disease (more likely if immunocompromised, i.e. HIV)
–
Can resemble human tuberculosis**
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