Mycobacterium

Question 1

Mycobacteria features

Answer 1

•rod shaped, non motile bacterial cells
•slow growing
•strict aerobes
•not classically gram neg or pos

Question 2

Mycobacteria cell wall

Answer 2

•lipid rich
•resists drying, acids, alcohol, lytic enzymes
•resists typical stains
•thin peptidoglycan
•mycolic acids

•’acid fast’ bacilli (AFB)
•resists decolourisation by acids during staining

Question 3

Mycobacteria groupings

Answer 3

M tuberculosis complex (MTBC)
•growth rate: slow (>7 days)
•cord positive
•TDM or ‘cord factor’ is primary glycolipid in exterior of M tuberculosis

Non-tuberculous mycobacteria (NTM or MOTT)
•atypical mycobacteria, don’t cause TB or leprosy
•growth rate is slow or rapid (2-7 days)
•cord negative

Mycobacterium leprae
•cant be cultured in vitro

Question 4

MTBC

Answer 4

•all species capable of causing tuberculosis in humans or animals
•slow growing (>7 days)

•tuberculosis, africanum, bovis, caprae, microti, canettii, pinnipedii

Question 5

TB disease

Answer 5

•chronic disease caused by MTBC
•pulmonary TB
•weakness/fatigue, weight loss, fever, night sweats, cough

Question 6

Pathophysiology of TB

Answer 6

Initial infection
•droplet nuclei inhaled, 1-3 bacilli

Innate immune phase
•AFB phagocytosed by alveolar macrophages or dendritic cells
•some survive by blocking lysosome fusion with phagosome
•macrophages stimulated, produce cytokines, recruit leukocytes

Adaptive immune system
•bacteria released from macro/dend cells
•travel via lymph, present AFB to lymphocytes

cell mediated immunity
•activation of T lymphs, migrate to infection
•lymphokines, monokines, cytokines by T cells