Mycobacterium Flashcards
Mycolic acids in cell wall
Gram+ weak staining: use acid-fast stain
or specific fluorescent detection
Mycobacteria
Facultative intracellular growth (in macrophages) Obligate aerobe (growth in lung macrophages)
Mycobacteria
Humans are reservoir
• airborne transmission (as few as 10 cells
can result in infection)
Mycobacteria
Don’t need alot of cells to infect
Mycobacteria
treat with alkaline-alcohol to extract lipid mycolic acids
Acid-fast stain
McKane ‘96 Table 3-3, Fig.3-13 Walker ’98 Fig.9-2
(
Acid fast cells stain what color.
Non acid fast?
Red
Blue
Mycobacterial cell wall structure
cord factor (glyco-lipid)
Structural mycobacterial cell wall components which are Virulence Factors
Mannose Caped lipoarabinomanna
Cord factor (glyco-lipid)
Arabinogalactin
Slow, cord-like growth
strongly correlates
with virulence.
Mycobacterium
Cord-like growth results from adherence of cell surface
lipid mycolic acids and glyco-lipids
Virulence Factors (2) M.tuberculosis and M.leprae
Facultative intracellular growth in alveolar and other macrophages:
inhibition of phago-lysosome fusion
disease is caused by the immune response,
NOT by the mycobacteria.
While many “virulence factors” are listed, their virulence results from the challenge that
they provide to the immune response (typically DTH: CD4+ T-cells + macrophages)
because (in most cases) the disease is caused by the immune response,
NOT by the mycobacteria.
Virulence Factors (2) M.tuberculosis and M.leprae
………………………. is a “life-long” pathogen:
once infected, you may be asymptomatic but never cured
Mycobacterium tuberculosis is a “life-long” pathogen:
once infected, you may be asymptomatic but never cured
TB granuloma surrounded by punctate nuclei
of lung tissue and inflammatory leukocytes.
Central area of necrosis where nuclei have
been destroyed.
CMI to Mycobacterium tuberculosis
TB granuloma surrounded by punctate nuclei
of lung tissue and inflammatory leukocytes.
Central area of necrosis where nuclei have
been destroyed.
Effective CMI is capable of localizing and stopping infection by …………………….. Chronic …………… is
typical.
Effective CMI is capable of localizing and stopping infection by M.tuberculosis. Chronic TB is
typical.
young children under 5 years have a high risk for developing progressive ………………… due
to insufficient immune system development/activation.
young children under 5 years have a high risk for developing progressive TB due
to insufficient immune system development/activation.
Breathing impairment in TB is not due to tuberculosis bacilli but by the …………………………………….
Breathing impairment in TB is not due to tuberculosis bacilli but by the macrophage-induced tissue
destruction
However, acute (‘open’) TB [also known as “secondary tuberculosis” or in older terms
“galloping consumption” caused by “……………..” of prior infection
- while rare (life-time risk is assessed as <12% for carriers, or less) it is VERY contagious!
Isolation of acute TB cases is mandatory.
Endogenous reactivation is stimulated by ………………..
However, acute (‘open’) TB [also known as “secondary tuberculosis” or in older terms
“galloping consumption” caused by “endogenous reactivation” of prior infection
- while rare (life-time risk is assessed as <12% for carriers, or less) it is VERY contagious!
Isolation of acute TB cases is mandatory.
Endogenous reactivation is stimulated by stress, malnutrition and HIV
OUTCOMES of untreated primary TB [results for non-immune-compromised patents]:
• …..% no disease
• …..% clinical TB (2% pulmonary + 3% extrathoracic + 1% both)
• …….% progressive systemic disease and death.
OUTCOMES of untreated primary TB [results for non-immune-compromised patents]:
• 91% no disease
• 6% clinical TB (2% pulmonary + 3% extrathoracic + 1% both)
• 3% progressive systemic disease and death.
Mantoux Reaction
A positive tuberculin test to subdermal PPD (processed protein derivative of the cell wall of the opportunistic intracellular pathogen Mycobacterial tuberculosis).
Mantoux Reaction
Positive and Negative results
Positive test: >10 mm redness
Strongly positive: >20mm red
M.bovis (
Exposure to living attenuated mycobacterium, known as Bacille Calmette-Guérin (BCG), a
derivative of M.bovis (which may be identical to M.tuberculosis based on whole genome sequencing):
• little virulence in humans (but infectious in immune-compromised persons)
• some protective immunity (when given to young children)
• BCG vaccination is discouraged in USA because it gives a positive tuberculin test, thus removing
an important diagnostic screening tool. (And M.bovis causes disease in immune-compromised persons.)
Bacille Calmette-Guérin (BCG),
Vaccination
Exposure to living attenuated mycobacterium, known as Bacille Calmette-Guérin (BCG), a
derivative of M.bovis (which may be identical to M.tuberculosis based on whole genome sequencing):
• little virulence in humans (but infectious in immune-compromised persons)
• some protective immunity (when given to young children)
• BCG vaccination is discouraged in USA because it gives a positive tuberculin test, thus removing
an important diagnostic screening tool. (And M.bovis causes disease in immune-compromised persons.)
TB and HIV
HIV infections, with its Acquired
Immune Deficiency Syndrome (AIDS),
has caused a recent increase in TB
Mycobacterium leprae:
diverse CMI responses
