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Microbiology ðŸ¦
Mycobacteria
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Cards (36)
What type of bacteria are mycobacteria?
Aerobic
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What shape are mycobacteria?
Rod-shaped
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What does it mean for mycobacteria to be acid fast?
They resist
decolorization
by acid or alcohol
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What are acid fast bacilli (AFB)?
Red,
straight
or slightly curved rods
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What contributes to the acid fastness of mycobacteria?
High content of
mycolic acid
and
lipids
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What are the main components of the mycobacterial cell wall?
Outer
lipids
Mycolic acid
Polysaccharides (
arabinogalactan
)
Peptidoglycan
Plasma membrane
Lipoarabinomannan
(LAM)
Phosphatidylinositol mannoside
Cell wall skeleton
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Why are mycobacteria difficult to stain using ordinary methods?
Due to their high
lipid
content in the
cell wall
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What is the primary stain used in Ziehl-Neelsen staining?
Carbol fuchsin
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How is staining enhanced in Ziehl-Neelsen staining?
By
steam heating
to melt the wax
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What is used to decolorize nonacid-fast cells in Ziehl-Neelsen staining?
20%
sulfuric acid
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What is the purpose of counterstaining in Ziehl-Neelsen staining?
To provide contrast against red
AFB
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What color do pus cells appear in Ziehl-Neelsen staining?
Green
or
blue
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What is the most significant pathogen for humans in the Mycobacterium tuberculosis complex?
Mycobacterium
tuberculosis
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What is the primary disease caused by Mycobacterium tuberculosis?
Tuberculosis
(TB)
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What parts of the body can tuberculosis affect?
Lungs
, bones, joints, brain,
kidneys
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How many people died from TB in 2022?
1.3 million
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What is the second leading infectious killer worldwide?
Tuberculosis
(TB)
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What was the TB case rate in Malaysia in 2022?
77.8
cases per 100,000 people
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What are the high-risk groups for tuberculosis?
Close contacts with TB patients
Immunocompromised patients
Substance abusers and smokers
People in overcrowded conditions
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How is Mycobacterium tuberculosis transmitted?
Through
airborne
particles called
droplet nuclei
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What factors determine the likelihood of MTB transmission?
Number of
organisms
, air
concentration
, exposure time
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What is latent TB?
Infection
without active disease or symptoms
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What are the common symptoms of pulmonary TB (PTB)?
Fatigue
Weakness
Loss of appetite
Weight
loss
Fever
Night
sweats
Chronic
cough
with
sputum
Haemoptysis
Pleuritic
chest
pain
Dyspnea
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What investigations are used for PTB?
Full Blood Picture (
FBP
)
ESR
or
C-reactive protein
Chest X-ray (
CXR
)
Mantoux test
or
IGRA
Microbiological investigation
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What is the Mantoux test used for?
To determine infection with
Mycobacterium tuberculosis
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What is the cut-off value for the Mantoux test?
Varies
by
risk
group
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What do Interferon-Gamma Release Assays (IGRA) measure?
Immune reactivity to
M. tuberculosis
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What are the advantages of IGRA tests?
Single patient visit required
Results available within 24 hours
No false-positive from prior
BCG
vaccination
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What are the methods for microbiological investigation of PTB?
Microscopic examination for
AFB
Isolation by
culture method
Identification tests
Antimycobacterial Susceptibility Testing
(AST)
Nucleic acid amplification testing
(NAAT)
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What is the main clinical sample for PTB diagnosis?
Sputum
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What is the limitation of microscopic examination for AFB?
Low
sensitivity
requiring high
bacilli
count
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What are the culture methods for diagnosing tuberculosis?
Conventional solid media (e.g.,
Lowenstein-Jensen
)
Agar-based media (e.g.,
Middlebrook 7H10
)
Liquid/broth media (e.g.,
Middlebrook 7H9
)
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What is the major constraint of culturing mycobacteria?
Slow growth
requiring at least
4 weeks
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What are traditional methods for identifying mycobacteria?
Growth rate
, pigment production,
colony morphology
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What are the first-line anti-TB drugs?
Rifampicin
Isoniazid
Pyrazinamide
Ethambutol
Streptomycin
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What are the second-line anti-TB drugs?
Amikacin
Ofloxacin
Ciprofloxacin
Cycloserine
Enviomycin
Clarithromycin
Azithromycin
Para amino salicylic acid
Ethionamide
Clofazimine
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