week 5 Mycobacterial disease Flashcards
What shape are mycobacteria?
slender bacillus
What makes mycobacteria different to all other bacterial genera?
Unusual waxy cell wall:
High lipid content
Slow growing
Different media requirements
What is the staining character of mycobacteria?
They have poor take up with standard Gram’s stains.
They also retain certain stains without decolourisation by acid / alcohol because they are acid fast bacilli” (AFBs).
Stains used to identify them are:
Ziehl Neelsen (ZN)
Phenol auramine.
What type of pathogens are mycobacteria and waht type of infection do they cause?
They are Intra - cellular pathogens
They cause chronic infections with Latent phase of infection
What is the treatment of mycobacteria compared to other bacteria genera
They are treated with different antimicrobial agents compared to other bacteria.
The much longer courses of therapy.
Combination of agents to prevent resistance emergence
What mycobacteria causes Tuberculosis?
M. tuberculosis complex:
M. tuberculosis
M. bovis
What mcyobacteria caues leprosy?
M.leprae
Name 3 atypical mycobacteria that are assoicated with HIV and Fish tank granuloma?
M. avium complex
M. kansasii
M. marinum
In terms of M.tuberculosis what % of population is infected, deaths per year and what disase is a co infection with?
One third of world population infected
2 million deaths per year.
Co-infection with HIV: Sub-Saharan Africa
TB has become more common in the developed world because of what factors?
HIV infection
Breakdown of control programmes
Increased global migration from endemic areas
Increased travel
How does Tb spread?
Person to person - inhalation of infected respiratory droplets
What is the couse of the Tb infection?
1) Primary infection (usually pulmonary disease) - Some patients will be symptomatic (flu like) and some completely asymptomatic
2) Latent infection period
3) Reactivation of TB (does not occur in all people some people it will remain latent forever)
4) Dissemination (doesn’t disseminate to affect other organs in all people who get reactivation) NB. Primary infection may disseminate completely skipping the latent phase (this can happen in children)
What is the common site of primary Tb infection?
In the periphery of lung midzone
How does the body repond to Tb infection?
Tubercle formation (granuloma formation) via a cell mediated response
What is the structure, route and action of tubercles formed in TB?
There is a central area of epitheloid cells and giant cells. Have a surrounding lymphocytic cell infiltration, with central area caseous necrosis. Eventually getting fibrosis and calcification of lesions. The tubercles aim to contain the infection.
The bacilli slowly die or amy remain viable for 20 yeas.
What group of people are more likely to see a reactivation of tuberculosis?
Lowered immunity Western countries : over 50 year old, men Malnutrition Alcoholism Debilitating illness HIV infection
How can you test for Tb when there is absent or mild clinical symptoms
Chest X ray.
Tuberculin skin test conversion
What 3 diseases make it more likely for reactivation of tuberculosis to occur?
Silicosis, chronic renal failure, gastrectomy
Taking what drug can increase the chances of reactivation of tuberculosis and why?
Taking Anti TNFα blockade (e.g. infliximab)
This is because Role of TNF alpha is to maintain the granuloma
Where does TB usually residde and be reactivated? Explain why
In the Lung apices due there highest oxygen tension.
What is the consequence of reactivation on tubercles of Tb.
Tubercles coalesce and get caseous necrosis Can also get cavitation - leading to a higher organism load so greater risk of transmission
What are the symptoms of reactivation of TB?
Chronic productive cough Haemoptysis Weight loss Fever Night sweats.
What is the name for dissemianted TB? Who is susceptible?
Miliary tuberculosis.
Very young/old or those who are immunocompromised
What is the consequence of Miliary tuberculosis?
Causes erosion of necrotic tubercle into blood vessel in secondary diseases.
Get wide spread infection
