block 3- TB Flashcards
mycobacterium tuberculosis (phylum Actinobacteria)
Phylogenetically Gram positive, =does not stain
-aerobe, high %GC
- Non-motile rods, no spores
- Slow growth, obligate pathogen
- Unusual thick cell envelope- dull and look wrinkly under electro -microscope
- has a type 7 secretion system = virulence factor
structure of the cell envolope of myobacterium
-Negative with Gram stain= due to membrane
- Special acid fast staining= stain cannot be washed out with acid because of the thick membrane
- Impermeable/resistant
- No LPS
- Outer membrane contains
“mycolate” virulence
factors
uses of Acid-fast staining
- diagnosis by microscopy= quicker than by cultures
-cheap and specific for Mycobacterium - PCR is sensitive and fast
- Culture useful to test
antimicrobial sensitivity
(patience, decontamination,
good aseptic technique)
How long can it take someone to get ill after being infected with TB
-shortest a few weeks and they will have symptoms
-longest= years or decades= symptom free.
This is called a latent infection
how do we obtain mycobacterium Tb
- ## via respiratory transmission(obligate human pathatgon)
What does Tb do to Alveolar macrophages?
engulf M. tuberculosis (innate
immune response)
- M. tuberculosis blocks macrophage function: special
type 7 secretion system, specialised lipids
- leads to a Granuloma response (recruitment of immune cells to
contain a pathogen that cannot be eliminated)
TB spread around the body
1.latent= most common=only one granuloma which successfully contains it
2. lung disease= multiple granulomas,fever,cough,weight loss
-extrapulmonary tuberculosis= more common in children and with HIV
BCG vaccine
Mycobacterium bovis highly related to M. tuberculosis (most genes 99.9% identical
-Attenuated strain M. bovis Bacille Calmette-Guérin (BCG) no longer caused disease
-deletes the type 7 secretion system
- Widely used in countries with high TB incidence
- Good protection against miliary TB in children, variable protection in adult
-
how does your environment give you a higher chance of catching TB
– Living conditions (transmission in crowded housing)
- Nutrition, smoking, air pollution (immune function)
- Access to diagnosis & treatment (cure vs continued disease and
transmission)
- Vaccination – BCG is a live attenuated vaccine
- useful but imperfect protection
treatment for TB
-multidrug therapy = Combination of 4 antimicrobials for 6 months
-ifampicin,Isoniazid,Pyrazinamide,Ethambutol
- Multidrug therapy is needed to prevent relapse
(kill every single bacterium)
- Multidrug therapy is needed to prevent
development of drug resistance
-effective but hard to follow
what is granuloma ?
collection of immune cells that gather together to surround and “wall off” the bacteria, preventing them from spreading throughout the body.
-it happens when M.TB survives macrophages so more immune cells gather
streptococcus pneumoniae
Member of normal oropharyngeal microbiota:
This means that Streptococcus pneumoniae is often found in the oropharynx (the part of the throat behind the mouth) of healthy people without causing harm. It’s part of the normal bacteria that live there.
Bullet-shaped diplococci that are sensitive to optochin and bile:
Shape: The bacteria are described as bullet-shaped and occur in pairs (called diplococci).
Sensitive to optochin and bile: These are special tests that help doctors identify this specific bacterium in the lab. When exposed to optochin or bile, this bacterium will stop growing or break down, which is a clue for diagnosis.
Produces α-haemolysis on blood agar:
When this bacterium is grown in the lab on a special medium called blood agar, it causes α-haemolysis. This is a partial breakdown of red blood cells, creating a greenish discoloration around the bacterial colonies.
Genetically flexible due to high rates of recombination resulting in expression of different capsular serotypes:
Genetically flexible: The bacterium can easily change or recombine its genes, which gives it the ability to express many different capsular serotypes (different versions of its outer protective layer). This genetic flexibility helps it avoid the immune system and makes it harder to fight with vaccines.
Causes pneumonia, otitis, and meningitis:
This bacterium is known to cause several diseases, including:
Pneumonia: Lung infection.
Otitis: Ear infection.
Meningitis: Infection of the brain and spinal cord lining.
In short, Streptococcus pneumoniae is a type of bacteria that normally lives in the throat but can sometimes cause serious infections like pneumonia and meningitis. It has unique features, such as its bullet-like shape, ability to break down red blood cells in a specific way, and a genetic capacity to change itself, making it harder to fight with treatment
virulences factors of S.pnemoniae
-has Capsule: pneumococci with
23 types of capsules which protect the bacteria from being attacked by immune cells
* IgA1 protease= This is an enzyme that breaks down IgA1, an important antibody that helps protect mucosal surfaces (like the lining of the mouth and throat). By destroying IgA1, the bacteria can evade the immune defenses in these areas and cause infections more easily.
* Pneumolysin
* Hyaluronidase
* Surface adhesins
* Anticomplement factors
non-encapsulated S.pneumoniae
-growing number of theses strains
-* Cause mainly non-invasive disease: conjunctivitis (85%)
and otitis media (8%
-Very high rates of antimicrobial resistance
* Increasing spread due to application of capsule-based
vaccines
pneumolysin
-a toxin produced by Streptococcus pneumoniae. It’s known as a pore-forming toxin, which means it creates holes (or pores) in the membranes of human cells
-inhibits neutrophil chemotaxis= makes it harder for the immune system to respond to infection
