Myco. TB Flashcards
Myco. TB is non-…, non-…., and non-…?
non-motile, non-sporing, non-capsulated
Is TB gram positive or gram negative and why?
Gram positive: it has thick peptidoglycan in outer membrane
What shape is TB?
rod shape
Do TB need oxygen to survive or not? What specific name are they given?
TB require oxygen to survive and are called OBLIGATE AEROBES
State the layers of TB membrane, starting from cell membrane (bottom)
cell membrane, thick peptidoglycan arbinogalactan mycolic acid myoside
What is a special function of the arbinogalactan found in the cell membrane?
it allows the bacterium to survive inside macrophages by preventing the fusion of lysosome and phagosome
What is the function of the mycolic acid in TB membrane?
makes the cell wall less permeable to certain substances such as ANTIBIOTICS - make it difficult for antibiotics to penetrate the bacterial wall
What staining is used for TB?
Gram staining - positive but not very strong
Zeel Niesen - red rods on blue cells due to acid fast
TB is an acid fast bacterium, explain why?
Has wax-like, nearly impermeable cell walls; contain mycolic acid + large amounts of fatty acids, waxes + complex lipids
What culture medium is used for TB?
At what temp. and pH?
How long is the growth rate?
Lowenstein Jensen
Petragnani
Finleisen
37 degrees
pH 6-6.8
4-6 weeks
Do they form colonies? what shape and what do they look like?
Yes they form colonies, R-shape colonies and look like bread crumbs
What is the generation time?
12-18h
Does TB produce any endo/exo toxins?
NO
State the virulence factors of TB
Capable to survive in macrophages due to arbinogalactan in the membrane (prevents the fusion of lysosome and phagosome)
Cord factor: mycoside - causes serpentine growth and inhibits leukocyte migration + disrupts mitochondrial respiration and oxidative phosphorylation
How is TB transmitted?
Humans: inhalation drinking contaminated cattle milk (cattles: M.bovis) through skin conjuctiva (eyes)
Who is at high risk from TB?
Prisoners (congregated settings) HIV P with weakened IS P in poverty and homeless Alcoholism + drug addicts Steroid use
Stages of TB/ clinical forms
1) Primary: cough/ blood in sputum/ weakness/ temp/ weight loss + TB in lungs
2) Secondary (reactivation) : affects upper part of lungs - extrapulmonar localisation = kidneys, BM, LN, brains, CNS, gut, sepsis
What type of immunity takes place?
Cell mediated immunity = means no Ab are produced, cells like T cells - cytotoxic cells work together to kill the bacteria
What is the microbiological diagnosis of TB? 3 steps involved
Specimens of TB taken: CF , blood, urine
following: Microscopy - Culture and Isolation - Identification
1) Microscopy: stains are used for the microscopy
- Ziehl Neelsen (acid fast reaction)
- Immunofluorescent assay (IFA)
2) Culture + Isolation:
- Lowenstein Jensen = egg containing medium for primary isolation of the TB
- Preliminary treatment = specimen is decontaminated from other microbes
- Culturing: incubate culture for 4-6 weeks
What 2 immunological tests are used for TB? Describe each test
1) Mantoux Test = in vivo - “TB SKIN TEST”
- injecting 0.1ml into skin
- produces wheal 6mm-10mm in diameter
- read the diameter reaction after 48-72h
- measure diameter
POSITIVE TEST - diameter > 15mm
2) Interferon gamma = in vitro
- test to detect interferon gamma especially produced by sensitised with TB Ag blood lymphocytes
Outline the prophylaxis for TB
- isolation of the sick
- specific type of prophylaxis
- antibacterial prophylaxis
- long term treatment
What is the specific prophylaxis for TB?
-BCG vaccine (vaccine for TB and leprosy) - immunised at birth and 7yrs after again
When is antibacterial prophylaxis used for TB?
for those ionised for contact persons
What are the long term treatments for TB?
- RIFAMPIN = inhibits RNA synthesis
- Streptomycin = Antibiotic
- Isoniazid = inhibits cell wall synthesis
- Ethambutol = inhibits cell wall synthesis
