Introduction to Mycobacteriology Flashcards
Describe the cell wall of Mycobacteria
- High lipid content
- Mycolic Acids
- Lipoarabinomannan
- Waxy coat
**Peptidoglycan layer is linked to arabinogalactan which is then linked to high-molecular weight mycolic acids. The arabinogalactan/mycolic acid layer is overlaid with a layer of polypeptides and mycolic acids consisting of free lipids, glycolipids, and peptidoglycolipids.
**It looks like lipoarabinomannan runs the width of the entire cell wall
How do you stain Mycobacteria for Identification?
- Acid Fast Staining
- They are acid fast bacilli which means that they bind to carbol fuchsin dye ina way that is not removed by acid alcohol (Resistance to decoklorization by acid)
Draw out the important pathogens table on SLIDE 4
Write them all out.
What causes the majority of TB in the US?
Mycobacterium Tuberculosis
**M. Bovis can also cause TB disease in people
Describe transmission of Mycobactria TB Via the respiratory route
- Particles can remain suspended in air for several hours. Large droplets are carried:
- > 6mm away by exhaled air at 50 m/s (sneezing)
- > 2mm away at 10m/s from coughing
- <1mm away at 1 m/s from breathing
What is is a granuloma?
- a mass of granulation tissue, typically produced in response to infection, inflammation, or the presence of a foreign substance.
- Granulomas form when the immune system attempts to wall off substances it perceives as foreign but is unable to eliminate.
- May include Epitheliod macrophages, Langhans giant cells, lymphocytes, plasma cells, and some PMN’S
What is Caseous Necrosis?
Morphological changes indicative of cell death caused by progresssive enzymatic degradation.
**The cellular outline is lost and the tissue appears crumbly and cheese-like
What is the Ghon Complex
-Calcified focus of infection and associate lymph node
- Tan-yellow subpleural granuloma that is the characteristic gross appearance with primary TB.
- Over time the granulomas decrease in size and can calcify as a reaction to tissue damage
Describe Latent TB infection. How prevalent is it among persons that have TB?
- Persons infected with TB but not sick, have no symptoms, and cannot spread TB
- This is about 90-95% of persons with TB
What is secondary TB? How is Progressive disease characterized?
- Reactivation of a previous latent infection
2. Progressive disease characterized by weight loss, toxicity of tumor-necrosis factor, cavitation, and fibrosis
What are the 2 categories for persons at risk for developing TB active disease?
- Those who have an increased likelihood of exposure to persons with TB disease
- Close Contacts
- Healthcare workers
- Congregate settings (shelters, prisons, nursing homes)
- Intravenous drug abusers
- Recent immigrants
- Those with clinical conditions that increase their risk of progressing fro LTBI to TB disease
- HIV-1 infection/AIDS
- Transplanation
- Age < 2 years
What is the Mantoux tuberculin skin test (TST)?
- Also called PPD for purified protein derivative
- It is the standard method of determining whether a person is infected with M. TB
How is TST Administered?
By injecting 0.1ml of tuberculid purified protein derivative into the inner surface of the forearm with tuberculin syringe and bevel of the needle facing upwards
How is TST read?
Read within 48 and 72 hours after administration by measuring millimeters of the induration
How is TST interpreted?
- Measurement in millimeters of the induration
2. Person’s risk of being infected with TB and of progression to disease if infected