Mycobacterium Flashcards
How long does it take to grow TB on a plate?
3-6 weeks for primary isolation
All are aerobes
Hallmark of TB stain
Acid fast staining
- 60% lipid (most are 15%) so it takes up stain easily, but cant get rid of it
Which bacteria results in the most deaths?
M.TB
Transmission of TB
Aerosol
- respiratory droplet nuclei
- small particles capable of reaching alveolus
How many people exposed to TB will result in an infxn?
How of those with a TB infxn will progress to primary disease?
How many of those that contain the TB infxn will result in reactivation?
30%
- due to inadequate non-immunologic defense
5% of 30%
- due to inadequate immunologic defense
5% of the 95% that was contained will reactivate
- due to inadequate immunologic defense.
TB replicates in macrophages, where do they get carried to?
draining lymp nodes –> blood –> other organs
What confers resistance to INH?
Down regulation of katG
*katG (bacterial catalase peroxidase)- normally activates INH
When are individuals who are recently infected, most prone to progressing?
1-2 yrs
classic pattern of reactivated (post primary) TB
Upper lobes
High risk conditions for TB
High risk:
- HIV
- close contact
- recently infected
- abnl chest x ray
Intermediate risk:
- Transplant or immunosuppression
- Medical conditions
- Injection drug users
- . Recent arrivals from endemic contries
Risk for new infxn
- Contacts to infxn diseases
- Health care workers
- Other workers exposed to TB cases
Pulmonary sx of TB
- COugh >3 weeks
- Chest pain
- Hemoptysis
Systemic:
- Fever
- Chills
- Night sweats
- Appetite loss
- Weight loss
diagnostic work up of TB
- 3x Sputum sample –> AFB (acid fast bacillus) smear
- Mycobacterial culture
- Species ID
- Drug susceptibility testing
What do you suspect if TB is resistant to Rifampin?
most likely multi drug resistant TB
Tx of TB
4 for 2 months
2 for 4 months
If you have no risk for TB, how many mm does it have to be to be considered positive on PPD?
What about if you are a child?
Immunosuppressed?
> 15 mm
Child: >10
Immunosuppressed: 5mm
Quantiferon IT
3 antigens
Draw 3 tubes of blood
Put an antigen into each tube (- control, + control, Ag)
- measure serum gamma interferon [ ] if Pos = TB
TSPOT TB
Use 2 antigens
Stimulate lymphocyte over night and observe plate
- each spot is a lymphocyte producing interferon
8 or more = Pos test
What test is best done on BCG vaccinated indiv?
Interferon Gamma release assays (IGRAs)
- high specificity
Shortest drug regimen for TB
Isoniazid and rifapentine
- longer half life
- 3 months (not 4 with RIF)
- less hepatotoxic
1 killer of AIDS pts
M.Tb
Nontuberculous Mycobacteria
Exposed to them a lot
Not transmissible fr hu to hu
- VERY resistant to Ab
Most common sx is in the lung
Which state has the most NTM ?
Hawaii
Cali
Florida
- hot and humid
- people moving there already having dz (arizona)
Lady wyndamere syndrome
Tall, Skinny women more likely to get TB
*named after play: Women may be suppressing their coughs
What stain uses the property of the acid fastness of mycobacteria to differentiate it form other bacteria?
Ziehl Neelson
What type hypersensitivity is TB?
Delayed type IV hypersensitivity
- disease manifestations are due to hypersensitivity to tubercular antigens and not the result of bacterial toxin
What type of immunity (cellular or humoral or both) plays a role in M. tuberculosis?
Cellular only
- develops at 2-6 weeks, dominated by TH1
- reactivation is usually due to cellular immune fxn
*humoral immunity has no major role in recovery or protection or diagnostic use.
SapM
protein produced that cleaves late endosomal vesicular PI3P in the phagosome membrane, which prevents fusion of the phagosome with the lysosome
Man-LAM
inhibits phagosomal maturation
Cathelicidin
kills intracellular M. tuberculosis in hu macrophages
Does drug resistance for TB come from acquiring foreign DNA that encodes resistance?
No.
Most accurate way to dz leprosy?
bioposy
or
- 1/m hypopoigmented skin patches
- 1/m thickened peripheral nerves
- (+) skin smear
