Microbio- mycobacterial infections Flashcards
2 broad groups of mycobacteria - phylogenetically and clinically
Clinically: Mycobacterium tuberculosis + Non-tuberculous mycobacteria
Phylogenetically - slow growing + rapid growing
Mycobacteria - morphology? do they grow fast?
Non-motile, rod shaped
Slow growing compared to other bacteria
Stains for Mycobacteria
Ziehl- Neelsen
Auramine
NTM - how do people get infected i.e. where do they come from?
Found in water and soil
No person-to person transmission
Name 3 slow growing NTM
M. avian intracellular
M. marinum
M. ulcerans
NTM often acquired from swimming pools
M. marinum
Which NTM results in huge chronic painless ulcers
M. ulcerans
Which NTM is associated with HIV? how does this same organism affect immunocompetent individuals
M. Avium
Will affect immunocompetent people if they have pre-existing bronchiectasis/cavities
M. abscessus/chelonae/fortuitum
What type of mycobacteria are these? when are they seen?
Rapid growing, in hospital settings
Requirements for diagnosis of NTM?
Lung disease AND
1 +VE sputum culture OR \+ve BAL OR \+ve biopsy w granulomata
Leprosy - name the causative organism
Mycobacterium leprae
Which type of leprosy –> limb loss?
Paucibacillary tuberculoid
V LITTLE PERSON-PERSON TRANSMISSION
Which type of leprosy is contagious?
Multibacillary lepromatous
A 23 year old HEALTHY male is aCLOSE CONTACT of a person with smear positive pulmonary TB, What is his lifetime risk of developing active TB?
10%
One person is exposed to TB. What are the 5 possible outcomes
- Uninfected
- Infection is cleared
- Contained infection (localised infection)
- Active TB
- Latent TB (at risk of developing active TB w triggers)
- Uninfected
- Infection is cleared
- Contained infection (localised infection)
- Active TB
- Latent TB (at risk of developing active TB w triggers)
^who will have a +ve mantoux test?
Latent TB
Active TB
3 most common forms of MTB
M. tuberculosis
M. bovis
M. africanum
Which form of TB is associated with contaminated milk
M. bovis
Why is TB so infectious? how is it transmitted?
Particles <10mcM therefore suspended in air and infectious for 30 mins
V low infectious dose
How can TB be prevented? Give 3 ways
- BCG vaccine
- -ve pressure isolation
- Detection of cases (mantoux)
Skin manifestation of TB?
Erythema nodosum
Wtf is miliary TB
Widespread and looks dotty on CXR
Due to haematogenous spred
What is post-primary TB? TF?
Latent TB that is reactivated approx 5 years later.
EtOH excess, immunosuppression, malnutrition, aging
Where are caseating granulomas seen in pulmonary TB?
Lung parenchyma
Mediastinal LNs
often upper lobe
In extra-pulmonary TB, which LNs tend to be affected?
cervical
Eggs of extra pulmonary TB?
LNs Peritoneal --> ascites GU --> renal disease Spine (eg Potts) Miliary Meningitis
Ix for clinical suspicion of TB
Sputum x 3 Histology Biopsy Stain for acid fast bacilli Culture NAAT - detecting mutations for MDR IGRA Mantoux test
Gold standard Ix for TB? how long does it take for results?
Culture
Takes up to 6 weeks!
what is IGRAs?
is it better than mantoux test?
detection of antigen specific IFNgamma production
It doesn’t cross react with BCG vaccine whereas Mantoux does (thus mantoux gives false positive result)
Tx of TB
RIPE
all drugs for 8 weeks. RI for a further 8 weeks
SEs of TB meds
Rifampicin - CYP450 inducer
Isoniazid - peripheral neuropathy
Pyrazinamide - hepatotoxicity
Ethambutol - visual disturbance
How to improve adherence to TB Tx?
Directly or video observed therapy
How does MDR arise?
Inadequate treatment or spontaneous mutation
Risk factors for MDR TB
Poor adherence to TB tx
HIV
Known contact
How does management of MDR TB differ to non-MDR?
Longer regimen
Quinolones, ahminoglycosides,
Why is diagnosis of TB so hard in HIV+ patients?
Less classical history - more likely extra pulmonary
Smear and mantoux test is more likely to be -ve despite active disease
