Mycobacterium and tuberculosis Flashcards
what causes tuberulosis
mycobacterium tuberculosis
obligate aerobe , facultative intracellular parasite
high lipid content
how is Tb spread
commonly spread in small droplets being coughed or sneezed in air
at risk groups of TB
immunosuppressed
those exposed to TB in youth
high rate country
malnourished
primary Tb
droplet nuclei inhaled
if taken up by alveolar macrophages, not activated due to lipids(therefore live within macrophages)
reach the alveoli - infection begins commonly in base of lungs
what does the immune system do when reacting to Tb
granuloma in lung (Ghon focus)
what is a primary complex
Ghon focus and enlarged lymph nodes
how can secondary TB occur
reactivation of dormant mycobacteria
reinfection in person previously sensitised to mycobacterial antigens
where is reactivation most common
at apex of lungs
highly oxygenated
what happens in the lungs during 2nd TB
caseous centres of tubercles liquefy
large antigen load, bronchi walls become necrotic rupture
cavity formation
oragnsism spills intoairway, coughed out therefore infectious
military tuberculosis
immune system overwhelmed
organism into bloodstream
x ray represents milit seeds
infection vs disease
1) TB infection
- Organism present
- Tuberculin skin test positive
- Chest X-ray normal
- Sputum smears negative
- Sputum culture negative
- No symptoms
- Not infectious
- Not defined as a case of TB
2) TB lung disease
- Organism present
- Tuberculin skin test positive
- Lesion on chest X-ray
- Sputum smear positive
- Sputum culture positive
- Symptoms
- Infectious
- Defined as a case of TB
what are symptoms causes by
cytokine activity
symptoms of TB
cough (with/without sputum) anorexia swollen glands fever night sweats sense of tiredness and being unwell
standard recommend regime for TB
isoniazid
rifampicin
pyraniamide
ethambutol
for 2 months
followed by isoniazid and rifampicin for 4 months
treatment min 6 months to prevent resistance developing
how to prevent MDR - TB
standardised drug regimes
directly obeserved treatmetn
good supply of quality drugs
isolation of infectious pts
what is the vaccine called and used fro
BCG - bacille calmée gurein
protection in childhood
only prevents disease not infection
invalidates tuberculin skin test
HIV and TB
HIV increases risk of acquireing TB
TB makes HIV worse
types of drug resistant TB and their treatment ? look lec/ppw when exam
MDR TB -
XDR TB -
obstacles to TB control
1) Lack of financial resources
2) social instability
3) HIV epidemic
- HIV/AIDS doubles the TB death rate
4) drug resistance
5) stigma
how to diagnose TB
chest x ray tuberculin ests blood tests microscopy sputum culture nucleic acid detection tests and typing
chest x ray
indicates but does not confirm
tuberculin tests
heaf, tine Mantoux
ascertains infection rather than disease
T spot - TB and quantiferon gold blood tests
Blood tests to replace tuberculin tests
- detects reactive T cells
- specific for MTB
- not affected by BCG – vaccine
microscopy
Rhodamine aura mine (fluorescence) more sensitive than ziehl Nelson stain (red)
sputum
- homogenise using sputasol
- Decontaminate (4% NaOH Petroff) - to kill all bacteria but leave mycobacterium behind
- concentrate (centrifugation)
- Middlebrooks medium
- Lowerstein Jensen-medium
- 4-6 weeks for visible colonies to form
- liquid media (kirchners)
automated culture
can use liquid media - media with fluorescent reaction
can also use laminar strip- looks for specific antigen
nucleic acid detection test
specific to DNA of organism
molecular method
look for rifampicin resistant genes, likely to be mutli drug resisant
how can you tell if TB is multi drug resistant strain
look for rifampicin resistant gene
how do the drugs work
targets the genes
typing
once organisms is identified and isolated it can be typed
- can follow epidemic spread via typing
methods of typing
methods
1) variable number of tandem repeats
2) Mucobacterial interspersed repetitive units
the number given is the fingerprint of the strain of mycobacteria of TB
