W05_04 Mycobacteria Flashcards
what is an m.tuberculosis complex?
a group of mycobacteria spp. that cause similar symptoms of tuberculosis. m. tuberculosis and m. bovis are most common
microbiology of mycobacteria?
non-gram staining; aerobes; don't form spores; non-motile; 10,000 cells/mL needed to see with light microscopy
which stains do we use for mycobacteria?
acid-fast stain (ziehl-nielesen or kinyoun);
fluorochrome dyes are more sensitive
how long does it take for mycobacteria to grow?
15-20 hours
non-tuberculous myco. are divided between slowly growing (>7d) and rapidly growing (~7d) and intermediate (7-10d)
okay.
can you culture m.leprae in vitro?
no.
what’s the gold standard for identifying mycobacteria?
culture.
nucleic acid amplification is an alternative for the ribosomal RNA/DNA
what’s the reservoir for mtb complex and m.leprae?
warm blooded animals;
in contrast, NTM are usually environmental, free-living, and usually around water
what percentage of reported TB in canada is by foreign born individuals?
66%
where is the primary focus of tuberculosis?
middle and lower lung zones
where is the secondary focus of tuberculosis?
upper lungs, lymph nodes, vertebral bodies, meninges
what’s the ghon complex?
granuloma PLUS an active lymph node (see two bright spots on CXR)
how many people become latent TB carriers after infection?
95%; 5% will go to actually get the disease
what’s miliary TB?
when the bacteria enter circulation and spread throughout the body, causing lesions everywhere
know latent vs. active TB
okay.
how do monocytes respond to the TB infection?
get activated with TNFa and prevent the intracellular replication of Mtb;
macrophages produce IL-1, TNFalpha
how do Th1 cells respond to TB? (cytokines?)
these CD4+ cells respond with IL-2, IFNy, IL-12 (all inflammatory)
what’s the mantoux test?
tuberculin skin test, using purified protein derivative 5 TU.
a positive TB skin test is defined by how big of a bump
> 10mm diameter.
>5 mm diameter in certain risk groups
false negatives: active TB, immunocompromised
false positives: other mycobacteria, BCG vaccine
how does the interferon gamma release assay (IGRA) work?
blood drawn and t cells exposed to Mtb. IFNy measured.
management of active TB?
2 or more drugs: isoniazid, rifampin, pyrazinamide, ethambutol
management of latent TB?
isoniazid for 9 months
note: BCG does NOT protect against infection.
it only prevents clinical disease and dissemination
what’s another name for hansen’s disease?
leprosy
how is m.leprae transmitted?
we don’t know; likely airborne, not contact
what’s the pathogenesis of m.leprae?
infects and multiplies in macrophages. they can resist oxidative killing by their surface phenolic glycolipid
what are the two extremes of leprosy?
tuberculoid,
lepromatous
what are clinical features of tuberculoid leprosy?
red blotchy lesions;
localized anaesthesia;
thickening of nerve sheaths;
what are clinical features of lepromatous leprosy?
local anesthesia causing secondary infections leading to disfigurement
reservoir for m. avium complex?
environment and birds
main disease of m. avium complex?
TB or disseminated in AIDS patients
