mycobacteria Flashcards
what are the 2 key examples of a mycobacteria
M.tuberculosis – causes TB ie. consumption
M.leprae – leprosy
what is the shape of mycobacteria ?
bacilli or cocci?
slightly curved,
beaded bacilli
are mycobacteria aerobic or anaerobic?
aerobic
can mycobacteria form spores and are they motile
non-spore forming
non-motile
why can’t mycobacteria be stained by the gram stain ?
what is the preferred staining method used
high lipid content in cell wall makes them resistant. gram stain appears weakly positive of colourless
acid fast staining
how does the ziehl-neeslesn stain work (a type of acid fast stain) ?
The Ziehl-Neelsen stain uses basic fuchsin and phenol compounds to stain the cell wall of Mycobacterium species.
it is a rapid and low cost test to detect acid-fast bacilli
what colour does mycobacteria appear after a ziehl-neeslesn stain
acid fast bacteria (mycobacteria) will stain red
are mycobacteria fast or slow growing ?
slow
what challenges does the thick lipid rich cell wall of mycobacteria present when we are trying to treat these infections?
eg. tuberculosis
Hard for immune cells to kill it
Hard for drugs to penetrate it
why does the fact that Mycobacterium tuberculosis is slow growing make it harder to treat and diagnose?
Gradual onset of disease
Therefore immune response is gradual
Takes much longer to diagnose because
symptoms don’t show for months
Takes longer to treat
how does TB transmit?
aerosol (coughing)
what is latent TB?
TB can remain dormant in the hosts macrophages for decades
it becomes invisible by being metabolically inactive
it creates cavities of dead tissue through the formation of granulomas and necrotic tissue
what is the more old fashioned technique for diagnosing TB?
Use solid L.J SLOPE culture - selective to TB, but takes 8 weeks which is too long
what is the newer better method for diagnosis TB?
use nucleic acid detection for a more rapid diagnosis
Nucleic acid amplification test using PCR
Using DNA to see if TB is present
what is an indirect method to detect TB when symptoms are not yet present?
the tuberculin skin tests (TST)
uses the immune response to see if ever been infected
