Mycobacterium L13 Flashcards
what bacteria are mycobacteria
gram-positive
is mycobacteria motile
non-motile
is mycobacteria sporing
non-sporing
does mycobacteria have a capsule
non-capsulate
what is mycobacteria respiration
aerobic
what shape are mycobacteria
rods
how many mycobacteria are there
more than 85
where are mycobacteria found
mostly found in soil and fresh water
what are mycobacteria like in liquid culture
often appear to grow as filaments due to the mycolic acid in cell wall
when are mycobacteria visible
upon disturbance rods or cocci are visible
what are the environmental stresses that mycobacteria are resistant to
- disinfectants
- host defences
- antibiotics
what is on top of the peptidoglycan layer
mycolic acid layer
why are mycobacteria resistant to staining
mycolic acid layer
why are mycobacteria difficult to see
resistant to stain
what are mycobacterium spp. characterised by
thick, lipid-rich cell walls that are resistant to decolorisation after staining with carbol fuschin (Ziehl-Nielsen Acid Fast)
what test is used to characterise mycobacterium
Ziehl-Nielsen Acid Fast
what does the mycolic acid bind to
carboxylic acid group of mycolic acid binds to red fuschin dye and isn’t removed by acid-alcohol wash
can mycolic acid be removed
binds irreversibly to mycolic acid
what is the counterstain for mycolic acid
methylene blue counter stain
what can stained sputum samples show
examined by microscopy and diagnosis may be confirmed in an hour
what dye is seen, using what
phenol auramine fluorescent dye visualised with a UV microscope
what does mycobacterium tuberculosis
main cause of primary and post-primary human tuberculosis
what does mycobacterium leprae cause
leprosy
what does mycobacterium leprae infect
only humans
and 7-banded armadillo
what is mycobacterium tuberculosis complex
four closely related species: M. tuberculosis M. bovis M. microti M. africanum
what is mycobacterium tuberculosis
a chronic granulomatous disease
what does mycobacterium tuberculosis cause
Granuloma-accumulation of macrophage
what is mycobacterium tuberculosis cultured on
3 to 8 weeks to culture on Lowenstein-Jensen agar slopes
how long does it take to detect mycobacterium tuberculosis
10 days to detect presence using 14CO2 production
where is 14C from in mycobacterium detection
palmitate in broth
how long does PCR detection usually take
<24hrs
how is mycobacteria usually spread
inhalation of infected respiratory droplets
how can mycobacterium survive
in alveoli, phagocytosed by macrophage
bacteria prevent lysosomes fusing with phagosomes and therefore survive
how does mycobacterium spread from alveoli
Other cells such as those lining the alveoli become infected with Mycobacterium
what is primary tuberculosis
mycobacterium infected in alveoli
what will mycobacterium cause in body
Inside body will trigger an immune response this can be done through phagocytosis
what does mycobacterium do during replication
kill the host cells during replication, triggering recruitment of more macrophage
what does mycobacterium do when emerging from dead macrophage
re-infect new macrophage
how long does primary tuberculosis cycle last
cycle may only last a short while and is normally asymptomatic or presents as mild fever
what happens when macrophage present mycobacterium to lymphocytes
- more lymphokines are released
- more macrophage are therefore activated (macrophage flood to infection site)
- inflammation begins (will trigger more immune response)
- macrophage surround infection site forming a tubercle
what causes inflammation in primary tuberculosis
a lot of macrophage infected, get a ball in the centre and this causes inflammation
what are the mycobacterium surrounded by in primary tuberculosis
cells of the tubercle containing the Mycobacterium are surrounded by collagen, wrap it up to keep out of the way
characteristic about TB
how long does the tubercle last
in some cases, over time the interior of tubercle dies
what causes the tubercle to die
incomplete proteolytic digestion of tissue results caseous necrosis
what causes a tuberculous cavity
centre of the tubercle may liquefy, rupture and fill with air tubercle rupture, contents ooze out, tissue damage and hole in the lung tissue where the tubercle was
what is the immune system like in the Ghon complex
Often the immune system and bacteria exist in equilibrium at this point
what are the possibilities in the Ghon complex
immune system may clear the bacteria
Mycobacterium may remain dormant but are capable of infecting other tissues
what happens if bacteria are cleared in Ghon complex
calcium will be deposited around the tubercle over time resulting in the formation of a Ghon complex
what is Ghon complex a good marker for
TB when Xray done, dark spots of calcium
what is the effect of primary tuberculosis - Ghon complex
Lung function can be significantly reduced
when does another infection cycle begin
if the bacteria succeed over the immune system the tubercle is ruptured and the infection cycle begins once more
post primary tuberculosis it is possible for infected macrophage to migrate through the blood and lymph to key organs such as:
- spleen
- kidney
- bone marrow
- spinal cord
- brain
what happens to the tissues that become infected
slowly degenerate
why are many common antibiotics ineffective
because mycobacterium grow so slowly the drugs are cleared before affecting the bacterial load
what are the drugs of choice for mycobacterium tuberculosis treatment
Isoniazid for 6 months
Rifampin for 6 months
Pyrazinamide for first 2 months
Ethambutol for first 2 months
what does isoniazid do
micolic acid synthesis inhibition
what does rifampin do
polymerase inhibiton
what does pyrazinamide do
unclear
what does ethambutol do
micolic acid synthesis inhibition
what is MDR
multi drug resistance
what is RR-TB
rifampicin-resistant TB
what is MDR-TB
Multi-drug resistant TB, defined as resistance to rifampicin and isoniazid
what is BCG
bacille Calmette-Guérin
how is mycobacterium tuberculosis preventing infection
immunisation with BCG live attenuated vaccine
what does BCG vaccination do
does not prevent infection but limits proliferation of the organisms
what are individuals that have had close contact with a case of tuberculosis
treated prophylactically with isoniazid
what is a challenge for TB control programs
HIV and AIDS
many AIDS-related deaths are due to TB
what are the two leprosy forms
progressive or non progressive
what is TT
Tuberculoid leprosy (TT) strong immune response, small numbers of bacilli
what is LL
Lepromatous leprosy (LL) poor immune response but large numbers of bacilli
what is tuberculoid leprosy characterised by
- blotchy red regions on the skin
- anaesthetic regions on the face, body and extremities
what type of leprosy is tuberculoid leprosy
non progressive
what is tuberculoid leprosy
localised tissue damage, but it non progressive, immune system will kill it
how is tuberculoid leprosy equivalent to post-primary tuberculosis
vigorous cell mediated immune response leads to phagocytic destruction of bacteria and sometimes an exaggerated allergic responses
what leads to lepromatous leprosy
Large numbers of bacteria accumulate in the infected areas
what does lepromatous leprosy cause
- palpable thickening of peripheral nerves, as bacteria multiply in nerve sheaths
- progressive destruction of nasomaxillary facial structures
- nasal mucosa is usually loaded with bacteria
what does palpable thickening of peripheral nerves cause
thickening of nostrils, ears and cheeks, loss of eyebrows
what is the problem with dapsone
resistance
what is used to overcome dapsone resistance
used in conjunction with
- rifampicin
- clofazimine (binds to guanine in DNA)
- normally given for two years, often longer, sometimes for life
what can destruction of organisms cause
a severe inflammatory response which is sometimes fatal
what can cure leprosy
effective multi-drug treatment for all types of leprosy
where are more mycobacterium cases emerging
emerging mycobacterium infection of HIV patients
what mycobacteria can infect skin
marinum
tuberculosis
ulcerans
what skin infections can be caused
fish tank granuloma
buruli granuloma
