mycobacteria

Question 1

what kind of bacteria are mycobacteria

Answer 1

• can grow on artifical media
• have a cell wall
• single cells
• rods
• ziehl/neelsen acid fast positive
• mycobacteria

Question 2

which mycobacteria are medically important

Answer 2

M.tuberculosis – tuberculosis
M.leprae – leprosy
M.avium – disseminated infection in AIDS, infections in patients with chronic lung disease
M.kansasii – chronic lung infection
M.marinum – fish tank granuloma
M.ulcerans – buruli ulcer
Rapidly growing mycobacteria – skin and soft tissue infections

Question 3

what makes mycobacteria resistant to gram stain

Answer 3

the high lipid content with mycolic acids in the cell wall

Question 4

what stain do you use for mycobacteria

Answer 4

Ziehl-Neelsen stain

Question 5

describe the microbiology of mycobacteria

Answer 5

Aerobic, non-spore forming, non motile bacillus

Question 6

describe the cell wall of mycobacteria

Answer 6

Cell wall contains high molecular weight lipids

• Weakly gram-positive or colourless
• Survive inside macrophages, even in low pH environment

Question 7

give 3 characteristics of mycobacteria

Answer 7

Slow reproduction
Slow response to treatment
Slow growing

Question 8

generation time for M tuberculosis

Answer 8

15-20h

vs. 1h for common bacterial pathogens

Question 9

challenges with TB

Answer 9

mycobacterium tuberculosis has a thick lipid-rich cell wall

this makes immune cell killing and penetration of drugs challenging

Question 10

3 characteristics of TB

Answer 10

gradual onset of disease
takes much longer to diagnose
takes longer to treat

Question 11

3 types of TB

Answer 11

• primary TB
• latent TB
• pulmonary TB

Question 12

describe primary TB

Answer 12

initial contact made by alveolar macrophages

bacilli taken in by lymphatics to hilar lymph nodes

Question 13

describe latent TB

Answer 13

cell mediated immune response from T cells

primary infection contained but CMI persists

no clinical disease

detectable CMI to TB on tuberculin skin test

Question 14

describe pulmonary TB

Answer 14

granulomas form around bacilli that have settled in apex

in apex of lung there is more air and less blood supply (fewer defending white cells to fight)

TB may spread in lung causing other legions

could occur immediately following primary infection or a month later after reactivation

Question 15

where can TB spread beyond the lungs

Answer 15

TB meningitis
Miliary TB
Pleural TB
Bone and Joint TB
Genito urinary TB

Question 16

how does TB infect us

Answer 16

aerosol transmission
primary TB in lung
latent TB can remain for decades
can spread beyond lungs

Question 17

impact of granulaoma formation on mycobacteria

Answer 17

if the granuloma works - mycobacteria shut down metabolically in order to survive dormancy

but if fails eg in lung - this can result in the formation of a cavity full of live mycobacteria and eventual disseminated disease

Question 18

what does our body do to protect us against TB

Answer 18

• primarily controlled by macrophages
• requires a CD4 T cell response to be controlled
• involves many cells of immunity - formation of granulomas
• granuloma stability controls reactivation of TB

Question 19

what is Acid fast bacilli used for

Answer 19

stain used to identify organisms with wax-like, thick cell walls e.g. mycobacteria (resistant to gram stain)

Question 20

describe nucleic acid detection

Answer 20

Nucleic acid amplification test using PCR

Sensitivity 88%, specificity 98%

Recommended for rapid diagnosis in TB endemic countries

Question 21

resistance mechanisms for TB drugs

Answer 21

drug inactivation

drug titration

alteration of drug target

Question 22

how do we study TB

Answer 22

• animal models are a way to understand complex immunology
• mouse not a natural host of TB
• fish have their own mycobacterial species that can be used to help investigate host directed therapies

Question 23

are mycobacteria common causes of diseaee

Answer 23

yes - Mycobacteria are common causes of human disease causing major human illness such a tuberculosis and leprosy

Question 24

why do mycobacteria have unqiue staining patterns

Answer 24

They have unique lipid rich cell walls which give them unique staining patterns

Question 25

why are mycobacteria hard to culture

Answer 25

They are slow growing

Question 26

describe immune responses for TB

Answer 26

The immune response requires cell mediated immunity but many of the features of disease are associated with an aberrant immune response