8 - mycobacterium

Question 1

mycobacterium morphology

Answer 1

rod shaped bacteria with mycelia acid content of their cell walls

Question 2

mycobacterium growth

Answer 2

grow very slowly, need special growth media

some are classified as rapid growers

Question 3

mycobacterium gram stain

Answer 3

cannot be easily seen on gram stain because they take up crystal violet poorly, use ZN stain instead

Question 4

mycobacterium cell wall

Answer 4

peptidoglycan in the cell wall is joined to a layer of mycolic acid with a layer of outer lipids
waxy hydrophobic cell wall

Question 5

mycolic acid

Answer 5

thick hydrophobic cell wall makes mycobacteria hardy and resistant to drying

Question 6

ZN stain

Answer 6

Ziehl-Neelsen stain
utilises strong carbon fuchsin at a higher concentration than that used in the gram stain
causes mycobacteria to appear red

Question 7

what colour does mycobacteria appear in ZN stain

Answer 7

red

Question 8

process of ZN stain

Answer 8

§ The specimen to be stained is heat fixed to a glass slide which is flooded with strong carbol fuchsin
§ The slide is heated until vapour comes off it
§ The carbol fuchsin is avidly taken up by the mycolic acid
§ Acid-alcohol mix used to decolourise the bacteria
§ Bacteria containing mycolic acid resist decolourisation and remain red
§ A blue counterstain (methylene blue) is used to provide a contrasting colour to the background

Question 9

what is used to decolourise bacteria in ZN stain

Answer 9

acid-alcohol mix

Question 10

why is mycobacteria not decolourised during decolorisation in ZN stain

Answer 10

mycelia acid resists decolorisation so mycobacteria remain red

Question 11

what colour counterstain is used in the ZN stain

Answer 11

blue - methylene blue

Question 12

mycobacteria often referred to as

Answer 12

○ Mycobacteria are often referred to as acid-fast bacilli, or ‘AFBs’, as they resist the acid decolourisation step of the ZN stain

Question 13

3 broad classifications of mycobacteria

Answer 13

• mycobacterium tuberculosis
• mycobacterium leprae
• atypical mycobacteria

Question 14

atypical mycobacteria also called

Answer 14

• NTM - non tuberculous mycobacteria
  - MOTB - mycobacteria other than TB
  - MOTT - mycobacteria other than tuberculosis

Question 15

mycobacterium tuberculosis complex

Answer 15

○ Mycobacterium tuberculosis complex

		- M tuberculosis 
		- M bovis 
		- M bovis BCG
		- M africanum 
		- Others

Question 16

mycobacterium leprae complex

Answer 16

not part of a complex

Question 17

mycobacterium rapid growers

Answer 17

mycobacterium fortuitous complex, mycobacterium chelonae/abscessus complex

Question 18

□ Most common cause of NTM infections

Answer 18

• Mycobacterium avium complex

Question 19

□ Second most common cause of NTM infections

Answer 19

• Mycobacterium kansasii

Question 20

• Mycobacterium avium complex

Answer 20

□ Most common cause of NTM infections
□ M avium
□ M intracellulare
□ Others

Question 21

• Mycobacterium fortuitum complex*

Answer 21

□ M fortuitum

□ Others

Question 22

• Mycobacterium chelonae/abscessus complex*

Answer 22

□ M chelonae
□ M abscessus
□ Others

Question 23

two other NTMs

Answer 23

• Mycobacterium marinum

- Mycobacterium ulcerans