Mycobacteriology Flashcards
Why do acid-fast bacteria stain acid fast?
Cell walls contain mycolic acid (long-chain fatty acids)
- When stained w/ special dye, cells can’t be decolorized w/ weak-acid-alcohol solution
- Acid-fast organisms stain red
What is the “ideal” contamination rate that mycobacteria labs should strive for when assessing their decontamination rate?
Mycobacterial culture contamination rate of 3-5% is tolerable
- < 3% → overly harsh decontamination
- > 5% → insufficient contamination
Which mycobacterium species are identified on the GeneXpert (Xpert MTB/RIF) system?
M. tuberculosis complex
What antimicrobial susceptiblity are identified on the GeneXpert (Xpert MTB/RIF) system?
Rifampin resistance
What two categories of solid media are used for the isolation of mycobacteria
Egg and agar
Give examples of egg-based media
- Lowentstein-Jensen
- American Trudeau Society
Give examples of agar-based media
- Middlebrook 7H10
- Middlebrook 7H11
What two types of broth media are used for the isolation of mycobacteria?
- MGIT
- Bactec Alert
Which type media, solid or broth, is able to recover organisms more quickly?
Broth
How do you set up a skin culture for mycobacteria, including temperature, media, etc.
Set up 7H10 @ 37C and 30C and set up MGIT @ 37C
Scotochromogen
Produces pigments independent of light exposure
Photochromogen
Produces pigments only after exposure to light
Nonchromogen
Never produces a pigment
Rapid grower
Requires < 7 days to produce colonies when subculutred onto certain media
Slow grower
Requires > 7 days to produce colonies on solid media under ideal culture conditions
What broth medium is used in MGIT, Bact/ALERT, and BACTEC Myco/F Lytic system?
Middlebrook 7H9
Which mycobacteria are nonpathogenic and may be isolated from tap water?
- M. avium
- M. genavense
- M. kansasii
- M. gordonae (common contaminant)
Which mycobacteria are acid-fast and modified acid-fast?
Acid-fast
- Gordonia spp (weakly-positive)
- Nocardia spp (positive, beaded appearance)
- Rhodococcus spp (weakly-positive)
- Segniliparus spp (strongly-positive)
- Tsukamurella spp (weakly-positive)
What do mycobacteria and the background look like when using the Ziehl-Neelsen or Kinyoun methods?
Mycobacteria are stained red; background is blue
List the strain of M. bovis which is used to produce the M. tuberculosis vaccine
BCG
List the species of Mycobacteria which cannot be cultured in the lab routinely (requires living cells)
- M. tuberculosis
- M. leporae
Differentiate the temperature(s) at which plates are incubated for skin cultures and sputum (respiratory) cultures
- Skin cultures are incubated at 30C
ALL cultures are set up on what media?
Solid and broth media
Outline the specimen collection recommendations for respiratory mycobacteria cultures
3 separate specimens must be collected at least 8 hours apart