T3: AFB Lab Practical

Question 0

Nucleic acid probes are available for which mycobacterium species?

Answer 0

M. Tuberculosis, M. avium-intracellulare complex, M. gordonae, M. kansasii

Question 1

Requires heme to grow, optimal temp is 30’C, generally Isolated from immunocompromised individuals

Answer 1

M. Haemophilum

Question 2

List three characteristics of Nocardia

Answer 2

Gram-positive, modified acid-fast stain positive (Red), Kinyoun acid-fast stain neg (blue)

Question 3

Never produces pigment

Answer 3

Nonchromogen

Question 4

Produces pigment only after exposure to light

Answer 4

Photochromogen

Question 5

Produces pigment independent of light exposure

Answer 5

Scotochromogen

Question 6

What reagent must be added to a negative nitrate test? Why?

Answer 6

Negative must be confirmed by adding zinc dust. You add zinc just to confirm nitrogen gas. (Clear=pos, Red=neg)

Question 7

Niacin accumulation test is used to differentiate between which two mycobacterial species?

Answer 7

M. tb (+, yellow) and M. bovis (-, no color change)

Question 8

Name there characteristics of M. Mucogenicum

Answer 8

Rapid grower, partially acid-fast, non-chromogen, wet/mucoid looking colonies

Question 9

How is Kinyoun stain interpreted?

Answer 9

Red=positive, blue/purple=negative

Question 10

The phenomenon known as cording is observed in which mycobacterium species?

Answer 10

M. Tuberculosis=virulent

Question 11

Name 3 characteristics of M. Marinum

Answer 11

Grows at 28°C, cutaneous infection associated with fish tanks or salt water, photo chromogen

Question 12

What type of stain is the auramine-rhodamine (AR) stain? List some advantages and disadvantages

Answer 12

Fluorochrome stain
A: most sensitive stain, stains both viable and nonviable organisms, performed directly on specimens
D: won’t stain rapid growers

Question 13

What reagents are used in the N-acetyl-L-cysteine method of decontamination?

Answer 13

N-acetyl-L-cysteine, NaOH, Sodium citrate, neutralizing buffer, phenol red

Question 14

Purpose of N-acetyl-L-cysteine

Answer 14

Works as a mucolytic agent

Question 15

Function of NaOH

Answer 15

Functions as a bacterial decontaminant

Question 16

Function of sodium citrate

Answer 16

Binds to heavy metals in the specimen

Question 17

Function of neutralizing buffer

Answer 17

Stabilizes the pH and stops the decontamination process

Question 18

Function of phenol red

Answer 18

Present in the digestion solution to monitor pH

Question 19

How is a semi-quantitative catalase test interpreted?

Answer 19

Column >or equal to 45mm is positive, <45mm is negative

Question 20

Incubation requirements for MAC w/o crystal violet

Answer 20

Ambient air at 28 to 30°C for 7 days

Question 21

Which two mycobacterial species is the sodium chloride tolerance test useful in identifying? Results?

Answer 21

M. Abscessus (+) and M. chelonae (-)

Question 22

Incubation requirements for the tween-80 hydrolysis test?

Answer 22

35 to 37°C ambient air for 10 days

Question 23

How is the tween-80 hydrolysis test interpreted?

Answer 23

Pink/red=positive, orange/no color change=negative

Question 24

What is HPLC and how do we use it in the lab?

Answer 24

High performance liquid chromatography; provides an ID based on mycolic acid pattern, analysis of mycolic acids contained within mycobacterial cell walls

Question 25

How do mycobacteria typically appear in gram stain?

Answer 25

Beaded it ghosted GPR (can look similar to strep)

Question 26

List three characteristics of M. gordonae

Answer 26

Found in tap water, scrotochromogen, not a pathogen

Question 27

Three characteristics of M. tuberculosis

Answer 27

Rough and buff, slow grower, non-chromogen, must confirm ID using biochemical methodS

Question 28

Which mycobacterium species demonstrates candycane striations?

Answer 28

M. Kansasii

Question 29

What is the MB Bottle used for?

Answer 29

Liquid medium used for blood, put into bacT alert instrument, has heme (choc) in media to break apart RBCs to release organism

Question 30

What is the MP Bottle used for?

Answer 30

Liquid medium used for all specimen except blood, put into BacT alert instrument, clear if uninoculated

Question 31

What is 7H10 slant used for?

Answer 31

All purpose, enriched for AFB, clear agar, if from a superficial source a second slant is set up and incubated at 30°C

Question 32

Purpose of chocolate slant?

Answer 32

Used for specimens rich in heme (BM, blood), incubated at 30°C

Question 33

Purpose of LJ slant?

Answer 33

Lowenstein-Jensen, used in biochemical testing

Question 34

Function of 7H10 plate?

Answer 34

Used when isolation of colonies is desired

Question 35

What PPE is used in the AFB lab?

Answer 35

Gloves, down, mask (N95 or better), foot covers

Question 36

What unique characteristic is seen in M. szulgai?

Answer 36

Smooth or rough colonies, nitrate positive, scotochromogen at 37°C, photochromogen at 25°C

Question 37

Remember…modified acid fast is a weaker decolorizer (partially acid fast) whereas Kinyoun positive is for _____ A-F organisms

Answer 37

Strong