Bacterial Diagnostics

Question 1

What do the different vacutainers contain?

red, red/gray, purple, green, green/gray, light blue

Answer 1

Red: no additive, or with clot activator
Red/Gray: clot activator, serum separator
Purple: EDTA anticoagulant
Green: lithium or sodium heparin anticoagulant
Green/Gray: lithlium heparin and plasma separator
Light Blue: sodium citrate anticoagulant

Question 2

What is the proper order of collecting urine samples?

Answer 2

1) Cystocentesis (needle through skin)
2) Catheter (often contaminated)
3) Free catch
4) Environment

Question 3

What are the different stains used?

Answer 3

Histopathology (H&E)
Wright’s/Romanowsky/Diff-Quick
Gram Stain
Acid-Fast Stain

Question 4

Describe the walls of Gram neg and Gram pos bacteria

Answer 4

Gram-Neg: thin peptidoglycan layer, and outer membrane
- stains pink
Gram-Pos: thick peptidoglycan layer, not outer membrane
- stains purple

Question 5

What are the steps of the Gram Stain?

Answer 5

1) application of crystal violet dye
2) application of iodine (mordant)
3) alcohol wash
4) application of safranin

Question 6

What does MacConkey agar test, and what is a positive reaction?

Answer 6

• tests gram-negative bacteria for lactose fermentation

- positive produces acid, lowers pH, and turns agar from yellow to pink

Question 7

What is the gold standard for bacterial identification and classification

Answer 7

16S ribosomal RNA PCR

Question 8

What are the benefits of using ID test strips?

Answer 8

save space, time, and raw materials

Question 9

Explain the Direct ELISA test

Answer 9

• sample with suspected antigen placed on surface of plate

- an antibody to that antigen is used to determine presence of the antigen

Question 10

Explain the Indirect ELISA test

Answer 10

• antigen already on plate
• put sample on plate, if sample has antibody, it will bind
• use secondary antibody with enzyme to determine presence of first antibody

Question 11

Explain the Sandwich ELISA test

Answer 11

• capture antibody on plate
• if sample has antigen, it will bind
• use two other antibodies to determine presence of antigen

Question 12

Explain agglutination using an antigen

Answer 12

• antigen placed on latex beads
• if IgM specific for that antigen is in the sample, it will attach to several latex beads, holding them together so they are visible

Question 13

Explain agglutination using antibodies

Answer 13

• antibodies placed on latex beads

- if antigen is in sample, it will attach and hold the beads together so they are visible

Question 14

What is the Kirby-Bauer Test

Answer 14

• using antibody discs placed on agar
• see if organisms are resistant or sensitive
• based on minimum inhibitory concentration