lab quiz 2

Question 1

Match the following reagents with the purpose they serve in Gram stain:

Answer 1

Crystal violet primary stain

Iodine mordant

Alcohol decolorizer

Safranin counterstain

Question 2

Which of the following statements is true regarding Gram+ bacteria? Check all that apply.

Answer 2

cell wall has a thick peptidoglycan layer

teichoic acids are present

lipopolysaccharide is absent

cell envelope lipid content is relatively low

Question 3

Which step in the Gram stain is the most critical?

Answer 3

decolorization

Question 4

In Gram staining, the alcohol acts on:

Answer 4

membrane lipid

Question 5

What would most likely occur if you applied alcohol for only 1 second?

Answer 5

Gram-negative bacteria would not decolorize like it should, and all bacteria would therefore remain purple (Gram-positive)
+

Question 6

What would most likely occur if you drenched the bacterial smear in alcohol for 1 minute?

Answer 6

All purple stain would escape as the cell wall of both Gram-positive and Gram-negative bacteria would dissolve

Question 7

How long does it take to perform and analyze the Gram stain?

Answer 7

A few minutes

Question 8

You have just performed Gram stain, and forgot to add the iodine. What colors would your Gram-positive (G+) and your Gram-negative (G-) bacteria look like?

Answer 8

G+ pink

G- pink

Question 9

You have just performed Gram stain, and forgot to do the alcohol decolorization step. What colors would your Gram-positive (G+) and your Gram-negative (G-) bacteria look like?

Answer 9

G+ purple

G- purple

Question 10

You have just performed Gram stain, and forgot to add safranin. What colors would your Gram-positive (G+) and your Gram-negative (G-) bacteria look like?

Answer 10

G- purple

G+ colorless

Question 11

You have just performed Gram stain, and realized that you have reversed the order between crystal violet and safranin (safranin-iodine-alcohol-crystal violet). What colors would your Gram-positive (G+) and your Gram-negative (G-) bacteria look like?

Answer 11

G+ purple

G- purple

Question 12

Match the following bacteria with their shape and arrangement.

Answer 12

Staphylococcus aureus Gram+ cocci

Bacillus subtilis Gram+ rod

Serratia marcescens Gram- rod

Chromobacterium violaceum Gram- rod

Question 13

Match the following dyes with their purpose for this week’s staining:

Answer 13

Calbofuchsin primary stain for acid-fast

methylene blue counter stain for acid-fast

malachite green primary stain for endospore staining

Safranin counter stain for endospore staining

Question 14

Arrange the steps of acid-fast smear preparation in the correct order.

Answer 14

1 smear S. aureus in a drop of water

2 air dry and heat fix

3 Chop M. smegmatis on top of S. aureus

4 heat fix and leave slide on warmer until ready to stain

Question 15

The reason you need to use steam heating for acid-fast staining is because:

Answer 15

High mycolic acid (wax) content in the cell wall of Mycobacterium
++

Question 16

Which of the following is the differentiating step in acid-fast stain?

Answer 16

Acid alcohol

Question 17

Place the staining procedure (acid-fast or endospore stains) in the correct order.

Answer 17

1 place a piece of bulbous paper on top of smear

2 saturate bulbous paper with primary dye

3 heat stream for 8-10 min, do not let slide dry

4 remove paper rinse and/or decolorize

Question 18

Which of the following diseases could be diagnosed with acid-fast stain? Mark ALL that apply.

Answer 18

Tuberculosis
Leprosy
Cryptosporidium infection

Question 19

Which bacteria are we using for endospore stain? Check all that apply.

Answer 19

Clostridium sporogenes
Bacillus cereus

Question 20

Match the components of endospores with the materials they are made of.

Answer 20

Core DNA, ribosomes, etc

Membrane phospholipids

Cortex peptidoglycan

Coat proteins

Question 21

Which of the following makes endospores resistant to extreme environments? Check all that apply.

Answer 21

DNA binding proteins
Low (no) metabolic activity
Cortex + Outer coat
Dipicolinic acid + Ca2+

Question 22

Why does the endospore stain exercise call for an older (48 hour or 5 day) culture of Bacillus?

Answer 22

A new cultured of microbes needs enough time to be subjected to enough stress before it trigger sporulation.

Question 23

If you were given a mixed culture containing gram-positive and gram-negative bacteria, and you need to separate them, what type of media would you use?

Answer 23

Selective

Question 24

Choose the bacteria that are on your unknown ID gram-positive list. Check all that apply.

Answer 24

C. xerosis

S. aureus

B. cereus

Question 25

Choose the bacteria that are on your unknown ID gram-negative list. Check all that apply.

Answer 25

K. pneumoniae
E. coli
S. enterica

Question 26

Phenylethyl alcohol agar (PEA) is a(n):

Answer 26

selective medium

Question 27

Bacteria in the genus Staphylococcus can grow on MSA because:

Answer 27

they live in high salt condition on the human skin

Question 28

Match the following bacteria with the expected growth pattern on MSA:

Answer 28

Staphylococcus aureus yellow growth and halo

Staphylococcus epidermidis Pink or red growth, no halo

E. coli poor growth or no growth

Question 29

Match the following color of phenol red with the correct pH range:

Answer 29

Yellow pH < 6.8

Red pH = 7.4 to 8.4

Pink pH > 8.4

Question 30

Match the following ingredients of MacConkey to their specific functions.

Answer 30

Inhibitors bile salts and crystal violet

pH indicator neutral red

differential substrate lactose

Nutrients pancreatic digests, peptic digest

Question 31

Match the following bacteria with the expected growth pattern on MacConkey:

Answer 31

Staphylococcus aureus poor growth or no growth

E. coli (fermenter) pink to red growth

Providencia stuartii (nonfermenter) colorless growth

Question 32

Match the following color of neutral red with the correct pH range:

Answer 32

pink or red pHH < 6.8
Colorless pH > 6.8