M4: Identifying Bacterial Cultures

Question 1

red colonies on MacConkey agar

Answer 1

bacteria = lactose fermentor (lac +)

Question 2

white/tan colonies on MacConkey agar

Answer 2

bacteria = lactose non-fermentor (lac -)

Question 3

yellow surrounding colonies on MacConkey agar

Answer 3

pH > 8

Question 4

dark red/pink colonies on MacConkey agar

Answer 4

pH < 6.8, and bacteria = lac +

Question 5

red colonies on Sorbitol MacConkey agar

Answer 5

non-pathogenic E coli

Question 6

white colonies on Sorbitol MacConkey agar

Answer 6

pathogenic E coli

Question 7

acidic colonies on Sorbitol MacConkey agar

Answer 7

non-pathogenic E coli

Question 8

neutral/basic colonies on Sorbitol MacConkey agar

Answer 8

pathogenic E coli

Question 9

purple/black colonies on EMB agar

Answer 9

bacteria = lac +

Question 10

white/tan colonies on EMB agar

Answer 10

bacteria = lac -

Question 11

colonies w/metallic green sheen on EMB agar

Answer 11

bacteria = E coli

Question 12

fermentation’s affect on pH

Answer 12

able to ferment –> more acidic

non-fermentor –> basic

Question 13

yellow colonies on Mannitol Salt Agar

Answer 13

pathogenic Staphylococci (able to ferment mannitol –> lower pH)

Question 14

red colonies on Mannitol Salt Agar

Answer 14

non-pathogenic Staphylococci (can’t ferment mannitol –> higher pH)

Question 15

non-selective agars (4)

Answer 15

• LB agar
• TSAYE
• Chocolate agar
• Blood agar

Question 16

selective agars for gram-positive bacteria (2)

Answer 16

• Columbia CNA agar

- Mannitol Salt agar

Question 17

agars for E coli (3)

Answer 17

• LB agar (to grow)
• Sorbitol MacConkey agar (to differentiate patho vs. non-patho)
• EMB (to ID presence of E Coli)

Question 18

agar for Streptococcus

Answer 18

blood agar

Question 19

agar for fastidious pathogenic bacteria

Answer 19

chocolate agar

Question 20

agar for Salmonella

Answer 20

MacConkey agar

Question 21

agar for Staphylococci

Answer 21

Mannitol Salt agar