MICRO Y1 S1: Culturing

Question 1

types of rich agar

Answer 1

• nutrient agar
• horse blood
• chocolate

Question 2

nutrient agar

Answer 2

• agar, peptone, yeast extract
• for most non-fastidious bacteria (don’t require much nutrition to grow)

Question 3

horse blood agar

Answer 3

• nutrient agar + 5% sterile horse blood
• detection of haemolysis (breakdown of RBC) to differentiate bacteria
• Y-haemolysis (no colour): no breakdown
• a-haemolysis (green): partial/incomplete breakdown
• B-haemolysis (clear): complete breakdown

Question 4

chocolate agar

Answer 4

• horse blood agar but heated to disrupt RBC > release extra growth factors
• incubated in 10% CO2

Question 5

selective and differential media + give 2 e.g.s

Answer 5

• selective: supports growth of desired microbe and inhibits growth of others
• differential: to differentiate b/n microbes
• e.g. macconkey and mannitol salt

Question 6

MacConkey agar

Answer 6

• selective and differential media
• contains bile salts which inhibit non-GIT pathogens (selective) - used for gram-negative enteric bacteria
• lactose provides a source of C for normal flora > produce acid > red stain
• pathogenic bacteria don’t use lactose so stain cream (differential)

Question 7

mannitol salt agar

Answer 7

• selective and differential media for S. aureus
• selective agent: high salt conc.
• differential agent: mannitol and neutral red indicator