Lab 8

Question 1

what do microbilogistsuse to isolate pure cultures?

Answer 1

selective, differential, and enriched media

Question 2

Types of medias?

Answer 2

• selective - selects certain bacteria causing them to grow and damage the others (some selective are differential)
• differential - contains chemical indicators that allow to tell the difference between bacterias
• enriched - contains chemical nutrients to support the growth of fastidious heterotrophs

Question 3

Mannitol salt agar

Answer 3

selective and differential
- contains 7.5% NaCl ( does not inhibit (halophilic)salt loving species) - staphylococcus
- selects for staph species
- differential medium = distinguish mannitol fermenters and non
Yellow zone is mannitol fermenters (produces acids making pH lower)
red is nonfermenters

Question 4

MacConkey agar

Answer 4

• differential medium
• Gram negative
• selective because crystal violet, and bile salts
  
  • inhibits growth of gram positive
• turns red because of low pH or acid
• turns white or colourless because they are non fermenting bacteria (no pH change)

Question 5

Phenylethyl alcohol agar(PEA)

Answer 5

Selective media non differential
- gram positive
gram negative tends to be more sensitive to affects of phenylethanol (interferes with DNA replication)

Question 6

Esoin methylene blue agar (EMB)

Answer 6

selective and differential
- Gram negative
- growth of positive is inhibited by the dyes eosin and methylene blue
- dark purple = fermentation occurs and pH decrease to acid (and dyes go to bacteria)
- green color = ph continued to drop