Exercise 6

Question 1

Why should agar be cooled to 45C before pouring?

Answer 1

To reduce condensation and to provide easier handling of liquid medium.

Question 2

At what temperature does agar solidify and melt?

Answer 2

42C; 100C

Question 3

Value of differential media

Answer 3

produces color changes in response to differences in reactions by bacteria such as differences in fermentation of sugars; contains fermentable sugars or other differential agents.

Question 4

Value of selective media

Answer 4

inhibits the growth of certain organisms while allowing others to grow; contains inhibitory dyes or chemicals.

Question 5

Value of enrichment media

Answer 5

enhances the growth of certain desired organisms; contains special additives or nutrients to enhance growth.

Question 6

Value of transport media

Answer 6

allows transfer of specimen from patient to lab without affecting specimen in any way; contains chemicals that do not allow specimen to multiply or dry out.

Question 7

Value of all purpose media

Answer 7

allows for the growth of almost any type of bacterium; contains basic food materials.

Question 8

Contrast chemically non-defined culture media with chemically defined media. Provide some examples of both non-defined and defined foods that would be consumed by humans.

Answer 8

Chemically non-defined media contains unknown chemicals and/or unknown amounts of these chemicals. Nutrient Agar media that contain beef extract would be a good example. Humans consume hot dogs.
Chemically defined media can be reproduced exactly and contains very precise types and amounts of chemicals. Fermentation media such as Phenol red Glucose broth would be a good example. Sugar and water mixed together would be an example of a chemically defined medium.