Microbial Media and Measurement EXAM 3

Question 1

What are two specific things that can be measured when measuring microbial growth?

Answer 1

1. Changes in mass population.
2. Changes in number of cells in a population.

Question 2

What are direct and viable methods to count cells?

Answer 2

1. Counting chamber.
2. Standard plate count.
3. Flow cytometry.
4. Electronic/Coulter counter.

Question 3

What are the advantages of the counting chamber method?

Answer 3

1. Easy.
2. Inexpensive.
3. Relatively quick.
4. Useful for both eukaryotes and prokaryotes.

Question 4

What information does the counting chamber method provide?

Answer 4

1. Size.
2. Morphology.

Question 5

What is the drawback of the counting chamber?

Answer 5

Cannot distinguish between living and dead cells.

Question 6

What is the standard plate count method?

Answer 6

A diluted sample of bacteria is spread over a solid agar surface or mixed with agar and poured into a Petri dish. After incubation, the number of colonies are counted.
*Can use membrane filter to plate.

Question 7

What is CFU and how is it calculated?

Answer 7

1. Colony forming units, how many colonies formed.
2. # of colonies formed * dilution factor.

Question 8

What is flow cytometry?

Answer 8

Forcing the microbial suspension through a small orifice so that it is forced through a laser light beam. As the light is scattered, an event is registered with the # of events being equal to the # of cells.

Question 9

What does flow cytometry allow to be determined about the cells?

Answer 9

1. Size differences.
2. Internal complexity.
3. External structures.

Question 10

How does an electronic counter work?

Answer 10

The microbial suspension is forced through a small hole and electrodes on both sides of the hole run a current through it to measure electrical resistance. Electrical resistance increases when a cell passes through the hole, resulting in an event.

Question 11

What are the 3 ways to measure cell mass?

Answer 11

1. Dry weight.
2. Spectrophotometry.
3. Concentration of a particular cell constituent.

Question 12

How is dry weight measured?

Answer 12

Drying the plate out and weighing it.

Question 13

What are the drawbacks of dry weight measurement?

Answer 13

1. Time consuming.
2. Not very sensitive.

Question 14

What is spectrophotometry?

Answer 14

Sending a beam of light through a sample. The amount of light scattering is proportional to the cell biomass.

Question 14

How is the concentration of a particular cell constituent measured?

Answer 14

Spectrophotometry, but the amount of the constituent per cell must be known beforehand.
ex: Protein, DNA, chlorophyll, ATP.