E: Measurement of Microbial Growth

Question 1

What is total count

Answer 1

number of all cells living and dead

Question 2

What is viable count

Answer 2

number of living cells only

Question 3

What is microscopic cell count

Answer 3

counting chamber that holds a specific volume of the sample. can use a dark-field microscope and a formula to determine total count

Question 4

What is plate count

Answer 4

using pour plate or spread plate, colonies are counted to determine the viable count

Question 5

What is membrane filtration

Answer 5

used for samples that are expected to have a very low concentration of bacteria. eg. water

Question 6

Describe the steps in membrane filtration

Answer 6

a 100ml sample is runned through a filter with a pore size of 0.45 um. filter is then placed bacteria side up on a plate. nutrients will diffuse through filter. isolated cells will form colonies that can be counted to determine a viable count

Question 7

What is a spectrophotometer

Answer 7

used to measure turbidity of a sln of bacteria (not absorbance).

Question 8

How does a spectrophotometer work

Answer 8

particulate matter like bacteria scatters light. machine measures amount of light passing through the sln and converts it mathematically to OD (optical density)

Question 9

If optical density increases, what happens to turbidity

Answer 9

turbidity increases

Question 10

Describe a standard curve

Answer 10

reading must be correlated with plate count (same species in same media) to produce viable count (only useful on samples over 10⁷)