6.2: standard plate count

Question 1

What is the purpose of standard plate count?

Answer 1

-allows microbiologists to estimate the population density in a liquid sample by plating a very dilute portion of that sample and counting the number of colonies it produces

Question 2

The inoculum that is transferred to the plate contains a known proportion of the ?? sample because it is the product of a ??

Answer 2

-original
-serial dilution

Question 3

SERIAL DILUTION:
-the series begins with a sample containing an unknown ?? of cells and ends with a very ??

Answer 3

-concentration
-dilute mixture (few or no cells)

Question 4

Each dilution receives a known volume from the mixture in the previous tube and delivers a known volume to the next, reducing the cell density to:

Answer 4

-1/10
-1/100
-1/1000
-1/10000
-1/100000 in each step

Question 5

from OG broth to test tube #1=
from test tube #1 to test tube #2=
from test tube #2 to #3=
from test tube #3 to #4=
from test tube #4 to #5=

Answer 5

-10-2
-10-4
-10-5
-10-6
-10-7

Question 6

A sample of each dilution is then spread onto ?? to produce at least one countable plate

Answer 6

-agar plates

Question 7

What is the term for the number of colonies that develop on the plate?

Answer 7

-CFU (colony forming units)
-because colonies can form from a single cell or from groups of cells

Question 8

A countable plate is one that contains between ?? and ?? colonies.

Answer 8

-30 to 300

Question 9

A count lower than ?? colonies is considered statistically unreliable and greater than ?? is typically too many to be viewed as individual colonies on a standard 100mm petri dish

Answer 9

-30
-300

Question 10

test tube #1 to agar plate=
test tube #2 to agar plate=
test tube #3 to agar plate=

Answer 10

-10-3
-10-5
-10-6

Question 11

reciprocal dilution:

Answer 11

-how much you dilute your sample

Question 12

For example:
32 colonies on a plate 10-6 equals:

Answer 12

-32 times 1,000,000= 32,000,000=
-3.2X107 UFC/ml

Question 13

In the spread plate technique, 120 colonies were found on the plate where 0.1 ml of a 1:100,000 dilution was plated. How many colony-forming units per ml were there?

Answer 13

-1.2X108 UFC/ml

Question 14

A plate with a sample volume of 10–6 mL produced 259 colonies. What was the original cell density?

Answer 14

-2.59x108 CFU/ml

Question 15

If you spread 0.1 mL of a 10–3 dilution tube on a plate, and 43 colonies grew. What was the original cell density in the sample?

Answer 15

-4.3x105 UFC/ml

Question 16

The number of serial dilutions that are necessary for a standard plate count assay will depend on:

Answer 16

-The estimated density of cells in the original sample

Question 17

In the spread plate technique, 256 colonies were found on the plate where 0.1 ml of a 1:10,000 dilution was plated. How many colony-forming units per ml were there?

Answer 17

-2.56x 107CFU/ml

Question 18

If you spread 0.1 mL of a 10–2dilution tube on a plate, and 54 colonies grew. What was the original cell density of the sample?

Answer 18

-5.4X104 CFU/ml

Question 19

A plate with a sample volume of 10–7mL produced 72 colonies. What was the original cell density?

Answer 19

-7.2x 108 CFU/ml

Question 20

In a viable plate count, each ____ represents a ____ from the sample population.

Answer 20

-colony
-CFU