Lecture 10

Question 1

What two methods to measure the cell growth?

Answer 1

Cell mass or cell number

Question 2

What indicates a microbial growth?

Answer 2

A growth in cell mass or cell number,

Question 3

Define microbial growth.

Answer 3

An increase in volume and in mass, then divides.

Question 4

What does microbial growth usually indicates?

Answer 4

Cell multiplication.

Question 5

Explain how to measure cells by the Dry weight determination.

Answer 5

A collection of cells is made from a measured volume of the broth culture. Then you dry the cells overnights in an over of 90 degrees celsius then weight the dried cells.

Question 6

By what qualificative measure is the cells reported?

Answer 6

x mg/mL.

Question 7

True of false, the Dry weight determination method distinguishes between living and dead cells.

Answer 7

False, they do not distinguish the difference.

Question 8

Explain the carbon, nitrogen, proteins content determinations for weighing cells.

Answer 8

This method states that with the increase of these elements, the cell mass increases.

Question 9

True or False. The carbon, nitrogen, protein content determination does not determine the dead to living cells?

Answer 9

True.

Question 10

Describe the turbidity measurement method.

Answer 10

This is the preferred method as it’s easily performed. As growth occurs, so does the turbidity of the broth (becomes opaque). The liquid is transferred to a cuvette where it’s placed in a spectrophotometer and reading is obtained. This method does not distinguishes living to dead cells.

Question 11

Define the measurement of cell mass to cell number.

Answer 11

Cell mass measurement mesures the group and cell count is individual cells.

Question 12

Define the measurement of the cell number using the direct microscope count method.

Answer 12

The cells are counted using a microscope and a special slide known as a counting chamber. This method does not differentiates living to dead cells.

Question 13

Define the Coulter counter method for cell number count.

Answer 13

This is an electronic counter that counts cells that are suspended in liquid. This method does not differentiates living to dead cells.

Question 14

Define the plate count method for cell number count.

Answer 14

This method is primarily based on assumptions that each cell deposited on or in the agar medium multiplies from one visible colony.

Question 15

As the pour plate method for cell number count, what if you have 1 mL of a suspension containing 100 bacteria / mL is plated out. How many colonies should you expect?

Answer 15

100 colonies to develop.

Question 16

Define “plated out”.

Answer 16

The addition of the inoculum to the agar medium and districting it over the surface or throughout the agar.

Question 17

Define confluent growth.

Answer 17

Also know as confluent lawn, it’s a covering of growth or colonies spread across the plate, making it difficult to differentiate the cells due to the lack of separation.

Question 18

If you have a suspension containing 2,500,000 bacteria / mL that is plated out, should you expect 2,500,000 colonies? Elaborate.

Answer 18

No, the confluent growth would occur. You could use other means to measure the growth.

Question 19

What means of measurement would be most suitable to measure large numbers of expected colony growths.

Answer 19

Making suitable dilutions of the suspended and plating out these dilutions.

Question 20

What does TNTC signify?

Answer 20

Too numerous to count.

Question 21

When given a bacterial culture ans asked to determine the number of visible cell/ mL, what should be the first step to follow?

Answer 21

Prepare a series of ten-fold dilutions.

Question 22

What frequency should the plating be done at?

Answer 22

Triplicate.

Question 23

True or false. You will need to apply aseptic technique to not contaminate and decrees the count.

Answer 23

False. Aseptic techniques are use to AVOID inflating the count due to contaminates.

Question 24

Plates containing between how many colonies should be used in determining the cell count.

Answer 24

30-300

Question 25

True or False. The number of viable bacteria /mL is determined with a specific formula.

Answer 25

True.

Question 26

Why do we name this method the viable count?

Answer 26

Because it’s capable of detecting the cells that are capable of growth on the plating medium under incubation conditions.

Question 27

Name three count errors.

Answer 27

1-pipette errors
2-counting errors
3-uneven distribution of the cells on the agar.

Question 28

What is the percentage of discrepancies acceptable for errors in count.

Answer 28

10 % is acceptable.

Question 29

Why do we say that the viable counting method gives a minimum estimate of the viable cells? Name 2.

Answer 29

1-Some organisms occur in clusters and do not break up during the procedure.
2-If 2 or more cells are close together and do not break up- a colony develops.

Question 30

True or false. Only cells that can grow on the plating medium can be accounted for and not all cultures will permit the growth of all species of bacteria.

Answer 30

True.

Question 31

How do you collect data for bacterial growth such expressed in a graphic?

Answer 31

By inoculating bacteria in a suitable medium and measuring the broth at different time periods.

Question 32

Describe a graphic curve when the viable count method is employed?

Answer 32

A upward slope, plateau and a slope (resembling a mountain).

Question 33

Describe a graphic curve when turbidity is used.

Answer 33

A upward slope that goes up and plateau and a straight line.

Question 34

Express the 4 phases of a typical growth curve when the cells are plotted as a function of time.

Answer 34

1-lag phase
2-logarithmic growth (exponential) also called the log phase
3-maximum stationary phase
4-death phase

Question 35

Explain the following statement with 2 supportive explanations. Microbial populations do not grow exponentially, at high rates, for very long. Growth is usually limited by one of these.

Answer 35

1-Exaustion of nutrients

2-the accumulation of toxic products of metabolism.

Question 36

To say the development of microbial population is self-limited is true or false?

Answer 36

True