Culturing and Counting Bacteria using Serial Dilution

Question 1

How is bacteria grown?

Answer 1

Bacteria/Microorganisms may be grown in the laboratory if supplied with suitable physical conditions, nutrients and water.

Different species vary in their requirements and usually grow over a range of temperatures and pH values, with an optimum within the range.

Nutrients are supplied in nutrient media and include: carbon compounds, usually organic compounds such as glucose; nitrogen, organic or inorganic; growth factors such as vitamins and mineral salts.

Question 2

What is culture media?

Answer 2

A nutrient containing gel or fluid that can be used for growing microorganisms. These are added to plates. A common type of nutrient is agar (a setting agent made from seaweed)

Question 3

What do nutrients for microorganisms include?

Answer 3

Nutrients for the microorganisms are supplied in nutrient media and include:
carbon compounds, usually organic compounds such as:
-glucose;
-nitrogen, (organic or inorganic)
-growth factors such as
- vitamins and
- mineral salts.

Question 4

What are the different nutrient media?

Answer 4

-Blood agar plate
-Chocolate agar plate
-Nutrient agar plate

Question 5

What makes total viable count and total cell count the same?

Answer 5

the original culture in both usually requires dilution e.g. by ten-fold dilution or serial dilution, in order to provide a final number within a countable range.

Question 6

what is cell count worked out in?

Answer 6

cells/ml

Question 7

What is a haemocytometer used for?

Answer 7

used to count cells

Question 8

How does a haemocytometer work?

Answer 8

The haemocytometer consists of a thick glass microscope slide with a rectangular indentation that creates a precision volume chamber. This chamber is engraved with a laser-etched grid of perpendicular lines. The device is carefully crafted so that the area bounded by the lines is known, and the depth of the chamber is also known.

By observing a defined area of the grid, it is therefore possible to count the number of cells or particles in a specific volume of fluid, and thereby calculate the concentration of cells in the fluid overall

Question 9

what is serial dilution?

Answer 9

the stepwise dilution of a substance in a solution

Question 10

what do we use serial dilutions for?

Answer 10

to establish cell count and see levels of bacteria (see levels of leptospirosis)

Question 11

why are petri dishes with bacteria placed in an incubator?

Answer 11

so its grown in the desired temperature

Question 12

How to carry out a serial dilution?

Answer 12

1. Using a marker pen, label the test tubes 10-1 10-2 10-3 10-4 and 10-5
2. Using a first pipette, drop 9ml of dilution liquid into each test tube
3. Then, using a second pipette, drop 1ml of E.coli into the first test tube labelled 10-1
4. Mix this thoroughly
5. Then, transfer 1ml of the solution from the first test tube (10-1) into the second test tube labelled 10-2 and mix this thoroughly.
6. Keep consecutively transferring this solution into the following test tube after mixing it thoroughly until it is transferred into test tube 10-5 and mixed thoroughly.
7. Prepare 4 petri dishes and label each petri dish with 10-2 10-3 10-4 and 10-5, excluding 10-1
8. Keeping the petri dishes within the sterile area (created by blue Bunsen burner flame), transfer 1ml of the solution from each test tube, excluding 10-1, into the corresponding plate using the labels, and using a separate pipette for each transfer.
9. While doing this, lift the lid of the petri dish open by only a small amount each time.
10. Use an L shaped spreader on each dish to spread the bacteria, so there is an equal distribution of it.
11. Incubate bacteria for 24 hours

Question 13

What technique is used to find viable cell count?

Answer 13

serial dilution

Question 14

In serial dilution, a known volume of organism is added to an (?) plate

Answer 14

Agar

Question 15

What is a limitation of using a Haemocytometer?

Answer 15

if sample is not dilute enough, you cant count the cells

Question 16

A haemocytometer slide is?

Answer 16

Thick

Question 17

in serial dilution: Number of colonies on plate x reciprocal of dilution factor=

Answer 17

number of bacteria/mm3

Question 18

On a Haemocytometer grid, how many medium squares are there?

Answer 18

16

Question 19

serial dilution is used to calculate…

Answer 19

the number of cells in the original inoculum

Question 20

What technique can be used to find bacteria in a liquid medium?

Answer 20

Turbidimetry can be used to find bacteria in a liquid medium

Question 21

Counting only living cells is an example of

Answer 21

Viable cell count

Question 22

bacteria on a plate can be seen by…

Answer 22

the naked eye

Question 23

using a haemocytometer, total cell count is calculated by…

Answer 23

Living cells + Dead cells

Question 24

using a Haemocytometer, how is viability calculated?

Answer 24

Live cell count / Total viability

Question 25

viable cells replicate and show visible colonies because…

Answer 25

they are alive

Question 26

in serial dilution, why are the plates incubated

Answer 26

to allow the bacteria to grow (and in the desired temperature)

Question 27

What technique can be used to find total cell count?

Answer 27

turbidimetry

Question 28

What is the difference between total cell count and viable cell count?

Answer 28

The key difference between total cell count and viable cell count is that total cell count estimates all cells including both living and dead microbial cells in a sample while viable cell count estimates only the living microbial cells in a sample.

Total cell count is independent of the growth of colonies on agar plates while viable cell count is a growth-based technique and it depends on the growth of microbial colonies on agar plates.

Question 29

What is Total Cell Count?

Answer 29

Total cell count is the method that involves counting all cells in a known volume of sample using a microscope and haemocytometer. Unlike viable counts, both living and dead cells are counted.

Question 30

What is Viable Cell Count?

Answer 30

Viable cell count is a method of counting living microbial cells in a sample. It only counts living cells in the sample. Viable plate count, membrane filtration, and most probable number are a few viable cell count techniques. These approaches are growth-based.

Question 31

What is a viable plate count?

Answer 31

Viable plate count method is a powerful method used in many microbiological fields, including food and dairy microbiology, medical microbiology, environmental microbiology.

Question 32

What are the Similarities Between Total Cell Count and Viable Cell Count?

Answer 32

Total cell count and viable cell count are two types of microbial techniques that quantify cells.
They are commonly used enumeration techniques in microbiology labs.

Question 33

What is the best website about viable and total cell counts?

Answer 33

This one:
https://www.differencebetween.com/difference-between-total-cell-count-and-viable-cell-count/