The serial dilution technique is used to count microbial colonies in environmental samples. It involves mixing a sample with diluent at ratios of 1:2 or 1:10 to reduce the microbial concentration to a countable level. The sample is serially diluted up to 10-8 and plated using the pour plate method. The plates are incubated and colonies are counted. The number of colonies per gram of sample is then calculated using the dilution factor. This technique allows microbiologists to study the number and types of microorganisms present in various environmental sources.

1. SERIAL DILUTION TECHNIQUE
M.J. Afra
UG Scholar
Department of Microbiology
Thassim Beevi Abdul Kader College
For Women Kilakarai

2. AIM
• To know the microbial population of the given
sample
• To study the number of microorganisms present
in the environment
• To dilute the sample to get countable number of
colonies
• To understand the serial dilution technique

3. INTRODUCTION
• The microbial population in our environment is large
and complex
• Microbes are isolated from various substrates and
sources
• Organisms are isolated from various places by using
culture media
• To study the number of microorganisms present in the
environment/qualitative analysis of microbial samples
• Colony means group of cells that are emerged from a
single cell by continuous transverse fission within the
prescribed time
• To avoid few types of problems microbiologists perform
serial dilution technique to count the colonies

4. DILUTION SCHEME
• One part of the sample is mixed with one part of
diluent, the result will be 1:2 dilution
• One part of sample is placed on nine parts of
diluent, the result will be 1:10 dilution
• One part of the 1:10 dilution was transferred to 9ml
of diluent results in additional one to ten dilution
Volume of sample
Dilution = --------------------------------------
Total volume of sample and diluent

5. MATERIALS REQUIRED
• 9ml water blanks in sterile test tubes
• Test tubes
• Pipettes
• Cotton
• Nutrient agar
• Potato dextrose agar
• Petri plates
• Markers
• Sample

6. PROCEDURE
1) SAMPLE:
Sterile samples were collected from the
environment, plants, animals or humans
2) STOCK PREPARATION
SOLID – 10g of sample taken and grinded by using
mechanical blender and suspended in 100ml of
diluent
LIQUID – 1ml is suspended in 9ml of water

7. PROCEDURE
3) DILUENT PREPARATION:
Arrange the tubes in a rack
Fill the tubes with 9ml of distilled water or saline
Insert cotton plug to all test tubes
Sterilize the test tubes for 15 minutes under 121oC
Keep the tubes ready for serial dilution

8. PROCEDURE
• The agar were calculated, mixed and sterilized
for 15 minutes under 121o C
• The glasswares were sterilized
• Work bench of laminar air flow chamber was
cleaned using disinfectant followed by UV lamp
for 15 minutes before working

9. PROCEDURE (serial dilution)
• Keep ready and arrange all materials required for the
dilution in laminar air flow chamber
• Arrange test tubes and label them (10-1, 10-2, …… , 10-10)
• Add 1ml of the sample from the diluent
• Makeup further dilution upto 10-8
• Perform plating from the appropriate dilution by pour
plate method
• Add 1ml of diluted sample to appropriately labelled petri
plates after dilution
• Pour 15ml -20ml of media to the petri plates
• Incubate all the plates at appropriate temperature and
observe the colonies

10. No of colonies * dilution factor
No of colonies (per gram) = -----------------------------------------
Dry weight of the sample

11. THANK YOU
M.J. Afra
UG Scholar
Department of Microbiology
Thassim Beevi Abdul Kader College
For Women Kilakarai