Serial Dilution Method in Microbiology

Definition of Serial Dilution Method

  • Serial dilution refers to the gradual step-by-step dilution of a solid solution, transforming it into a solution that is easier to use and manipulate for various applications.
  • In simple terms, serial dilution is the process of gradual dilution of a solution with an associated dilution factor.
  • In the realm of microbiology, serial dilution plays an integral role in reducing the concentration of cells within a culture, resulting in solutions that are considerably simpler and more manageable.

who discovered the serial dilution technique?

  • The serial dilution technique was used in a microbiological laboratory for more than a hundred years.
  • This technique was discovered by the scientist Heinrich Hermann Robert Koch (1883).
  • In 1905, the Nobel Prize was bestowed upon him for his monumental discovery of Tuberculosis, a breakthrough that significantly propelled the field of medical science.
Serial Dilution Method
Serial Dilution Method

Serial dilution Formula and Calculations

  • Serial dilution involves the process of taking a sample and diluting it through a series of standard volumes of sterile diluent, which can be either distilled water or 0.9 % saline solution.
  • After that, a small average volume of each purifier is used to make a series of pouring or dispersing plates.
  • Depending on the relative concentration of cells/organisms in the sample, the size of the stretch is determined. For example, if a water sample is taken from a very polluted environment, the dilution factor is increased. On the other hand, for a less contaminated sample, a low dilution factor might be sufficient.
  • Serial two-fold and ten-fold dilutions are commonly used to titer antibodies or prepare diluted analytes in the laboratory.
  • The dilution factor in serial dilution can either be ascertained per test tube or taken into account as a collective diluting entity throughout the entire dilution series.
  • The serial dilution formula for the dilution factor of each tube is –
Formula of dilution factor
Serial dilution Formula

After the first tube, each tube is cleaned of the previous mixing tube.

  • Now, for the total dilution factor,

Total dilution factor for the second tube = dilution of first tube × dilution of the second tube

Example :

For the first tube, dilution factor = 10-1 (1 ml added to 9 ml)

For the second tube, dilution factor = 10-1 (1ml added to 9 ml)

Total dilution factor = previous dilution × dilution of next tube

Top 5 Online serial dilution calculator

Here top 5 online serial dilution calculators we are going to provide you for easy calculations. These calculators may help you to calculate serial dilution.

  1. AAT Bioquest, Inc. (
  2. Merck, a prominent figure in the science and technology realm, offers a potent tool for solution dilution calculations. Access it here:
  3. Omni Calculator (
  4. Endmemo (
  5. Handymath (

Procedure of Serial dilution

Beneath is an elucidated ten-step process designed to achieve a purification factor of 10-6, providing an extensive understanding of every stage involved.

  1. Take a given sample/culture in a test tube and six test tubes, each containing 9 ml of sterile diluent, which can be pure water or 0.9% saline.
  2. Take a sterile pipette.
  3. Add 1 ml of a well-mixed sample/culture is drawn into the pipette.
  4. Then add sample solution to the first tube to form a total volume of 10 ml. This provides an initial dilution of 10-1.
  5. Dilution is thoroughly mixed by removing and filling the pipette several times.
  6. Discharge a tip of pipette, and insert a new pipe tip into the pipette.
  7. Now, take 1 ml of mixture from the 10-1 concentration test tube.
  8. Then dilute it and pour into a second test tube.
  9. The second tube now has a total dilution factor of 10-2.
  10. Repeat the same process with the remaining test tube, taking 1 ml from the previous tube and adding to the next 9 ml diluents.
  11. As six tubes are used, the final reduction of germs/cells will be 10-6 (1 in 1,000,000).

Uses of Serial Dilution method

The technique of serial dilution is widely executed across an array of experimental sciences like biochemistry, pharmacology, physics, and homeopathy. This widespread usage stems from its versatility and the scope it provides in various scientific scenarios.

Serial Dilution in Microbiology –...
Serial Dilution in Microbiology – Definition, Formula, Procedure and Calculator
  • Serial dilution is used in microbiology to measure the concentration or number of cells/organisms in a sample to obtain an incubated plate with colonial numbers easily.
  • In biochemistry, serial dilution is used to obtain the desired combination of reagents and chemicals from high concentrations.
  • In medical laboratories, serial dilution is performed to obtain the necessary chemical and chemical diagnoses as this method works better than each dilution.
  • In homeopathy, homeopathic dilutions are used when the substance is diluted with water or distilled. It is believed that there is a purification that enhances the power of the purified substance by making its vital energy.

Limitations of Serial Dilution

Although serial dilution is a useful method in laboratories, it faces some challenges. Some of which are:

  • Should any errors be encountered during the distribution of the sample, the resulting transmission inaccuracies could lead to varying degrees of accuracy. This could consequently produce a high purity solution with compromised precision.
  • Because serial processing is done in a non-invasive manner, it requires more time determined by the efficiency of the method.
  • Purification of the product allows only the reduction of germs/cells but not the separation of germs/cells as in other techniques such as flow cytometry.
  • It should be noted that the successful execution of this procedure requires proficient microbiologists and specialists with expertise in aseptic techniques. Their skills ensure the technique's proper execution and its safe use.

FAQs – Serial Dilution in Microbiology

1. Why are serial dilutions important?

Answer: Serial dilution is of paramount importance in laboratory practices. It is employed to dilute highly concentrated solutions, enabling these to be appropriate for further experimentation and analysis.

References and Sources

Further Readings

  1. 8 Qualitative Tests for Protein
  2. Acid Fast Staining
  3. Algae
  4. Aseptic Transfer Technique
  5. Bacterial Flagella, Fimbriae and Pili
  6. Bacterial Growth and Nutrition
  7. Growth Curve of Bacteria
  8. Instruments Used in Microbiology Laboratory
  9. MacConkey agar
  10. McFarland Standards
  11. Monochrome Staining
  12. Negative Staining
  13. Ninhydrin Test
  14. Nutritional Requirements of Micro-Organisms
  15. Preparation and Sterilization of Culture Media
  16. Spread Plate Technique
  17. Streak Plate Technique