Miles and Misra method

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The Miles and Misra Method or surface variable count is a technique for counting the number of colony forming units in a bacterial suspension. It was developed by Miles and Misra in 1938.

The procedure is as follows:

Prepare serial dilutions of the bacterial suspension as required.
Materials required:
- A calibrated dropping pipette, delivering drops of about 0.02ml;
- 6 plates of clear nutrient agar.
The plates are divided into numbered sectors.
The inoculum / suspension is deposited as drops of 0.02ml from a height of 2.5cm on to the medium where it spreads over an area of 1.5 – 2.0cm diameter.
Each of the 6 plates receives one drop of each dilution in separate numbered sectors.
The plates are incubated for 18 – 24 hours and observed for growth.
Sectors where more than 20 colonies are present without any confluence are utilized to make the viable counts.
Viable count per 0.02ml for a dilution is obtained by taking the average of counts for that dilution in all the six plates.