Miles and Misra method

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.