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.

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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.

See also

• Colony-forming unit

References

Miles, A.A & Misra, S.S. (1938). J. Hyg. (London), 38, 732.