Incubation Incubate the prepared dishes, inverted, at 35±10C for 72±3hours.
Counting the colonies Following incubation, count all colonies on dishes containing 30 -300 colonies and record the results per dilution counted.
When the dishes examined contain no colonies, the result is expressed as; less than 1x101 bacteria per g or ml.
When the dishes (dilution 1in 10) contain less than 30 colonies, the result
is expressed (30x10=3x102).
When the colonies are more than 30, count the colonies in both plates of a dilution and calculate the average,
retaining only two significant digits multiply by the inverse of corresponding dilution to obtain
and the the
number of bacteria per g or ml. Example: dilution 1/100 dish 1: 175 colonies
Result: 1.9x104 bacteria per g of food.