Serial dilution and colony counting. Serial dilution and colony counting Also know as “viable cell counts” Concentrated samples are diluted by serial dilution The diluted samples can be either plated by spread plating or by pour plating. Serial dilution and colony counting.
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Count the number of colonies on a plate that has between 25 and 250 colonies. Any plate which has more than 250 colonies is designated as "too numerous to count" (TNTC).
Also any plate which has fewer than 25 colonies is designated as "too few to count" (TFTC).
Notes:According to FDA Bacteriological Analytical Manual ( in rare situations)
If there is no 25-250 colony plate, use plate having nearest to 25 or 250 colonies.
If all plates from a sample show no colonies, record count as 0.
Optical density is directly proportional to the number of cells. When the bacterial population doubles, the optical density of the bacterial suspension also doubles.