Introduction. Many studies require the quantitative determination of bacterial populations. The two most widely used methods for determining bacterial numbers are: The standard plate count method. Spectrophotometer (turbid metric) analysis.
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In addition, some of the bacteria may be clumped together. Therefore, when doing the plate count technique, we generally say we are determining the number of Colony-Forming Units (CFUs) in that known dilution.
A plate having 30-300 colonies is chosen because this range is considered statistically significant.
Likewise, if there are more than 300 colonies on the plate, there will be poor isolation and colonies will have grown together. (too numerous to count (TNTC).
Using a fresh pipette, transfer 1 mL from the first blank to the second blank. Mix as before. Label the second bottle "10-2“.
Using a fresh pipette, transfer 1 mL from the first blank to the second blank. Mix as before. Label the second bottle "10-2."
One at a time, add a tube of molten nutrient agar to each Petri dish. After adding the agar, gently swirl the dishes in pattern for 30 seconds to mix the bacteria with the agar.
After the agar has thoroughly solidified, incubate the plates at 37°C for 24 to 48 hours.
Count the number of colonies on a plate that has between 30 and 200 colonies. Any plate which has more than 200 colonies is designated as "too numerous to count" (TNTC). Plates with fewer than 30 colonies do not have enough individuals to be statistically acceptable.
transfer liquid from the dilution blanks to the Petri dishes. Use a separate pipette for each blank, not for each plate (i.e. if more than one plate uses liquid from a single blank, a single pipette may be used for that blank).
1/100 * 0.1
= 46 * 100 * 10 =46000 CFU/ml