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CFU Calculation Formula:
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CFU (Colony Forming Units) calculation is a method used in microbiology to estimate the number of viable microorganisms in a sample. It accounts for dilution factors and plating volume to determine the original concentration of microorganisms.
The calculator uses the CFU calculation formula:
Where:
Explanation: The formula calculates the original concentration of microorganisms by accounting for the dilution factor and the volume of sample used for plating.
Details: Accurate CFU calculation is crucial for determining microbial concentrations in various samples, assessing microbial growth, evaluating disinfection effectiveness, and conducting quality control in food, pharmaceutical, and environmental microbiology.
Tips: Enter the number of colonies counted, the dilution factor as a decimal (e.g., 0.001 for 1:1000 dilution), and the volume plated in ml. All values must be valid positive numbers.
Q1: What is an appropriate dilution factor to use?
A: The dilution factor should be chosen to yield 30-300 colonies per plate for accurate counting. Too few or too many colonies can affect accuracy.
Q2: How should colonies be counted?
A: Count all distinct colonies, avoiding overlapping ones. Use a colony counter for accuracy and consistency in counting.
Q3: What if multiple dilutions were plated?
A: Use the plate with 30-300 colonies for calculation. If multiple dilutions fall within this range, average the results for better accuracy.
Q4: Are there limitations to CFU counting?
A: CFU counts estimate viable cells only, not total cells. Some cells may be injured but viable, and clumping can affect accuracy.
Q5: How should results be reported?
A: Report as CFU per ml (or per gram) with appropriate significant figures, typically 2-3 significant figures based on colony count precision.