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CFU Calculation Formula:
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CFU (Colony Forming Units) calculation is a microbiological method used to estimate the number of viable bacteria or fungal cells in a sample. It provides a quantitative measure of microbial concentration in CFU/mL.
The calculator uses the CFU formula:
Where:
Explanation: The formula accounts for both the dilution of the original sample and the volume plated to calculate the concentration of viable microorganisms in the original sample.
Details: Accurate CFU calculation is crucial for determining microbial load in various samples, assessing water and food safety, monitoring bacterial growth in research, and evaluating the effectiveness of antimicrobial treatments.
Tips: Enter the number of colonies counted, the dilution factor applied to the sample (as a decimal), and the volume of diluted sample plated (in mL). All values must be positive numbers.
Q1: What is an appropriate dilution factor range?
A: Dilution factors typically range from 10⁻¹ to 10⁻⁸ depending on the expected microbial concentration in the original sample.
Q2: How many colonies should be counted for accuracy?
A: For statistical reliability, aim for 30-300 colonies per plate. Counts below 30 may lack precision, while counts above 300 may be too numerous to count accurately.
Q3: What if multiple dilutions yield countable plates?
A: Use the plate with 30-300 colonies and its corresponding dilution factor for the most accurate calculation.
Q4: Are there limitations to CFU counting?
A: CFU counts only measure viable cells that can grow under the specific conditions used. They don't account for dead cells, viable but non-culturable cells, or cells that form chains or clusters.
Q5: How should results be reported?
A: Report as CFU/mL (or CFU/g for solid samples) with appropriate significant figures, typically 2-3 significant figures depending on the precision of the measurement.