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CFU/ml Formula:
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CFU/ml (Colony Forming Units per milliliter) is a measurement used in microbiology to estimate the number of viable bacteria or fungal cells in a sample. It provides a standardized way to quantify microbial concentration in liquid samples.
The calculator uses the CFU/ml formula:
Where:
Explanation: The formula calculates the concentration of viable microorganisms by accounting for the dilution of the original sample and the volume used for plating.
Details: Accurate CFU/ml calculation is essential for microbial research, quality control in food and pharmaceutical industries, clinical microbiology, and environmental monitoring. It helps determine microbial load and assess the effectiveness of antimicrobial treatments.
Tips: Enter the number of colonies counted, the dilution factor used, and the volume plated. All values must be valid positive numbers (colonies ≥ 0, dilution factor > 0, volume > 0).
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. Serial dilutions are often necessary for accurate counting.
Q2: How many colonies should be counted for accuracy?
A: Ideally, plates should have 30-300 colonies for statistical reliability. Fewer than 30 may lack precision, while more than 300 may be too numerous to count accurately.
Q3: What if I have multiple dilution plates with countable colonies?
A: Use the plate with colonies between 30-300 for the most accurate calculation. If multiple plates fall in this range, average the results.
Q4: How should results be reported?
A: Report as CFU/ml with appropriate significant figures. For very low counts, report as "less than" the detection limit. For high counts, use scientific notation if needed.
Q5: Are there limitations to CFU counting?
A: CFU counts only detect viable cells that can grow under the specific conditions used. Some cells may be viable but non-culturable, and clumping can cause underestimation.