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CFU/ml Equation:
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The CFU/ml (Colony Forming Units per milliliter) calculation is used in microbiology to estimate the number of viable bacteria or fungal cells in a water sample. It provides a quantitative measure of microbial contamination in water systems.
The calculator uses the CFU/ml equation:
Where:
Explanation: The equation accounts for both the dilution of the sample and the volume used to determine the original concentration of microorganisms in the water sample.
Details: Accurate CFU/ml calculation is crucial for water quality assessment, monitoring microbial contamination in drinking water, recreational water, and industrial water systems. It helps in determining compliance with safety standards and identifying potential health risks.
Tips: Enter the number of colonies counted, the dilution factor used, and the volume of sample plated. All values must be valid (colonies ≥ 0, dilution factor > 0, volume > 0).
Q1: What is an acceptable CFU/ml level for drinking water?
A: Standards vary by jurisdiction, but typically drinking water should have less than 500 CFU/ml for heterotrophic plate count bacteria.
Q2: Why is dilution necessary in CFU counting?
A: Dilution is necessary to obtain countable colonies (typically 30-300 colonies per plate) and to avoid overcrowding that can inhibit colony growth.
Q3: What factors can affect CFU/ml results?
A: Incubation temperature, time, media composition, sample handling, and microbial physiological state can all affect CFU results.
Q4: How should water samples be collected for CFU analysis?
A: Use sterile containers, collect representative samples, maintain proper temperature during transport, and process samples within 6-24 hours.
Q5: What's the difference between CFU/ml and MPN?
A: CFU/ml counts visible colonies while MPN (Most Probable Number) uses statistical estimation from dilution series. CFU is generally more precise for enumerating cultivable microorganisms.