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CFU/ml Formula:
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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 sample. It provides a quantitative measure of microbial concentration.
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 plated.
Details: Accurate CFU/ml calculation is crucial for microbial enumeration, quality control in food and pharmaceutical industries, clinical microbiology, and research applications to determine microbial load in samples.
Tips: Enter the number of colonies counted, the dilution factor used, and the volume plated. All values must be valid positive numbers.
Q1: What is a typical range for CFU/ml in various samples?
A: CFU/ml values can vary widely depending on the sample type, from less than 10 CFU/ml in sterile products to millions in environmental or clinical samples.
Q2: Why is the dilution factor important in CFU calculation?
A: The dilution factor accounts for the serial dilutions performed to obtain countable colonies, ensuring accurate estimation of the original microbial concentration.
Q3: What is considered a countable range of colonies?
A: Typically 30-300 colonies per plate are considered countable for statistical accuracy. Fewer than 30 may lack precision, while more than 300 may be too numerous to count accurately.
Q4: Are there limitations to CFU counting?
A: CFU counting only detects viable cells that can grow under the specific conditions used. It may underestimate total microbial load as some cells may be viable but non-culturable.
Q5: How should results be reported?
A: Results should be reported as CFU/ml (or CFU/g for solid samples) with appropriate significant figures, typically rounded to two significant figures.