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CFU/ml Formula:
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The CFU per ml (Colony Forming Units per milliliter) calculation is used in microbiology to estimate the number of viable bacteria or fungal cells in a liquid sample. It provides a quantitative measure of microbial concentration.
The calculator uses the CFU per ml formula:
Where:
Explanation: The formula calculates the concentration of viable microorganisms by accounting for the dilution factor and the volume of sample plated.
Details: Accurate CFU per ml calculation is crucial for microbial quantification in various applications including water testing, food safety, pharmaceutical quality control, and clinical microbiology.
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 an appropriate colony count range for accurate results?
A: For statistical accuracy, colony counts between 30-300 are generally considered ideal. Counts outside this range may be less reliable.
Q2: How do I determine the dilution factor?
A: The dilution factor is calculated as the reciprocal of the dilution. For example, a 1:10 dilution has a dilution factor of 10.
Q3: What if I have multiple dilution plates with countable colonies?
A: Use the plate with colony counts between 30-300. If multiple plates fall in this range, calculate CFU/ml for each and average the results.
Q4: Are there limitations to this calculation?
A: This method assumes each colony arises from a single viable cell and doesn't account for cell clumping. It also requires proper aseptic technique and incubation conditions.
Q5: How should results be reported?
A: Results should be reported as CFU/ml with appropriate significant figures, typically rounded to two significant figures for very high counts.