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The No. of Colonies calculation determines the number of bacterial colonies grown on a solid agar medium based on colony forming units, culture plate volume, and dilution factor. This is a fundamental technique in microbiology for quantifying viable microorganisms.
The calculator uses the formula:
Where:
Explanation: The formula calculates the actual number of colonies by accounting for the dilution factor applied to the original sample.
Details: Accurate colony counting is essential for determining microbial concentration in samples, assessing water/food safety, conducting medical diagnostics, and performing quality control in various industries.
Tips: Enter Colony Forming Unit per ml in Cells per m³, Volume of Culture Plate in m³, and Dilution Factor as a unitless value. All values must be positive numbers.
Q1: What is a Colony Forming Unit (CFU)?
A: A CFU is a unit used to estimate the number of viable bacteria or fungal cells in a sample that are capable of forming visible colonies.
Q2: Why is dilution factor important in colony counting?
A: Dilution factor accounts for the serial dilutions performed to obtain countable colony numbers (typically 30-300 colonies per plate for accurate counting).
Q3: What is the ideal number of colonies for accurate counting?
A: For statistical accuracy, plates should contain between 30-300 colonies. Too few colonies lack statistical significance, while too many are difficult to count accurately.
Q4: Are there limitations to colony counting methods?
A: Yes, this method only counts viable cells, may not detect slow-growing organisms, and assumes each colony arises from a single cell.
Q5: How should results be reported?
A: Results should be reported as colony forming units per milliliter (CFU/ml) or per gram (CFU/g) of the original sample, including the dilution factor used.