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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 quantitative assessment of microbial concentration.
The calculator uses the CFU/mL formula:
Where:
Explanation: This calculation accounts for both the dilution of the original sample and the volume plated to determine the concentration of microorganisms in the original undiluted sample.
Details: Accurate CFU/mL calculation is crucial for determining microbial load in various samples, assessing water and food safety, monitoring bacterial growth in research, and evaluating the effectiveness of antimicrobial treatments.
Tips: Enter the number of colonies counted, the dilution factor used, and the volume plated. All values must be positive numbers. For accurate results, plate counts should ideally be between 30-300 colonies.
Q1: Why is the dilution factor important in CFU calculation?
A: The dilution factor accounts for how much the original sample was diluted before plating, allowing calculation of the concentration in the original undiluted sample.
Q2: What is the ideal range of colonies to count?
A: 30-300 colonies is considered the statistically reliable range. Fewer than 30 may lack precision, while more than 300 may be too crowded for accurate counting.
Q3: How should I report CFU/mL results?
A: Report as CFU/mL with appropriate significant figures, typically using scientific notation for very high or low concentrations.
Q4: Are there limitations to CFU counting?
A: CFU counts only measure viable cells that can grow under the specific conditions used. They don't account for dead cells, viable but non-culturable cells, or cells that grow in chains or clusters.
Q5: How does this differ from direct microscopic counting?
A: CFU counting measures only viable cells that can proliferate, while direct counting includes all cells (both living and dead) but doesn't distinguish viability.