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CFU/mL Formula:
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The CFU (Colony Forming Units) calculation formula is used in microbiology to estimate the number of viable bacteria or fungal cells in a sample. It provides a standardized way to quantify microbial concentration in various samples.
The calculator uses the CFU formula:
Where:
Explanation: The formula accounts for both the dilution of the original sample and the volume plated to calculate the concentration of viable microorganisms in the original sample.
Details: Accurate CFU calculation is crucial for microbial enumeration in food safety testing, pharmaceutical quality control, environmental monitoring, and clinical microbiology. It helps determine microbial load and assess contamination levels.
Tips: Enter the number of colonies counted, the dilution factor used, and the volume plated. All values must be valid positive numbers for accurate calculation.
Q1: What is an appropriate colony count range for accurate results?
A: Ideally, plates should have between 30-300 colonies for accurate counting. Below 30 may be statistically unreliable, while above 300 may be too numerous to count accurately.
Q2: How do I determine the dilution factor?
A: The dilution factor is calculated based on how many times the original sample was diluted. For example, a 1:10 dilution has a factor of 10, a 1:100 dilution has a factor of 100.
Q3: What if I have multiple dilutions with countable colonies?
A: Use the plate with colonies in the ideal range (30-300) and the lowest dilution factor to get the most accurate result.
Q4: Can this formula be used for different volume units?
A: Yes, but ensure all units are consistent. If volume is in μL instead of mL, adjust the calculation accordingly.
Q5: What are the limitations of CFU counting?
A: CFU counting only detects viable cells that can grow under the specific conditions used. It may not detect injured cells, slow-growing organisms, or those with specific nutrient requirements.