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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 standard CFU/ml formula:
Where:
Explanation: This calculation accounts for both the dilution of the original sample and the volume used for plating to determine the original concentration of microorganisms.
Details: Accurate CFU/ml calculation is crucial for microbial enumeration in various applications including water quality testing, food safety monitoring, pharmaceutical quality control, and clinical microbiology diagnostics.
Tips: Enter the number of colonies counted, the dilution factor used, and the volume plated in milliliters. All values must be positive numbers for accurate calculation.
Q1: What is an ideal colony count range for accuracy?
A: For statistical accuracy, aim for 30-300 colonies per plate. Counts below 30 may lack statistical significance, while counts above 300 may be too numerous to count accurately.
Q2: How do I determine the dilution factor?
A: The dilution factor is the reciprocal of the dilution. For example, a 1:10 dilution has a dilution factor of 10, while a 1:100 dilution has a factor of 100.
Q3: What if I need to calculate CFU/g instead of CFU/ml?
A: For solid samples, multiply the result by the initial sample weight (in grams) divided by the volume used for the first dilution.
Q4: When should serial dilutions be used?
A: Serial dilutions are necessary when the microbial concentration is unknown or expected to be high, to ensure countable colonies on at least one dilution plate.
Q5: What are common sources of error in CFU counting?
A: Common errors include inaccurate dilution preparation, uneven spreading of samples, colony overlap, and miscounting due to contamination or non-viable cell counting.