1. What is CFU Calculation?

CFU (Colony Forming Units) calculation is a method used in microbiology to estimate the number of viable bacteria or fungal cells in a sample. It provides a quantitative measure of microbial concentration.

2. How Does the Calculator Work?

The calculator uses the standard CFU formula:

Where:

• \( colonies \) — Number of colonies counted on the plate
• \( dilution \) — Dilution factor of the sample
• \( volume \) — Volume of diluted sample plated (mL)

Explanation: The formula accounts for the dilution series and the volume plated to calculate the original concentration of microorganisms in the sample.

3. Importance of CFU Calculation

Details: CFU calculation is essential for determining microbial load in various samples, assessing contamination levels, monitoring bacterial growth, and evaluating the effectiveness of antimicrobial treatments.

4. Using the Calculator

Tips: Enter the number of colonies counted, the dilution factor used, and the volume plated. All values must be positive numbers. The result is expressed as CFU/mL.

5. Frequently Asked Questions (FAQ)

Q1: What is an appropriate dilution factor range?
A: Dilution factors typically range from 10⁻¹ to 10⁻⁸ depending on the expected microbial concentration in the original sample.

Q2: How many colonies should be counted for accuracy?
A: For statistical reliability, counts between 30-300 colonies per plate are generally considered optimal.

Q3: What if colonies are too numerous to count?
A: If colonies are too crowded (TNTC), use a higher dilution factor and recount.

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 or cells that require different growth conditions.

Q5: How should results be reported?
A: Report as CFU/mL (or CFU/g for solid samples) with appropriate significant figures based on countable colonies.