1. What is Colony Forming Unit?

Colony Forming Unit per ml is a measure of viable bacterial or fungal cells. In direct microscopic counts where all cells, dead and living, are counted, CFU provides an estimate of the number of viable microorganisms in a sample.

2. How Does the Calculator Work?

The calculator uses the CFU formula:

Where:

• \( nc \) — Number of colonies counted
• \( DF \) — Dilution factor used
• \( vc \) — Volume of culture plate (mL)

Explanation: The formula calculates the concentration of viable microorganisms by accounting for the dilution factor and the volume plated.

3. Importance of CFU Calculation

Details: Accurate CFU calculation is crucial for microbiological studies, quality control in food and pharmaceutical industries, and clinical microbiology for determining bacterial load in samples.

4. Using the Calculator

Tips: Enter the number of colonies counted, the dilution factor used, and the volume of culture plate. All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical range for CFU counts?
A: CFU counts can vary widely depending on the sample type, from few CFU/mL in clean water to millions CFU/mL in rich bacterial cultures.

Q2: Why is dilution factor important in CFU calculation?
A: Dilution factor accounts for the serial dilutions made to the original sample to obtain countable colony numbers on the plate.

Q3: What is considered a countable range of colonies?
A: Typically 30-300 colonies per plate are considered countable for accurate results. Too few or too many colonies can lead to inaccurate counts.

Q4: Can CFU calculation be used for all microorganisms?
A: CFU calculation works best for bacteria and fungi that form distinct colonies. It may not be suitable for microorganisms that grow in chains or clusters.

Q5: How does CFU differ from direct cell counting?
A: CFU counts only viable cells that can grow and form colonies, while direct counting methods (like hemocytometer) count all cells, both living and dead.