Colony-forming unit

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Colony-forming unit (CFU) is a term used in microbiology to estimate the number of viable bacteria or fungi cells in a sample. Viable cells are those that are capable of dividing and forming colonies. The CFU is an important measure in various fields such as clinical microbiology, food microbiology, and environmental microbiology.

Overview

A colony-forming unit is defined as a single cell or a group of cells that can grow into a visible colony when cultured on an appropriate agar plate. The number of colonies formed on the agar plate is used to estimate the number of viable microorganisms in the original sample. This method is widely used because it provides a reliable estimate of the number of living cells, which is crucial for understanding the microbial load in a sample.

Methodology

The process of determining CFUs involves several steps: 1. **Sample Preparation**: The sample is diluted to ensure that the number of colonies formed is countable. 2. **Plating**: A small volume of the diluted sample is spread onto an agar plate. 3. **Incubation**: The agar plate is incubated under suitable conditions to allow the microorganisms to grow. 4. **Counting**: After incubation, the colonies are counted. Each colony is assumed to arise from a single CFU.

Applications

CFUs are used in various applications, including:

• **Clinical Microbiology**: To diagnose infections by estimating the number of pathogenic microorganisms in a sample.
• **Food Microbiology**: To ensure food safety by determining the microbial load in food products.
• **Environmental Microbiology**: To assess the microbial quality of water, soil, and air samples.

Limitations

While CFUs provide valuable information, there are some limitations:

• **Viable but Non-Culturable (VBNC) Cells**: Some microorganisms may be alive but unable to form colonies under standard laboratory conditions.
• **Clumping**: Cells that clump together may form a single colony, leading to an underestimation of the actual number of viable cells.

Related Pages

• Microbiology
• Agar plate
• Cell division
• Clinical microbiology
• Food microbiology
• Environmental microbiology

See Also

• Bacterial colony
• Viable but non-culturable state
• Microbial load

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