Viable count

Viable count is a method used in microbiology to determine the number of living microorganisms in a sample. This method is often used in food industry, water treatment, and medical microbiology to ensure safety and quality control.

Overview

The viable count method, also known as the plate count method or colony count method, involves spreading a diluted sample on a solid growth medium and allowing the organisms to grow into colonies. Each colony represents a single viable organism from the original sample. By counting the number of colonies, scientists can estimate the number of viable organisms in the original sample.

Method

The viable count method involves several steps:

1. Sample Collection: The sample is collected in a sterile manner to prevent contamination.
2. Dilution: The sample is diluted to ensure that the colonies will be countable. This is often done using a series of ten-fold dilutions.
3. Plating: A known volume of the diluted sample is spread onto the surface of a solid growth medium.
4. Incubation: The plates are incubated at an appropriate temperature to allow the organisms to grow.
5. Counting: After incubation, the number of colonies is counted. The count is usually expressed as colony forming units (CFU) per milliliter of the original sample.

Limitations

While the viable count method is widely used, it has several limitations. It only counts organisms that can grow in the specific conditions provided, so it may underestimate the total number of organisms. It also assumes that each colony arises from a single organism, which may not always be the case.

See Also

• Microbiology
• Colony Forming Unit
• Growth medium
• Microorganism

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