What must be assumed when using the plate counting method for measuring microbial growth?

• A. A single cell is formed from a colony on each plate.
• B. Each colony that you count on a plate is formed from a group of cells that you must average after.
• C. Each colony that you count on a plate is formed from a single cell.
• D. Each colony forming unit (CFU) you count is formed from multiple cells.

Answer: (C)

Verified step by step guidance

1. Understand the plate counting method: This method is used to estimate the number of viable microorganisms in a sample by counting the number of colonies formed on an agar plate.
2. Recognize the concept of a colony: In microbiology, a colony is a visible mass of microorganisms all originating from a single mother cell, meaning they are genetically identical.
3. Identify the assumption: The key assumption in the plate counting method is that each colony arises from a single viable cell. This is crucial for accurately estimating the number of cells in the original sample.
4. Consider the term Colony Forming Unit (CFU): CFU is used to express the number of viable bacteria or fungal cells in a sample. It assumes that each colony originates from a single cell, although in reality, some colonies may arise from clusters of cells.
5. Evaluate the implications: If the assumption that each colony comes from a single cell is incorrect, it could lead to an overestimation or underestimation of the microbial population in the sample.