* Turbidity measures total cell count, not just living cells: Turbidity is a measurement of how much light is scattered by particles in a solution. While bacteria contribute to turbidity, so do dead cells, cell debris, and other particulate matter.
* Different bacteria have different sizes and shapes: A culture with a high turbidity could be due to a large number of small bacteria or a smaller number of larger bacteria. This makes it difficult to directly correlate turbidity to the number of viable bacteria.
* Growth phase matters: Bacteria grow in phases, and the relationship between turbidity and viable cell count can vary significantly during different phases. For example, in the stationary phase, cell death may balance cell division, leading to constant turbidity even though the number of viable bacteria might be decreasing.
Therefore, while turbidity can be a useful indicator of bacterial growth, it is not a reliable measure of viable bacteria.
To accurately determine the number of viable bacteria, you need to use techniques like:
* Plate counts: This involves diluting the culture and plating it on agar. The colonies that grow represent viable bacteria.
* Direct microscopic counts: This method uses a microscope to count the number of bacteria in a specific volume of culture. However, this method does not distinguish between live and dead cells.
* Flow cytometry: This technique uses lasers to count and identify cells based on their size, shape, and fluorescence. It can be used to distinguish between live and dead cells.
In summary, turbidity provides a general idea of bacterial growth but does not accurately reflect the number of viable bacteria. To obtain an accurate measure of viable bacteria, you need to use more specific techniques.
