What are the common methods for bacteria counting?

The two most widely used methods for bacteria counting are the standard plate count method and turbidimetric analysis.

The standard plate count method is based on the assumption that each viable bacterial cell is separate from all others and will develop into a single discrete colony (CFU). The final plates should have 30-300 colonies to obtain acceptable accuracy.

The turbidimetric analysis uses a spectrophotometer to measure the increased turbidity due to bacterial growth. The amount of transmitted light decreases as the cell population increases. Turbidimetric analysis is faster but has a lower sensitivity than the standard plate count.