In the presumptive test of the Multiple Tube Fermentation Test, how many test tubes are used in total?

In the presumptive test of the Multiple Tube Fermentation Test, a total of 15 test tubes are typically used. This method is designed to estimate the number of coliform bacteria present in a water sample through a series of dilutions. Each set of test tubes is inoculated with various dilutions of the water sample, allowing for multiple conditions to be tested simultaneously.

The reason for using 15 tubes is to create a robust statistical basis for calculating the Most Probable Number (MPN) of coliforms. This larger number of tubes increases the likelihood of detecting coliform bacteria and provides a more accurate estimate of their concentration. Essentially, having multiple tubes at different dilutions helps account for variability and improves the reliability of the results.