In the multiple tube fermentation test, what are the two tests performed?

In the multiple tube fermentation test, the two tests performed are indeed the presumptive and confirmed tests. The presumptive test is designed to identify the presence of coliform bacteria in a water sample by detecting gas production and acid formation during fermentation in a nutrient broth at a specified temperature. The results from this test provide an initial indication of potential contamination.

Following the presumptive test, the confirmed test is conducted to verify the results obtained. This typically involves transferring a portion of the sample from the presumptive test into a selective medium that favors the growth of coliforms while inhibiting other types of bacteria. This step ensures that the identified coliforms are indeed the organisms of interest, confirming the findings from the initial test.

The combination of these two tests allows for a more accurate assessment of water quality, making it a crucial aspect of monitoring and ensuring the safety of drinking water. Understanding this process is vital for water operators seeking to maintain compliance with public health standards.