Which two test methods for coliform bacteria include a three-step process?

Which two test methods for coliform bacteria include a three-step process?

• A. MF
• B. MTF
• C. MNO-MUG
• D. MF and MTF

Answer: (D)

The three-step approach in coliform testing involves: first, concentrating bacteria by filtering the water sample; second, growing and identifying presumptive coliform colonies on a selective, differential medium; and third, confirming the identity of the colonies with a follow-up test (such as a lactose fermentation indicator or MUG-based confirmation). The membrane filtration method and its related membrane-based approach both use this exact sequence: filter the sample, incubate on a medium that reveals coliform colonies, then perform a confirmatory test to verify they are coliforms. The MNO-MUG method, while it detects coliforms and uses a MUG-based confirmation, follows a different workflow that does not hinge on this explicit three-step sequence, so it isn’t counted as the three-step method. Therefore, the two methods with a three-step process are MF and MTF.

The three-step approach in coliform testing involves: first, concentrating bacteria by filtering the water sample; second, growing and identifying presumptive coliform colonies on a selective, differential medium; and third, confirming the identity of the colonies with a follow-up test (such as a lactose fermentation indicator or MUG-based confirmation). The membrane filtration method and its related membrane-based approach both use this exact sequence: filter the sample, incubate on a medium that reveals coliform colonies, then perform a confirmatory test to verify they are coliforms. The MNO-MUG method, while it detects coliforms and uses a MUG-based confirmation, follows a different workflow that does not hinge on this explicit three-step sequence, so it isn’t counted as the three-step method. Therefore, the two methods with a three-step process are MF and MTF.