What must all positive samples in the presence-absence test be confirmed using?

The presence-absence test is an initial screening method used to detect the presence of coliforms, specifically E. coli, in water samples, indicating potential contamination. Positive results from this test must be confirmed to ensure accuracy and reliability.

Brilliant Green Bile tubes are specifically designed to isolate and confirm the presence of coliform bacteria and fecal coliforms in water samples. These tubes contain selective agents, which suppress the growth of non-target organisms while allowing coliforms to grow. This characteristic makes them suitable for confirming positive results from the presence-absence test.

In contrast, MacConkey agar plates, while also used for isolating and differentiating Gram-negative bacteria, including coliforms, are not typically the standard confirmatory method for the presence-absence test. Lactose broth tubes are part of similar detection methods but do not specifically serve as confirmatory agents in this context. Peptone water is a general-purpose media and does not provide the selective conditions required for confirming the presence of coliforms.

Using Brilliant Green Bile tubes for confirmation helps ensure that the results from the test are reliable and that any detected coliforms are accurately identified, safeguarding public health from waterborne pathogens.