What are the three phases in the MPN test?

What are the three phases in the MPN test?

• A. Presumptive, Confirmed, Completed
• B. Inoculation, Incubation, Evaluation
• C. Preparation, Growth, Identification
• D. Screening, Confirmation, Quantification

Answer: (A)

The MPN test uses a stepwise approach to estimate how many organisms are present by screening, verifying, and finalizing the result. In the presumptive phase, many tubes with lactose-containing broth are inoculated across several dilutions, and any gas production suggests probable presence of lactose-fermenting coliforms. Those tubes are the presumptive positives. In the confirmed phase, those presumptive positives are tested in a more selective/differential medium to verify that the gas-producing organisms are indeed coliforms, not other microbes. A positive result here strengthens the identification as coliforms. In the completed phase, a final verification is performed—often involving subculturing and additional confirmatory tests—to solidify the identity and provide the data needed to calculate the most probable number. This three-phase structure—presumptive, confirmed, completed—offers screening, verification, and final confirmation/quantification, giving a reliable estimate. Other sequences describe general lab steps but do not capture this specific MPN workflow.

The MPN test uses a stepwise approach to estimate how many organisms are present by screening, verifying, and finalizing the result. In the presumptive phase, many tubes with lactose-containing broth are inoculated across several dilutions, and any gas production suggests probable presence of lactose-fermenting coliforms. Those tubes are the presumptive positives. In the confirmed phase, those presumptive positives are tested in a more selective/differential medium to verify that the gas-producing organisms are indeed coliforms, not other microbes. A positive result here strengthens the identification as coliforms. In the completed phase, a final verification is performed—often involving subculturing and additional confirmatory tests—to solidify the identity and provide the data needed to calculate the most probable number. This three-phase structure—presumptive, confirmed, completed—offers screening, verification, and final confirmation/quantification, giving a reliable estimate. Other sequences describe general lab steps but do not capture this specific MPN workflow.