Which of the following correctly lists the steps of the pour plate method in the proper order?

• A. Mixing, pouring melted agar, addition of sample to Petri dish, serial dilution, incubation
• B. Incubation, pouring melted agar, serial dilution, addition of sample to Petri dish, mixing
• C. Addition of sample to solidified agar, serial dilution, pouring melted agar, incubation, mixing
• D. Serial dilution of sample, addition of diluted sample to empty Petri dish, pouring melted agar, mixing, solidification, incubation

Answer: (D)

Verified step by step guidance

1. Begin with performing a serial dilution of the original microbial sample to reduce the concentration of microorganisms to a countable number.
2. Next, add a measured volume of the diluted sample to an empty sterile Petri dish.
3. Then, pour melted agar (cooled to about 45-50°C to avoid killing microbes) into the Petri dish containing the sample.
4. After pouring, gently mix the agar and sample by swirling the Petri dish to evenly distribute the microorganisms throughout the agar.
5. Finally, allow the agar to solidify at room temperature, then incubate the plate under appropriate conditions to allow microbial colonies to grow.