In the example given, which organism's colonies are used to illustrate colony forming units?

In the example given, which organism's colonies are used to illustrate colony forming units?

• A. Saccharomyces cerevisiae
• B. Escherichia coli
• C. Staphylococcus aureus
• D. Bacillus subtilis

Answer: (A)

The concept being tested is how colony forming units connect the number of viable cells in a sample to the number of colonies that appear on a plate after plating and incubation. Saccharomyces cerevisiae is used because it’s a safe, well-known yeast that grows readily on standard media and forms discrete, easily visible colonies. This makes counting straightforward and helps illustrate how each colony corresponds to a viable organism in the original sample. The other organisms listed are bacteria, which can also be counted as CFUs, but the example in question specifically uses a yeast due to its clear colony morphology and teaching-friendly growth, making it the best illustration here.

The concept being tested is how colony forming units connect the number of viable cells in a sample to the number of colonies that appear on a plate after plating and incubation. Saccharomyces cerevisiae is used because it’s a safe, well-known yeast that grows readily on standard media and forms discrete, easily visible colonies. This makes counting straightforward and helps illustrate how each colony corresponds to a viable organism in the original sample. The other organisms listed are bacteria, which can also be counted as CFUs, but the example in question specifically uses a yeast due to its clear colony morphology and teaching-friendly growth, making it the best illustration here.