A physician sends a stool sample to your lab,and wants to know if there are lactose fermenting microbes in the sample.How might you determine if these microbes are present or not from this mixed-microbe specimen?
A)Streak the sample for isolation on Thayer-Martin agar (which contains lactose and particular antibiotics for selectivity).
B)Streak the sample for isolation on a blood agar plate (which contains lactose AND red blood cells that enrich the culture for iron).
C)Streak the sample for isolation on a MacConkey agar plate (which contains lactose and a pH indicator that turns pink when acid byproducts are present).
D)None of the above would work-there's no way to reliably determine this feature from the specimen given.

Question

Quizplus · Accepted Answer

Streaking the sample for isolation on a MacConkey agar plate would be the best choice. The plate contains lactose and a pH indicator that turns pink when acid byproducts are present, indicating the presence of lactose fermenting microbes. Thayer-Martin agar is selective for certain pathogens and would not necessarily show lactose fermentation, and blood agar plates would not show a clear indication of lactose fermentation either.

A Physician Sends a Stool Sample to Your Lab,and Wants