When adult amphibian skin harbors populations of the bacterium, Janthinobacterium lividum (Jl), chytrid infection seems to be inhibited. Which of the following represents the best experimental design to test whether this inhibition is real?

A) Inoculate uninfected amphibians with Jl, and determine whether the amphibians continue to remain uninfected by chytrids.

B) Inoculate infected amphibians with Jl, and determine whether the amphibians recover from infection by chytrids.

C) Take infected amphibians and assign them to two populations. Leave one population alone; inoculate the other with Jl. Measure the rate at which infection proceeds in both populations.

D) Take infected amphibians and assign them to two populations. Inoculate one population with a high dose of Jl; inoculate the other with a low dose of Jl. Measure the survival frequency in both populations.

C: Take infected amphibians and assign them to two populations. Leave one population alone; inoculate the other with Jl. Measure the rate at which infection proceeds in both populations.

Explanation:

In scientific investigations, the best way to determine the effect of certain experimental factor on the population of study is to have a baseline for comparison. This is usually referred to as controlled experiment.

In the case of the observation that chytrid infection in amphibians seems to be inhibited by Janthinobacterium lividum, the best way experimental design is to get a population of amphibians suffering from the disease, divide them into two groups and subject them to the same conditions except the introduction of Janthinobacterium lividum to the skin of one of the groups.

A suitable method can thereafter be employed to measure the rate at which infection proceeds in both population. If indeed, the bacterium has the capacity to inhibit the infection, the rate of infection in the group with the bacterium will be significantly less than that of the group without the bacterium.

The correct option is C.