There are any number of reasons why drugs don't work on humans when they do work on other animals. It could be gut bacteria, but it could just be that the anima

There are any number of reasons why drugs don't work on humans when they do work on other animals. It could be gut bacteria, but it could just be that the animal has some other physiological trait that causes the drug to be more or less effective. In this case, they weren't testing a drug, they were testing the deadliness of the bacteria. It doesn't matter _how_ toxic the bacteria is to humans relative to mice, it only matters that the bacteria is more deadly (or less deadly) to the mice when the sugar is present.