Certain bacteria are sensitve to bile salts, in particular, Streptococcus pneumoniae. To test for this sensitivity the bacteria are suspended in a buffer and an amount of deoxycholate is added to the mixture. If the bacteria are sensitive they will break open and the solution will clear. If not, then the bacteria will remain intact and the solution will remain cloudy. Below is a picture of this test with the "insoluble" bacteria on the left and the "soluble"  bacteria in the tube on the right.