Discuss the beneficial uses of bacterial toxins in medicine?

In molecular Biology the B protein from Cholera toxin is used to identify gangliOSides (an important class of biological compounds) visually with a microscope. This enables researchers to perform advanced experiments on many different diseases.

Many promising drugs for treatment of brain disorders are rendered ineffective because they can not get past the "blood-brain barrier". Within the last month, researchers reported that they have been able to use a toxin from Rabies to successfully administer a drug of their choice into brain tissue. (Rabies is a virus not a bacteria though...)