Order of authorship in the original publication: Zimmermann, Simmerman-Kogadeeva, Wegmann....The authors looked at 271 drugs and 68 different species from the main taxonomic microbiome groups. Of the 271 drugs, 176 underwent a substantial metabolic change caused by at least one bacterial strain which resulted in a reduction of the level of the active drug. Every bacterial strain tested metabolized some of the drugs. 

Using a practical example drug like Diltiazem (for the treatment of hypertension) the authors found that a specific gene (bt4096) in the common microbiome species Bacteroides thetaiotaomicron is required for the human body to metabolize the drug, and that this specific bacteria is needed to metabolize that drug because only the metabolite of that drug is active in the body as a blood pressure medicine. 

The paper drew three conclusions:

1. Bacteria can metabolize a drug and convert it to its active and useful molecular version.

2. Bacteria can metabolize a drug and inactivate it.

3. Bacteria can metabolize a drug and convert it into a toxic product.

(Thanks to Juan Weiss for this reference and its interpretation.)