It would be interesting if the doctor could tell you what specific type of bacteria is causing your Acne and what is the specific method by which minocycline destroys that bacteria. The key word here is specific.
Don't be fooled by the vague assumptions that uninformed doctors throw at you (they assume most patients will swallow the info without questioning it).
Most Antibiotics affect bacteria one way or the other - some cannot cope with it fast enough while others develop mechanisms to defend against a specific drug (developing resistance).