In 1943, there was streptomycin, the first cure for tuberculosis, and on the heels of that came chloramphenicol, chlortetracycline, neomycin, erythromycin.

The medicine—either penicillin, vancomycin, a combination of the two, or chlortetracycline—was given at doses comparable to those approved by the U.S.

But many of the microbes Chénier's team studied harbored a chlortetracycline resistance gene on plasmids, even after years without the antibiotic.