The effect of tetracycline upon the spread of bacterial resistance from calves to man.

Calves were fed Escbericbia coli of bovine origin containing an R factor with resistance determinants found rarely in human and bovine populations. Some of these calves received tetracycline. Fecal samples from human subjects in daily contact with the calves were analyzed for the R factor, the bovine E. coli, and changes in the levels of tetracycline resistant coliforms. Crossover from the calves to the human subjects of the bovine E. coil was shown to occur but was unrelated to whether or not the calves were receiving tetracycline. The levels of tetracycline resistant coliforms in the feces of the human subjects were not influenced by contact with the calves or tetracycline. (