Before the large-scale medical use of antibiotics, the effect of drug resistance is almost meaningless to bacteria and the harmful effect of mutation itself is more important. Normal use of antibiotics can kill almost all target bacteria and individual missed fish are usually wiped out by the body's immune system. Some of these bacteria are already in the bud of drug resistance, but these buds are not enough to resist normal doses of antibiotics and will disappear as the individual dies.
If there is no abuse of antibiotics, drug resistance will not spread rapidly can be inferred.