True, but for one, the antibiotic will be produced and used in really large doses once it enters the market, meaning there are trillions of bacterial cells enco

True, but for one, the antibiotic will be produced and used in really large doses once it enters the market, meaning there are trillions of bacterial cells encountering it, which raises the likelihood of development of resistance. And second, horizontal gene transfer between bacteria means different strains of bacteria can cooperate in defeating it (https://en.wikipedia.org/wiki/Horizontal_gene_transfer https://en.wikipedia.org/wiki/Horizontal_gene_transfer)