cept ible ▁b acter ia ▁is ▁in hib ited ▁by ▁the ▁drug . ▁For ▁example , ▁ant ib acter ial ▁selection ▁for ▁stra ins ▁having ▁previously ▁acquired ▁ant ib acter ial - res istance ▁gen es ▁was ▁demonstrated ▁in ▁ 1 9 4 3 ▁by ▁the ▁L uria – Del br ück ▁experiment . ▁Ant ib iot ics ▁such ▁as ▁pen ic ill in ▁and ▁er yth rom yc in , ▁which ▁used ▁to ▁have ▁a ▁high ▁effic acy ▁against ▁many ▁b acter ial ▁species ▁and ▁stra ins , ▁have ▁become ▁less ▁effective , ▁due ▁to ▁the ▁increased ▁resistance ▁of ▁many ▁b acter ial ▁stra ins . ▁ ▁Res istance ▁may ▁take ▁the ▁form ▁of ▁bi ode g red ation ▁of ▁ph arma ce ut ical s , ▁such ▁as ▁sul f am eth azine - de grad ing ▁soil ▁b acter ia ▁introduced ▁to ▁sul f am eth azine ▁through ▁medic ated ▁p ig ▁f ec es . ▁The ▁surv ival ▁of ▁b acter ia ▁often ▁results ▁from ▁an ▁inher itable ▁resistance , ▁but ▁the ▁growth ▁of ▁resistance ▁to ▁ant ib acter ial s ▁also ▁occurs ▁through ▁horizontal ▁gene ▁transfer . ▁Hor izontal ▁transfer ▁is ▁more ▁likely ▁to ▁happen ▁in ▁locations ▁of ▁frequent ▁ant ib i otic ▁use . ▁ ▁Ant ib acter ial ▁resistance ▁may ▁imp ose ▁a ▁bi ological ▁cost , ▁thereby ▁reducing ▁fit ness ▁of ▁resist ant ▁stra ins , ▁which ▁can ▁limit ▁the ▁spread ▁of ▁ant ib acter ial - res istant ▁b acter ia , ▁for ▁example