▁atoms ▁as ▁the ▁base . ▁The ▁second ▁is ▁called ▁" C ohen ' s ▁parameter ", ▁c , ▁and ▁is ▁the ▁distance ▁between ▁the ▁carbon ▁atom ▁of ▁the ▁car box yl ate ▁and ▁the ▁o xygen ▁atom ▁of ▁the ▁ β - la ct am ▁car b ony l . ▁This ▁distance ▁is ▁thought ▁to ▁correspond ▁to ▁the ▁distance ▁between ▁the ▁car box yl ate - binding ▁site ▁and ▁the ▁o xy an ion ▁hole ▁of ▁the ▁P B P ▁en zym e . ▁The ▁best ▁ant ib iot ics ▁are ▁those ▁with ▁higher ▁h ▁values ▁( more ▁re active ▁to ▁hydro ly s is ) ▁and ▁lower ▁c ▁values ▁( bet ter ▁binding ▁to ▁P B P s ). ▁ ▁M odes ▁of ▁resistance ▁By ▁definition , ▁all ▁ β - la ct am ▁ant ib iot ics ▁have ▁a ▁ β - la ct am ▁ring ▁in ▁their ▁structure . ▁ ▁The ▁effect iveness ▁of ▁these ▁ant ib iot ics ▁re lies ▁on ▁their ▁ability ▁to ▁reach ▁the ▁P B P ▁int act ▁and ▁their ▁ability ▁to ▁bind ▁to ▁the ▁P B P . ▁ ▁Hence , ▁there ▁are ▁two ▁main ▁modes ▁of ▁b acter ial ▁resistance ▁to ▁ β - la ct ams : ▁ ▁En zym atic ▁hydro ly s is ▁of ▁the ▁ β - la ct am ▁ring ▁If ▁the ▁b acter ium ▁produces ▁the ▁en zym e ▁ β - la ct am ase ▁or ▁the ▁en zym e ▁pen ic ill in ase , ▁the