▁this ▁case , ▁failure ▁to ▁use ▁the ▁most ▁appropriate ▁ β - la ct am ▁ant ib i otic ▁ther apy ▁at ▁the ▁on set ▁of ▁treatment ▁could ▁result ▁in ▁selection ▁for ▁b acter ia ▁with ▁higher ▁levels ▁of ▁ β - la ct am ase ▁expression , ▁thereby ▁making ▁further ▁efforts ▁with ▁other ▁ β - la ct am ▁ant ib iot ics ▁more ▁difficult . ▁ ▁Poss ession ▁of ▁alter ed ▁pen ic ill in - binding ▁prote ins ▁As ▁a ▁response ▁to ▁the ▁use ▁of ▁ β - la ct ams ▁to ▁control ▁b acter ial ▁in fe ctions , ▁some ▁b acter ia ▁have ▁evol ved ▁pen ic ill in ▁binding ▁prote ins ▁with ▁novel ▁structures . ▁ β - la ct am ▁ant ib iot ics ▁cannot ▁bind ▁as ▁effectively ▁to ▁these ▁alter ed ▁P B P s , ▁and , ▁as ▁a ▁result , ▁the ▁ β - la ct ams ▁are ▁less ▁effective ▁at ▁dis rupt ing ▁cell ▁wall ▁synth esis . ▁Notable ▁examples ▁of ▁this ▁mode ▁of ▁resistance ▁include ▁m eth ic ill in - res istant ▁St ap hy loc oc cus ▁a ure us ▁( MR SA ) ▁and ▁pen ic ill in - res istant ▁Stre pt oc oc cus ▁p neum onia e . ▁ ▁Alter ed ▁P B P s ▁do ▁not ▁necessarily ▁rule ▁out ▁all ▁treatment ▁options ▁with ▁ β - la ct am ▁ant ib iot ics . ▁ ▁N omen cl ature ▁▁ β - la ct