<Li> Drug inactivation or modification: e.g., enzymatic deactivation of Penicillin G in some penicillin - resistant bacteria through the production of β - lactamases . </Li> <Li> Alteration of target site: e.g., alteration of PBP--the binding target site of penicillins--in MRSA and other penicillin - resistant bacteria . </Li> <Li> Alteration of metabolic pathway: e.g., some sulfonamide - resistant bacteria do not require para-aminobenzoic acid (PABA), an important precursor for the synthesis of folic acid and nucleic acids in bacteria inhibited by sulfonamides . Instead, like mammalian cells, they turn to utilizing preformed folic acid . </Li> <Li> Reduced drug accumulation: by decreasing drug permeability and / or increasing active efflux (pumping out) of the drugs across the cell surface . </Li>

Explain one possible mechanism for the evolution of drug-resistance in microbes