Final answer:
Sulfonamides are distinguished from other drugs used to treat bacterial infections by their mechanism of action. They competitively inhibit the bacterial enzyme involved in the synthesis of folic acid, which is necessary for nucleic acid synthesis. This selectivity makes sulfonamides selectively toxic for bacteria.
Step-by-step explanation:
A characteristic that distinguishes sulfonamides from other drugs used to treat bacterial infection is their mechanism of action. Sulfonamides are competitive inhibitors of the bacterial enzyme sulfihydropteroate synthase, which is responsible for the conversion of para-aminobenzoic acid (PABA) into dihydrofolic acid, the immediate precursor of folic acid. This inhibition blocks bacterial biosynthesis of folic acid, which is necessary for the production of pyrimidines and purines required for nucleic acid synthesis. Since humans obtain folic acid from food instead of synthesizing it intracellularly, sulfonamides are selectively toxic for bacteria.