Which class of antibiotics works by inhibiting folic acid synthesis?

The class of antibiotics that works by inhibiting folic acid synthesis is sulfonamides. This mechanism is critical because folic acid is essential for the synthesis of nucleic acids, and bacteria must synthesize their own folate as they cannot take it up from the environment. Sulfonamides mimic para-aminobenzoic acid (PABA), a substrate for the enzyme dihydropteroate synthase, leading to the inhibition of folate production.

The reduction of folic acid synthesis ultimately disrupts the growth and replication of bacteria, making sulfonamides effective antimicrobial agents. This mechanism is particularly important in the treatment of various bacterial infections.

Other classes of antibiotics, such as beta-lactams, tetracyclines, and macrolides, operate through different mechanisms. Beta-lactams target bacterial cell wall synthesis, tetracyclines inhibit protein synthesis by binding to the 30S ribosomal subunit, and macrolides also inhibit protein synthesis but do so by binding to the 50S ribosomal subunit. Each of these actions is distinct from the folic acid synthesis inhibition provided by sulfonamides, which is why sulfonamides are the correct answer in this context.