Which of the following antibiotics inhibits folic acid synthesis in bacteria?

• A. Penicillin
• B. Sulfonamides
• C. Tetracycline
• D. Vancomycin

Answer: (B)

Verified step by step guidance

1. Understand the role of folic acid in bacterial cells: Folic acid is essential for the synthesis of nucleotides, which are the building blocks of DNA and RNA. Bacteria must synthesize folic acid themselves, as they cannot take it up from the environment.
2. Recall the mechanism of action of different antibiotics: Penicillin and Vancomycin inhibit bacterial cell wall synthesis, while Tetracycline inhibits protein synthesis by binding to the 30S ribosomal subunit.
3. Identify which antibiotic class targets folic acid synthesis: Sulfonamides are structural analogs of para-aminobenzoic acid (PABA), a substrate in the folic acid synthesis pathway. They competitively inhibit the enzyme dihydropteroate synthase, blocking folic acid production.
4. Connect the inhibition of folic acid synthesis to bacterial growth: By preventing folic acid synthesis, sulfonamides inhibit the production of nucleotides, thereby stopping DNA replication and bacterial growth.
5. Conclude that among the options given, sulfonamides are the antibiotics that inhibit folic acid synthesis in bacteria.