How does penicillin kill Streptococcus pyogenes during an infection?

• A. It blocks folic acid synthesis by inhibiting dihydropteroate synthase.
• B. It disrupts bacterial DNA replication by inhibiting DNA gyrase.
• C. It interferes with protein synthesis by binding to the 30S ribosomal subunit.
• D. It inhibits the synthesis of peptidoglycan in the bacterial cell wall.

Answer: (D)

Verified step by step guidance

1. Understand the mechanism of action of penicillin: Penicillin is a beta-lactam antibiotic that targets bacterial cell wall synthesis.
2. Recall that Streptococcus pyogenes is a Gram-positive bacterium, which has a thick peptidoglycan layer in its cell wall essential for maintaining cell shape and integrity.
3. Penicillin works by binding to and inhibiting enzymes called penicillin-binding proteins (PBPs), which are involved in the cross-linking of peptidoglycan strands during cell wall synthesis.
4. Inhibition of PBPs prevents the formation of the peptidoglycan cross-links, weakening the cell wall and leading to osmotic instability and eventual bacterial cell lysis.
5. Therefore, penicillin kills Streptococcus pyogenes by inhibiting the synthesis of peptidoglycan in the bacterial cell wall, not by affecting folic acid synthesis, DNA replication, or protein synthesis.