The antibiotic which acts by interfering with addition of new cell wall subunits (Muramyl pentapeptides) is:
**Core Concept**
Cell wall synthesis is a critical process for bacterial growth and division. Inhibiting cell wall synthesis is a common mechanism of action for several antibiotics. The addition of new cell wall subunits, specifically Muramyl pentapeptides, is a crucial step in this process.
**Why the Correct Answer is Right**
The correct answer, Cephalosporin, acts by inhibiting the enzyme Transpeptidase, which is responsible for the cross-linking of Muramyl pentapeptides in the bacterial cell wall. This results in weakened cell walls, ultimately leading to bacterial cell lysis and death. Cephalosporins, like other beta-lactam antibiotics, bind to and inactivate this enzyme, preventing the formation of new cell wall subunits.
**Why Each Wrong Option is Incorrect**
* **Option A:** Vancomycin acts by binding to the D-Alanyl-D-Alanine terminus of the cell wall precursor, preventing its incorporation into the cell wall. This is a different mechanism of action compared to Cephalosporins.
* **Option B:** Aminoglycosides act by inhibiting protein synthesis, not cell wall synthesis. They bind to the 30S subunit of the bacterial ribosome, interfering with the initiation complex and leading to misreading of mRNA.
* **Option D:** Carbapenems, like Cephalosporins, also inhibit cell wall synthesis. However, they act by inhibiting the enzyme Penicillin-binding protein (PBP), which is essential for the elongation of the bacterial cell wall. While they share a similar mechanism of action, they are a distinct class of antibiotics.
**Clinical Pearl / High-Yield Fact**
When choosing an antibiotic for a patient with a bacterial infection, it's essential to consider the mechanism of action and potential resistance patterns. Inhibiting cell wall synthesis is a common and effective strategy, but resistance can develop through the production of beta-lactamases or altered PBPs.
**Correct Answer:** C. Cephalosporin