First generation cephalosporins are active against-
**Core Concept**
First generation cephalosporins are a class of beta-lactam antibiotics that exhibit antimicrobial activity by inhibiting bacterial cell wall synthesis. They are relatively narrow-spectrum agents, primarily effective against Gram-positive cocci, including Staphylococcus aureus.
**Why the Correct Answer is Right**
First generation cephalosporins, such as cefazolin, exert their antibacterial effects by binding to penicillin-binding proteins (PBPs) located inside the bacterial cell wall. This binding prevents the completion of the bacterial cell wall, ultimately leading to cell lysis and death. They are particularly effective against S. aureus, including both methicillin-sensitive and methicillin-resistant strains.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because first generation cephalosporins have limited activity against Gram-negative bacteria, which are characterized by their outer lipid bilayer membrane.
**Option B:** This option is incorrect because second generation cephalosporins, such as cefoxitin, have enhanced activity against Gram-negative bacteria, but not first generation cephalosporins.
**Option C:** This option is incorrect because third generation cephalosporins, such as ceftriaxone, have broad-spectrum activity against both Gram-positive and Gram-negative bacteria, but not first generation cephalosporins.
**Clinical Pearl / High-Yield Fact**
First generation cephalosporins are often used as a first-line treatment for skin and soft tissue infections, as well as for surgical prophylaxis in patients undergoing procedures involving the skin or musculoskeletal system.
**Correct Answer:** C. Staphylococcus aureus