## **Core Concept**
The patient presents with symptoms of pneumonia, including cough, hemoptysis, high fever, and radiographic evidence of increased density in the right middle lobe. The sputum smear and culture confirm the presence of penicillinase-producing *Staphylococcus aureus*, a type of Gram-positive coccus.

## **Why the Correct Answer is Right**
The correct answer, , is appropriate for treating infections caused by penicillinase-producing *Staphylococcus aureus*. This organism produces beta-lactamase enzymes (penicillinases) that inactivate penicillin and other beta-lactam antibiotics. is a beta-lactam antibiotic that is resistant to beta-lactamase degradation, making it effective against penicillinase-producing *Staphylococcus aureus*. It works by inhibiting cell wall synthesis in bacteria, ultimately leading to bacterial cell death.

## **Why Each Wrong Option is Incorrect**
* **Option A:** is a first-generation cephalosporin with good activity against Gram-positive cocci, but it is not the best choice for penicillinase-producing *Staphylococcus aureus* due to potential resistance. Some strains may produce cephalosporinases that can inactivate first-generation cephalosporins.
* **Option B:** is a macrolide antibiotic effective against a range of bacterial infections, particularly those caused by Gram-positive cocci. However, resistance rates among *Staphylococcus aureus* can be high, making it less reliable for empirical treatment without susceptibility testing.
* **Option C:** is a fluoroquinolone antibiotic with broad-spectrum activity. While it can be effective against some Gram-positive cocci, its use as a first-line agent for *Staphylococcus aureus* pneumonia, especially in a hospital setting, may not be optimal due to concerns about resistance and side effects.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that penicillinase-producing *Staphylococcus aureus* infections require treatment with beta-lactamase-resistant antibiotics. is a classic example of such an agent. Additionally, it's crucial to consider local resistance patterns and patient-specific factors when choosing an antibiotic.

## **Correct Answer:** . **Oxacillin**