Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1671: All of the following bind to the 50S ribosomal unit except:

A. Macrolide
B. Lincosamide
C. Tetracycline (Correct Answer)
D. Chloramphenicol

Explanation: ***Tetracycline*** - **Tetracyclines** bind to the **30S ribosomal subunit**, specifically inhibiting protein synthesis by blocking the binding of aminoacyl-tRNA to the A-site. - This mechanism is distinct from the other listed antibiotics which target the 50S subunit. *Macrolide* - **Macrolide antibiotics** bind to the **50S ribosomal subunit** to inhibit bacterial protein synthesis by blocking translocation and peptidyl transferase activity. - This binding prevents the ribosome from moving along the mRNA, effectively halting protein elongation. *Lincosamide* - **Lincosamides**, such as clindamycin, also bind to the **50S ribosomal subunit** at a site overlapping with macrolides and chloramphenicol. - They inhibit protein synthesis by hindering peptidyl transferase and stalling chain elongation. *Chloramphenicol* - **Chloramphenicol** binds to the **50S ribosomal subunit** and inhibits protein synthesis by blocking the peptidyl transferase activity. - This prevents the formation of peptide bonds between amino acids, thereby stopping protein chain elongation.

Question 1672: Which specific beta-lactamase inhibitor is commonly used to enhance the efficacy of beta-lactam antibiotics in the treatment of bacterial endocarditis?

A. Clavulanic acid
B. Sulbactam
C. Tazobactam (Correct Answer)
D. Avibactam

Explanation: ***Tazobactam*** - **Tazobactam** is a widely used **beta-lactamase inhibitor** that, when combined with **piperacillin (piperacillin/tazobactam)**, provides **broad-spectrum coverage** against beta-lactamase-producing bacteria [2]. - In the context of **bacterial endocarditis**, particularly for **empirical therapy** when the causative organism is unknown, **piperacillin/tazobactam** offers excellent coverage for Gram-positive cocci (including some staphylococci), Gram-negative bacteria, and anaerobes. - This combination is frequently used in **prosthetic valve endocarditis** or when multidrug-resistant organisms are suspected, making tazobactam a valuable choice for enhancing beta-lactam efficacy in serious endocardial infections. *Clavulanic acid* - **Clavulanic acid** is a beta-lactamase inhibitor typically combined with **amoxicillin** (amoxicillin/clavulanic acid) or **ticarcillin** (ticarcillin/clavulanic acid) [1]. - While effective for many infections, the amoxicillin combination is primarily available in oral formulation and has a **narrower spectrum** compared to piperacillin/tazobactam. - It is generally not preferred for severe infections like bacterial endocarditis requiring parenteral therapy and broad coverage. *Sulbactam* - **Sulbactam** is a beta-lactamase inhibitor commonly paired with **ampicillin** (ampicillin/sulbactam) [1]. - The **ampicillin/sulbactam combination** is actually used in endocarditis, particularly for **Enterococcus species** infections. - However, for **broad empirical coverage** in endocarditis (covering resistant Gram-negatives and anaerobes), piperacillin/tazobactam is more commonly selected. *Avibactam* - **Avibactam** is a newer beta-lactamase inhibitor combined with **ceftazidime** (ceftazidime/avibactam) or **ceftaroline**. - It is particularly effective against **carbapenem-resistant Enterobacteriaceae** and certain **multidrug-resistant organisms**. - While valuable in resistant infections, it is not a first-line or commonly used choice for typical bacterial endocarditis compared to piperacillin/tazobactam.

Practice by Chapter

Beta-Lactam Antibiotics

Practice Questions

Aminoglycosides

Practice Questions

Macrolides and Ketolides

Practice Questions

Tetracyclines

Practice Questions

Quinolones

Practice Questions

Sulfonamides and Trimethoprim

Practice Questions

Antimycobacterial Drugs

Practice Questions

Antifungal Agents

Practice Questions

Antiviral Drugs

Practice Questions

Antiparasitic Agents

Practice Questions

Principles of Antimicrobial Selection

Practice Questions

Antimicrobial Resistance

Practice Questions

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