Mechanisms compared: Which statement is TRUE for both penicillins and fluoroquinolones?

Introduction / Context:
Understanding antimicrobial mechanisms helps anticipate activity and resistance. Penicillins (beta-lactams) and fluoroquinolones target different proteins, yet both exert their effects by binding to and inhibiting specific bacterial enzymes.

Given Data / Assumptions:

• Penicillins target penicillin-binding proteins (transpeptidases).
• Fluoroquinolones target DNA gyrase and topoisomerase IV.
• We are seeking a statement that is correct for both classes simultaneously.

Concept / Approach:
Penicillins acylate the active site serine of transpeptidases, blocking peptidoglycan cross-linking. Fluoroquinolones form drug–enzyme–DNA ternary complexes with DNA gyrase/topoisomerase IV, halting replication. In both cases, drug binding inactivates a bacterial protein essential for viability.

Step-by-Step Solution:
Check option a: true for both (PBPs for penicillin; gyrase/topo IV for fluoroquinolones). Option b: only penicillins inhibit cross-linking; fluoroquinolones do not. Option c: β-lactamase inactivates penicillins, not fluoroquinolones. Option d: fluoroquinolones must reach the cytoplasm; penicillins act in the periplasm (Gram-negatives) or at the cell wall (Gram-positives), not necessarily inside the cytoplasm. Option e: folate antagonism pertains to sulfonamides/trimethoprim, not these drug classes.

Verification / Alternative check:
Mechanism chapters consistently affirm protein targets: PBPs vs DNA gyrase/topo IV. Cell localization of action differs, reinforcing why option d is not universally true.

Why Other Options Are Wrong:
b, c, d, e each describes only one class or a different class entirely.

Common Pitfalls:
Assuming all antibiotics require cytoplasmic entry; beta-lactams target extracytoplasmic PBPs. Confusing enzymatic inactivation (β-lactamase) with target inhibition.

Final Answer:
Bind to and inactivate a bacterial protein.