Mechanism of action of thimerosal:

• A. Irreversibly bind to the phospholipids and proteins of the membrane, thereby impairing permeability
• B. Causes cell membrane disruption and denaturation of bacterial proteins
• C. Precipitation of proteins and oxidation of sulfhydryl groups
• D. Crosslinking of macromolecules

Answer: (C)

Thimerosal works mainly by reacting with sulfhydryl (thiol) groups in proteins. The mercury component binds to these -SH sites, causing oxidation of sulfhydryl groups and crosslinking that leads to protein precipitation. This inactivates essential enzymes and structural proteins, disrupting cellular functions and producing its antimicrobial effect. The description of precipitating proteins and oxidizing sulfhydryl groups captures this specific interaction with thiol groups, which is the hallmark of its action.

It isn’t best described by membrane disruption or irreversible binding to membrane phospholipids, nor by broad, non-specific crosslinking of macromolecules alone. Those patterns don’t precisely reflect thimerosal’s primary mechanism, which centers on thiol-targeted protein modification.