Which mechanism best describes thimerosal action on bacterial cells?

• 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 targeting proteins that contain sulfhydryl (-SH) groups. Mercury from thimerosal binds strongly to these thiol sites, causing changes to the protein's shape and function. This binding can lead to oxidation of the SH groups and promote protein precipitation or irreversible inactivation of essential enzymes. When key proteins and enzymes are inactivated, bacterial cells can no longer carry out necessary processes, leading to cell death.

Other descriptions describe membrane disruption or broad crosslinking of macromolecules, but the defining action of thimerosal is its high affinity for sulfhydryl groups in proteins, resulting in precipitation and loss of function rather than primarily tearing apart membranes or indiscriminately crosslinking all macromolecules.