Mechanism of action — Which disinfectant class primarily kills by disrupting microbial cytoplasmic membranes and causing leakage of cell contents?

Introduction / Context:
Understanding the primary mode of action helps select disinfectants for specific applications and anticipate activity gaps (e.g., poor efficacy on spores or certain nonenveloped viruses). Quaternary ammonium compounds (QACs), also called cationic detergents, are widely used for environmental surface disinfection and some medical instrument cleaning steps.

Given Data / Assumptions:

• We compare chemical classes with distinct mechanisms.
• Target mechanism: membrane disruption leading to leakage and death.
• Microbial spectrum varies with soil load and organism type.

Concept / Approach:
Cationic detergents interact with negatively charged microbial membranes, solubilizing lipids and disrupting membrane integrity, which increases permeability and causes leakage of essential intracellular components. Halogens oxidize proteins; heavy metals denature enzymes via sulfhydryl binding; aldehydes crosslink proteins and nucleic acids.

Step-by-Step Solution:

Verification / Alternative check:
Disinfection manuals classify QACs as membrane-active agents with good activity against Gram-positive bacteria and enveloped viruses, reduced activity against spores, mycobacteria, and some Gram-negatives in organic soil.

Why Other Options Are Wrong:

• Halogens: oxidative damage to proteins and nucleic acids.
• Heavy metals: enzyme inactivation via thiol binding.
• Aldehydes: covalent crosslinking; high-level disinfection/sterilization.

Common Pitfalls:
Overusing QACs on heavily soiled or spore-contaminated surfaces; pre-cleaning is essential and sporicidal agents may be required.

Final Answer:
Cationic detergents