Infection Control · patient case question
By what mechanism does an alcohol-based sanitizer kill microorganisms?
Patient case: A murmur, a virus and a bottle of hand sanitizer
Patient: Two patients and a practice question
Chief Complaint: A: “I need this broken tooth out.” B: attends with his sister, who has questions.
Background: A, 52-year-old male: a heart murmur was noted years ago at a routine physical and never investigated further. No prosthetic valve, no previous endocarditis, no congenital heart disease, no transplant. B, 38-year-old male: HIV positive, on antiretroviral therapy, viral load undetectable, CD4 610. His sister asks whether it is safe for the family to share utensils with him.
Vital Signs: A: BP 126/78 mmHg · HR 74 bpm
Findings: A: tooth #31 non-restorable. Alcohol-based hand rub is in use throughout the practice.
Show answer and explanation
Correct answer: A. Denaturation and coagulation of proteins
- A. CORRECT. Alcohols — ethanol and isopropanol — act physically rather than metabolically: they DENATURE and COAGULATE proteins, which disrupts the cell membrane and inactivates cellular enzymes. Water is required for the process, which is why 60–90% alcohol is MORE effective than absolute alcohol: the water allows the protein to unfold so it can be denatured. Because there is no specific metabolic target, resistance does not develop.
- B. Inhibition of cell wall synthesis is the mechanism of the beta-lactam ANTIBIOTICS — a selective metabolic target inside a living cell, not a topical biocidal action.
- C. Alkylation of nucleic acids and proteins is the mechanism of GLUTARALDEHYDE and ETHYLENE OXIDE, which is why those are high-level disinfectants and sterilants rather than hand agents.
- D. Free-radical oxidation describes HYDROGEN PEROXIDE and PERACETIC ACID.
Note: The limits follow from the mechanism. Alcohol is NOT sporicidal, has poor activity against non-enveloped viruses such as norovirus, and is INACTIVATED BY VISIBLE SOIL — so hands that are visibly contaminated must be washed with soap and water, not rubbed. Alcohol is also a poor ENVIRONMENTAL surface disinfectant because it evaporates before the required contact time is achieved and it fixes organic debris.
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