General Microbiology — MCQs

Q: Which agent is used for the sterilization of a cystoscope?

Glutaraldehyde. **Explanation:** The correct answer is **Glutaraldehyde (Option A)**. Cystoscopes are classified under **Spaulding’s Classification** as **semi-critical items** because they come into contact with mucous membranes but do not penetrate sterile tissue. These instruments require **High-Level Disinfection (HLD)**. **2% Glutaraldehyde (Cidex)** is the gold standard for heat-sensitive endoscopes. It acts by alkylation of amino, carboxyl, and hydroxyl groups, effectively killing bacteria, spores, fungi, and viruses. For HLD, an immersion time of **20 minutes** is standard, while **10 hours** is required for absolute sterilization (sporicidal action). **Why other options are incorrect:** * **Formaldehyde (B):** While a strong disinfectant, it is rarely used for endoscopes due to its pungent odor, irritating fumes, and potential carcinogenicity. It is primarily used for preserving tissues or fumigating rooms. * **Isopropyl alcohol (C):** This is a low-to-intermediate level disinfectant. It lacks sporicidal activity and can damage the lensed components and adhesives of a cystoscope. * **Ethylene oxide (D):** ETO is a method of sterilization for heat-sensitive items. However, it is a slow process requiring long aeration times to remove toxic residues, making it impractical for the rapid turnover required for cystoscopes in clinical practice. **High-Yield Clinical Pearls for NEET-PG:** * **Cidex Stability:** Once "activated" by adding an alkalizing agent, the solution is stable for only **14 days**. * **Ortho-phthalaldehyde (OPA):** A newer alternative to glutaraldehyde that is more stable and does not require activation, though it is more expensive. * **Plasma Sterilization (H2O2):** Increasingly used for modern robotic instruments and some endoscopes, but glutaraldehyde remains the most frequent answer for traditional "cold sterilization" questions.

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