Sterilization and Disinfection Practice Questions

Q: Which of the following is used as a skin antiseptic?

Chlorhexidine. **Explanation:** **Chlorhexidine (Option C)** is the correct answer because it is a potent biguanide antiseptic widely used for skin and mucous membranes. It works by disrupting bacterial cell membranes and precipitating cell contents. It is highly favored in clinical settings due to its **sustained residual activity** (it binds to the skin and remains active for hours) and its efficacy even in the presence of organic matter like blood. It is the gold standard for preoperative skin preparation and hand hygiene (e.g., Savlon, which is a combination of Chlorhexidine and Cetrimide). **Why the other options are incorrect:** * **Cidex (Option A):** This is a brand name for **2% Glutaraldehyde**. It is a high-level disinfectant used for "cold sterilization" of heat-sensitive instruments like endoscopes and bronchoscopes. It is too toxic and irritating for use on human skin. * **Cresol (Option B):** These are phenol derivatives. While effective against a wide range of microbes, they are generally too corrosive for skin application and are primarily used for disinfecting inanimate objects like floors and drains. * **Lysol (Option D):** This is a commercial disinfectant containing **Saponated Cresol**. Like pure cresol, it is intended for environmental surfaces (disinfection) rather than living tissue (antisepsis). **High-Yield Clinical Pearls for NEET-PG:** * **Antiseptics** are applied to living tissue; **Disinfectants** are applied to inanimate objects. * **Chlorhexidine** is contraindicated for use in the middle ear (risk of ototoxicity) and neurosurgical procedures (risk of neurotoxicity). * **Glutaraldehyde (Cidex)** requires 10 hours for sterilization (killing spores) but only 20 minutes for high-level disinfection. * **Cetrimide** is a quaternary ammonium compound often paired with chlorhexidine to enhance its detergent action.

Q: Which method is used for the sterilization of glassware?

Hot air oven. **Explanation:** **1. Why Hot Air Oven is Correct:** The **Hot Air Oven** is the method of choice for sterilizing **glassware** (such as Petri dishes, flasks, pipettes, and test tubes) because it utilizes **dry heat**. Dry heat causes sterilization by the oxidation of bacterial components and the denaturation of proteins. Unlike moist heat, dry heat does not cause moisture to condense on the glass, preventing the "clouding" of glassware and ensuring that items remain dry and ready for immediate use. The standard cycle is **160°C for 2 hours**. **2. Why Other Options are Incorrect:** * **Autoclaving (Moist Heat):** While highly effective, autoclaving can leave glassware wet, which may interfere with certain laboratory procedures. It is primarily used for culture media, surgical dressings, and heat-stable liquids. * **5% Cresol:** This is a chemical disinfectant (phenolic compound) used for environmental surfaces and disinfecting excreta. It achieves disinfection, not sterilization, and is unsuitable for laboratory glassware. * **Hot Water Bath:** This is used for incubation or heating reagents at controlled temperatures (e.g., 37°C or 56°C). It does not reach temperatures high enough to achieve sterilization. **3. High-Yield Clinical Pearls for NEET-PG:** * **Dry Heat Indicators:** The biological indicator used for Hot Air Ovens is **_Bacillus atrophaeus_** (formerly *B. subtilis var. niger*). * **Items Sterilized by Hot Air Oven:** Glassware, metallic instruments (forceps, scalpels), and anhydrous materials like **liquid paraffin, fats, grease, and dusting powder**. * **Important Note:** Sharp instruments are ideally sterilized in a Hot Air Oven to prevent the dulling of edges that occurs with autoclaving. * **Temperature-Time Ratios:** 160°C for 120 mins, 170°C for 60 mins, or 180°C for 30 mins.

Q: Disinfection of sputum is done by which method?

All. **Explanation:** The disinfection of sputum is a critical practice in infection control, particularly for preventing the transmission of *Mycobacterium tuberculosis*. The correct answer is **"All"** because each method listed effectively neutralizes the infectious pathogens found in respiratory secretions. 1. **Burning (Incineration):** This is the **most preferred method** for disposing of sputum collected in disposable containers (like cardboard cups). It ensures complete destruction of the organic matter and the pathogens within. 2. **Autoclaving:** This is the most reliable method for sterilization. Sputum samples or containers subjected to steam under pressure (121°C for 15-20 mins) ensure the destruction of all vegetative forms and highly resistant spores. 3. **Boiling:** While less effective than autoclaving, boiling for 20 minutes is a practical and common method for disinfecting sputum in resource-limited settings, as it kills most respiratory pathogens, including the tubercle bacilli. **Why "All" is correct:** In clinical practice, the choice of method depends on the setting. While incineration is best for disposal, autoclaving is used for laboratory decontamination, and boiling/chemical disinfection (using 5% Cresol or 1% Hypochlorite) is used when other methods are unavailable. **High-Yield Clinical Pearls for NEET-PG:** * **Chemical Disinfection:** If heat is not used, **5% Cresol (Lysol)** for 1 hour is the standard chemical disinfectant for sputum. * **Pre-treatment:** Sputum should be mixed with a disinfectant before disposal to prevent aerosolization. * **Culture Gold Standard:** For TB diagnosis, the **Lowenstein-Jensen (LJ) medium** is used, but for disinfection/sterilization questions, always prioritize methods that achieve complete microbial kill. * **Incineration** is the method of choice for **Biomedical Waste (BMW) Category Yellow** (infectious waste).

Q: Glassware and syringes are sterilized by which method?

Hot air oven. **Explanation:** The correct answer is **Hot air oven**. This method utilizes **dry heat** to achieve sterilization, primarily through the oxidation of cellular components and protein denaturation. **Why Hot Air Oven is correct:** Glassware (like Petri dishes, flasks, and pipettes) and all-glass syringes are heat-stable but can retain moisture or be damaged by high-pressure steam. Dry heat is the preferred method because it does not leave moisture residue, prevents the corrosion of glass surfaces, and effectively penetrates the materials. The standard cycle is **160°C for 2 hours** or **170°C for 1 hour**. **Why other options are incorrect:** * **Autoclave (Moist Heat):** While highly effective for surgical instruments and culture media, it is not ideal for glassware intended for dry use, as it leaves them wet and prone to re-contamination. * **Ethylene Oxide (ETO):** This is a form of chemical "cold sterilization" used for heat-sensitive items like plastic syringes, heart-lung machines, and catheters. It is unnecessary and expensive for heat-stable glassware. * **Irradiation:** Gamma rays (Cold Sterilization) are used for large-scale industrial sterilization of disposable plastic items (e.g., plastic syringes, swabs). **High-Yield Clinical Pearls for NEET-PG:** * **Sterilization Control:** The biological indicator for a Hot Air Oven is ***Bacillus subtilis* (var. *niger*)**, whereas for an Autoclave, it is ***Geobacillus stearothermophilus***. * **Dry Heat Items:** Besides glassware, it is used for **oils, powders, and greases** which are impermeable to steam. * **Note on Syringes:** While **all-glass** syringes are sterilized in a Hot Air Oven, **disposable plastic** syringes are sterilized by **Gamma Irradiation**.

Q: Which of the following agents is most commonly used to disinfect dental units and handpieces?

Glutaraldehyde. **Explanation:** **Glutaraldehyde** (Option B) is the correct answer because it is a high-level disinfectant and a potent "cold sterilant." In dental practice, handpieces and units often contain delicate components, lenses, or heat-sensitive materials that cannot withstand the high temperatures of an autoclave. Glutaraldehyde (typically used as a 2% alkaline solution, e.g., Cidex) works by alkylating amino, carboxyl, and hydroxyl groups of proteins. It is effective against bacteria, spores, fungi, and viruses (including HBV and HIV), making it the gold standard for semi-critical dental instruments. **Why other options are incorrect:** * **Clorox (Sodium Hypochlorite):** While a powerful disinfectant, it is highly corrosive to metals and can damage the internal turbine and gears of dental handpieces. * **Betadine (Povidone-iodine):** This is an antiseptic used on living tissues (skin/mucosa). It is not used for equipment disinfection as it causes staining and is not sporicidal at standard concentrations. * **Ethyl alcohol:** This is an intermediate-level disinfectant. It evaporates too quickly to ensure adequate contact time and is ineffective against bacterial spores and certain non-enveloped viruses. **High-Yield Clinical Pearls for NEET-PG:** * **Contact Time:** 2% Glutaraldehyde requires **20 minutes** for disinfection and **10 hours** for absolute sterilization (sporicidal action). * **Shelf Life:** Once "activated" by adding an alkalizing agent, the solution is typically stable for **14 days**. * **Alternative:** Ortho-phthalaldehyde (OPA) is a newer alternative to glutaraldehyde that is more stable and less irritating to the eyes and nasal passages. * **Classification:** According to Spaulding’s classification, dental handpieces are **Semi-critical items** (touch mucous membranes but do not penetrate sterile tissue).

Q: Sterilization accuracy is assessed by using which of the following biological indicators?

Clostridium perfringens. **Explanation** Biological indicators are the most reliable method for monitoring sterilization because they test the process against the most resistant microbial forms: bacterial spores. **Why Clostridium perfringens is the correct answer:** In the context of **Gaseous Sterilization (specifically Formaldehyde)**, *Clostridium perfringens* (formerly *C. welchii*) is the standard biological indicator used to ensure efficacy. While less common than other indicators in general hospital practice, it is the specific gold standard for validating formaldehyde sterilizers. **Analysis of Incorrect Options:** * **B. Geobacillus stearothermophilus:** This is the indicator for **Autoclaving (Moist Heat)** and **Plasma sterilization**. It is thermophilic, meaning it thrives at high temperatures, making it ideal for testing steam efficacy at 121°C. * **D. Bacillus subtilis (var. niger/globigii):** This is the indicator for **Dry Heat sterilization (Hot Air Oven)** and **Ethylene Oxide (EtO)**. It is highly resistant to desiccation. * **C. Clostridium butyricum:** This is a saprophytic bacterium and is not used as a standard biological indicator for any major sterilization process. **High-Yield Clinical Pearls for NEET-PG:** * **Autoclave:** *Geobacillus stearothermophilus* (spores). * **Hot Air Oven:** *Bacillus subtilis* (var. niger). * **Ethylene Oxide (EtO):** *Bacillus subtilis* (var. niger). * **Ionizing Radiation (Gamma rays):** *Bacillus pumilus*. * **Filtration:** *Brevundimonas diminuta* (used to test 0.22 µm filters). * **Formaldehyde:** *Clostridium perfringens*. **Note:** If the question does not specify the method of sterilization, *Geobacillus stearothermophilus* is the most frequently tested indicator in exams due to the ubiquity of autoclaving. However, per the specific key provided, *C. perfringens* is the specific indicator for formaldehyde.

Question 1

Mandatory washing of hands by a physician after examining each patient can reduce the incidence of iatrogenic infections. This is an example of:

Accepted Answer

Pre-current disinfection

Answer

Terminal disinfection

Answer

Concurrent disinfection

Answer

Post-current disinfection

Question 2

Which of the following is not affected by routine chlorination?

Accepted Answer

Polio virus

Answer

Rota virus

Answer

E. coli

Answer

None

Question 3

Which of the following is used as a skin antiseptic?

Accepted Answer

Chlorhexidine

Answer

Cidex

Answer

Cresol

Answer

Lysol

Question 4

Which method is used for the sterilization of glassware?

Accepted Answer

Hot air oven

Answer

Autoclaving

Answer

5% cresol

Answer

Hot water bath

Question 5

Sharps like needles and syringes, used for patients whose HIV status is unknown, should be immersed in what, for effective disposal?

Accepted Answer

None of the above

Answer

1% Povidone-iodine solution

Answer

Boiling water

Answer

1% Sodium hypochlorite solution

Question 6

Disinfection of sputum is done by which method?

Accepted Answer

All

Answer

Boiling

Answer

Autoclaving

Answer

Burning

Question 7

Glassware and syringes are sterilized by which method?

Accepted Answer

Hot air oven

Answer

Autoclave

Answer

Ethylene oxide

Answer

Irradiation

Question 8

What is the recommended temperature for autoclaving?

Accepted Answer

120°C for 10 minutes

Answer

120°C for 15 minutes

Answer

135°C for 3 minutes

Answer

140°C for 5 minutes

Question 9

Which of the following agents is most commonly used to disinfect dental units and handpieces?

Accepted Answer

Glutaraldehyde

Answer

Clorox

Answer

Betadine

Answer

Ethyl alcohol

Question 10

Sterilization accuracy is assessed by using which of the following biological indicators?

Accepted Answer

Clostridium perfringens

Answer

Geobacillus stearothermophilus

Answer

Clostridium butyricum

Answer

Bacillus subtilis

Sterilization and Disinfection — MCQs

Sterilization and Disinfection — MCQs

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