Sterilization and Disinfection Practice Questions

Q: Glass vessels and syringes are best sterilised by -

Dry heat sterilization in a hot air oven. **Dry heat sterilization in a hot air oven** - **Dry heat sterilization** (160-180°C for 1-2 hours) is the **traditional and preferred method** for **glassware and glass syringes**. - **Hot air ovens** achieve sterilization by oxidative destruction and protein denaturation, leaving items completely **dry** and free from moisture. - **Advantages**: No corrosion, no rusting, items remain dry, ideal for **powders, oils, and glassware** that can withstand high temperatures. - **Note**: This question refers to **glass syringes** (historically used, now largely replaced by disposable plastic syringes which are pre-sterilized by radiation). *Steam sterilization in an autoclave* - **Autoclaving** uses **moist heat** (121°C at 15 psi for 15 minutes) and is highly effective for most medical instruments. - **Disadvantage for glassware**: Rapid temperature changes and steam exposure can cause **thermal shock, cracking, or etching** of delicate glassware. - Items emerge **wet** and require drying, which is undesirable for certain laboratory applications. - **Modern context**: Standard method for surgical instruments and heat-stable plastics. *Ethylene oxide sterilization* - **Ethylene oxide (ETO)** is a **low-temperature chemical sterilization** method (50-60°C) for heat-sensitive items. - Used for plastics, rubber, electronics, and endoscopes that cannot tolerate heat. - Requires **long exposure** (12-24 hours) and **aeration period** (up to 7 days) to remove toxic residues. - **Not preferred** for routine glassware sterilization when heat methods are suitable. *Radiation sterilization* - **Gamma radiation or electron beam** sterilization is used for **pre-packaged disposable medical devices**, pharmaceuticals, and plastic syringes. - Highly effective but **expensive** and requires specialized facilities. - Not practical for **routine laboratory glassware** sterilization in clinical or research settings.

Q: Prions are best killed by

Autoclaving at 134°C (for 18 minutes). ***Autoclaving at 134°C (for 18 minutes)*** - **Prions** are highly resistant to conventional sterilization methods, and **autoclaving at 134°C for at least 18 minutes** is the **most effective method for sterilizing reusable medical instruments** contaminated with prions. - This high temperature and pressure protocol (WHO/CDC recommended) helps to denature the misfolded protein structure of prions, reducing their infectivity to safe levels. - **In the context of sterilization and disinfection**, this is the best practical method for surgical instruments that cannot be discarded. *Incineration at high temperatures* - **Incineration at 800-1000°C** achieves complete combustion and is **highly effective** at destroying prions. - However, incineration is used only for **single-use disposable items** and prion-contaminated waste, not for reusable surgical instruments. - In the clinical context of sterilization (implied by this topic), autoclaving is the preferred answer as it applies to reusable equipment. *Sodium hypochlorite solution* - **Sodium hypochlorite** (bleach) at **high concentrations** (20,000 ppm or 2% available chlorine) for extended contact times (1+ hours) can inactivate prions. - However, it is **corrosive to instruments**, damages tissue samples, and requires precise concentration and exposure conditions, making it less practical than autoclaving. *5% formalin solution* - Formalin is **not effective at inactivating prions**; it can actually **preserve and stabilize** prion infectivity. - Formalin cross-links proteins and preserves tissue morphology but does not reliably break down the highly stable **beta-sheet structures** characteristic of prions.

Q: Syringes and glassware are sterilized by:

Autoclave. ***Autoclave*** - An **autoclave** uses **moist heat** (steam under pressure) which is highly effective for sterilizing medical equipment like syringes and glassware by denaturing proteins and destroying microorganisms. - The combination of **high temperature** (typically 121°C or 132°C) and **pressure** rapidly penetrates materials, ensuring sterilization. *Irradiation* - **Irradiation** (using gamma rays or electron beams) is primarily used for sterilizing heat-sensitive materials, very large volumes, or items that need to remain packaged, such as pre-packaged disposable medical devices. - While effective, it's not the standard or preferred method for routine sterilization of reusable syringes and glassware in a clinical setting due to cost and logistical considerations. *Cidex* - **Cidex** (glutaraldehyde-based solution) is a **high-level disinfectant** used for sterilizing heat-sensitive instruments that cannot be autoclaved. - While it can achieve sterilization with prolonged exposure, it is a liquid chemical method and not the primary choice for glassware and syringes when an autoclave is available, as it requires rinsing and careful handling of toxic chemicals. *Hot air oven* - A **hot air oven** uses **dry heat** for sterilization, typically at higher temperatures (e.g., 160-170°C) for longer durations (e.g., 1-2 hours) than an autoclave. - It is primarily used for sterilizing materials that are sensitive to moisture, such as powders, oils, and some glassware that needs to remain dry, but it is less efficient and slower than an autoclave for general sterilization of syringes and standard glassware.

Q: The minimum time required for the sterilization of surgical instruments by moist heat at 134°C is:

3 minutes. ***Correct: 3 minutes*** - At a temperature of **134°C**, the high pressure of **moist heat** (prevacuum sterilization) effectively denatures proteins and destroys all microorganisms, including spores, requiring only **3-4 minutes** of exposure time. - This short duration ensures rapid turnaround time for surgical instruments while achieving complete **sterilization**, making it ideal for urgent or flash sterilization cycles. - This is a standard protocol widely used in hospital autoclaves for wrapped instruments. *Incorrect: 15 minutes* - While 15 minutes is a common sterilization time, it is typically used at a lower temperature of **121°C** (gravity displacement sterilization) for moist heat sterilization. - At 134°C, a 15-minute exposure would be unnecessarily long, consuming more energy and time without additional sterilization benefit. *Incorrect: 30 minutes* - A 30-minute sterilization cycle is excessive for moist heat at **134°C**, indicating a misunderstanding of standard sterilization parameters. - This duration is more typical for sterilization at **121°C** with gravity displacement, or for large/dense loads requiring extended heat penetration time. *Incorrect: 60 minutes* - A 60-minute cycle is far too long for routine sterilization of surgical instruments at **134°C** with moist heat. - Such extended times are generally reserved for **dry heat sterilization** (160-180°C for 60-120 minutes) or very specific difficult-to-sterilize items with complex lumens.

Q: Heat-labile liquids are sterilized by?

Membrane filter. ***Membrane filter*** - **Membrane filtration** is a method used for **sterilizing heat-labile liquids** as it physically removes microorganisms without using heat. - This technique is essential for materials like **vaccines**, **antibiotics**, and **serum** that would be damaged by high temperatures. *Hot air oven* - A **hot air oven** uses **dry heat** for sterilization, typically at very high temperatures (e.g., 160-180°C for 2 hours). - This method is suitable for **heat-resistant materials** like glassware and metal instruments, but would destroy heat-labile liquids. *Autoclaving* - **Autoclaving** employs **moist heat under pressure** (e.g., 121°C at 15 psi for 15-20 minutes) to achieve sterilization. - It is effective for many materials, but the high temperatures involved would still **denature or degrade heat-labile substances**. *Moist heat* - **Moist heat** (like that used in autoclaving or boiling) is generally more effective than dry heat at lower temperatures. - However, even lower temperatures of moist heat, if sustained, can still **damage heat-sensitive liquids**, making filtration a preferred method.

Q: Which of the following agents is not considered a complete sterilization agent?

Absolute alcohol. ***Absolute alcohol*** - **Absolute alcohol** (70-90% ethanol or isopropanol) is a **disinfectant** that reduces the number of microorganisms on surfaces but does not reliably kill **bacterial spores**. - Sterilization requires the **complete elimination** of all microbial life forms, including spores, which alcohol cannot achieve. *Glutaraldehyde* - **Glutaraldehyde** is a **high-level disinfectant** and **sterilant** when used at appropriate concentrations and exposure times. - It is effective against **bacteria**, **viruses**, **fungi**, and **bacterial spores**. *Hydrogen peroxide* - **Hydrogen peroxide** in concentrated forms (e.g., 6-25%) is used as a **sterilant** for heat-sensitive medical devices. - It effectively kills **bacteria**, **viruses**, **fungi**, and **bacterial spores** by generating destructive free radicals. *Sodium hypochlorite* - **Sodium hypochlorite** (bleach) is a powerful oxidizing agent that can achieve **sterilization** at higher concentrations and longer contact times, particularly for surfaces. - It works by denaturing proteins and inactivating microorganisms, including **bacterial spores**.

Q: What is the preferred method for sterilizing disposable syringes?

Gas sterilization (Ethylene oxide). ***Steam sterilization (Autoclave)*** - While generally effective, **disposable syringes** are typically **pre-sterilized** by the manufacturer using methods like radiation or ethylene oxide and are not meant for resterilization. - Reusing and resterilizing disposable syringes, even with an autoclave, is **not recommended** due to potential material degradation and safety concerns. *Chemical sterilization (Cidex)* - **Cidex (glutaraldehyde)** is a high-level disinfectant primarily used for **heat-sensitive instruments** that cannot withstand high temperatures, such as endoscopes. - It involves **immersion** and is not suitable for the rapid, high-volume sterilization of plastic disposable syringes due to potential residue and material incompatibility. *Dry heat sterilization (Hot air oven)* - Requires **prolonged exposure** to high temperatures and is suitable for **glassware** and **oil-based substances**. - **Plastic disposable syringes** would melt or degrade at the required temperatures (160-170°C) for effective dry heat sterilization. *Gas sterilization (Ethylene oxide)* - **Ethylene oxide (EtO)** is the **preferred industrial method** for sterilizing heat-sensitive and moisture-sensitive medical devices, including **disposable plastic syringes**, by manufacturers. - It penetrates packaging effectively and sterilizes without damaging plastic, but requires specialized equipment and extensive aeration due to its **toxic and flammable nature**, making it impractical for point-of-use sterilization.

Q: Endoscope is sterilized by:

Glutaraldehyde. **Glutaraldehyde** - **Glutaraldehyde** is a high-level disinfectant used for sterilizing heat-sensitive instruments like endoscopes, as it effectively kills bacteria, viruses, fungi, and spores without damaging the instruments. - Endoscopes cannot withstand the high temperatures of autoclaving, making chemical disinfection with agents like **glutaraldehyde** the preferred method. *Formalin* - **Formalin** (formaldehyde solution) is a strong disinfectant and sterilant, but it is highly toxic, irritating, and has a strong pungent odor, making it less suitable for routine clinical sterilization of endoscopes compared to glutaraldehyde. - While effective, its safety profile and handling difficulties mean it is not the primary choice for endoscope reprocessing in most healthcare settings. *Autoclaving* - **Autoclaving** uses high-pressure steam and high temperatures to sterilize instruments, which would damage the delicate optical fibers, electronics, and heat-sensitive plastics of endoscopes. - For this reason, endoscopes are considered **heat-labile** and cannot be sterilized using an autoclave. *Boiling* - **Boiling** is a low-level disinfection method that is insufficient to achieve sterilization as it does not kill bacterial spores and some viruses. - While it can disinfect some instruments, it is inadequate for complex medical devices like endoscopes that require high-level disinfection or sterilization.

Q: Which of the following agents is both a disinfectant and an antiseptic?

Hydrogen peroxide. ***Hydrogen peroxide*** - It is used as a **disinfectant** for surfaces and medical equipment, effectively killing bacteria, viruses, fungi, and spores. - It is also applied as an **antiseptic** for wound cleaning and oral rinses due to its ability to release oxygen, which is toxic to anaerobic bacteria. - H₂O₂ represents the **classic example** of a dual-purpose agent with **balanced use** in both roles. *Sodium hypochlorite* - Primarily used as a **disinfectant** for surfaces and water purification due to its strong oxidizing properties. - While it has antimicrobial properties, it is generally considered too **irritating and corrosive** for direct application to living tissues as an antiseptic. *Glutaraldehyde* - This is a **high-level disinfectant** and sterilant, often used for heat-sensitive medical instruments like endoscopes. - Its high toxicity and irritant nature make it unsuitable for use as an **antiseptic** on living tissues. *Methylated spirit* - Methylated spirit (denatured ethanol) is **predominantly used as an antiseptic** for skin preparation before injections or minor procedures. - While alcohols do have disinfectant properties for surfaces, methylated spirit's **primary clinical role** is skin antisepsis rather than environmental disinfection. - Unlike hydrogen peroxide, it lacks the **balanced dual-purpose application** that makes H₂O₂ the classic textbook example.

Question 1

Glass vessels and syringes are best sterilised by -

Accepted Answer

Dry heat sterilization in a hot air oven

Answer

Steam sterilization in an autoclave

Answer

Ethylene oxide sterilization

Answer

Radiation sterilization

Question 2

Prions are best killed by

Accepted Answer

Autoclaving at 134°C (for 18 minutes)

Answer

Incineration at high temperatures

Answer

5% formalin solution

Answer

Sodium hypochlorite solution

Question 3

Syringes and glassware are sterilized by:

Accepted Answer

Autoclave

Answer

Irradiation

Answer

Cidex

Answer

Hot air oven

Question 4

What is the definition of an antiseptic?

Accepted Answer

An agent applied on skin to inhibit the growth of pathogenic microbes.

Answer

Used to sterilize inanimate objects.

Answer

An agent that kills bacteria and some viruses.

Answer

An agent that can reduce the number of microorganisms but does not necessarily kill all.

Question 5

The minimum time required for the sterilization of surgical instruments by moist heat at 134°C is:

Accepted Answer

3 minutes

Answer

15 minutes

Answer

30 minutes

Answer

60 minutes

Question 6

Heat-labile liquids are sterilized by?

Accepted Answer

Membrane filter

Answer

Hot air oven

Answer

Autoclaving

Answer

Moist heat

Question 7

Which of the following agents is not considered a complete sterilization agent?

Accepted Answer

Absolute alcohol

Answer

Hydrogen peroxide

Answer

Sodium hypochlorite

Answer

Glutaraldehyde

Question 8

What is the preferred method for sterilizing disposable syringes?

Accepted Answer

Gas sterilization (Ethylene oxide)

Answer

Steam sterilization (Autoclave)

Answer

Chemical sterilization (Cidex)

Answer

Dry heat sterilization (Hot air oven)

Question 9

Endoscope is sterilized by:

Accepted Answer

Glutaraldehyde

Answer

Formalin

Answer

Autoclaving

Answer

Boiling

Question 10

Which of the following agents is both a disinfectant and an antiseptic?

Accepted Answer

Hydrogen peroxide

Answer

Sodium hypochlorite

Answer

Glutaraldehyde

Answer

Methylated spirit

Sterilization and Disinfection — MCQs

Sterilization and Disinfection — MCQs

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