Sterilization and Disinfection — MCQs

Sterilization and Disinfection Indian Medical PG Practice Questions and MCQs

Question 231: Syringes and glassware are sterilized by:

A. Irradiation
B. Cidex
C. Autoclave (Correct Answer)
D. Hot air oven

Explanation: ***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.

Question 232: What is the definition of an antiseptic?

A. An agent applied on skin to inhibit the growth of pathogenic microbes. (Correct Answer)
B. Used to sterilize inanimate objects.
C. An agent that kills bacteria and some viruses.
D. An agent that can reduce the number of microorganisms but does not necessarily kill all.

Explanation: ***An agent applied on skin to inhibit the growth of pathogenic microbes.*** - Antiseptics are specifically formulated for use on **living tissues**, such as the skin, to prevent infection. - Their primary role is to **inhibit the growth** and reproduction of microorganisms rather than necessarily killing all of them. *Used to sterilize inanimate objects.* - This definition describes a **disinfectant** or a sterilant, which are harsh chemicals not suitable for living tissue. - **Sterilization** aims to eliminate all forms of microbial life, including spores, which is a more rigorous process. *An agent that kills bacteria and some viruses.* - While some antiseptics can kill microbes, this definition is too broad and could apply to **disinfectants** as well. - The key differentiator for an antiseptic is its **safety for application on living tissue**. *An agent that can reduce the number of microorganisms but does not necessarily kill all.* - This statement is partially true for antiseptics in terms of their action, but it lacks the crucial context of their **application on living tissue**. - Without specifying application on skin or living surfaces, this definition could also describe a **sanitizer**.

Question 233: The minimum time required for the sterilization of surgical instruments by moist heat at 134°C is:

A. 15 minutes
B. 30 minutes
C. 60 minutes
D. 3 minutes (Correct Answer)

Explanation: ***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.

Question 234: Heat-labile liquids are sterilized by?

A. Hot air oven
B. Autoclaving
C. Membrane filter (Correct Answer)
D. Moist heat

Explanation: ***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.

Question 235: Which of the following agents is not considered a complete sterilization agent?

A. Hydrogen peroxide
B. Sodium hypochlorite
C. Absolute alcohol (Correct Answer)
D. Glutaraldehyde

Explanation: ***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**.

Question 236: What is the preferred method for sterilizing disposable syringes?

A. Gas sterilization (Ethylene oxide) (Correct Answer)
B. Steam sterilization (Autoclave)
C. Chemical sterilization (Cidex)
D. Dry heat sterilization (Hot air oven)

Explanation: ***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.

Question 237: Which of the following agents is both a disinfectant and an antiseptic?

A. Hydrogen peroxide (Correct Answer)
B. Sodium hypochlorite
C. Glutaraldehyde
D. Methylated spirit

Explanation: ***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 238: All are methods of sterilization except.

A. Filtration
B. Heat
C. Gases
D. Sunlight (Correct Answer)

Explanation: ***Sunlight*** - While sunlight has some **disinfectant** properties due to its **UV radiation**, it is not considered a reliable method of **sterilization** because it cannot kill all forms of microbial life, including bacterial spores. - Sterilization requires the **complete elimination of all viable microorganisms**, which sunlight cannot consistently achieve. *Gases* - Certain gases, such as **ethylene oxide** and **hydrogen peroxide vapor**, are effective **sterilizing agents** used for heat-sensitive materials and medical devices. - These gases penetrate packaging and kill microorganisms by **alkylating proteins** and **nucleic acids**. *Filtration* - **Filtration** is a method of **sterilization** for liquids and gases that cannot withstand heat, by physically removing microorganisms. - Filters with very small pore sizes (e.g., **0.22 micrometers**) can retain bacteria and fungi, even though they do not kill them. *Heat* - **Heat** is one of the most common and effective methods of sterilization, used in various forms like **dry heat** (e.g., sterilization ovens) and **moist heat** (e.g., autoclaving). - **Autoclaving** with **saturated steam under pressure** is particularly effective as it rapidly coagulates and denatures microbial proteins.

Question 239: Autoclave works at which of the following settings?

A. 160 degree C, 20 psi, 15 min
B. 121 degree C, 15 psi, 15 min (Correct Answer)
C. 120 degree C, 15 psi, 10 min
D. 121 degree C, 15 psi, 15 sec

Explanation: ***121 degree C, 15 psi, 15 min*** - The standard operating conditions for **autoclave sterilization** are **121°C (250°F)**, achieved at **15 pounds per square inch (psi)** of pressure, maintained for a duration of **15 to 30 minutes**. - These parameters ensure the effective **killing of bacterial spores**, including those of *Geobacillus stearothermophilus*, which is the biological indicator for steam sterilization. *160 degree C, 20 psi, 15 min* - A temperature of **160°C** is typically used for **dry heat sterilization**, which requires a longer exposure time (e.g., 2 hours). - This option combines an inappropriate temperature for steam sterilization with an insufficient time for dry heat, making it ineffective for both. *120 degree C, 15 psi, 10 min* - While close, **120°C** is slightly below the standard **121°C** required for optimal steam sterilization, which may compromise efficacy. - A duration of **10 minutes** is also generally considered insufficient to achieve sterility for all materials, particularly for larger loads or resistant spores. *121 degree C, 15 psi, 15 sec* - Although the temperature and pressure are correct at **121°C and 15 psi**, a duration of only **15 seconds** is far too short to achieve proper sterilization. - Sterilization processes require adequate exposure time to ensure that heat penetrates all items and inactivates all microorganisms, including resistant spores.

Question 240: In the context of filtration, what type of filter is a Seitz filter?

A. Depth filter (Correct Answer)
B. Candle filter
C. Membrane filter
D. Sintered glass filter

Explanation: ***Depth filter*** - A **Seitz filter** is a classic example of a **depth filter**, which works by trapping particles within a thick matrix of fibrous material. - Its mechanism involves both **adsorption** and **mechanical retention** as fluid passes through the tortuous path of the filter medium. *Candle filter* - **Candle filters**, such as ceramic filters, are generally **surface filters** that retain particles on their outer surface. - They are often used for larger particle removal and can be cleaned more easily than depth filters. *Membrane filter* - **Membrane filters** operate primarily as **surface filters** with very precise pore sizes, providing absolute filtration efficiency for submicron particles. - They are typically made from polymeric materials and are used for sterile filtration and precise particle separation. *Sintered glass filter* - **Sintered glass filters** are made by fusing glass particles to create a porous structure used primarily in **laboratory settings** for chemical filtration. - While they can act as a depth filter, they are distinct from the industrial-scale fibrous depth filters like the Seitz filter.

Practice by Chapter

Physical Methods of Sterilization

Practice Questions

Chemical Methods of Sterilization

Practice Questions

Disinfectants and Antiseptics

Practice Questions

Sterilization Monitoring

Practice Questions

Hospital Sterilization Protocols

Practice Questions

Surgical Instruments Sterilization

Practice Questions

Endoscope Reprocessing

Practice Questions

Biological Indicators

Practice Questions

Factors Affecting Sterilization

Practice Questions

Quality Control in Sterilization

Practice Questions

Biofilm and Its Implications

Practice Questions

Regulatory Aspects of Sterilization

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free