Sterilization and Disinfection — MCQs

Sterilization and Disinfection Indian Medical PG Practice Questions and MCQs

Question 241: Sterilization accuracy is assessed by using:

A. Clostridium botulinum
B. Geobacillus stearothermophilus (Correct Answer)
C. Staphylococcus aureus
D. Clostridium perfringens

Explanation: ***Geobacillus stearothermophilus*** - This organism forms **highly resistant spores** and is used as a **biological indicator** to validate steam sterilization processes. - The presence or absence of growth after sterilization indicates whether critical parameters like temperature, pressure, and time were met. *Clostridium perfringens* - This bacterium is a common cause of **gas gangrene** and food poisoning, forming spores, but it is not typically used for sterilization validation. - Its spores are **not considered as resistant** to heat as those of *Geobacillus stearothermophilus*. *Staphylococcus aureus* - This is a well-known human pathogen causing a variety of infections and is **not a spore-forming bacterium**. - Therefore, it is **not suitable for assessing sterilization efficacy** against highly resistant microbial forms. *Clostridium botulinum* - This is a spore-forming bacterium known for producing a potent **neurotoxin** and is a concern in food preservation. - While spore-forming, its spores are **less heat-resistant** than *Geobacillus stearothermophilus* and it is not the standard biological indicator.

Question 242: Which item cannot be effectively sterilized using a hot air oven?

A. Liquid paraffin
B. Instruments
C. Culture media (Correct Answer)
D. Needles

Explanation: ***Culture media*** - Heat sterilization in a hot air oven would cause **dehydration** and **degradation of nutrients** in most culture media, rendering them unusable for microbial growth. - Many components of culture media, such as **sugars** and **proteins**, are heat-sensitive and will break down at the high temperatures required for sterilization in a hot air oven. *Liquid paraffin* - **Oils** and **greases** can be effectively sterilized by a hot air oven because they are unable to be sterilized by steam due to its inability to penetrate oil-based substances. - The dry heat effectively kills microorganisms by causing **oxidative damage** to cellular components without causing unwanted chemical reactions. *Instruments* - **Surgical instruments** made of metal are ideal for sterilization in a hot air oven as dry heat can penetrate their surfaces and kill microorganisms without causing corrosion common with moist heat. - This method is effective for instruments that can withstand high temperatures and are sensitive to moisture. *Needles* - **Metal needles** can be safely sterilized in a hot air oven, as it effectively destroys all microbial life including spores, and prevents **rusting** or **dulling** often caused by steam sterilization. - The dry heat ensures that instruments remain sharp and undamaged after sterilization.

Question 243: Which of the following statements about iodophores is incorrect?

A. Surfactants
B. Release iodine
C. Inorganic compounds (Correct Answer)
D. Disinfectant

Explanation: ***Inorganic compounds*** - Iodophores are **organic** complexes containing iodine, not inorganic compounds. - They are formed by combining iodine with a **solubilizing agent**, such as a surfactant or polymer. *Release iodine* - Iodophores are designed to **slowly release free iodine**, which is responsible for their bactericidal activity. - This gradual release mechanism provides a sustained antimicrobial effect. *Surfactants* - Many iodophores utilize **surfactants** (e.g., povidone-iodine) as the carrier molecule to improve solubility and penetration. - Surfactants help in the wetting and spreading of the iodine complex, enhancing its efficacy. *Disinfectant* - Iodophores are widely used as **antiseptics and disinfectants** due to their broad-spectrum microbicidal activity. - They are effective against **bacteria, viruses, fungi, and spores**.

Question 244: Which method is suitable for sterilizing media containing serum?

A. Micropore filter (Correct Answer)
B. Gamma radiation
C. Centrifugation
D. Autoclaving

Explanation: ***Micropore filter*** - This method uses **physical exclusion** to remove microorganisms from heat-sensitive liquids by passing them through a filter with pores small enough to trap bacteria but allow the liquid to pass. - Since serum proteins are **heat-labile**, filtration is ideal as it avoids high temperatures that would denature the proteins and destroy essential growth factors. *Autoclaving* - **Autoclaving** uses high-pressure saturated steam at temperatures typically around 121°C, which would cause **denaturation** and precipitation of serum proteins. - This method is suitable for heat-stable media but is destructive to heat-sensitive components like serum, vitamins, and certain antibiotics. *Gamma radiation* - While effective for sterilizing heat-sensitive materials, **gamma radiation** can cause chemical changes and generate reactive free radicals within serum. - This can potentially alter the biological activity of crucial growth factors and hormones present in the serum, making it unsuitable for cell culture applications. *Centrifugation* - **Centrifugation** separates components based on density and size, primarily used for harvesting cells or removing large debris, not for sterilizing liquids. - It does not effectively remove or kill **bacteria, viruses, or spores** from a liquid medium, which are necessary for true sterilization.

Question 245: The quality control agent for sterilization in an autoclave is:

A. Bacillus globigii
B. Bacillus subtilis
C. Bacillus pumilus
D. Bacillus stearothermophilus (Correct Answer)

Explanation: ***Bacillus stearothermophilus*** - **_Bacillus stearothermophilus_** spores are used as **biological indicators** for **autoclave sterilization** (moist heat) due to their high resistance to heat. - Their destruction indicates that the sterilization cycle has been effective in achieving sterility. *Bacillus subtilis* - **_Bacillus subtilis_** spores are typically used as biological indicators for **ethylene oxide sterilization**, not autoclaving. - While robust, they are not the standard indicator for **moist heat sterilization** due to their lower resistance compared to _B. stearothermophilus_. *Bacillus pumilus* - **_Bacillus pumilus_** spores are used as biological indicators primarily for **radiation sterilization** processes. - They are not the standard **biological indicator** for **autoclave efficacy**. *Bacillus globigii* - **_Bacillus globigii_** (now known as _Bacillus atrophaeus_) spores are used as biological indicators for **dry heat sterilization**. - They are not the appropriate indicator for **moist heat sterilization** using an autoclave.

Question 246: Which spores are used to test the efficacy of moist heat sterilization?

A. Bacillus stearothermophilus (Correct Answer)
B. Clostridium tetani
C. Bacillus subtilis
D. Clostridium botulinum

Explanation: ***Bacillus stearothermophilus*** - The spores of **Bacillus stearothermophilus** (now referred to as **Geobacillus stearothermophilus**) are highly resistant to heat. - Due to their heat resistance, they are used as the **standard biological indicator** for monitoring the efficacy of **moist heat sterilization** (autoclaving) processes. - These spores can survive temperatures up to 121°C, making them ideal for testing autoclave effectiveness. *Clostridium tetani* - While **Clostridium tetani** forms highly resistant spores, it is **not used as a biological indicator** for sterilization processes. - This organism is clinically significant as the causative agent of tetanus, not as a sterilization test organism. - Standard biological indicators are specially selected *Bacillus* and *Geobacillus* species with known resistance characteristics. *Bacillus subtilis* - **Bacillus subtilis** (and **Bacillus atrophaeus**) spores are used as biological indicators for **dry heat sterilization** and **ethylene oxide gas sterilization**. - Their spores are **less resistant to moist heat** compared to *Bacillus stearothermophilus*, making them unsuitable for testing autoclaves. - They have different resistance profiles better suited to testing other sterilization methods. *Clostridium botulinum* - **Clostridium botulinum** spores are known for producing a potent neurotoxin and are important in food safety and canning industry sterilization standards. - However, they are **not used as biological indicators** for routine laboratory or hospital sterilization monitoring. - Their primary relevance is in food preservation where their spore destruction is the target endpoint.

Question 247: Gamma radiations are used for sterilizing:

A. Syringes (Correct Answer)
B. Metal instruments
C. Endoscopes
D. Surgical drapes

Explanation: ***Syringes*** - Gamma radiation sterilization is ideal for items that are sensitive to **heat** or **moisture**, like disposable plastic syringes. - This method ensures deep penetration and effective killing of microorganisms without damaging the integrity of the plastic materials. *Endoscopes* - Endoscopes are typically sterilized using **liquid chemical sterilants** (e.g., glutaraldehyde, peracetic acid) or **low-temperature sterilization methods** due to their delicate optical and electronic components. - Gamma radiation can **damage the optical fibers and delicate electronics** of endoscopes. *Surgical drapes* - Surgical drapes, especially those made of fabrics, are commonly sterilized by **steam sterilization (autoclaving)** due to its cost-effectiveness and efficacy for heat-resistant materials. - While gamma radiation could sterilize them, it is not the primary or most economical method for fabric drapes. *Metal instruments* - Metal instruments are typically sterilized using **steam sterilization (autoclaving)** due to their heat resistance and the method's effectiveness and cost-efficiency. - Gamma radiation is effective but generally reserved for heat-sensitive items not suitable for steam.

Question 248: The color code of plastic bag for disposing microbial laboratory culture waste is:

A. Black
B. Blue
C. Red
D. Yellow (Correct Answer)

Explanation: ***Correct Option: Yellow*** - **Yellow bags/containers** are specifically designated for **infectious waste including microbial laboratory cultures, stocks or specimens of microorganisms, live or attenuated vaccines, and human and animal cell cultures** as per **Indian Biomedical Waste Management Rules (2016, amended 2018-2019)**. - Category 4 (Yellow) explicitly covers **waste generated from laboratory and microbiology cultures** requiring treatment through autoclaving/microwaving/hydroclaving followed by shredding or mutilation before disposal. - This ensures proper **disinfection and safe disposal** of potentially infectious laboratory waste. *Incorrect Option: Red* - **Red bags** are used for **contaminated (recyclable) waste** such as tubing, catheters, intravenous sets, and other items contaminated with blood or body fluids. - They are meant for **recyclable** plastic waste after proper disinfection, not for laboratory cultures requiring destruction. *Incorrect Option: Black* - **Black bags** are used for **general non-hazardous, non-recyclable solid waste** such as kitchen waste and housekeeping waste. - They are not suitable for infectious or biohazardous waste disposal. *Incorrect Option: Blue* - **Blue bags** are used for **glassware and metallic body implants** in some classification systems. - They are not designated for microbial culture waste disposal according to Indian BMW Rules.

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