Sterilization and Disinfection — MCQs

Sterilization and Disinfection Indian Medical PG Practice Questions and MCQs

Question 211: Which of the following is LEAST effective in cleaning pseudomonal infections?

A. Dettol (Correct Answer)
B. Betadine
C. Chlorine
D. Hypochlorite

Explanation: ***Dettol*** - **Dettol**, a household antiseptic containing **chloroxylenol**, has limited efficacy against *Pseudomonas aeruginosa* compared to other disinfectants. - While it has broad-spectrum antimicrobial activity, it is generally less potent against **gram-negative bacteria** like *Pseudomonas* which have robust **efflux pumps** and a resistant outer membrane. *Betadine* - **Betadine**, or **povidone-iodine**, is an effective broad-spectrum antiseptic, including against *Pseudomonas aeruginosa*. - Its mechanism involves the release of **free iodine**, which oxidizes bacterial cell components and disrupts their structure. *Chlorine* - **Chlorine** and its compounds are powerful disinfectants with excellent efficacy against *Pseudomonas aeruginosa*. - They work by disrupting bacterial cell membranes and inhibiting enzymatic processes through **oxidation**. *Hypochlorite* - **Sodium hypochlorite** (bleach) is a potent disinfectant commonly used in healthcare settings and is highly effective against *Pseudomonas aeruginosa*. - It rapidly denatures proteins and oxidizes cellular components, leading to microbial death.

Question 212: Temperature required in a hot air oven for a holding period of 1 hour in degree Celsius is –

A. 140
B. 160 (Correct Answer)
C. 100
D. 120

Explanation: ***Correct: 160°C*** - A hot air oven sterilizes by **dry heat**, which requires higher temperatures and longer exposure times compared to moist heat. - The standard sterilization cycle for a hot air oven is **160°C for 1 hour**, or 170°C for 30 minutes, to ensure effective microbial destruction. *Incorrect: 140°C* - A temperature of **140°C** for 1 hour is generally considered insufficient for achieving complete sterilization in a hot air oven. - While it may reduce microbial load, it might not consistently kill all **spore-forming bacteria**. *Incorrect: 100°C* - **100°C** in a dry heat oven is too low for sterilization; this temperature primarily achieves disinfection, not sterility. - At this temperature, vegetative forms of bacteria might be killed, but bacterial **spores will largely survive**. *Incorrect: 120°C* - A temperature of **120°C** for 1 hour is typically used in an autoclave with **moist heat** for sterilization. - In a **dry heat oven**, this temperature is not high enough to guarantee thorough sterilization within a 1-hour holding period.

Question 213: The most commonly used method for sterilizing sharp instruments in hospital settings is-

A. Lysol
B. None of the options (Correct Answer)
C. Hot air
D. Radiation

Explanation: ***None of the options*** - The **most commonly used method** for sterilizing sharp instruments in hospital settings is **autoclaving (steam sterilization)**, which is **not listed among the options**. - **Autoclaving** uses saturated steam under pressure (121°C for 15-20 minutes or 134°C for 3-4 minutes) and is the **gold standard** for sterilizing surgical instruments including scalpels, scissors, and forceps. - It is preferred because it is **fast, effective, non-toxic, and economical**, and modern stainless steel instruments are designed to withstand repeated autoclaving without damage. *Hot air* - **Hot air oven** sterilization uses dry heat (160°C for 2 hours or 180°C for 30 minutes) and is **less commonly used** than autoclaving for routine instrument sterilization. - It is primarily reserved for items that **cannot tolerate moisture** (oils, powders, petroleum products) or may corrode with steam (certain cutting edges, mirrors). - The **longer sterilization time** and requirement for higher temperatures make it less practical for routine use compared to autoclaving. *Radiation* - **Radiation sterilization** (gamma rays, electron beams) is used for **industrial sterilization** of single-use, pre-packaged medical devices and heat-sensitive items. - It requires **specialized facilities** and is not used for routine in-hospital sterilization of reusable instruments. *Lysol* - **Lysol** is a **chemical disinfectant**, not a sterilizing agent—it reduces microbial load but does not eliminate bacterial spores. - It is used for surface disinfection and cannot achieve the **sterility** required for instruments that penetrate tissue or contact sterile body sites.

Question 214: What is the process of destroying all microbes, including spores?

A. Disinfection
B. Antisepsis
C. Asepsis
D. Sterilization (Correct Answer)

Explanation: ***Sterilization*** - **Sterilization** is the process that aims to destroy or eliminate all forms of microbial life, including highly resistant bacterial **spores**. - It is crucial for medical devices and equipment that penetrate sterile tissues or contact the bloodstream, such as surgical instruments. *Disinfection* - **Disinfection** reduces the number of pathogenic microorganisms but typically does not eliminate bacterial **spores**. - It is commonly used for cleaning surfaces and non-critical items that come into contact with intact skin. *Antisepsis* - **Antisepsis** refers to the reduction of microbial flora on **living tissue**, such as skin, to prevent infection. - Antiseptics are generally less potent than disinfectants and do not achieve the high level of microbial inactivation required for sterilization. *Asepsis* - **Asepsis** is a state of being free from **contamination** with pathogenic microorganisms, often achieved through aseptic techniques. - It involves practices that prevent the introduction of infectious agents into sterile areas, but it is not a direct process of destroying all microbes.

Question 215: Which of the following is a chemical method of sterilization?

A. Autoclaving
B. Hot air oven
C. Ethylene oxide (Correct Answer)
D. Filtration

Explanation: ***Ethylene oxide*** - **Ethylene oxide** sterilization is a **chemical process** that uses a gas to sterilize heat- and moisture-sensitive instruments and devices. - It works by **alkylating microbial proteins** and nucleic acids, disrupting metabolic processes and replication. *Autoclaving* - **Autoclaving** is a method of **heat sterilization** that uses **steam under pressure** to achieve high temperatures. - It is highly effective but unsuitable for heat-sensitive materials. *Hot air oven* - A **hot air oven** is a method of **dry heat sterilization** used for items that cannot be subjected to steam. - It requires **higher temperatures** and **longer exposure times** compared to autoclaving. *Filtration* - **Filtration** is a method of sterilization that physically **removes microorganisms** from liquids or gases. - It does not kill microorganisms but rather separates them, making it a physical method, not chemical.

Question 216: What is the temperature used in Tyndallization?

A. 40°C
B. 60°C
C. 80°C
D. 100°C (Correct Answer)

Explanation: ***100°C*** - Tyndallization, also known as **fractional sterilization**, involves heating and cooling cycles to sterilize heat-sensitive media. - The heating phase typically involves exposure to **100°C for 30-60 minutes** on consecutive days. *40°C* - This temperature is too low to effectively kill most vegetative bacteria or bacterial spores. - It falls within the range where many microorganisms optimally grow, making it unsuitable for sterilization. *60°C* - While this temperature can inhibit the growth of some microbes and is used in **pasteurization**, it is insufficient for sterilization. - Many bacterial spores can survive this temperature, requiring higher heat for inactivation. *80°C* - This temperature is higher than pasteurization but still generally not enough to achieve complete sterilization. - It would kill most vegetative cells but would likely not destroy resistant bacterial endospores which are the primary target of Tyndallization.

Question 217: What is the method used for sterilizing culture media containing serum?

A. Gamma radiation
B. Autoclaving
C. Membrane filtration (Correct Answer)
D. Chemical sterilization

Explanation: ***Membrane filtration*** - **Membrane filtration (0.22 μm filters)** is a gentle method that removes microorganisms without involving heat, which would otherwise denature the sensitive proteins in serum. - This method is suitable for **heat-sensitive components** like growth factors, antibodies, and hormones present in serum. - The **0.22 μm pore size** effectively removes bacteria while preserving the biological activity of serum components. *Autoclaving* - **Autoclaving** uses high temperature (121°C) and pressure, which would cause **denaturation of proteins** in the serum, making it unsuitable for cell culture. - The high heat would destroy essential growth factors and nutrients, compromising the media's ability to support cell growth. *Gamma radiation* - **Gamma radiation** can cause chemical changes and degradation of sensitive components in serum, including proteins and vitamins. - While it effectively sterilizes, the potential for **molecular degradation** makes it less ideal for maintaining the integrity of complex biological media. *Chemical sterilization* - **Chemical sterilizing agents** can leave toxic residues and alter the chemical composition of the serum, making it unsuitable for cell growth. - It is difficult to completely remove all traces of chemical sterilants without further processing, posing a risk of **cytotoxicity** to cells.

Question 218: Which of the following methods is classified as cold sterilization?

A. Sterilization by low temperature
B. Sterilization by liquid nitrogen
C. Sterilization by ultraviolet light
D. Sterilization by gamma radiation (Correct Answer)

Explanation: ***Sterilization by gamma radiation*** - **Cold sterilization** refers to sterilization methods that do not use heat, allowing treatment of heat-sensitive materials at room or low temperatures. - **Gamma radiation** (ionizing radiation) effectively kills all microorganisms including bacterial spores by damaging their DNA, making it a reliable cold sterilization technique. - Widely used for sterilizing heat-sensitive medical devices, pharmaceuticals, tissues, and single-use medical supplies. *Sterilization by low temperature* - While low temperatures (e.g., refrigeration or freezing) inhibit microbial growth, they typically do not achieve **sterilization** by reliably killing all microorganisms, including spores. - This method is more accurately described as **preservation** rather than sterilization. *Sterilization by liquid nitrogen* - Liquid nitrogen is used for **cryopreservation**, which involves storing biological materials at extremely low temperatures to maintain their viability, not to kill all microorganisms. - While it can inactivate many microorganisms, it does not guarantee complete **sterilization** as spores and some resistant organisms may survive. *Sterilization by ultraviolet light* - **Ultraviolet (UV) light** is a non-ionizing radiation method that can disinfect by damaging microbial DNA, but its effectiveness is limited by its poor penetration. - It is primarily used for **surface disinfection** or treating clear liquids and air, and it cannot sterilize items with shadowing or complex geometries.

Question 219: Best indicator for sterilization by autoclaving?

A. Clostridium
B. Geobacillus (Correct Answer)
C. Bacillus subtilis
D. Bacillus pumilus

Explanation: ***Geobacillus*** - **Geobacillus stearothermophilus** spores are the standard biological indicator for **autoclave sterilization** due to their extreme resistance to moist heat. - Their inactivation provides the strongest assurance that the autoclaving process has achieved the necessary **sterilization parameters**. *Bacillus subtilis* - **Bacillus subtilis** spores are typically used as a biological indicator for **ethylene oxide** or **dry heat sterilization**, not autoclaving. - While resistant, they are not as resistant to moist heat as **Geobacillus stearothermophilus** and thus are not the best indicator for autoclaves. *Clostridium* - While some **Clostridium** species form highly resistant spores (e.g., *C. difficile*, *C. tetani*), they are not routinely used as **biological indicators** for general sterilization processes. - Their primary relevance is in disease pathogenesis and antibiotic resistance, not as a standardized sterilization challenge organism. *Bacillus pumilus* - **Bacillus pumilus** spores are primarily used as a biological indicator for **radiation sterilization** (e.g., gamma irradiation), not for heat-based methods like autoclaving. - They are known for their resistance to radiation but do not possess the optimal resistance profile for moist heat.

Question 220: Which virus is most sensitive to inactivation by biocides?

A. Adenovirus
B. Parvovirus
C. Herpes virus (Correct Answer)
D. Poliovirus

Explanation: ***Herpes virus*** - **Enveloped viruses** like herpes virus are generally the **most sensitive to inactivation** by biocides because their outer lipid envelope is easily disrupted. - The integrity of the **envelope is crucial** for the virus's infectivity. *Adenovirus* - **Non-enveloped viruses** like adenovirus are typically **more resistant** to biocides due to their robust protein capsid. - While generally resistant, they are less resistant than parvoviruses and polioviruses. *Parvovirus* - This is a **small, non-enveloped DNA virus** with a highly stable capsid, making it one of the **most resistant** viruses to inactivation by disinfectants. - Its robust structure allows it to survive harsh environmental conditions and a wide range of chemical treatments. *Poliovirus* - As a **non-enveloped enterovirus**, poliovirus is also **highly resistant** to many common disinfectants and can persist in the environment. - Its resistance is due to its durable protein capsid, which protects its genetic material.

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

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