Sterilization and Disinfection Practice Questions

Q: Plasma sterilization is done by

Hydrogen peroxide. ***Hydrogen peroxide*** - Plasma sterilization uses **hydrogen peroxide vapor** that is converted into plasma state by electromagnetic energy (radiofrequency or microwave) - The plasma contains **highly reactive free radicals** (hydroxyl and hydroperoxyl) that destroy microorganisms by disrupting cell membranes and DNA - Common system: **STERRAD** (Sterilization by Reactive Gas Discharge) - Advantages: **Low temperature** process (suitable for heat-sensitive instruments), **non-toxic**, leaves no residue, and has a **short cycle time** *UV rays (Incorrect)* - Used for surface disinfection and air sterilization, not plasma sterilization - Limited penetration power *Ethylene oxide (Incorrect)* - Gas sterilization method, not plasma-based - Requires longer aeration time due to toxicity *Gamma rays (Incorrect)* - Ionizing radiation sterilization method - Used for industrial sterilization, not plasma sterilization

Q: The following instrument is sterilized by:

Ethylene oxide. ***Ethylene dioxide*** - The image shows a **heart-lung machine (cardiopulmonary bypass machine)**. These complex devices contain various materials, including plastics and electronics, that cannot withstand high temperatures. - **Ethylene oxide (ETO) sterilization** is a low-temperature gaseous sterilization method suitable for heat-sensitive and moisture-sensitive medical devices, making it ideal for the intricate components of a heart-lung machine. *Glutaraldehyde* - **Glutaraldehyde** is a high-level disinfectant and sterilant typically used for instruments that can be **immersed in liquid**, such as endoscopes. - It is not practical or effective for sterilizing large, complex electronic equipment like a heart-lung machine, which has many non-immersible parts. *Aniline dye* - **Aniline dyes** are primarily used as histological stains and in some antiseptic preparations, but they are **not a method of sterilization**. - They lack the broad-spectrum microbicidal activity required for sterilizing medical devices. *Beta-propiolactone* - **Beta-propiolactone** is a chemical sterilant that has been used in the past, primarily for sterilizing vaccines and tissue grafts due to its rapid microbicidal action. - However, its use has been largely **limited due to its carcinogenic properties**, and it is not a common or preferred method for sterilizing large medical equipment like a heart-lung machine.

Q: The following instrument is sterilized using:

Ortho-phthalaldehyde. ***Ortho-phthalaldehyde (OPA)*** - The instrument shown is an **endoscope**, which is a heat-sensitive, semi-critical device requiring high-level disinfection. - **OPA** is a common and effective high-level disinfectant used for endoscopes, as it offers a rapid disinfection time, broad microbicidal activity, and is stable. *Ethylene dioxide* - **Ethylene oxide (EO)** is a gas sterilant primarily used for heat and moisture-sensitive medical devices that cannot be effectively disinfected by liquid chemicals. - EO sterilization requires specific, highly controlled chambers and aeration periods to remove toxic residuals, making it less practical for routine endoscope disinfection in clinical settings compared to liquid agents. *Beta-propiolactone* - **Beta-propiolactone** is a chemical sterilant with broad-spectrum activity but is notable for being a probable human carcinogen and a strong irritant. - Due to its significant toxicity and potential health risks, its use in medical sterilization, particularly for instruments like endoscopes, has largely been phased out or is very restricted. *Formaldehyde* - **Formaldehyde** is a strong disinfectant and sterilant that can be used in both liquid and gaseous forms; however, it is a known carcinogen and has strong irritating fumes. - While effective, its high toxicity and safety concerns limit its routine use for endoscopes, especially when less hazardous high-level disinfectants like OPA are available.

Q: Autoclaving is a method of sterilization. The process involves heating by steam at

15 lb pressure, 121 °C temperature for 15 minutes. ***15 lb pressure, 121 °C temperature for 15 minutes*** - This is the **standard recommended parameter** for routine sterilization in an autoclave, ensuring the destruction of most pathogenic and non-pathogenic microorganisms, including spores. - The combination of **steam at 121°C** (equivalent to 15 psi) for at least 15 minutes provides efficient heat transfer and penetration required for effective sterilization. *10 lb pressure, 100 °C temperature for 10 minutes* - This temperature (100 °C) is used for **boiling** or pasteurization, which is generally not sufficient for complete sterilization as it may not kill highly resistant spores. - The **lower pressure and temperature** would likely not achieve the required sterility assurance level. *20 lb pressure, 120 °C temperature for 20 minutes* - While higher pressure can achieve sterilization, this is **not the standard parameter** used for typical autoclave sterilization. - The standard combination of 15 lb at 121°C is more commonly recommended and taught in medical curricula. *25 lb pressure, 120 °C temperature for 25 minutes* - This combination of **higher pressure and longer duration** would likely achieve sterilization, but it exceeds the minimum standard parameters. - While effective, it is not the most **efficient or commonly recommended** setting and could potentially lead to material degradation for some items.

Q: Tetanus spores can be effectively killed by

Gamma irradiation. ***Gamma irradiation*** - **Gamma irradiation** denatures proteins and damages nucleic acids, effectively destroying bacterial spores like those of *Clostridium tetani*. - This method is used for sterilizing heat-sensitive materials and achieving a high level of **microbial inactivation**. *Anti tetanus Serum* - **Anti-tetanus serum (ATS)** contains pre-formed antibodies that neutralize the circulating tetanus **toxin**, not the spores. - ATS is used for **passive immunization** and treatment of tetanus, but it does not kill the bacterial spores themselves. *Tetanus toxoid* - **Tetanus toxoid** is an inactivated bacterial toxin used to stimulate an immune response and provide **active immunization** against the toxin. - It does not directly kill tetanus spores; instead, it prevents the effects of the toxin produced by the spores. *Large doses of penicillin* - **Penicillin** is an antibiotic that can kill *Clostridium tetani* bacteria, but it is much less effective against the dormant and highly resistant **tetanus spores**. - While it can help eradicate active infection, spores often require more potent physical or chemical sterilization methods.

Q: Which of the following represent the properties of an ideal disinfectant? 1. It is broad spectrum 2. It is fast acting 3. It is non-toxic Select the correct answer using the code given below:

1, 2 and 3. ***Correct Answer: 1, 2 and 3*** An **ideal disinfectant** should possess all three properties: - **Broad spectrum activity** - It should effectively kill or inactivate a wide range of microorganisms, including bacteria, viruses, fungi, and spores - **Fast-acting** - It should achieve rapid antimicrobial effect after application, which is crucial in clinical settings to prevent pathogen spread and minimize exposure time - **Non-toxic** - It should be safe for humans and animals when used as directed, minimizing adverse effects on users, patients, and the environment Additional desirable properties include stability, solubility in water, non-corrosive nature, pleasant odor, and cost-effectiveness. *Incorrect: 1 and 3 only* - While broad spectrum and non-toxic nature are crucial, **fast action** is also an essential property for an ideal disinfectant to ensure rapid microbial elimination - A disinfectant that is not fast-acting would be less practical in situations requiring quick decontamination *Incorrect: 2 and 3 only* - A disinfectant that is fast-acting and non-toxic is insufficient without **broad-spectrum activity** - Without broad-spectrum activity, it may fail to eliminate certain pathogens, limiting its overall utility in infection control *Incorrect: 1 and 2 only* - Although broad spectrum and fast-acting properties are important, an ideal disinfectant must also be **non-toxic** - Toxicity would severely limit its application, especially in healthcare settings where human contact is frequent

Q: Blood spill in the operation theater is cleaned with _____?

Chlorine compound. ***Chlorine compound*** - **Chlorine-releasing agents** like 1% sodium hypochlorite (bleach) are highly effective against a broad spectrum of microorganisms, including **blood-borne pathogens** such as HIV and Hepatitis B. - Their rapid action and strong oxidizing properties make them the preferred choice for disinfecting surfaces contaminated with blood spills in healthcare settings, ensuring efficient **decontamination**. *Phenolic compounds* - Phenolic compounds are generally used for cleaning and disinfecting **hard, non-porous surfaces** but are less preferred for blood spills due to their slower action and potential for leaving residues. - They are effective against some bacteria and fungi but may not be as rapidly virucidal as chlorine compounds, especially against enveloped viruses in organic matter. *Quaternary ammonium compounds* - **Quaternary ammonium compounds** (Quats) are good general disinfectants for routine cleaning and disinfection of environmental surfaces but have a **lower efficacy against non-enveloped viruses** and spores. - They tend to be inactivated by organic matter, making them less suitable for effective decontamination of **blood spills with high protein content**. *Alcoholic compounds* - **Alcoholic compounds** (e.g., 70% ethanol or isopropanol) are effective disinfectants but are often limited to **small surface areas** or for antiseptic use on skin. - They evaporate quickly and are not ideal for cleaning large blood spills as they may not provide sufficient contact time for effective sterilization in the presence of organic material.

Q: After the admission of a road traffic accident (RTA) case, there is a spillage of blood on the hospital floor. Which disinfectant should be used to clean the floor?

Sodium Hypochlorite. ***Sodium Hypochlorite*** - **Sodium hypochlorite** is highly effective against a broad spectrum of microorganisms, including **viruses, bacteria, and fungi**, making it ideal for blood spills. - Its **oxidizing action** denatures proteins and nucleic acids, effectively decontaminating surfaces potentially contaminated with bloodborne pathogens. *Formaldehyde* - Primarily used as a **sterilant** or for **tissue preservation**, not typically for general surface cleaning due to its toxicity and strong odor. - Its slow action and **irritating fumes** make it unsuitable for routine decontamination in a clinical setting. *Chlorhexidine* - Primarily an **antiseptic** used for skin disinfection and surgical scrubs due to its residual activity. - It has limited efficacy against some viruses and is not the first choice for large-scale surface decontamination of blood spills due to potential staining and cost. *Ethyl alcohol* - Effective as a **disinfectant** for small surfaces and medical equipment, but evaporates quickly, limiting its contact time for thorough disinfection of large spills. - It is flammable and can damage certain materials, making it less suitable for blood on floors.

Question 1

Irradiation can be used to sterilize which of the following?

Accepted Answer

Bronchoscope

Answer

Bone graft

Answer

Suture

Answer

Artificial tissue graft

Question 2

Plasma sterilization is done by

Accepted Answer

Hydrogen peroxide

Answer

UV rays

Answer

Ethylene oxide

Answer

Gamma rays

Question 3

The following instrument is sterilized by:

Accepted Answer

Ethylene oxide

Answer

Glutaraldehyde

Answer

Aniline dye

Answer

Beta-propiolactone

Question 4

The following instrument is sterilized using:

Accepted Answer

Ortho-phthalaldehyde

Answer

Ethylene oxide

Answer

Beta-propiolactone

Answer

Formaldehyde

Question 5

All are correct about the method of sterilization shown here except:

Accepted Answer

Biological indicator is Bacillus subtilis strips containing spores

Answer

Hold time of $180^{\circ}$ Celsius for 3 hours

Answer

Swab sticks should be placed inside test tubes

Answer

Chemical indicator of sterilization is Browne's tube number 3

Question 6

Autoclaving is a method of sterilization. The process involves heating by steam at

Accepted Answer

15 lb pressure, 121 °C temperature for 15 minutes

Answer

10 lb pressure, 100 °C temperature for 10 minutes

Answer

20 lb pressure, 120 °C temperature for 20 minutes

Answer

25 lb pressure, 120 °C temperature for 25 minutes

Question 7

Tetanus spores can be effectively killed by

Accepted Answer

Gamma irradiation

Answer

Anti tetanus Serum

Answer

Tetanus toxoid

Answer

Large doses of penicillin

Question 8

Which of the following represent the properties of an ideal disinfectant?

1. It is broad spectrum
2. It is fast acting
3. It is non-toxic

Select the correct answer using the code given below:

Accepted Answer

1, 2 and 3

Answer

1 and 3 only

Answer

2 and 3 only

Answer

1 and 2 only

Question 9

Blood spill in the operation theater is cleaned with _____?

Accepted Answer

Chlorine compound

Answer

Phenolic compounds

Answer

Quaternary ammonium compounds

Answer

Alcoholic compounds

Question 10

After the admission of a road traffic accident (RTA) case, there is a spillage of blood on the hospital floor. Which disinfectant should be used to clean the floor?

Accepted Answer

Sodium Hypochlorite

Answer

Formaldehyde

Answer

Chlorhexidine

Answer

Ethyl alcohol

Sterilization and Disinfection — MCQs

Sterilization and Disinfection — MCQs

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