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.

Q: Biological indicator for determining efficacy of autoclaving is

Bacillus stearothermophilus. ***Bacillus stearothermophilus*** - *Bacillus stearothermophilus* (now *Geobacillus stearothermophilus*) is a **thermoduric spore-forming bacterium** used as a biological indicator for **autoclave efficacy**. - Its spores are highly **resistant to heat**, making them ideal for challenging the sterilization process. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is a **Gram-negative bacterium** known for causing hospital-acquired infections, but it is **not used as a biological indicator** for autoclaving. - It is **less resistant to heat** and sterilization methods compared to bacterial spores. *Clostridium perfringens* - *Clostridium perfringens* is a **spore-forming anaerobic bacterium** associated with gas gangrene and food poisoning. - While it forms spores, its **heat resistance profile is different** from that of *Bacillus stearothermophilus*, and it is not the standard biological indicator for autoclaving. *Salmonella typhi* - *Salmonella typhi* is a **Gram-negative bacterium** that causes typhoid fever. - It is a **pathogen but not a spore-former**, and therefore, it is easily killed by autoclaving and not suitable as a biological indicator for monitoring sterilization effectiveness.

Question 1

Plasma sterilization is done by

Accepted Answer

Hydrogen peroxide

Answer

UV rays

Answer

Ethylene oxide

Answer

Gamma rays

Question 2

The following instrument is sterilized by:

Accepted Answer

Ethylene oxide

Answer

Glutaraldehyde

Answer

Aniline dye

Answer

Beta-propiolactone

Question 3

The following instrument is sterilized using:

Accepted Answer

Ortho-phthalaldehyde

Answer

Ethylene oxide

Answer

Beta-propiolactone

Answer

Formaldehyde

Question 4

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 5

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 6

Tetanus spores can be effectively killed by

Accepted Answer

Gamma irradiation

Answer

Anti tetanus Serum

Answer

Tetanus toxoid

Answer

Large doses of penicillin

Question 7

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 8

Blood spill in the operation theater is cleaned with _____?

Accepted Answer

Chlorine compound

Answer

Phenolic compounds

Answer

Quaternary ammonium compounds

Answer

Alcoholic compounds

Question 9

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

Question 10

Biological indicator for determining efficacy of autoclaving is

Accepted Answer

Bacillus stearothermophilus

Answer

Pseudomonas aeruginosa

Answer

Clostridium perfringens

Answer

Salmonella typhi

Sterilization and Disinfection — MCQs

Sterilization and Disinfection — MCQs

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