Sterilization and Disinfection Practice Questions

Q: What are the recommended conditions for autoclaving?

121 degrees C for 15 minutes. **Explanation:** **1. The Core Concept: Moist Heat Sterilization** Autoclaving is the most reliable method of sterilization, utilizing **moist heat under pressure**. The principle is that water boils at a higher temperature when pressure is increased. At a pressure of **15 psi** (pounds per square inch) above atmospheric pressure, the temperature of steam reaches **121°C**. This specific combination of temperature and time (15 minutes) is sufficient to cause irreversible denaturation of structural proteins and enzymes, effectively killing all vegetative forms of bacteria, fungi, viruses, and—most importantly—highly resistant **bacterial spores**. **2. Analysis of Options:** * **Option B (Correct):** 121°C for 15 minutes at 15 psi is the standard holding period for routine laboratory sterilization. * **Option A & C:** These temperatures are insufficient to guarantee the destruction of thermophilic spores (like *Geobacillus stearothermophilus*) within the specified timeframe. * **Option D:** While 124°C would sterilize the load, it is not the standard "recommended" protocol for routine autoclaving; higher temperatures (e.g., 134°C for 3 minutes) are typically reserved for "flash sterilization" or specific prion protocols. **3. High-Yield Clinical Pearls for NEET-PG:** * **Sterilization Control (Biological Indicator):** The efficacy of an autoclave is tested using spores of ***Geobacillus stearothermophilus*** (formerly *Bacillus stearothermophilus*). * **Chemical Indicator:** **Browne’s tubes** (color change from red to green) or **Bowie-Dick tape**. * **Prion Disinfection:** Requires higher parameters—134°C for 1-1.5 hours or immersion in 1N NaOH for 1 hour. * **Uses:** Ideal for culture media, surgical instruments, and infectious waste. It is **not** suitable for heat-sensitive plastics, sharp instruments (dulls them), or volatile liquids.

Q: Which of the following is an example of a high-level disinfectant?

Glutaraldehyde. **Explanation:** Disinfectants are categorized based on their efficacy against microorganisms into High, Intermediate, and Low levels. **1. Why Glutaraldehyde is Correct:** **Glutaraldehyde** is a **High-Level Disinfectant (HLD)**. It works by alkylation of sulfhydryl, hydroxyl, carboxyl, and amino groups, which alters RNA, DNA, and protein synthesis. Crucially, HLDs are capable of destroying all microorganisms, including vegetative bacteria, mycobacteria, fungi, and viruses. While they can kill bacterial spores with prolonged exposure (making them "chemical sterilants"), in standard clinical practice, they are used as HLDs for heat-sensitive equipment. **2. Analysis of Incorrect Options:** * **Phenol (Option A):** This is a **Low to Intermediate-level disinfectant**. It acts by cell membrane disruption and protein precipitation. It is not effective against bacterial spores or all viruses. * **Alcohol (Option B):** 70% Ethyl or Isopropyl alcohol are **Intermediate-level disinfectants**. They denature proteins but lack sporicidal activity and are ineffective against non-enveloped viruses. * **Povidone Iodine (Option D):** An iodophor, which is an **Intermediate-level disinfectant/antiseptic**. It acts by iodinating proteins and oxidizing cell constituents but cannot reliably kill spores. **3. High-Yield NEET-PG Pearls:** * **Glutaraldehyde (Cidex):** Used for "cold sterilization" of endoscopes, cystoscopes, and bronchoscopes. Standard immersion time for HLD is 20 minutes (2% solution). * **Ortho-phthalaldehyde (OPA):** A newer HLD that is more stable and faster-acting than glutaraldehyde. * **Spaulding’s Classification:** Semicritical items (those touching mucous membranes but not entering sterile body cavities) require at least High-Level Disinfection.

Q: Which of the following statements about Ethylene oxide is FALSE?

Sterilization control used is Bacillus pumilus.. Ethylene oxide (EtO) is a potent alkylating agent used for the gaseous sterilization of heat-sensitive items. Understanding its properties and monitoring is high-yield for NEET-PG. ### **Why Option C is False** The correct biological indicator for Ethylene oxide sterilization is **_Bacillus atrophaeus_** (formerly known as *Bacillus subtilis var. niger*). * **_Bacillus pumilus_** is the biological indicator specifically used for **Ionizing Radiation** (Gamma rays). Using the wrong indicator would fail to validate the sterilization process for EtO. ### **Analysis of Other Options** * **Option A (High penetration power):** EtO is a gas with exceptional penetrating ability. It can pass through plastic films, cardboard, and complex lumens, making it ideal for pre-packaged medical devices like heart-lung machines and catheters. * **Option B (Highly inflammable):** In its pure form, EtO is highly explosive and flammable. To mitigate this risk, it is usually used in a diluted form (e.g., 10% EtO with 90% CO₂ or with hydrofluorocarbons). * **Option D (Irritant and Carcinogenic):** EtO is toxic. It is a known skin and mucosal irritant and is classified as a mutagen and carcinogen. Therefore, sterilized items must undergo a period of **aeration** to remove residual gas before patient use. ### **Clinical Pearls for NEET-PG** * **Mechanism of Action:** Alkylation of amino, carboxyl, and hydroxyl groups in bacterial proteins and nucleic acids. * **Best for:** Heart-lung machines, respirators, sutures, dental equipment, and disposable plastic syringes. * **Biological Indicators Summary:** * **Autoclave:** *Geobacillus stearothermophilus* * **Hot Air Oven:** *Bacillus atrophaeus* * **Ethylene Oxide:** *Bacillus atrophaeus* * **Ionizing Radiation:** *Bacillus pumilus* * **Plasma Sterilization:** *Geobacillus stearothermophilus*

Q: What is the temperature used in the Flash method of pasteurization?

72°C. **Explanation:** Pasteurization is a process of heat treatment used to eliminate pathogenic microorganisms (like *Mycobacterium bovis*, *Brucella*, and *Salmonella*) from milk without significantly altering its nutritional value or flavor. **1. Why 72°C is Correct:** The **Flash Method**, also known as the **High-Temperature Short-Time (HTST)** method, involves heating milk to **72°C for 15 to 20 seconds**, followed by rapid cooling to 4°C or below. This rapid heating and cooling cycle is highly effective at killing vegetative bacteria while preserving the quality of the milk. **2. Analysis of Incorrect Options:** * **63-66°C (Option A):** This temperature range is used in the **Holder Method** (Low-Temperature Holding), where milk is heated to 63-66°C for a longer duration of **30 minutes**. * **100°C (Option B):** This is the boiling point of water. While it achieves sterilization of some media, it is not used for pasteurization as it causes protein denaturation and alters the taste of milk. * **125°C (Option C):** This temperature is typically reached in an **Autoclave** (at 15 psi) for 15 minutes to achieve complete sterilization, including the destruction of bacterial spores. **High-Yield Clinical Pearls for NEET-PG:** * **Indicator of Pasteurization:** The **Phosphatase Test** is used to check the efficiency of pasteurization. If the enzyme alkaline phosphatase is destroyed, pasteurization is considered successful. * **Target Organism:** Historically, *Coxiella burnetii* (the causative agent of Q fever) is the most heat-resistant non-spore-forming pathogen in milk; therefore, pasteurization parameters are designed to ensure its destruction. * **Sterilization vs. Pasteurization:** Pasteurization does **not** kill bacterial spores; it only targets vegetative pathogens.

Q: Autoclaving is typically performed under which conditions?

Steam at 121°C for 15 minutes. ### Explanation **1. Why Option C is Correct:** Autoclaving is the most reliable method of sterilization, utilizing **moist heat (saturated steam) under pressure**. The underlying principle is that increasing the pressure in a closed vessel raises the boiling point of water. At **15 pounds per square inch (psi)** of pressure, the temperature of steam reaches **121°C**. This specific combination of temperature and time (15 minutes) is sufficient to denature microbial proteins and enzymes, effectively killing all vegetative forms and highly resistant **bacterial spores**. **2. Why Other Options are Incorrect:** * **Option A:** Autoclaving uses moist heat, not dry air. Dry air has lower penetrative power and requires much higher temperatures to achieve sterilization. * **Option B:** Steam at 100°C (Tyndallization or boiling) is a form of disinfection or fractional sterilization. It does not reliably kill all bacterial spores in a single 30-minute session. * **Option C:** This describes the standard cycle for a **Hot Air Oven** (Dry Heat Sterilization), typically used for glassware and oil-based substances that steam cannot penetrate. **3. NEET-PG High-Yield Clinical Pearls:** * **Mechanism of Action:** Moist heat kills by **denaturation and coagulation of proteins**, whereas dry heat kills by **oxidation** and damage to DNA. * **Sterilization Indicator:** The biological indicator used to check the efficacy of an autoclave is **_Geobacillus stearothermophilus_** (formerly *Bacillus stearothermophilus*). * **Flash Sterilization:** A rapid autoclave cycle used in OTs for urgent instruments, typically at **134°C for 3 minutes** at 30 psi. * **Uses:** Autoclaving is the gold standard for surgical instruments, gowns, drapes, and culture media. It is **not** suitable for heat-sensitive plastics or sharp instruments (which may blunt).

Q: Lodophores are mixtures of the following:

Iodine and surface-active agents. **Explanation:** **Iodophores** are modern antiseptic formulations consisting of **iodine combined with a carrier molecule**, typically a **surface-active agent** (surfactant) like polyvinylpyrrolidone (Povidone). 1. **Why Option C is Correct:** The carrier (surface-active agent) acts as a reservoir that slowly releases small amounts of free iodine into the solution. This "slow-release" mechanism provides sustained germicidal action while significantly reducing the common drawbacks of pure iodine, such as skin irritation, staining, and hypersensitivity. **Povidone-iodine (Betadine)** is the most common example. 2. **Why Other Options are Incorrect:** * **Option A (Iodine and Alcohol):** This mixture is known as **Tincture of Iodine**. While effective, it is highly irritating to tissues and stains skin, unlike iodophores. * **Option B & D (Iodine and Aldehyde/Phenol):** These are distinct classes of disinfectants. Aldehydes (e.g., Glutaraldehyde) and Phenols (e.g., Lysol) are not used as carriers for iodine; combining them would not offer the stabilizing benefits of a surfactant. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Iodine acts by oxidizing essential microbial proteins and halogenating tyrosine residues. * **Spectrum:** Iodophores are bactericidal, fungicidal, and virucidal. They are **not reliably sporicidal** unless used for prolonged contact times. * **Advantages:** Unlike Tincture of Iodine, iodophores are non-staining, non-toxic, and can be used on both skin and mucous membranes (e.g., pre-operative surgical scrubbing). * **Inactivation:** Their activity is significantly reduced in the presence of organic matter (blood, pus).

Q: Which disinfectant is commonly used in laboratories?

Sodium hypochlorite. **Explanation:** **Sodium hypochlorite (Option A)** is the gold standard disinfectant used in laboratories, particularly for decontaminating surfaces and managing biological spills (e.g., blood or body fluids). Its efficacy stems from its broad-spectrum antimicrobial activity, acting as a powerful oxidizing agent that denatures proteins and inactivates nucleic acids. It is highly effective against bacteria, fungi, and most importantly, blood-borne viruses like HIV, HBV, and HCV. In lab settings, a 1% solution (10,000 ppm) is typically used for large spills, while a 0.1% solution is used for routine surface cleaning. **Why other options are incorrect:** * **Soap solution (Option B):** These are surfactants used for physical cleaning and removal of debris but lack the germicidal potency required for laboratory-grade disinfection. * **Alcohol (Option C):** While 70% Isopropyl or Ethyl alcohol is a common antiseptic and surface disinfectant, it is volatile, lacks sporicidal activity, and is less effective than hypochlorite against non-enveloped viruses. * **Chlorhexidine (Option D):** This is a cationic biguanide used primarily as a skin antiseptic (pre-operative scrubbing) rather than a surface disinfectant, as its activity is neutralized by organic matter and many plastics. **High-Yield Clinical Pearls for NEET-PG:** * **Contact Time:** Sodium hypochlorite requires a contact time of at least 10–30 minutes to be fully effective. * **Stability:** It is unstable and must be prepared fresh daily; it is also corrosive to metals. * **HIV/HBV Protocol:** For blood spills in a clinical or lab setting, the immediate step is to cover the spill with absorbent paper and pour **1% Sodium Hypochlorite** over it. * **Glutaraldehyde (2%):** Remember this as the "cold sterilant" of choice for endoscopes and cystoscopes.

Question 1

What type of filters are used to purify air in biological safety cabinets?

Accepted Answer

HEPA (High efficiency particulate air) filters

Answer

Sietz filters

Answer

Berkfield filters

Answer

Millipore/Porcelain filters

Question 2

What are the recommended conditions for autoclaving?

Accepted Answer

121 degrees C for 15 minutes

Answer

115 degrees C for 20 minutes

Answer

118 degrees C for 15 minutes

Answer

124 degrees C for 15 minutes

Question 3

Which of the following is an example of a high-level disinfectant?

Accepted Answer

Glutaraldehyde

Answer

Phenol

Answer

Alcohol

Answer

Povidone Iodine

Question 4

Which of the following statements about Ethylene oxide is FALSE?

Accepted Answer

Sterilization control used is Bacillus pumilus.

Answer

It has high penetration power.

Answer

It is highly inflammable.

Answer

Ethylene oxide is irritant and carcinogenic.

Question 5

What is the temperature used in the Flash method of pasteurization?

Accepted Answer

72°C

Answer

66-66°C

Answer

100°C

Answer

125°C

Question 6

Autoclaving is typically performed under which conditions?

Accepted Answer

Steam at 121°C for 15 minutes

Answer

Dry air at 121°C and 15 psi

Answer

Steam at 100°C for 30 minutes

Answer

Dry air at 160°C for 30 minutes

Question 7

Glutaraldehyde is preferred over formaldehyde because:

Accepted Answer

It has no deleterious effect on the cement and lenses of instruments.

Answer

It has greater bactericidal activity.

Answer

It has greater bacteriostatic activity.

Answer

Its application is easier.

Question 8

Lodophores are mixtures of the following:

Accepted Answer

Iodine and surface-active agents

Answer

Iodine and alcohol

Answer

Iodine and aldehyde

Answer

Iodine and phenol

Question 9

Which disinfectant is commonly used in laboratories?

Accepted Answer

Sodium hypochlorite

Answer

Soap solution

Answer

Alcohol

Answer

Chlorhexidine

Question 10

Glassware is sterilized in a hot air oven at what temperature and for what duration?

Accepted Answer

160°C for 1 hour

Answer

170°C for 1 hour

Answer

180°C for 1 hour

Answer

190°C for 1 hour

Sterilization and Disinfection — MCQs

Sterilization and Disinfection — MCQs

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