Sterilization and Disinfection Practice Questions

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.

Q: Which is false regarding Spaulding's criteria?

Semi critical items need low level disinfection. ***Semi critical items need low level disinfection*** - This statement is **FALSE** and is the **correct answer** to this question. - **Semi-critical items** require **high-level disinfection**, NOT low-level disinfection. - Semi-critical items come into contact with mucous membranes or non-intact skin and require removal of all vegetative bacteria, fungi, mycobacteria, and most viruses. - Examples include endoscopes, laryngoscope blades, and respiratory therapy equipment. *Non critical items require only decontamination* - This statement is **TRUE** (or at least acceptable in context). - Non-critical items contact intact skin and require **cleaning** and **low-level disinfection** (which falls under the umbrella term "decontamination"). - Examples include blood pressure cuffs, stethoscopes, and bedpans. *Cardiac catheters are examples of critical items* - This statement is **TRUE**. - **Cardiac catheters** enter the **vascular system** (sterile tissue), making them **critical items**. - Critical items require **sterilization** to prevent severe systemic infection. *Semi critical items are those which come in contact with mucous membrane or non intact skin* - This statement is **TRUE** and correctly defines **semi-critical items** according to Spaulding's classification. - This is the standard definition used in medical device processing protocols.

Q: Browne's tube is used for -

Steam sterilization. ***Steam sterilization*** - **Browne's tubes** are chemical indicators used to monitor the effectiveness of **steam sterilization** processes. - They contain a **temperature-sensitive chemical** that changes color when exposed to specific temperatures and steam for a sufficient duration, indicating proper sterilization parameters have been met. *Radiation* - **Radiation sterilization** typically uses methods like **gamma radiation** or **electron beam radiation** to kill microorganisms. - Browne's tubes are not designed or used to monitor the efficacy of these radiation-based sterilization methods. *Filtration* - **Filtration** is a method used to remove microorganisms from liquids or gases, often without killing them, by trapping them in a filter medium. - This process does not involve heat or steam, and Browne's tubes have no role in monitoring filtration efficacy. *Chemical sterilization* - **Chemical sterilization** uses chemical agents like **ethylene oxide** or **hydrogen peroxide plasma** to sterilize heat-sensitive instruments. - While chemical indicators exist for these methods, Browne's tubes are specifically formulated for and calibrated to respond to the parameters of steam sterilization.

Q: Disinfection by autoclaving is NOT recommended for -

Sharp instrument. ***Sharp instrument*** - While **stainless steel sharp instruments** can technically withstand autoclaving, repeated exposure to **high heat** and **steam** under pressure can lead to the dulling or corrosion of delicate cutting edges over time. - This is particularly true for **carbon steel blades** and instruments not made from high-grade stainless steel. - Alternative sterilization methods like **chemical sterilization** or **low-temperature sterilization** may be preferred to preserve the **sharpness** and extend the functional lifespan of precision cutting instruments. - In practice, disposable sharp instruments are increasingly preferred to avoid this issue. *Linen* - **Autoclaving** is highly effective and commonly used for sterilizing linen materials, such as surgical gowns, drapes, and towels, as it ensures the destruction of microorganisms. - The heat and moisture penetrate the fabric efficiently, making it a reliable method for rendering textiles **pathogen-free**. *Sputum* - Autoclaving is an appropriate method for **sterilizing biological waste** contaminated with infectious agents, including sputum. - It effectively **decontaminates** the material before its disposal, preventing the spread of pathogens. *Glass syringes* - **Glass syringes** are resistant to the high temperatures and pressures of autoclaving, making it a suitable method for their sterilization. - The process ensures that the syringes are **sterile** and safe for reuse in medical procedures, provided they are designed for such repeated sterilization.

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

Dettol. ***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.

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

160. ***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.

Q: Cetrimide is

Quaternary ammonium compounds. ***Quaternary ammonium compounds*** - Cetrimide is a **cationic surfactant** belonging to the class of **quaternary ammonium compounds**. - Its mechanism of action involves disrupting microbial cell membranes, leading to **cell leakage** and death, making it effective as an antiseptic. *Halogen* - Halogens (e.g., **iodine, chlorine**) exert antimicrobial effects through **oxidation** and halogenation of microbial cellular components. - While effective, their chemical structure and mechanism are distinct from that of cetrimide. *Aldehyde* - Aldehydes (e.g., **formaldehyde, glutaraldehyde**) act by **alkylating** proteins and nucleic acids, leading to broad-spectrum antimicrobial activity. - This class of disinfectants has a different chemical structure and mode of action compared to cetrimide. *Phenol* - Phenols (e.g., **phenol, cresol**) denature proteins and disrupt cell membranes, and are characterized by a **hydroxyl group** attached to an aromatic ring. - Cetrimide does not possess the phenolic chemical structure or its associated mechanism of action.

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

None of the options. ***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.

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

Membrane filtration. ***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 1

Biological indicator for determining efficacy of autoclaving is

Accepted Answer

Bacillus stearothermophilus

Answer

Pseudomonas aeruginosa

Answer

Clostridium perfringens

Answer

Salmonella typhi

Question 2

Which is false regarding Spaulding's criteria?

Accepted Answer

Semi critical items need low level disinfection

Answer

Non critical items require only decontamination

Answer

Cardiac catheters are examples of critical items

Answer

Semi critical items are those which come in contact with mucous membrane or non intact skin

Question 3

Browne's tube is used for -

Accepted Answer

Steam sterilization

Answer

Radiation

Answer

Filtration

Answer

Chemical sterilization

Question 4

Disinfection by autoclaving is NOT recommended for -

Accepted Answer

Sharp instrument

Answer

Linen

Answer

Sputum

Answer

Glass syringes

Question 5

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

Accepted Answer

Dettol

Answer

Betadine

Answer

Chlorine

Answer

Hypochlorite

Question 6

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

Accepted Answer

160

Answer

140

Answer

100

Answer

120

Question 7

Cetrimide is

Accepted Answer

Quaternary ammonium compounds

Answer

Halogen

Answer

Aldehyde

Answer

Phenol

Question 8

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

Accepted Answer

None of the options

Answer

Lysol

Answer

Hot air

Answer

Radiation

Question 9

A laboratory technician is tasked with sterilizing heat-sensitive surgical instruments. Which sterilization method should be chosen and why?

Accepted Answer

Ethylene oxide gas due to its effectiveness at low temperatures

Answer

Autoclaving because it ensures complete sterility

Answer

Dry heat for its cost-effectiveness

Answer

UV radiation for its ease of use

Question 10

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

Accepted Answer

Membrane filtration

Answer

Gamma radiation

Answer

Autoclaving

Answer

Chemical sterilization

Sterilization and Disinfection — MCQs

Sterilization and Disinfection — MCQs

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