Sterilization and Disinfection — MCQs

Q: Which spores are used to test the efficacy of moist heat sterilization?

Bacillus stearothermophilus. ***Bacillus stearothermophilus*** - The spores of **Bacillus stearothermophilus** (now referred to as **Geobacillus stearothermophilus**) are highly resistant to heat. - Due to their heat resistance, they are used as the **standard biological indicator** for monitoring the efficacy of **moist heat sterilization** (autoclaving) processes. - These spores can survive temperatures up to 121°C, making them ideal for testing autoclave effectiveness. *Clostridium tetani* - While **Clostridium tetani** forms highly resistant spores, it is **not used as a biological indicator** for sterilization processes. - This organism is clinically significant as the causative agent of tetanus, not as a sterilization test organism. - Standard biological indicators are specially selected *Bacillus* and *Geobacillus* species with known resistance characteristics. *Bacillus subtilis* - **Bacillus subtilis** (and **Bacillus atrophaeus**) spores are used as biological indicators for **dry heat sterilization** and **ethylene oxide gas sterilization**. - Their spores are **less resistant to moist heat** compared to *Bacillus stearothermophilus*, making them unsuitable for testing autoclaves. - They have different resistance profiles better suited to testing other sterilization methods. *Clostridium botulinum* - **Clostridium botulinum** spores are known for producing a potent neurotoxin and are important in food safety and canning industry sterilization standards. - However, they are **not used as biological indicators** for routine laboratory or hospital sterilization monitoring. - Their primary relevance is in food preservation where their spore destruction is the target endpoint.

Q: Gamma radiations are used for sterilizing:

Syringes. ***Syringes*** - Gamma radiation sterilization is ideal for items that are sensitive to **heat** or **moisture**, like disposable plastic syringes. - This method ensures deep penetration and effective killing of microorganisms without damaging the integrity of the plastic materials. *Endoscopes* - Endoscopes are typically sterilized using **liquid chemical sterilants** (e.g., glutaraldehyde, peracetic acid) or **low-temperature sterilization methods** due to their delicate optical and electronic components. - Gamma radiation can **damage the optical fibers and delicate electronics** of endoscopes. *Surgical drapes* - Surgical drapes, especially those made of fabrics, are commonly sterilized by **steam sterilization (autoclaving)** due to its cost-effectiveness and efficacy for heat-resistant materials. - While gamma radiation could sterilize them, it is not the primary or most economical method for fabric drapes. *Metal instruments* - Metal instruments are typically sterilized using **steam sterilization (autoclaving)** due to their heat resistance and the method's effectiveness and cost-efficiency. - Gamma radiation is effective but generally reserved for heat-sensitive items not suitable for steam.

Q: The color code of plastic bag for disposing microbial laboratory culture waste is:

Yellow. ***Correct Option: Yellow*** - **Yellow bags/containers** are specifically designated for **infectious waste including microbial laboratory cultures, stocks or specimens of microorganisms, live or attenuated vaccines, and human and animal cell cultures** as per **Indian Biomedical Waste Management Rules (2016, amended 2018-2019)**. - Category 4 (Yellow) explicitly covers **waste generated from laboratory and microbiology cultures** requiring treatment through autoclaving/microwaving/hydroclaving followed by shredding or mutilation before disposal. - This ensures proper **disinfection and safe disposal** of potentially infectious laboratory waste. *Incorrect Option: Red* - **Red bags** are used for **contaminated (recyclable) waste** such as tubing, catheters, intravenous sets, and other items contaminated with blood or body fluids. - They are meant for **recyclable** plastic waste after proper disinfection, not for laboratory cultures requiring destruction. *Incorrect Option: Black* - **Black bags** are used for **general non-hazardous, non-recyclable solid waste** such as kitchen waste and housekeeping waste. - They are not suitable for infectious or biohazardous waste disposal. *Incorrect Option: Blue* - **Blue bags** are used for **glassware and metallic body implants** in some classification systems. - They are not designated for microbial culture waste disposal according to Indian BMW Rules.

Practice by Chapter

Physical Methods of Sterilization

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Chemical Methods of Sterilization

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Disinfectants and Antiseptics

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Sterilization Monitoring

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Hospital Sterilization Protocols

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Surgical Instruments Sterilization

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Endoscope Reprocessing

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Biological Indicators

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Factors Affecting Sterilization

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Quality Control in Sterilization

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Biofilm and Its Implications

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Regulatory Aspects of Sterilization

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