The minimum sterilizing conditions in a steam autoclave are
160°C for 2 hours.
71.6°C for 15 seconds.
100°C at 10 psi for 30 minutes.
63°C at 5 psi for 30 minutes.
121°C at 15 psi for 15 to 30 minutes.
The Correct Answer is E
A. 160°C for 2 hours: This temperature and duration correspond to dry heat sterilization rather than steam sterilization in an autoclave. Dry heat sterilization is commonly performed in hot air ovens for glassware or metal instruments that cannot tolerate moisture. Autoclaves rely on moist heat under pressure, which allows sterilization at lower temperatures compared with dry heat.
B. 71.6°C for 15 seconds: This condition corresponds to high-temperature short-time (HTST) pasteurization, commonly used in the dairy industry to reduce microbial load in milk. Pasteurization reduces pathogenic microorganisms but does not destroy all microbes or bacterial spores. Therefore, it does not achieve sterilization.
C. 100°C at 10 psi for 30 minutes: Boiling water reaches 100°C at atmospheric pressure and can kill many vegetative bacteria and viruses. However, many bacterial endospores, such as those produced by Bacillus and Clostridium species, can survive this temperature. True sterilization requires higher temperatures achieved through pressurized steam.
D. 63°C at 5 psi for 30 minutes: This temperature corresponds to low-temperature long-time (LTLT) pasteurization, also known as batch pasteurization. Like other pasteurization methods, it reduces microbial numbers but does not eliminate all microorganisms or spores. As a result, it cannot achieve sterilization.
E. 121°C at 15 psi for 15 to 30 minutes: These are the standard minimum conditions for steam sterilization in an autoclave. Pressurized steam at 121°C effectively denatures proteins, destroys cellular structures, and kills all forms of microbial life, including highly resistant bacterial endospores. This method is widely used for sterilizing laboratory media, surgical instruments, and medical equipment.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. Conjugation: Conjugation is a form of bacterial DNA recombination in which genetic material is transferred directly from one bacterial cell to another through a pilus. This process allows for the exchange of plasmids or chromosomal fragments, contributing to genetic diversity and the spread of traits like antibiotic resistance.
B. Transformation: Transformation involves the uptake of free, naked DNA from the environment by a bacterial cell. This DNA can integrate into the recipient’s genome, leading to genetic variation. Transformation is commonly observed in naturally competent bacteria such as Streptococcus pneumoniae.
C. Transduction: Transduction is the process by which bacterial DNA is transferred from one bacterium to another by a bacteriophage (virus). The phage accidentally incorporates host DNA and introduces it into a new bacterial cell, facilitating genetic recombination without direct cell-to-cell contact.
D. Induction: Induction is not a type of bacterial DNA recombination. Instead, it refers to the activation of gene expression, often in response to environmental signals, such as the induction of operons in bacteria. It does not involve the exchange or incorporation of DNA between cells and therefore does not contribute to genetic recombination.
Correct Answer is C
Explanation
A. Glycolysis: Glycolysis produces a small amount of ATP directly through substrate-level phosphorylation, yielding 2 ATP molecules per glucose molecule. While it initiates the breakdown of glucose to pyruvate, the majority of energy is not generated at this stage.
B. All phases produce the same number of ATP molecules: ATP production is not uniform across the phases of cellular respiration. Each phase contributes differently, with oxidative phosphorylation generating the largest share of ATP, making this statement incorrect.
C. Oxidative phosphorylation (Electron Transport Chain): The electron transport chain and chemiosmosis in oxidative phosphorylation produce the majority of ATP during cellular respiration, typically yielding 34 ATP per glucose molecule. High-energy electrons from NADH and FADH₂ drive proton pumping across the mitochondrial membrane, creating a proton gradient that powers ATP synthase to generate large quantities of ATP.
D. Krebs cycle: The Krebs cycle produces a small number of ATP molecules directly through substrate-level phosphorylation (1 ATP per cycle per acetyl-CoA). Its main contribution is generating NADH and FADH₂, which carry electrons to the electron transport chain for the production of most ATP.
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