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 B
Explanation
A. Allosteric inhibition: Allosteric inhibition occurs when a molecule binds to a site other than the enzyme’s active site (the allosteric site), causing a conformational change that reduces enzyme activity. It does not involve direct competition between similar substrates for the active site.
B. Competitive inhibition: Competitive inhibition occurs when two molecules that are similar in shape and size compete for binding at the enzyme’s active site. One molecule (the inhibitor) can occupy the active site, preventing the other substrate from binding. This type of inhibition can often be overcome by increasing the concentration of the actual substrate.
C. Active inhibition: “Active inhibition” is not a standard term in enzymology. It does not specifically describe the process in which molecules compete for the same active site and therefore does not accurately represent the scenario described.
D. Noncompetitive inhibition: Noncompetitive inhibition occurs when an inhibitor binds to a site other than the active site, changing the enzyme’s shape and reducing its activity regardless of substrate concentration. Unlike competitive inhibition, the inhibitor does not compete with the substrate for the active site.
Correct Answer is A
Explanation
In gram-negative bacteria, the cell envelope is a complex structure composed of three main layers: an inner (cytoplasmic) membrane, a periplasmic space, and an outer membrane. The inner membrane is a phospholipid bilayer that regulates transport and energy production. The periplasmic space lies between the inner and outer membranes and contains a thin layer of peptidoglycan along with enzymes involved in nutrient processing and defense. The outer membrane contains lipopolysaccharides (LPS), porins, and other proteins that provide structural support, act as a barrier to certain antibiotics, and contribute to the organism’s pathogenicity.
100 Multiple Choice 0.5 points
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