Concept explainers
Videos
The thermal death time for a suspension of Bacillus subtilis endospores is 30 minutes in dry heat and less than 10 minutes in an autoclave. Which type of heat is more effective? Why?
To review:
Which type of heat is more effective based on the thermal death time for a suspension of Bacillus subtilis endospores.
Introduction:
Bacillus subtilis is a rod-shaped, Gram-positive bacterium that are naturally found in soil and vegetation. B. subtilis grow in the mesophilic temperature range. The optimal temperature for the growth of this organism is 25ºC -35ºC.
Explanation of Solution
The cell wall is a rigid structure present outside the cell. Bacillus species are generally isolated by soil sprinkle technique and are used in the production of antibiotics. Ethanol, or strong acid or alkali are not effective in destroying the spores of B. subtilis. The use of chemicals generally does not kill the spores, and it only controls their growth and kills the living cells.
The effective way of destroying the endospores is by passing heat. Dry heat will take more time to penetrate through the cell. As moist heat easily penetrates through the cell, it is the effective way for the destruction of the endospores.
Based on the thermal death time (10 minutes) for B. subtilis endospores in an autoclave, moist heat is the effective method to kill B. subtilis endospores. In a sterilizing chamber, autoclave employs high temperature under pressure. It is used in the sterilization for surgical equipment and medical instruments. It is also used in pharmaceutical and food industries. The elevated temperature and pressure with steam creates an environment that is too high for any microorganisms or spores to live.
Moist heat penetrates into the bacterial cells easily and effectively kills vegetative bacteria as well as their spores. Compared to dry heat (thermal death time for B. subtilis endospores: 30 minutes), B. subtilis endospores are more effectively killed by an autoclave (moist heat).
Want to see more full solutions like this?
Chapter 7 Solutions
Microbiology: An Introduction Plus Mastering Microbiology with Pearson eText -- Access Card Package (13th Edition) (What's New in Microbiology)
Additional Science Textbook Solutions
Human Anatomy & Physiology (11th Edition)
HUMAN ANATOMY
Microbiology: Principles and Explorations
Human Physiology
Campbell Essential Biology (6th Edition) - standalone book
Campbell Biology: Concepts & Connections (8th Edition)
- Which B. megaterium culture, a culture in the exponential growth phase or a culture in the stationary phase, would show the best survival following exposure to UV radiation? Explain.arrow_forwardsix Staphylococcus aureus are inoculated into a cream pie by the hands of a pastry chef. The generation time of S. aureus in cream pie at room temperature is 30 minutes. a) How many S. aureus are in the pie after 4 hours at RT? b) After 24 hours?arrow_forwardYou just finished plating your electroporatio products on your YPD-Zeocin plate and you think you did everything perfectly but you come back the folloeing week and have zero colonies. Which of the following could be the reason for the absence of colonies? A) You centrifuged your electroporated cells for 30 sec at 16,000 rpm instead of 4,000 rpm before plating them B) You added sorbitol+YPD to your cells thirty minutes after pulsing your cells C) The Zeocin had not been added to the plates when they were made. D) All of the above E) Both a and b onlyarrow_forward
- When is sterilization by filtration preferred over sterilization by heat? Why? What makes heat an effective sterilizing agent? Why are the conditions required for sterilization greater for dry heat (160-180°C for 1-2hrs) than for steam (121°C for 15min)?arrow_forwardA batch of turkey rolls (10 lb—approximately 4.5 Kg—each) were cooked to 165°F internal temperature in bags, opened, sliced, vacuum-packaged, and stored at 40°F. The product was expected to have a refrigerated shelf life of 50 days. However, after 40 days, the packages contained gas and approximately 107 bacterial cells/g of meat. The bacterial species involved in the spoilage was found to be Leuconostoc carnosum, which is killed at 165°F. What could be the sources of the bacterial species in this cooked product?arrow_forwardIf the generation time of Bacillus cereus is 28 minutes, how many cells of B. cereus will there be after an 90 minutes?arrow_forward
- Why might clinical medicine have an interest in understanding bacterial cell division at the molecular level? Explain why a hyperthermophile would probably not be a human pathogen. Describe four factors that may have an influence on the effectiveness of an antimicrobial treatment. Explain why 70% or 80% alcohol is more effective than 100% alcohol in controlling microorganisms.arrow_forwardWhich type of hemolysis characterizes Streptococcus pyogenes, the bacterium that causes strep throat?arrow_forwardWhat is the most difficult type of microbial cell or structure to kill? What methods can be used to sterilize a sample contaminated with these?arrow_forward
- Compare and contrast antiseptic and disinfectant. What is the hazard of the splattering tendency in flame sterilizing an inoculating loop? Can inoculation loops and needles be sterilized by autoclaving? Explain.arrow_forwardIs the telluride glycine agar? (TGA) a complex or defined medium? Explain based on its composition. What kind of Media is TGA explaining based on what kind of microorganisms it allows to grow?arrow_forwardThe thermal death point refers to: O 1) The time it takes to kill an organism in an autoclave 2) The temperature it requires to kill an organism within 10 minutes 3) The time it takes to kill an organism at a chosen temperature O 4) The temperature required to kill prions O 5) The time required to disinfect a surfacearrow_forward
