Chapter 7 Flashcards
The Control of Microbial Growth
Which heat method does not kill endospores
Pasteurization
What is the most affective for sterilizing mattresses and plastic petri dishes
Ethylene oxide
Which disinfectant does not act by just disrupting the plasma membrane
Halogens
Which can not be used to sterilize a heat-labile solution stored in a plastic container
Autoclaving
What is not a characteristic of quaternary ammonium compounds
Sporicidal
A classmate is trying to determine how we disinfectant my kill cells. You observed that when he spilled the disinfectant in your reduced litmus milk, the litmus turned blue again. You said just to your classmate that
The disinfectant might oxidize molecules
Which of the following is most likely to be bactercidal A. Membrane filtration B. Ionizing radiation C. Lyophilization D. Deep freezing
B. Ionizing Radiation
What is used to control microbial growth in foods
Organic acids
The thermal death time for a suspension bacillus subtilis endospores is 30 minutes in dry heat and less than 10 minutes in an autoclave. Which type of heat is more affective and why
Autoclave because of the high specific heat of water, moist heat is readily transfer to cells
If pasteurization does not achieve sterilization, why is it used to treat food
Pasteurization destroys most organisms that can cause disease or rapid spoilage of food.
What are factors that can alter thermal death point
- Innate heat resistance of the strain of bacteria
- The past history of the culture whether it was freeze dried, wetted, ect
- The clumping of the cells during the test
- The amount of water present
- The organic matter present
- Media and incubation temperature used to determine viability of the culture after heating
The antimicrobial effect of gamma radiation is due to a ________________, the antimicrobial effect of ultra Violet radiation is due to _________________
a. The ability of ionizing radiation to break DNA directly. However because of the high water content of cells, free radicals that break DNA strands are likely to form.
b. Formation ofthymine dimers
How do autoclaving, hot air, and pasteurization illustrate the concept of equivalent treatments
All 3 processes kill microorganisms, However as moisture and/or temperature are increased less time is required to achieve the same result
How do salt and sugars preserve foods? Why are these considered physical rather than chemical methods of mycrobial control
Salts and sugars create a hypertonic environment. Salts and sugars do not directly affect cell structures or metabolism, rather they alter the osmotic pressure.
Name one food that is preserved with sugar and one preserved with salt
Jams and jellies are preserved with sugar, Meats are usually preserved with salt
How do you account for the occasional growth of penicillin mold in jelly, which is 50% sucrose
Mold are more capable of growth and high osmotic pressure than are bacteria
The use-dilution values for two disinfectants tested under the same conditions are as follows:
Disinfectant A–1:2
Disinfectant B 1:10,000
It’s both disinfectants are designed for the same purpose which would you select
Disinfectant be is preferable because it can be diluted more and still be effective
A large hospital washes burn patients and a stainless steel tub. After each patient the tub is cleaned with a quat. It was noticed that 14 of 20 burn patients Rico acquired Pseudomonas infections after being bathed. Provide an explanation for this high rate of infection
Quaternary ammonium compounds are most effective against gram positive bacteria. Gram negative bacteria that were stuck in the cracks or round the drain of the tub would not have been washed away when the tub was cleaned. These gram negative bacteria could survive the washing procedure. Some pseudomonas can grow on quats that have accumulated.
What bacterium has porins, is resistant to Trilclosan, and survives and make grow in quats
Pseudomonas
Sterilization
The destruction or removal of all forms of microbial life including Endospores and viruses but with the possible exception of prions
What are the different methods of sterilizing
Moist heat sterilization Steam sterilization Dry heat sterilization Filtration Radiation
What is the most common form of sterilization
High steam under pressure or use of sterilizing gas such as ethylene oxide
Liquids or gasses can be sterilized by
Filtration
Disinfection
Destruction or removal of non and dose for foreign mean vegetative pathogens; living cells that are dividing
