Control of Microbial Growth II Flashcards
What are the 5 categories of physical methods of control
Moist heat, dry heat, filtration, radiation, and high pressure
What is the only method that is not bactericidal
Filtration
What are the three methods of moist heat
Boiling
Pasteurization
Autoclaving
What are the two methods of dry heat
incineration
dry heat ovens
what are the two ways to filtrate
filtration of fluids, filtration of air
What are the two methods of radiation
Ionizing radiation and UV radiation
Moist heat can be used to….
sterilize or disinfect
Describe the method of boiling
- destroys most microorganisms and viruses
- achieves disinfection
- bactericidal
Describe the method of pasteurization
destroys only pathogens and spoilage organisms
- bacteriostatic (reduction in the # of microbes)
- bactericidal since it kills the pathogens
What does the term bacteriostatic mean
reduction in the number of microbes
What does the term bactericidal mean
kills the microbes (does not necessarily reach sterilization)
Describe the method of autoclaving
- achieves sterilization using pressurized steam
- Occurs at 121 degrees C, 15 psi in 15 minutes
- bactericidal method
- can destroy prions if settings are changed
What is the purpose of commercial canning processes
designed to destroy Clostridium botulinum endospores
-canned food is commercially sterile (removal of only these endospores)
Which is more effective, moist heat of dry heat
moist heat;
dry heat does not penetrate well and takes longer times and higher temperatures (200 degrees celsius for 90 minutes)
describe the method of hot air ovens
oxidize cell components and denature proteins
- bactericidal
- can achieve sterilization
describe the method of incineration
- achieves sterilization
- oxidizes cell to ashes
- used to destroy medical waste and animal carcasses
- can destroy prions very effectively
T/F you can sterilize your inoculating loop by flaming it
True
When is filtration option used
when materials cannot withstand heat treatment
what type of filter would be used for fluids
membrane filter, they contain small pores that even the smallest virus can not fit through, thus physically separating microbes from the sample
What type of filter is used for the filtration of air
HEPA: high efficiency particulate air, removes nearly all microbes from air
T/F filtration is considered both bactericidal and bacteriostatic
False, it is neither since the microbes are only separated, they are not inhibited in growth or killed
T/F Filtration does not achieve sterilization
False
When is a radiation method used
typically with solid objects, generally after packing
-FDA has approved its use in fruits, veggies, pork, poultry, etc..
What are two forms of ionization radiation? what level of control do they achieve?
Gamma rays and X rays
both achieve sterilization
How does Ultraviolet radiation work as a control method? what level of control does it achieve?
- destroys microbes directly in air, water or on surfaces
- will only disinfect since they cannot penetrate endospores
Is UV radiation ionizing or non-ionizing
non-ionizing
What is the drawback on using UV radiation
It has poor penetrating power, it cannot kill microbes in solids or turbid liquids
Describe microwaves as a method of control
- kill by generate heat, not directly
- heats food unevenly so cells can survive
Drawbacks of microwaves as a method of control
-operates in a bactericidal method but does not effectively achieve disinfection evenly so not a good control method
Describe the method of high pressure as a control method
- used in pasteurization of commercial foods (ex. guac)
- avoids problems with high temperature pasteurization
- products maintain color, flavor associated with fresh food
What level of control does high pressure reach
- Not sterilization, but extension of shelf life
- disinfection
- bactericidal but does not kill endospores
What are the 10 examples of chemical control methods
- Alcohols
- Aldehydes
- Biguanides
- Ethylene Oxide gas
- Halogens
- Metals
- Ozone
- Peroxygens
- Phenolic Compounds
- Quaternary Ammonium compounds
Describe the use of alcohol as a control method
- aqueous solution of ethyl or isopropyl alcohol
- kills vegetative bacteria and fungi
- not reliable against endospores and some naked viruses
What is alcohol commonly used as in terms of chemical control
an antiseptic or disinfectant
What are the limitations for using alcohol as a control method
- evaporates quickly, limiting contact time
- much use aqueous solution
What is the importance of using an aqueous alcohol solution? What is the proper range of dilution?
100% will not work bc it will denature proteins and effect the lipid membrane
-also needs water for the chemical reaction to occur (70% alcohol is most commonly used) but the range could be anywhere from 60-98%
What is the role of aldehydes as a chemical control method
- used as a commercial sterilant
- bactericidal with sterilizing effects
What are examples of aldehydes used in chemical control methods and what is an example of their use
Glutaraldehyde- -immersion in 2% alkaline glutaraldehyde will kill all microbial life in 10-12 hours
formaldehyde- used as a gas or as formalin (37% solution) used commonly in hospital settings
What is the drawback of using formaldehyde as a method of aldehyde chemical control?
can be toxic if used over a long period of time with high concentration
What is the role of biguanides as a chemical control method?
- Bactericidal with antiseptic effects
- stays on skin and mucous membranes
- common in skin cream, mouth wash, soaps and lotions
What is the most effective biguanides
chlorhexidine- adheres very tightly to the mucous membrane, remains there for a particular period of time
what is the role of ehtylene oxide gas as a chemical control method?
- very powerful sterilant
- Used generally for sterilization of disposable lab items, equipment, implantable devices such as pacemakers and artificial hips
- major use in the medical industry
What are the role of metal compounds as a chemical control method?
- Used as a disinfectant
- High concentrations may be too toxic to use medically
- Silver still used in creams and bandages as well as silver nitrate drops for infants
T/F Mercury, tin, and copper were once widely used as preservatives
True, but mercury is not longer used because of its toxicity levels
What are two types of Halogens used for chemical control methods
- Chlorine
2. Iodine
Role of Chlorine as a halogen control method
- used as a disinfectant
- bactericidal
- casustic to skin and mucous membranes
- used in household bleach
Drawback to using chlorine
it is not very effective with the presence of organic compounds
Role of Iodine as a halogen control method
- mild enough to be used as an antiseptic/disinfectant
- bactericidal
Drawback of using iodine
unreliable on endospores and difficult to treat organic compounds with
Iodine is commonly used as what
an Iodophore, which slowly releases iodine from a carrier molecule
What are two examples of peroxygens
- Hydrogen peroxide
2. Peracetic Acid
Why are peroxygens good in control and what level of control do they achieve
they are powerful oxidizers, can be used as a disinfectant or antiseptic
What does the effectiveness of Hydrogen peroxide depend on
The surface being treated
T/F hydrogen peroxide is more effective as an antiseptic
False, because aerobic bacteria produce the enzyme catalase which breaks it down to water and oxygen and both human cells and microbes have the ability to break down hydrogen peroxide
What kind of wounds is hydrogen peroxide more effective in disinfecting
deeper wounds because Hydrogen peroxide broken down will produce oxygen which will prevent the establishment of anaerobic microbes
Hydrogen peroxide is more effective as either a disinfectant or an antiseptic
better as a disinfectant
What phase of hydrogen peroxide can be used as a sterilant
the vapor-phase
Which is more potent, peracetic acid of Hydrogen peroxide?
Peracetic acid
What is the advantage of using peracetic acid as a peroxygen
- effective on organic material
- useful on a wide range of material
T/F Phenolics were one of the earliest used disinfectants
True, used by Joseph Lister
What is the level of control achieved by a phenolic compound
can be used as a disinfectant or an antiseptic
What is the advantage of using a phenolic compound
- wide activity range, reasonable cost and will remain effective in presence of detergents and organic matter
- some sufficiently non-toxic, used in soaps and lotions
T/F you can use phenols directly on your skin
False, need to be a modified form, used as a phenolic because a phenol will burn your skin
Ex: Triclosan used in soap and lotion
What is the role of Quaternary Ammonium compounds as a chemical control method?
- It is a positively (cationic) charged detergent
- Nontoxic used to disinfect food preparation surfaces
What are two methods of Preservation of Perishable products
- Chemical preservatives
2. Low Temperature storage
T/F all methods of preservation or perishable products are bacteriostatic
True, that stop the growth but will still have the microbes present
What are two different types of chemical preservatives?
- Weak organic acids
2. Nitrate and nitrite used in processed meats
What is the role of weak organic acids as chemical preservatives and what are some examples
-benzoic, sorbic, propionic acids
Control molds and bacteria in foods and cosmetics
What is the role of nitrate and nitrite as chemical preservatives
- Inhibit endospore germination and vegetative cell growth
2. Higher concentrations give meats pink color
What is the importance of refrigeration for low-temperature storage of perishable products
it inhibits (without killing) growth of pathogens and spoilage organisms by slowing or stopping enzyme reactions
T/F psychrotrophs, psychrophillic organisms can still grow in refrigeration
True
T/F Freezing preserves by slowing all microbial growth
False, it preserves by STOPPING all microbial growth
What are three ways you can reduce available water to preserve perishable products
- Accomplished by salting, adding sugar
- Lyophilization
- Drying
** All are bacteriostatic methods
What is the role of adding salt and sugar to preserve perishable products
- increases environmental solutes
- causes cellular plasmolysis where water exits the bacterial cells
What is the role of lyophilization in order to preserve perishable products
- freeze-drying
- also dehydrates, stopping the growth of microbes
- application of low temperature and drying
- ex: in coffee, milk, meats, fruits, veggies
What is the role of drying in preservation of perishable products
- stops microbial growth but does not reliably kill
- drying=dehydration
