Exam II: Controlling Microbial Growth Flashcards
Bacterial growth means…
Increase in number of cells, not the size!
Bacterial growth depends on… (5 things)
Temperature, pH, osmotic pressure, oxygen, nutrients
Log phase cultures are most sensitive to…?
Growth inhibition
Define “generation time”
The time required for the cell to divide/population to double
Average bacteria generation time
1-3 hours
E. coli generation time
20 minutes
Define: Antisepsis
Reduction of # of microorganisms and viruses on LIVING tissue
Define: Aseptic
An environment or procedure free of pathogenic contaminants
Define: -cide / -cidal
Indicates kills/destruction of a type of microbe
Define: Degerming
Removal of microbes by mechanical means
Define: Disinfection
Destruction of most microorganisms and viruses on NON-LIVING tissue
Define: Pasteurization
Use of heat to destroy pathogens and reduce spoilage microorganisms in foods and beverages
Define: Sanitization
Removal of ENOUGH pathogens from objects to meet public health standards
Define: -stasis / -static
Indicates INHIBITION. Prevents growth of microbe (not a complete destruction)
Define: Sterilization
Destruction of ALL microorganisms and viruses in or on an object.
What factors affect how long it takes to kill bacteria? (4 things)
Number of microbes, Environment, Time of exposure, Characteristics of microbes
What environmental conditions slow the time to kill microbes?
Organic materials, Biofilm (such as feces, sewage, etc)
What environmental conditions speed up the time to kill microbes?
Prior cleaning, Heat
What microbe characteristics are most resistant to kill? (3 things)
Spores, Thick lipid coats, Protozoan cysts
What are the 3 actions of microbial control agents?
Alteration of membrane permeability, Damage to proteins and nucleic acids prevents functions of proteins and enzymes, Mutation/messing up the DNA to make non functional proteins
Define: Thermal Death Time
How long it takes to kill a certain bacteria at a certain temperature
What is the time/temp for pasteurization, and what does it do?
63’C for 30 minutes. Lowers # of pathogens in food products that would be damaged by longer heating times
What is the time/temp for UHT sterilization, and what is a potential side effect of using this method?
140’C 1-3 seconds. It may cause the loss of nutritional value of the food product.
How does moist heat work to control microbes?
It coagulates proteins by denaturing (breaking hydrogen bonds).
How long do most pathogens need to boil to kill microbes?
10 minutes
How long does something need to boil to kill Hepatitis virus?
30 minutes
How long does it take for boiling to kill spores?
20 hours
How does an autoclave work?
Heat + pressure
What are the specifications for using an autoclave?
15 psi for 15 minutes at 121 ‘C
What temp/time is used for dry heat in an oven? When would you use dry heat?
170’C for 2 hours. When things cannot go into the autoclave, or would be damaged by steam/moisture
What is resistant to dry heat?
Spores
Low temperature: Refrigeration is….
Bacteriostatic
What microbe is psycrotolerant, and can grow in a refrigerator?
Listeria
What is the problem with ice crystals that are formed when freezing something?
The crystals mechanically shear the plasma membrane
How is freezing used for preservation, in some cases? (What is used?)
Dry ice and 95% ethanol
Dessication is …
Bacteriostatic
What is the term and an example of when drying out is used for preservation?
Lyophilization (eg freeze drying)
What is most resistant to water limiting methods of killing or preserving?
Molds and yeasts
What type of radiation would you use on spices, vegetables, and certain meats?
Low Level Ionizing Radiation
What type of radiation would you use on medical supplies?
High Energy Electron Beams
How does radiation work?
It causes mutations and death of cells
What is affected in UV radiation to cause gene mutations?
Thymine dimers in DNA
How would you use UV radiation? When would you use it?
Germicidal lamps, Vaccine disinfection. Might use it to kill organisms when something is sensitive to moisture, heat, etc.
What kind of effect does a microwave have on microbes?
Very little
What is the problem with microwaves?
It works by activating water molecules, so solid foods are heated unevenly
Phenols are a type of…
Disinfectant/Antiseptic
Disinfectants/Antiseptics are chemicals with what kind of effect?
antigermicidal
How do Phenols work?
Damage lipid membranes
Where are phenols active?
In presence of organic matter
Which type of disinfectants/antiseptics are broad spectrum?
Bisphenols
What type of substance are hexachlorophine and triclosan? Where are they commonly used?
Bisphenols. Used in antibacterial soaps and toothpastes.
Chlorhexidine is what type of disinfectant/antiseptic?
Biguanide
What is a benefit of chlorhexidine, and where might it be used?
Low toxicity, can be used on skin and mucous membranes. Used as surgical scrub in veterinary hospitals.
Iodine and Chlorine are example of what kind of substance?
Halogens
How does chlorine work? What warnings should be considered?
Destroys cell walls and enzymes. It is nondiscriminatory, therefore not good on human tissues.
What is the name of chlorine gas, and how is it adapted for use for disinfection?
Hypochlorite. It is dissolved into water to form bleach.
How does alcohol (disinfectant/antiseptic) work?
Protein denaturation and membrane damage
What aspect of alcohol use is both good and bad? Why is it bad?
Evaporates quickly. Bad because it takes 90 seconds to kill organisms
What are 2 examples of alcohols?
Ethanol, isopropanol
Why is 100% alcohol not good?
The water component is needed to denature proteins.
How do heavy metals work as a disinfectant?
Denatures proteins
What is an example of a heavy metal used as a topical cream?
Silver nitrate
What poisonous heavy metal disinfectant was used to treat syphilis and is painted on?
Mercuric chloride
What is the copper sulfite heavy metal disinfectant used for?
Algaecide
Where might you find zinc as a heavy metal disinfectant?
Mouthwash, paints
How do surfactants work?
Decrease surface tension and damage lipid membranes. They essentially poke holes in membrane! They are often used in conjunction with something else (but not always)
What disinfectant/surfactant combination is often used for mold abatement?
10% bleach (disinfectant) + Ivory soap (surfactant)
Sodium benzoate is a chemical food preservative that is used in what kind of foods? It works by doing what to the pH, which in turn affects what enzyme in what way?
Used in acidic foods. It REDUCES pH, which INACTIVATES PHOSPHOFRUCTOKINASE.
Sorbic acid is a chemical food preservative that works in what way?
Inhibits enzymes
Calcium proponate is a non-toxic chemical food preservative that is used on what type of food? How does it work?
Bread. Inhibits growth.
Sodium nitrate and sodium nitrite are toxic chemical food preservatives that work in what way, and on what microbe?
Inhibits Clostridium botulinum.
Formaldehyde and glutaraldehyde are examples of what, and what action do they take?
Aldehydes. Preserving
How do aldehydes work?
Irreversibly cross-link protein molecules (they will not work anymore)
What are 2 examples of when aldehydes may be used?
Instrument disinfection, Tissue preservation for pathology
What is ethylene oxide used for and how does it work?
Gas sterilization. It denatures proteins.
What is a benefit of gas sterilization, and when would you use it?
High penetration! It kills all spores and microbes with lengthy exposure. Use it when something would otherwise be sensitive to heat or moisture.
Ozone, hydrogen peroxide, benzoyl peroxide, and paracetic acid are examples of what?
Oxidizing agents
What is a downside to hydrogen peroxide?
It is very toxic
What is paracetic acid especially good for, and how does it work?
Anaerobes. Interferes with metabolism
In practical terms, what does the term “sterilization” refer to?
The elimination of all harmful microorganisms and viruses (although some microbes may still be present)
Which substance/process would one use to kill microbes on laboratory surfaces?
Disinfectants
