Chapter 9 Flashcards
Sterilization does not apply to prions which are infectious proteins because?
Standard sterilization techniques do not destroy them
In practical terms, sterilization indicates only the?
Eradication (complete destruction of something) of harmful microorganisms and viruses ; some innocuous microbes may still be present & viable in an environment that is considered sterile
Does commercial sterilization of canned foods kill all hyperthermophilic microbs?
No, however, because they do not cause disease & they cannot grow & spoil food at ambient temperatures, they are of no practical concern
An environment or procedure free of contamination by pathogens
Aseptic
Vegetables & fruit juices are available in _______ packaging, & surgeons & lab technicians use _______ techniques to avoid contaminating a surgical field or lab equipment
Aseptic
Refers to the use of physical or chemical agents known as _______, including ultraviolet light, heat, alcohol, and bleach, to inhibit or destroy microorganisms, especially pathogens
Disinfection
disinfectants
Unlike sterilization, disinfections does not guarantee that?
All pathogens are eliminated, indeed disinfectants alone cannot inhibit endospores or some viruses
The term disinfection is only used when?
In reference to treatment of inanimate objects, when a chemical is used on skin or other tissue, the process is called antisepsis
The term disinfection is only used when?
In reference to treatment of inanimate objects, when a chemical is used on skin or other tissue, the process is called antisepsis, and the chemical is called an antiseptic
Though chemicals such as soap or alcohol are common during degerming, the action of?
Thoroughly scrubbing the surface may be more important than the chemical in removing microbes
Steam, high-pressure hot water, & scrubbing are used to?
Sanitize restaurant utensils and dishes, & the chemicals are used to sanitize public toilets
The difference between disinfecting dishes at home and sanitizing dishes in a restaurant is the?
Arena, private verses public in which the activity takes place
There are two major types of microbial control
Sterilization, which is the elimination of all microbes; and antisepsis or disinfection, which each denote the destruction of vegetative (non spore) cells & many viruses
Chemical agents that destroy pathogenic microorganisms in general
Germicides
Define microbial death
The permanent loss of reproductive ability under ideal environmental conditions
One technique for evaluating the efficacy of an antimicrobial agent is to calculate the microbial death rate which is?
Usually found to be constant over time for any particular microorganism under a particular set of conditions
Describe how to evaluate the efficacy of an antimicrobial agent by calculating the microbial death rate
A scientist treats a broth containing 1 billion (10 to the 9th) microbes with an agent that kills 90% of them in 1 minute. The most susceptible cells die first, leaving 100 million (10 to the 8th) hardier cells after the first minute. After another minute of treatment, another 90% die leaving 10 million (10 to the 7th) cells that have even greater resistance to and require longer exposure to the agent before they die.
There are many types of chemical & physical microbial controls, but their modes of action fall into two basic categories
1) Those that disrupt the integrity of cells by adversely altering their cell walls or cytoplasmic membranes
2) Those that interrupt cellular metabolism & reproduction by interfering with the structures of proteins & nucleic acids
Describe how alteration of cell walls and membranes is a mode for microbial control
Beneath a cell wall is a cytoplasmic membrane which acts as a bag that contains the cytoplasm & it controls the passage of chemicals into and out of the cell. Extensive damage to a membranes proteins or its phospholipids by any physical or chemical agent allows the cellular contents to leash out and if it’s not immediately repaired it will cause death
Describe the alteration of cell walls and membranes is a mode for microbial control for enveloped viruses
The envelope is a membrane composed of proteins & phospholipids that is responsible for the attachment of the virus to its target cell; thus when damage happens to the envelope by physical or chemical agents it fatally interrupts viral replication. The lack of an envelope in non enveloped viruses accounts for their greater tolerance of harsh environmental conditions, including antimicrobial agents
Describe the damage to proteins and nucleic acids which is a mode that antimicrobal agents use
A proteins function depends on an exact three-dimensional shape, which is maintained by hydrogen & disulfide bonds between amino acids. When these bonds are broken by extreme heat or certain chemicals, the proteins shape changes. These denatured proteins cease to function, bringing cellular death. Chemicals, radiation & heat can alter and even destroy nucleic acids. Since genes of a cell/virus are composed of nucleic acids disruption of these molecules can produce fatal mutations
Describe how antimicrobial agents can interfere with protein synthesis
The portion of a ribozyme that catalyzes the synthesis of proteins is a ribozyme (an enzymatic enzyme) so physical or chemical agents that interfere with nucleic acids also stop protein synthesis
Temp. & pH affect microbial death rates & the efficacy of antimicrobial methods. Warm disinfectants generally work better than cool ones because?
Chemicals react faster at higher temps.
Acidic conditions enhance the antimicrobial effect of heat. Some chemical disinfectants, such as household chlorine bleach are more effective at?
Low pH
Why is it important to clean objects before sterilization or disinfection?
Organic materials like fat, feces, vomit, blood and the intercellular secretions in biofilms interferes w/the penetration of heat, chemicals & some forms of radiation . In some cases these materials inactivate chemical disinfectants.
Why is it important to clean objects before sterilization or disinfection so that antimicrobial agents can thoroughly contact all the objects surfaces?
Organic materials like fat, feces, vomit, blood and the intercellular secretions in biofilms interferes w/the penetration of heat, chemicals & some forms of radiation . In some cases these materials inactivate chemical disinfectants.
A phenol coefficient greater than 1.0 indicates that?
An agent is more effective than phenol, and the larger the ratio the greater the effectiveness
Heat can be used for sterilization (all cells & viruses are deactivated) or for commercial preparation of canned goods. In commercial sterilization what happens?
Hyperthermophilic prokaryotes remain viable but are harmless because they can’t grow at the normal (room) temp. in which canned foods are stored
lowest temp. that kills all cells in a broth in 10 minutes
Thermal death point
The time it takes to completely sterilize a particular volume of liquid at a set temperature
Thermal death time
Time required to destroy 90% of the microbes in a sample
Decimal reduction time (D). Researchers calculate this when measuring the effectiveness of heat sterilization. This concept is useful to food processors because they must heat foods to eliminate all endospores of Clos. botulinum which could germinate & produce botulism toxin inside sealed cans
The standard in food processing is to apply heat such that a population of 10 to the 12th pwr C. botulinum endospores is reduced to?
10 to the 0 pwr (that is 1) endospore which leaves only a small change that the can of food contains an endospore
Moist heat is commonly used to?
Disinfect, sanitize, sterilize, and pasteurize, kills cells by denaturing proteins & destroying cytoplasmic membranes
Moist heat is more effective in microbial control than dry heat because?
Water is a better conductor of heat than air. Example, you can safely stick into an oven at 350 degrees F for a few moments but putting it into boiling water at the lower temperature of 212 degrees F would severely burn you
Boiling kills the?
Vegetative cells of bacteria & fungi, the trophozoites of protozoa, & most viruses within 10 minutes at sea level
Water at a rapid boil is no hotter than that at a slow boil; boiling water at normal atmospheric pressure cannot exceed boiling temperature (100 degrees C at sea level) why is that?
Because escaping steam carries excess heat away
For boiling the time is the critical factor. Also at higher elevations water will boil at?
Lower temps. because atmospheric pressure is lower, thus, a longer boiling time is required in Denver than in LA to get the same antimicrobial effect
What can survive boiling at sea level?
Bacterial endospores, protozoan cysts, and some viruses (hepatitis) can survive boiling at sea level for many minutes or even hours. Because they can withstand boiling for more than 20 hrs, boiling is NOT recommended when true sterilization is required.
Boiling is effective for?
Sanitizing restaurant tableware or disinfecting baby bottles
True sterilization using heat requires what?
Higher temps. than that of boiling water. To achieve higher temperatures, pressure is applied to boiling water in order to prevent the escape of heat in steam.
Why does applying pressure achieve sterilization?
The temperature at which water boils (& steam is formed) increases as pressure increases
Who uses autoclaving techniques?
Scientists and medical personnel routinely use a piece of equipment called an autoclave to sterilize chemicals & objects that can tolerate moist heat. There are alternative techniques that must be used for the items that are damaged by heat or water, such as some plastics & vitamins
An autoclave (used by scientists & medical personnel) consists of what?
A pressure chamber, pipes to introduce
An autoclave (used by scientists & medical personnel) consists of what?
A pressure chamber, pipes to introduce & evacuate steam, valves to remove air & control pressure, & pressure & temp. gauges to monitor the procedure. As steam enters an autoclave chamber, it forces air out, raises the temp. of the contents, & increases the pressure, until a set temp. & pressure are reached
What is the temp. and pressure to destroy all microbes and how long does it take.
Temp. of 121 Degrees C, which requires the addition of 15 pounds per square inch (psi) of pressure above that of normal air pressure this destroys all microbes in a small volume in about 10 minutes, it can hold pressure & temp. for 15 minutes for a safety margin
Can an autoclave sterilize large volumes of liquids & solids?
Yes it is just a slower process because they require more time for heat to penetrate. Thus, it requires more time to sterilize 1 liter of fluid in a flask than the same volume of fluid distributed into smaller tubes. Autoclaving solid substances such as meat also requires extra time because it takes longer for heat to penetrate to their centers
Sterilization in an autoclave requires?
That steam be able to contact all liquids & surfaces that might be contaminated with microbes; therefore, solid objects must be wrapped in porous cloth or paper, not sealed in plastic or aluminum foil, which are impermeable to steam. Containers of liquids must be sealed loosely enough to allow steam to circulate freely, and all air must be forced out by steam. Since steam is lighter than air, it cannot force air form the bottom of an empty vessel; empty containers must be tipped so that air can flow out
What are ways to ensure that an autoclave has sterilized its contents?
A common method is a chemical that changes color when the proper combination of temp. & time have been reached. Often this color indicator is impressed in a pattern on tape or paper so the word sterile or a pattern or design appears. Another method use plastic beads that melt when proper conditions met
A biological indicator of sterility used endospores of the bacterium Bacillus stearothermophilus impregnated into tape. After autoclaving, the tape is?
Aseptically inoculated into sterile broth. If no bacterial growth appears, the original material is considered sterile. In a variant of this technique the endospores are on a strip in one compartment of a vial that also induces a growth medium containing a pH color indicator. After autoclaving, a barrier between the two compartments is broken, putting the endospores into contact with the medium. In this case the absence of a color change after incubation indicates sterility
What types of bacteria are controlled by pasteurization?
Brucella melitensis, Mycobacterium bovis, and Escherichia coli, the causative agents of undulant fever, bovine tu
What types of bacteria are controlled by pasteurization?
Brucella melitensis, Mycobacterium bovis, and Escherichia coli, the causative agents of undulant fever, bovine tuberculosis, and one kind of diarrhea, are controlled in this manner
Moist Heat Treatments of milk: Process
1) Historical (batch) pasteurization
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Moist Heat Treatments of milk:
Process
1) Historical (batch) pasteurization
Treatment
Moist Heat Treatments of milk: Process 1) Historical (batch) pasteurization 2) Flash pasteurization 3) Ultrahigh-temperature pasteurization 4) Ultrahigh-temperature sterilization
Treatment
1) 63 Degrees C for 30 minutes
2) 72 Degrees C for 15 seconds
3) 135 Degrees C for 1 second
4) 140 Degrees C for 1-3 seconds
Pasteurization is not sterilization. Thermoduric and theromphilic- heat tolerant and heat loving- prokaryotes survive pasteurization, but they do not?
Cause spoilage over the relatively short times during which properly refrigerated and pasteurized foods are stored before consumption.
The combination of time and temperature required for effective pasteurization varies with the product. Milk is the most familiar pasteurized product. Describe the pasteurization of milk
Historically milk was pasteurized by batch method for 30 minutes at 63 Degrees C, but most milk processors today use a high temperature short time method known as flash pasteurization, in which milk flows through heated tubes that raise its temperature for 72 degrees C for only 15 seconds. This treatment effectively destroys all pathogens. Ultrahigh-temperature pasteurization heats the milk to 134 Degrees C for only 1 second, some consumers claim it adversely affects the taste
What is ultrahigh-temperature sterilization?
The dairy industry and other food processors use it which involves flash heating milk or other liquids to rid them of all living microbes. Process involves passing liquid through superheated steam at 140C for 1-3 seconds and then cooling rapidly. Treated liquids can be stored indefinitely at room temp. w/out microbial spoilage, though after months of storage chemical degradation results in flavor changes. Small packages of dairy creamer served in restaurants are often sterilized by this method
For substances such as powders & oils that cannot be sterilized by boiling or with steam, or for materials that can be damaged by repeated exposure to steam (such as some metal objects, sterilization can be achieved by?
The use of dry heat, as occurs in an oven
Why is hot air an effective sterilization agent?
Because it denatures proteins and fosters the oxidation of metabolic & structural chemicals; however in order to sterilize, dry heat requires higher temps. for longer times than moist heat because dry heat penetrates more slowly. For instance, whereas an autoclave needs less than 15 minutes to sterilize an object at 121C, an oven at the same temp. requires at least 16 hours to achieve sterility. Typically use higher temps (171C for 1 hr or 160C for 2 hrs) to sterilize objects in an oven, but objects made of rubber, paper & many types of plastic oxidize rapidly (combust) under these conditions
Complete incineration is the ultimate means of sterilization.
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Complete incineration is the ultimate means of sterilization. As part of standard aseptic technique in microbiological laboratories, inoculating loops are sterilized by heating them in the flame of a Bunsen burner or with an electric heating coil until?
They glow red (about 1500C). Health care workers incinerate contaminated dressings, bags, and paper cups; field epidemiologists incinerate the carcasses of animals that have diseases such as anthrax or bovine spongiform encephalopathy (mad cow disease)
Refrigeration and freezing temperatures
Refrigeration temps.- Between 0 degrees C and 7 C
Freezing temps.- Below 0 degrees C
How does refrigeration and freezing control microbial growth?
They decrease microbial metabolism, growth, and reproduction because chemical reactions occur more slowly at low temperatures, and because liquid water is not available at subzero temps. However, psychrophilic (cold-loving) microbes can multi. in refrigerated food and spoil its taste and suitability for consumption
Refrigeration halts the growth of most pathogens, which are predominantly mesophiles. Exceptions are?
The bacteria Listeria, which can reproduce to dangerous levels in refrigerated food, and Yersinia which can multiply in refrigerated blood products and be passed onto blood recipients
Slow freezing, during which ice crystals have time to form an puncture cell membranes, is more effective than quick freezing in?
Inhibiting microbial metabolism, though microorganisms also vary in their susceptibility to freezing. Whereas the cysts of tape worms perish after several days in frozen meat, many vegetative bacterial cells, bacterial endospores, & viruses can survive subfreezing temperatures for years.
Scientists store many bacteria & viruses in low temperature freezers at -30 C to -80 C and are able to reconstitute the microbes into viable populations by warming them in media containing proper nutrients. Therefore because of this we must?
Take care in thawing and cooking frozen food, because it can still contain many pathogenic microbes
Desiccation, or drying, has been used for thousands of years to preserve such foods as fruits, peas, beans, grains, nuts, and yeast. Desiccation inhibits what?
Microbial growth because metabolism requires liquid water. Drying inhibits the spread of most pathogens, including the bacteria that cause syphilis, gonorrhea, & the more common forms of bacterial pneumonia & diarrhea. However, most molds can grow on dried raisins, & apricots, which have as little as 16% water content
Scientists use lyophilization, a technique combining freezing & drying, to preserve microbes & other cells for many years. In this process?
Scientists instantly freeze a culture in liquid nitrogen or frozen carbon dioxide (dry ice); they they subject it to a vacuums that removes frozen waters through a process called sublimation, in which the water is transformed directly from solid to gas. Lyophilization prevents the formation of large, damaging ice crystals. Although not all cells survive, enough are viable to enable the culture to be reconstitute many years later
What is filtration
The passage of a fluid (either liquid or a gas) through a sleeve designed to trap particles- in this case to cells or viruses and separate them from the fluid. Researchers often use a vacuum to assist the movement of fluid through the filter
How does filtration work
It traps microbes larger than the pore size, allowing smaller microbes to pass through.
In the late 1800s, filters were able to trap cells, but their pores were too large to trap?
The pathogens of such diseases as rabies and measles. These pathogens were thus named filterable viruses, which today have been shortened to viruses. Now filters with pores small enough to trap even viruses
In the late 1800s, filters were able to trap cells, but their pores were too large to trap?
The pathogens of such diseases as rabies and measles. These pathogens were thus named filterable viruses, which today have been shortened to viruses. Now filters with pores small enough to trap even viruses are available, so filtration can be sued to sterilize such heat sensitive
In the late 1800s, filters were able to trap cells, but their pores were too large to trap?
The pathogens of such diseases as rabies and measles. These pathogens were thus named filterable viruses, which today have been shortened to viruses. Now filters with pores small enough to trap even viruses are available, so filtration can be sued to sterilize such heat sensitive materials as ophthalmic solutions, antibiotics, vaccines, liquid vitamins, enzymes, and culture media
In order to construct filters today scientists typically use?
Thin circular membrane filters manufactured of nitrocellulose or plastic and containing specific pore sizes ranging from 25 micrometers to less than 0.01 micrometers in diameter
Health care & laboratory workers routinely use filtration to prevent?
Airborne contamination by microbes. Medical personnel wear surgical masks to prevent exhaled microbes from culture vessels to prevent contamination by airborne microbes
Another ancient method of microbial control is the used of high concentrations of salt or sugar in foods to inhibit microbial growth by?
Osmotic pressure
Osmosis is the net movement of water across a semipermeable membrane (such as the cytoplasmic membrane) from an area of higher concentration to an area of lower concentration.
Cellular metabolism because enzymes are fully functional only in aqueous environments.
What does osmosis preserve?
osmosis preserves honey, jerky, jams, jellies, salted fish, and some types of pickles from most microbial attacks
Osmosis is the net movement of water across a semipermeable membrane (such as the cytoplasmic membrane) from an area of higher concentration to an area of lower concentration. Cells in hypertonic solution of salt & sugar lose water, and desiccates.
Cellular metabolism because enzymes are fully functional only in aqueous environments.
Osmosis is the net movement of water across a semipermeable membrane (such as the cytoplasmic membrane) from an area of higher concentration to an area of lower concentration. Cells in hypertonic solution of salt & sugar lose water, and desiccates.
Removal of water inhibits cellular metabolism because enzymes are fully functional only in aqueous environments.
What does osmosis preserve?
Preserves honey, jerky, jams, jellies, salted fish, and some types of pickles from most microbial attacks
Fungi have a greater ability than bacteria to tolerate hypertonic environments with little moisture, which explains why?
Jelly in your refrigerator may grow a colony of penicillium mold but is not likely to grow the bacterium Salmonella
Another physical method of microbial control is the use of radiation. There are two types of radiation
1) Particulate radiation
2) Electromagnetic radiation
What does particulate radiation consist of?
High-speed subatomic particles, such as protons, that have been freed from their atoms
What is electromagnetic radiation?
Energy w/out mass traveling in waves at the speed of light. Energy is released from atoms that have undergone internal changes. The wavelength of electromagnetic radiation, defined as the distance between two crests of a wave, ranges from very short gamma rays, through X rays, ultraviolet light, & visible light, to long infrared rays, & finally to very long radio waves
Electromagnetic radiation: Though they are particles, electrons also have a wave nature, with wavelengths that are even shorter than gamma rays.
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