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Microbiology Ch. 7
Terms in this set (63)
The removal or destruction of ALL forms of microbial life. Heating is the most common method
Killing C. botulinum endospores in canned foods
Control directed at destroying harmful microorganisms- removing pathogens
Destruction of pathogens on living tissue
Removal of microbes from a limited area, such as the skin around an injection site.
Treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels
inhibiting, not killing, microbes
When bacterial populations are heated or treated with antimicrobial chemicals, they usually die at a WHAT rate? If the death curve is plotted logarithmically, the death rate is constant.
Several factors influence the effectiveness of antimicrobial treatments: The WHAT of microbes. The more microbes there are to begin with, the longer it takes to eliminate the entire population.
Several factors influence the effectiveness of antimicrobial treatments: WHAT? The presence of organic matter often inhibits the action of chemical antimicrobials. Microbes in surface biofilms are difficult for biocides to reach effectively. Temperature- disinfectants work somewhat better under warm conditions
Several factors influence the effectiveness of antimicrobial treatments: WHAT of exposure. Chemical antimicrobials often require extended exposure for more-resistant microbes or endospores to be affected.
Several factors influence the effectiveness of antimicrobial treatments: WHAT? Microbial characteristics affect chemical and psychical control methods.
A microorganism's WHAT is the target of many microbial control agents. This membrane actively regulates the passage of nutrients into the cell and the elimination of wastes from the cell. Damage to the lipids or proteins of the plasma membrane by antimicrobial agents causes cellular contents to leak into the surrounding medium and interferes with the growth of the cell.
Enzymes, which are primarily WHAT are vital to all cellular activities. Breakage in this results in denature of the protein.
WHAT- DNA and RNA are the carriers of the cell's genetic information. Damage to this by heat, radiation, or chemicals is frequently lethal to the cell; the cell can no longer replicate or synthesize enzymes.
WHAT appears to kill microorganisms by denaturing their enzymes; the resultant changes to the 3D shapes of these proteins inactivate them.
thermal death point
(TDP) The lowest temperature at which all the microorganisms in a particular liquid suspension will be killed in 10 minutes.
thermal death time
(TDT) The minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature.
Decimal reduction time
(DRT) The minutes in which 90% of a population of bacteria at a given temperature will be killed
WHAT kills microorganisms by denaturing proteins, which is caused by breakage of the hydrogen bonds that hold the proteins in their 3D structure. Ex.) Egg white frying Ex.) Boiling, Autoclave
Reliable sterilization with moist heat requires temperatures above that of boiling water. These high temperatures are most commonly achieved by steam under pressure in a WHAT?
a process of heating food to a temperature that is high enough to kill most harmful bacteria without changing the taste of the food. It is not sterilization because it only reduces spoiled organisms
Many relatively heat-resistant WHAT bacteria survive pasteurization, but these are unlikely to cause disease or cause refrigerated milk to spoil.
(HTST) Most milk pasteurization today uses higher temperatures, at least 72 degrees celsius but only for 15 seconds. This treatment is known as WHAT? HTST Pasteurization lowers total bacterial counts, so the milk keeps well under refrigeration.
(UHT) Milk can also be sterilized by WHAT so that it can be stored without refrigeration. The milk undergoes superheated steam and reaches 140 degrees celsius is less than a second.
WHAT sterilization kills by oxidation effects? Examples of this are flaming, incineration, and hot-air sterilization
One of the simplest methods of dry heat sterilization is WHAT? To effectively sterilize the inoculating loop, you heat the wire to a red glow.
Dry heat sterilization is also used by WHAT and is similar to flaming. It is an effective way to sterilize and dispose of contaminated paper cups, bags, and dressings.
Items to be sterilized by this procedure are placed in an oven about 170 degrees celsius for nearly 2 hours. The longer period and higher temperature (relative to moist heat) are required bc the heat in water is more readily transferred to a cool body than is the heat in air.
WHAT is the passage of liquid or gas through a screenlike material with pores small enough to retain microorganisms. It is used to sterilize heat-sensitive materials, such as some culture media, enzymes, vaccines, and antibiotic solutions. It is used ti remove microbes
High-efficiency particulate air
(HEPA) HAT removes almost all microorganisms larger than about 0.3 um in diameter through filtration
Filtration. The sample is placed into the upper chamber and forced through the membrane filter by a vacuum in the lower chamber. Pores in the membrane filter are smaller than the bacteria, so bacteria are retained on the filter.
The effect of WHAT on microorganisms depends on the particular microbe and the intensity of the application. The temperatures of ordinary refrigerators, the metabolic rate is reduced so that they cannot reproduce or synthesize toxins. In ordinary refrigeration has a bacteriostatic (inhibiting, not killing, microbes) effect.
Low temperatures. WHAT temperatures tend to render microbes dormant but do not necessarily kill them.
WHAT denatures proteins, resulting in the rapid inactivation of vegetative (non-endospore forming) bacterial cells. Endospores are relatively resistant to this.
In the absence of water, a condition that is known as WHAT (prevents metabolism), microorganisms cannot grow or reproduce but can remain viable for years. Then, when water is made available to them, they can resume their growth and division. This ability is used in the laboratory when microbes are preserved by lyophilization, or freeze-drying.
Desiccation is used in the laboratory when microbes are preserved by WHAT, or freeze-drying. Certain foods are also freeze-dried like coffee and some fruit additives for dry cereals.
The use of high concentrations of salts and sugars to preserve food is based on the effects of WHAT? It causes plasmolysis. High concentrations of these substances create a hypertonic environment that causes water to leave the microbial cell. This principle of WHAT is used in the preservation of foods. Ex.) Concentration salt solutions are used to cure meats. Molds and yeasts are more capable than bacteria of growing in materials with low moisture or high osmotic pressures.
WHAT that kills microorganisms (sterilizing radiation) is of two types: ionizing and nonionizing
WHAT- gamma rays, X rays, or high-energy electron beams has a wavelength shorter than that of nonionizing radiation. Therefore it carries much more energy. The principle effect of this radiation is the ionization of water, which forms highly reactive hydroxyl radicals. These radicals react with organic cellular components, especially DNA.
WHAT has a wavelength longer than that of ionizing radiation. The best example of it is UV (ultraviolet) light. UV light damages the DNA of exposed cells. UV radiation is also used to control microbes in teh air. It is found in hospital rooms or nurseries. A major disadvantage of UV light as a disinfectant is that the radiation is not very penetrating, so the organisms to be killed must be directly exposed to the rays. Organisms protected by solids and such coverings as paper, glass, and textiles are not affected.
Principles of effective disinfection
Principles of effective disinfection: 1. Concentration of disinfection 2. Nature of the material- organic materials present that might interfere with the action of the disinfectant 3. pH 4. Time- disinfection is a gradual process
Evaluates the effectiveness of disinfectants and antiseptics. Metal carrier rings are dipped into standardized cultures of the test bacteria, removed, and dried at 37 degrees. The dried cultures are then placed in the disinfectant for 10 minutes at 20 degrees celsius. The carrier rings are transferred to a medium that will permit the growth of any surviving bacteria. The effectiveness of the disinfectant can then be determined by the number of cultures that grow. (Used to determine whether bacteria survived the treatment)
Used in teaching laboratories to evaluate the efficacy of a chemical agent. A disk of filter paper is soaked with a chemical and placed on an agar plate that has been previously inoculated and incubated with the test organism. After incubation, if the chemical is effective, a clear zone representing inhibition of growth can be seen around the disc.
Lister was the first to use WHAT to control surgical infections in the operating room. It is now rarely used as an antiseptic or disinfectant because it irritates the skin and has a disagreeable odor. It is used in throat lozenges and has little antimicrobial effect.
Derivates of phenol called WHAT, contain a molecule of phenol that has been chemically altered to reduce its irritating qualities or increase its antibacterial activity in combination with soap or detergent. They exert antimicrobial activity by injuring lipid-containing plasma membranes, which results in leakage of cellular contents. A useful property of these as disinfectants is that they remain active in the presence of organic compounds, they are stable, and they persist for long periods after application. They are suitable agents for disinfecting pus, saliva, and feces. Ex.) Lysol
WHAT are derivatives of phenol that contain two phenolic groups connected by a bridge. One bisphenol, hexachlorophene used for surgical and hospital microbial control procedures. Another widely used WHAT is triclosan. It inhibits an enzyme needed for the biosynthesis of fatty acids (lipids), which mainly affects the integrity of the plasma membrane.
Chlorhexidine is a member of the WHAT? It is frequently used for microbial control on skin and mucous membranes. IT is also used for surgical hand scrubs and preoperative skin preparations in patients. Its killing effect is related to the injury it causes to the plasma membrane by blocking an enzyme needed for lipid synthesis. It is biocidal (destruction to living organisms) against most vegetative bacteria and yeasts. Mycobacteria are relatively resistant, and endospores and protozoan cysts are not affected.
WHAT particularly iodine and chlorine are effective antimicrobial agents.
(Halogen) (I2) is one of the oldest and most effective antiseptics. It is effective against all kinds of bacteria, many endospores, various fungi, and some viruses. Iodine is available as tincture- that is, in solution in aqueous alcohol. An iodophor is a combination of iodine and an organic molecule. Iodophores have the antimicrobial activity of iodine, but they do not stain and are less irritating. They are used mainly for skin disinfection and wound treatment
Iodine is available as a WHAT- that is, in solution in aqueous alcohol- and as an iodophor. An iodophor is a combination of iodine and an organic molecule. Iodophores have the antimicrobial activity of iodine, but they do not stain and are less irritating
WHAT is a combination of iodine and an organic molecule. They have the antimicrobial activity of iodine, but they do not stain and are less irritating
(Halogen) (Cl2) is another widely used disinfectant. Its germicidal action is caused by the hypochlorous acid (HOCl) that forms when chlorine is added to water. It is a strong oxidizing agent that prevents much of the cellular enzyme from functioning. Bleach is an HOCl
WHAT effectively kill bacteria and fungi but not endospores and nonenveloped viruses. The mechanism of action of alcohol is usually protein denaturation, but alcohol can also disrupt membranes and dissolve many lipids. Two of the most commonly used alcohols are ethanol and isopropanol. Pure ethanol is less effective than aqueous solutions (ethanol mixed with water) because denaturation requires water.
(heavy metals) The ability of very small amounts of heavy metals, especially silver and copper, to exert antimicrobial activity is referred to as WHAT? Silver is used as an antiseptic in a 1% silver nitrate solution. States require that the eyes of newborns be treated with a few drops of silver nitrate to guard against an infection of the eyes called gonorrheal ophthalmia neonatorum, which the infants might have contracted as they passed through the birth canal.
WHAT can decrease surface tension among molecules of a lipid. Soap= degerming; acid-anionic detergents= sanitizing; Quaternary ammonium compounds= Bacterial, denature proteins, disrupt plasma membrane
WHAT are frequently added to foods to retard spoilage. Among the more additives are sodium benozate, sorbic acid, and calcium propinate. These chemicals are simple organic acids, which the body readily metabolizes and which are generally judged to be safe in foods. Sorbic acid and sodium benozate prevent molds from growing in certain acidic foods such as cheese and soft drinks. Sodium nitrate and sodium nitrite are added to many meat products such as ham, bacon, hot dogs and sausage. They preserve the pleasing red color of the beat by reacting with blood components in the meat, and to prevent the germination and growth of any botulism endospores that might be present.
(Antibiotics) WHAT is often added to cheese to inhibit the growth of certain endospore-forming spoilage bacteria. A protein that is produced by one bacterium and inhibits another. It is present naturally in small amounts in many dairy products.
WHAT is most effective antimicrobials. They inactivate proteins by forming covalent cross-links with several organic functional groups on proteins (-NH2, -OH, -COOH, and -SH). Before, formaldehyde was used. Glutaraldehyde is a chemical relative of formaldehyde that is less irritating and more effective than formaldehyde. It is used to disinfect hospital instruments. A possible replacement for glutaraldehyde is ortho-phthaldehyde (OPA) which is more effective against many microbes that has fewer irritating properties.
WHAT are chemicals that sterilize in a closed chamber (similar to an autoclave) A gas suitable for this method is ethylene oxide. It denatures proteins. Ethylene oxide kills all microbes and endospores but requires a long time period. One of its advantages is that it is highly penetrating (able to go through). Because of their ability to sterilize without heat, ethylene oxide is widely used on medical supplies and equipment.
WHAT exert antimicrobial activity by oxidizing cellular components of the treated microbes. Ex.) ozone, hydrogen perozide, and peracetic acid. Ozone is often used to supplement chlorine in the disinfection of water because it helps neutralize tastes and odors. It is a poor antiseptic and not good for open sounds, but it is a good disinfectant. Benzyl peroxide is another compound useful for treating wounds infected by anaerobic pathogens. Peratic acid is one of the most effective liquid chemical sporicides and a sterilant. Used in disinfection of food-processing and medical equiment because it leaves no toxic residues and is minimally affected by the presence of organic matter.
Resistance of microorganisms to chemical biocides:
Resistance of microorganisms to chemical biocides: Least resisting (bottom-up): viruses with lipid envelopes, gram-positive bacteria,viruses without envelopes, fungi. More resistant (bottom-up): gram-negative bacteria, vegetative protozoa, mycobacteria, endospores of bacteria
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