CHAPTER 7 MICROBIOLOGY
What is high-temperature short-time pasteurization? When is it used?
High-temperature short-time (HTST) pasteurization: killed pathogens, pasteurization lowers total bacterial counts, so the milk keeps well under refrigeration. Most milk pasteurization today uses temperatures of at least 72 degrees celcius, but only for 15 seconds
64. Which heavy metals are used to control microbes?
-a combination of silver and the drug sulfadiazine "silversuldadiazine" -mercuric chloride -copper in the form of copper sulfate and other copper containing additives. -zinc
What is a germicide? What does the suffix "cide" mean?
-cide means kill. Kills microorganisms
68. Give two examples of popularly used quats.
-zephiran, a brand name of benzalkonium chloride -cepalcol, a brand name of cetylpyridinium chloride
List the major cellular and molecular targets used by control agents to kill or inhibit microbes.
A microorganism's plasma membrane (see Figure 4.14, page 89), located just inside the cell wall, is the target of many microbial control agents. This membrane actively regulates the passage ofnutrients 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.
What are the advantages and disadvantages of using an autoclave?
A:sterilize culture media, instruments, dressings, intravenous equipment, applicators, solutions, syringes, transfusion equipment, and numerous other items that can with- stand high temperatures and pressures. D: Heat requires extra time to reach the center of solid materials, such as canned meats, because such materials do not develop the efficient heat-distributing convection currents that occur in liquids. Heating large containers also requires extra time.
58. How do alcohols control microbial growth?
Alcohols effectively kill bacteria and fungi but not endospores and nonenveloped viruses. The mechanism of action can also disrupt membranes and dissolve many lipids, including the lipid component of enveloped viruses.
59. What are advantages and disadvantages of using alcohols to control microbial growth?
Alcohols have the advantage of acting and then evaporating reap idly and leaving no residue. however alcohols are unsatisfactory antiseptics when applied to wounds. they cause coagulation of a layer of protein under which bacteria continue to grow.
What is triclosan and why is it important?
An ingredient in antibacterial soaps and at least one toothpaste, triclosan inhibits an enzyme needed for the biosynthesis of fatty acids(lipids), which mainly affects the integrity of the plasma membrane
What is an antiseptic? How does it differ from a disinfectant?
Antiseptic:the use of a chemical to treat an inert surface or substance. Differs: Treatment is only directed at living tissues.
Why is it a bad idea to use aluminum foil when sterilizing with an autoclave?
Because they aren't directly contacted by the steam
What are chlorhexidine and alexidine? What are the advantages and disadvantages of using them?
Chlorhexidine-Best known biguanide, which is frequently used for microbial control on skin and mucous membranes, combined with a detergent or alcohol it is very often used for surgical hand scrubs and preoperative skin preparation in patients Alexidine- is similar and is not more rapid in its action, eventually alexidine is expected to replace Betadine in many applications
What are the advantages and disadvantages of using phenolics as disinfectants?
Contain a molecule of phenol that has been chemically altered to reduce its irritating qualities or increase its antibacterial activity in combination with a soap or detergent. Phenolics exert antimicrobial activity by injuring lipid-containing plasma membranes which results in leakage of cellular contents. The cell wall of mycobacteria, the causes of tuberculosis and leprosy, are rich in lipids, which make them susceptible to phenol derivatives Advantage- they remain active in the presence of organic compounds, are stable, and persist for long periods after application
What is degerming? How does it differ from disinfection? From sterilization?
Degerming: the mechanical removal rather than killing of the microbes in a limited area. (i.e. when someone is about to receive an injection & is swabbed with an alcohol wipe)
What effects do low temperatures have on miccroorganisms?
Depend on the particular microbe and the intensity of the application ex- ordinary refrigerators the metabolic rate for most microbes is so reduced that they can not reproduce or synthesize toxins
What is disinfection? What is a disinfectant?
Disinfection: control directed at destroying harmful microorganisms. Disinfectant:To treat an inert surface or substance.
How does iodine control microbial growth? When is it used?
Effective antimicrobial agents, is one of the oldest and most effective antiseptics, it is active against all kinds of bacteria, iodine impairs protein synthesis and alters cell membranes, apparently by forming complexes with amino acids and unsaturated fatty acids, used mainly for skin disinfectants and wound treatment and for water treatment
How does chorine in its various forms control microbial growth?
Effective antimicrobial agents. It's germicidal action is caused by the hypochlorous acid that forms when chlorine is added to water, used for disinfecting municipal drinking water, water in swimming pools an sewage
Which microbes are biguanides effective against? Which ones can they not control?
Especially effective against gram-positive bacteria also against gram-negative bacteria with the exception of most pseudomonads. They are not sporicidal but have some activity against enveloped viruses
List two forms of dry heat sterilization, what are there advantages and disadvantages of each?
Flaming- simplest methods if dry heat sterilization using fire to kill off any bacteria on the item Hot-air sterilization- items are placed into an oven for 2 hours at 170c to kill off any thing
If a population of bacteria dies at a constant rate of 90% per minute, what does that mean if the population starts at 1 million cells?
For example, suppose a population of 1 million microbes has been treated for 1 minute, and 90% of the population has died. We are now left with 100,000 microbes. If the population is treated for another minute, 90% of those microbes die, and we are left with 10,000 survivors. In other words, for each minute the treatment is ap- plied, 90% of the remaining population is killed
What effects does ionizing radiation have on microbes? When is it used?
Gamma-Rays,X rays, or high-energy electron beams- has a wavelength shorter than that of non-ionizing radiation, therefor it carries much more energy, used to sterilize pharmaceuticals and disposable dental and medical supplies, such as plastic syringes, surgical gloves, suturing materials and catheters. As a Protection against bioterrorism, the postal service often uses electron beam radiation to sterilize certain classes of mail
Why might sterilization time increase when using an autoclave?
Heat requires extra time to reach the center of solid materials, such as canned meats, because such materials do not develop the efficient heat-distributing convection currents that occur in liquids. Heating large containers also requires extra time.
Which situations might require sterilization? Which one would not and why?
Heat treatment is required to canned foods in the supermarket to ensure sterilization. Complete sterilization is not require for a drinking glass or fork in a restaurant requires only enough microbial control to prevent the transmission of possibly pathogenic microbes from one person to another.
List all the physical methods of microbial control that you can think of.
Heat, filtration, low temperatures, high pressure, desiccation, osmotic pressure, radiation
What are the advantages and disadvantages of using high pressure to control microbes?
If the pressure is high enough, it alters the molecular structures of proteins and carbohydrates, resulting in the rapid inactivation of vegetative bacterial cells. Endospores are relatively resistant to high pressure. Advantage- preserve flavors,colors, and nutrient values of the products
What is desiccation and why is it used? When is it useful and when isn't it?
In the absence of water micro organisms cannot grow or reproduce but can remain viable for years. Then with the presence of water can resume their growth and division. Important in a hospital setting
What is sanitization? When is it usually used?
Intended to lower microbial counts to safe public health levels and minimize the chances of disease transmission from one user to another. Used in restaurants for glassware, china, and tableware
Name some halogens that are effective in controlling microbial growth
Iodine and chlorine
What is hexachlorophene? And why is it important?
Is an ingredient of a prescription lotion, pHisoHex used for surgical and hospital microbial control procedures but over use can cause neurological damage
When is filtration used? What kinds of filters may be used?
Is that passsage of a liquid or gas theough a screen like material with pores small enough to retain microorganisms, used to sterilize heat-sensitive materials, such as some culture media, enzymes, vaccines, and antibiotic solutions -High-efficiency particulate air(HEPA) removes almost all miccroorganisms larger then .3um in diamyer for burn patients to lower numbers of airborne microbes
What is ultra-high temperature pasteurization? When is it used?
It is sterilized. It can then be stored for several months without refrigeration
77. What is the listing of microorganisms in descending order of resistance to chemical biocides? Why are they placed in this particular order?
MOST RESISTANT prions endospores of bacteria mycobacteria cysts of protozoa vegetative protozoa gram negative bacteria fungi, including most fungal spores viruses without envelopes gram positive bacteria viruses with lips envelopes LESS RESISTANT
What does the suffix "stat or stasis" mean? What is bacterostasis?
Means to stop or steady. The stop of bacteria (the stop of growth.)
What is the use-dilution test? When might it be used?
Metal or glass cylinders are dipped into standardized cultures of the test bacteria grown in liquid media, removed, and dried at 37c for a short time. The dried cultures are then placed into a solution of the disinfectant at the concentration recommended by the manufacturer and left for 10 mins at 20c then transferred to a medium that permits the growth of any surviving bacteria, the effectiveness is determined by the number of cultures grown
What kind of sterilization method is used when one uses an autoclave?
Moist Heat Sterilization (autoclave-- the higher the temp in an autoclave, the higher the temperature.)
What are the three heat methods of controlling microbial growth?
Moist Heat Sterilization-utilizes hot air that is heavily laden with water vapour and where this moisture plays the most important role in the process of sterilization Pasteurization- high heat treatments kill bacteria & sterilization of bacteria. Dry Heat Sterilization
How could microwaves control microbial growth?
Moisture containing foods are heated by microwave action and the heat will kill most vegetative pathogens. Solid foods heat unevenly because of the uneven distribution of moisture which can cause out breaks of certain pathogens
Which microbes grow more easily in low moister or high osmotic pressure environments?
Molds and Yeasts
79. Are microbial control methods uniformly effective against all microbes?
NO
Are low temperatures sterilizing
No, some bacteria can grow at temperatures several degrees below freezing
What are conditions needed for sterilization when using an autoclave?
Organisms are contacted directly by steam or contain in a small volume of aqueous liquid, steam at a pressure of 15 psi
60. When is ethanol an effective antiseptic?
Pure ethanol is less effective than aqueous solutions (ethanol mixed with water) because denaturation requires water.
What factors are important when deciding on which disinfectants to use?
Read the label-indicates what groups of organisms the disinfectant is effective against, consider the nature of the material being disinfected. And whether the disinfectant will easily make contact with the microbes
What effects do freezing have on bacteria?
Render microbes dormant but do not necessarily kill them, slow freezing is more harmful to bacteria, the ice crystals that form and grow disrupt the cellular and molecular structure of the bacteria. Thawing, being inherently slower, is actually the more damaging part of a freeze-thaw cycle
Define sepsis and asepsis
Sepsis: from the Greek for decay or putrid indicates bacterial contamination, as in septic tanks for sewage treatment. Asepsis: the absence of significant contamination
What forms of chlorine are used to control microbial growth? Under what circumstances are they used?
Solutions of calcium hypochlorote are used to disinfect dairy equipment and restaurant eating utensils Chloride of lime- to soak hospital dressings before the germ theory for disease was developed Sodium hypochlorite is used as a house-hold disinfectant a and bleach as a disinfectant in diaries, food processing, and hemodialysis systems
What happens if air is not exhausted during the autoclaving process?
Steam under pressure will fail to sterilize when the air is not completely exhausted.
Define sterilization and sterilant
Sterilization: the removal or destruction of all living microorganisms. Heating is the most common method used for killing microbes, including the most resistant forms, such as endospores. Sterilant: sterilizing agent
What is the Thermal Death Point (TDP), and why is it important?
The lowest temperature at which all the microorganisms in a particular liquid suspension will be killed in 10 minutes.
What is Thermal Death Time (TDT), and why is it important?
The minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature.
What factors influence the rate of antimicrobial treatments?
The number of microbes. The more microbes there are to begin with, the longer it takes to eliminate the entire population (Figure 7.1b). ● Environmental influences. The presence of organic matter often inhibits the action of chemical antimicrobials. In hospitals, the presence of organic matter in blood, vomitus, Microbial Exponential Death Rate: TABLE 7.2 An Example or feces influences the selection of disinfectants. Microbes in surface biofilms (see page 160) are difficult for bio- cides to reach effectively. Because their activity is due to temperature-dependent chemical reactions, disinfectants work somewhat better under warm conditions. The nature of the suspending medium is also a factor in heat treatment. Fats and proteins are especially protective, and a medium rich in these substances protects microbes, which will then have a higher survival rate. Heat is also measurably more effective under acidic conditions. ● Time of exposure. Chemical antimicrobials often require extended exposure to affect more-resistant microbes or endospores. See the discussion of equivalent treatments on page 188. ● Microbial characteristics. The concluding section of this chapter discusses how microbial characteristics affect the choice of chemical and physical control methods.
What is Decimal reduction time (DRT or D value), and why might it be useful?
The time, in minutes, in which 90% of a population of bacteria at a five temperature will be killed
Describe methods of controlling microbial growth using osmotic pressure
The use of high concentrations of salts and sugars to preserve food. High concentrations of these substances create a hypertonic environment that causes water to leave the cell.
62. Why are ethanol and isopropanol used with other chemical agents?
They are used to enhance the effectiveness of other chemical agents. Ex. an aqueous solution of Zephiran kills about 40% of the population of a test organism in 2 minutes, whereas a tincture of zephiran kills about 85% in the same period.
How does UV light kill microbes? What are the advantages and disadvantages of using UV light to control microbes?
UV light damages the DNA of exposed cells by causing bonds to form between adjacent pyrimidine bases, usually thymines, in DNA chains. UV radiation is also used to control microbes in the air, and used to disinfect vaccines and other medical products. 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 UV light can damage human eyes and prolonged exposure can cause burns and skin cancer in humans
What is the disk-diffusion method? When might it be used?
Used in teaching laboratories to evaluate the efficacy of a chemical agent. A disk of the filter paper is soaked with a chemical and placed on a agar plate that has been previously inoculated and incubated with test organism. After incubation of growth can be seen around the disk, disks containing antibiotics are commercially available used to determine microbial susceptibility to antibiotics
What is Betadine and why is it useful? When is it used?
Which is a povidone-iodine. The most common commercial preparation is Betadine, improves the wetting action and serves as a reservoir of free iodine
78. Ignoring endospores, why are gram-negative bacteria more resistant to chemical biocides than gram-positive bacteria?
a factor in this relative resistance to biocides is the external lipopolysaccharide layer of gram negative bacteria. within gram negative bacteria, members of the genera pseudomonas and burkholderia are of special interest. these closely related bacteria are usually resistant to to biocides and will even grow actively in some disinfectants and antiseptics, most notably the quaternary ammonium compounds. this resistance to chemical antimicrobials is related mostly to the characteristics of their porins (structural openings in the wall go gram negative bacteria).
71. Name at least one aldehyde and state why they can be useful in controlling microbial growth.
aldehyde are the most effective antimicrobials, they inactivate proteins by forming covalent cross-links with several organic functional groups on proteins. Glutaraldeyde: is used to disinfect hospital instruments, including endoscopes and respiratory therapy treatment. is one of the few liquid chemical disinfectants that can be considered a sterilizing agent.
What is the relationship between change in temperature and change in time for heat based sterilization methods?
as the temperature is increased, much less time is needed to kill the same number of microbes (equivalent treatments)
66. What are surfactants? List some examples.
can decrease surface tension among molecules of a liquid. such agents include soaps, and detergents
82. List all the different methods that you can think of that lead to disinfection.
chlorine
74. What is supercritical sterilization and when might it be used?
combines chemical and physical methods. when carbon dioxide is compressed into a supercritical states, it has properties of both a liquid and a gas. organisms exposed to supercritical carbon dioxide are inactivated, including most vegetative organisms that cause spoilage and foodbourne pathogens. even endospore inactivation requies a temp of only 45c. used in treating certain foods, supercritical carbon dioxide has more recently use to decontaminate medical implants, such as bone, tendons, or ligaments taken from donor patients.
72. List at least two chemical sterilizers and state under what circumstances they are used.
ethylene oxide: kills all microbes and endospores but requires a lengthy exposure period of several hours. it is too toxic in pure form so it is mixed with carbon dioxide. an advantage is that is carries out sterilization at ambient temperatures and it is highly penetrating. used to sterilize mattresses in hospitals chlorine dioxide: is a short lived gas that is usually manufactured at the place of use. used to fumigate enclosed building areas contaminated with endospores of anthrax. more stable in a mixed aqueous solution. most common use is in water treatment prior to chlorination, where its purpose is to remove, or reduce the formation of certain carcinogenic compounds sometimes formed in the chlorination of water.
75. When is hydrogen peroxide used to control microbial growth? What are advantages and disadvantages of using it? Can it sterilize?
found in many household medicine cabinets and in hospital supply rooms. disadvantage: is not a good antiseptic for open wounds. it is quickly broken down to water and gaseous oxygen by the action of the enzyme catalase, which is present in human cells. advantage: disinfect inanimate objects in such applications, it is even sporicidal at high concentrations. on a non-living surface, normally protective enzymes of aerobic bacteria and facultative anaerobes are overwhelmed by high concentrations of peroxide. because of these factors, and its rapid degradation into harmless water and oxygen, the food industry is increasing its use of hydrogen peroxide for aseptic packaging. Heated, gaseous hydrogen peroxide can be used as a sterilant of atmosphere and surfaces. hospital rooms can be decontaminated quickly and routinely with equipment available under the brand name Bioquell.
What is pasteurization? When is it used? Why is it used?
heating was enough to kill most of the bacteria that caused spoilage, preventing these beverages from turning sour. Used for milk, used to prevent spoilage of milk
81. List all the different methods that you can think of that lead to sterilization. Explain how each one is able to destroy spores.
heats, chemicals, irridation, high pressure, and filtration
61. When is isopropanol an effective antiseptic and disinfectant?
isopropanol is superior to ethanol. Sold as rubbing alcohol .
67. What are quats? What are the advantages and disadvantages of using them?
most widely used surface agents their cleansing ability is related to the positively charged portion, the cation, of the molecule. their name is derived from the fact that they are modifications of the four-valence ammonium ion, NH+4. Quaternary ammonium compounds are strongly bactericidal against gram positive bacteria and less active against gram negative bacteria. Quats are also fungicidal, amebicidal, and virucidal against enveloped viruses. they do to not kill endospores or mycobacteria. their chemical mode of action is unknown, but they probably affect the plasma membrane. they change the cell's permeability and cause the loss of essential cytoplasmic constituents, such as potassium
84. Why can norovirus survive more than many other viruses?
noroviruses are highly contagious can get the virus more than once
76. What is peracetic acid and can it sterilize?
one of the most effective liquid chemical sporicides available and can be used as a sterilant. effective on endospores and viruses within 30 min and kills vegetative bacteria and fungi in less than 5 min. also has many applications in the disinfection of food-processing and medical equipment.
80. What methods are being used to destroy prions on inanimate objects?
prions are infectious proteins that are the cause of neurologist diseases known as spongiform encephalopathies, such as mad cow disease. the combined use of a solution of sodium hydroxide and autoclaving at 134c surgical instruments have been successfully treated to inactivate prions, which are proteins, by addition of protease enzymes to the cleaning solution.
65. When may heavy metals be used to control microbes? What are some examples? Why do they work?
silversuldadizaine: available as a topical cream for use on burns. mercuric chloride: their effect is primarily bacteriostatic, but their use is now limited because of their toxicity. copper: used to destroy green algae that grow in reservoirs, stock ponds, swimming pools, and fish tanks. zinc:seen on weathered roofs of buildings down slope from galvanized fittings. zinc chloride is a common ingredient in mouthwashes, and zinc pyrithione is an ingredient in antidandruff shampoos
83. If washing with soap and water does not kill microbes, why is it used?
soap helps removes microbes, not kill them.
70. Why are nitrites used to preserve some foods?
sodium nitrate are added to many meats. the active ingredient is sodium nitrite, which certain bacteria in the meats can also produce from sodium nitrate. these bacteria use nitrate as a substitute for oxygen under anaerobic conditions. the nitrate have two main functions: to preserve the red color of the meat by reacting with blood components in the meat, and to prevent the germination and growth of any botulism endopsores that might be present
69. What are some examples of chemical food preservatives and how do they control microbial growth?
sulfur dioxide: used as a disinfectant, especially in wine-making. sorbic acid, potassium sorb ate, and sodium benzoate: prevent molds from growing in certain acidic foods, such as cheese and soft drinks. calcium propionate: an effective fungi stat used in bread, prevents the growth of surface molds and the bacillus bacterium that causes ropy bread.
63. Why are heavy metals sometimes useful as antimicrobial agents?
the ability of very small amounts of heavy metals, especially silver and copper, to exert antimicrobial activity is referred to as oligodynamic action. Silver-impregnanted dressings that slowly release silver ions have proven especially useful against antibiotic-resistant bacteria. incorporating silver in all manny consumer products is increasing. plastic food contains infused with slier nano particles, which are intended to keep food fresher, and silver infused athletic shirts and socks, which are claimed to minimize odors.
73. What is plasma sterilization and why is it used?
used for such devices that have hollow tubes long tubes. the instruments are placed in a container in which a combination of a vacuum, electromagnetic field, and chemicals such as hydrogen peroxide from the plasma. such plasmas have many free radicals that quickly destroy even endospore forming microbes. the advantage of plasma sterilization, which has elements of both physical and chemical sterilization, is that it requires only low temperatures, but it relatively expensive.
