Control of Microorganisms
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-the scientific control of microbial growth began only about 100 years ago
-Pasteur’s experiments led scientists to believe that microbes were a possible cause of disease
-Joseph Lister used this information to develop some of the first microbial control practices for medical procedures
1) hand washing with microbe killing chloride of lime
2) aseptic surgery techniques to prevent microbial contamination of surgical wounds
-scientists have continued to develop a variety of physical methods and chemical agents to control microbial growth
Implications for the Embalmer:
-controlling the growth of organisms is one of the most important aspects of the embalming process
-embalmers must be knowledgeable of both the physical and chemical methods of controlling the growth of infectious organisms
-embalmers must also retard the growth of microorganisms that contribute to the decomposition of the human remains if successful preservation is to be achieved
-embalming can be defined as “temporary disinfection, preservation, and restoration of human remains”
-disinfection and preservation involve controlling the growth of microorganisms
Readings question #1: What is the difference between sterilization, disinfection, and antisepsis?
Sterilization: “a process of completely removing or destroying all life forms and/or their products on or in a substance”
-heat is the most common method used for killing microbes, including the most resistant forms such as endospores
-sterilization of liquids and gases can be done using filtration
Disinfection: “the destruction of disease-causing microorganisms by chemical or physical means”
-offers less control of the growth of microorganisms
-does not inactivate microbial endospores but does kill most vegetative microorganisms
-can be accomplished using chemicals, ultraviolet radiation, boiling water, or steam
Antisepsis: “the prevention or inhibiting of the growth of causative microorganisms”
-disinfectants are applied to inanimate objects
-antiseptics are applied to living tissue
-a chemical might be called a disinfectant for one use, and an antiseptic for another
-many chemicals suitable for use as disinfectants, would be too harsh to use as antiseptics
Actions of Microbial Control Agents
-there are 2 basic ways that various agents actually kill or inhibit microbes
1) Alteration of Membrane Permeability: many microbial control agents target the cell membrane that lines the cell wall
- this membrane regulates the passage of nutrients into the cell and the elimination of wastes from the cell
- damage to the membrane by antimicrobial agents causes the contents of the cell to leak and thereby interfering with the growth of the cell
2) Damage to Proteins and Nucleic Acids: bacteria contain enzymes that are vital to cellular activities
-these enzymes are primarily protein
-heat or certain chemicals can cause the hydrogen bonds in the protein structure to break……and this breakage denatures the protein
-the nucleic acids DNA and RNA carry the cell’s genetic information
-heat, radiation, or chemicals can damage these nucleic acids
-when this happens, the cell can no longer replicate or carry out its normal metabolic functions……and this is frequently lethal to the cell
Physical Methods of Controlling Microorganisms
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Scrubbing: a manual process by which microorganisms are removed from a surface
-sterilizers, disinfectants, and antiseptics will not be as effective if the surfaces are covered in visible contaminants
-should be vigorous on inanimate objects
-HR should be treated gently to avoid damaging skin, hair, nails and tissue
-broken tissue allows microorganisms to spread from the decedent to the public, and microorganisms from the environment can invade the decedent’s tissues
-environmental microorganisms could also promote decomposition
-embalming creates tissue changes that render the embalmed body an unsuitable food source for microorganisms
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Heat: heat kills microorganisms by denaturing the proteins they contain
-proteins are more easily denatured when they are wet
-heat resistance varies among different microbes
-thermal death point: lowest temperature at which all microorganisms are killed in 10 minutes
-thermal death time: the minimum time it takes to kill all microorganisms present
-decimal reduction time: the time in minutes it takes to kill 90 percent of the present microorganisms
Dry Heat: dry heat kills by oxidation effects that sterilize
-one of the simplest methods is “flaming”
-instruments are placed directly into the flame and are heated to a red glow
-incineration is another form of dry heat sterilization
Incineration: hazardous waste handlers use this method most frequently to treat the hazardous waste from funeral homes
-it reduces the hazardous waste to ashes
-all the waste matter must be incinerated
-if some of the waste matter does not burn completely, it is possible that some of the microorganisms will survive
-this is a form of sterilization that inactivates both vegetative bacteria and the bacterial endospore
Cremation: a form of incineration
-retort is maintained at a temperature of 1600 degrees F (871 degrees C) until the remains have undergone complete combustion
-at the end of the process, the remains are devoid of soft tissues and are completely sterilized
-they can no longer harbor pathogenic microorganisms that could be spread to the public, and the crematory personnel
-hot-air sterilization is another form of dry heat sterilization
-items to be sterilized are placed in an oven
-generally a temperature of 170 degrees C (338 degrees F) for 2 hours ensures sterilization
-dry heat sterilization is generally preferred to chemical methods of decontamination, which may leave behind a toxic residue
-dry heat methods require much more exposure time than moist heat methods because proteins do not denature as quickly when they are dry
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Moist Heat: kills microorganisms primarily by the coagulation of the proteins (denaturation)
-denaturation occurs because the hydrogen bonds that hold the proteins in their three-dimensional structure are broken
-this coagulation process is similar to watching an egg in a frying pan
-the liquid egg white first becomes thick and gelatinous, and then it becomes firm and dry as the heat causes the proteins in the egg white to coagulate
- 3 basic methods of moist heat decontamination:
1) boiling
2) free flowing steam
3) steam under pressure
Boiling: has been used since Ancient times
-it takes approximately 10 minutes to sterilize water that does not contain endospores
-kills vegetative bacteria, most viruses, and fungi
-it does not guarantee that endospores are killed
Free Flowing Steam: (Unpressurized Steam) is equivalent in temperature to boiling water
-fractional sterilization: items are placed in free flowing steam for 30 minutes on successive days
-first day: items are introduces to the free flowing steam which kills the vegetative bacteria but not the endospores
-materials are incubated overnight to allow the endospores to germinate into vegetative cells
-second day: objects are introduced to the free flowing steam again which kills the new vegetative cells
-objects are allowed to incubate overnight again, which allows any remaining endospores to germinate
-third day: objects are introduced to the free flowing steam again and the new vegetative cells are destroyed
Steam Under Pressure: the most effective form of controlling microbial growth
-pressure, temperature, and length of exposure can be controlled
-accomplished using an autoclave Figure 23-1 page 304
-autoclave works like a pressure cooker
-water or liquid chemical is placed into the autoclave
-the items are placed on a tray and inserted into the autoclave
-the door is closed and sealed
-the timer is set for a certain time and temperature
-because the steam is under pressure, higher temperatures can be reached in a shorter time than can be achieved by boiling
-the pressure allows the steam to penetrate the objects to achieve great decontamination
Pasteurization: a practical method of preventing the spoilage of beer and wine developed by Louis Pasteur
-Pasteur used mild heating which was sufficient to kill the microorganisms that caused the particular spoilage problem without seriously damaging the taste of the product
-the same principle was applied to milk to produce what we now call pasteurized milk
-the pasteurization process is intended to eliminate pathogenic microbes in the milk
-it also lowers the number of microbes which prolongs the milk’s good quality under refrigeration
-heat-resistant bacteria will survive pasteurization however, they are unlikely to cause disease or the milk to spoil
-products like milk,ice cream, yogurt, and beer all have their own pasteurization times and temperatures which may differ considerably
- viscous foods and fatty foods tend to require higher temperatures and longer periods of time for pasteurization to be successful
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Cold: can be an effective method of controlling microbial growth
-the effect on the particular microbe will depend upon the intensity of the application
-the temperatures of ordinary refrigerators (0-7 degrees C) tends to reduce the metabolic rate of most microbes so that they cannot reproduce or synthesize toxins
- ordinary refrigeration has a “bacteriostatic” effect
-psychotrophs do grow slowly at refrigerator temperatures and will alter the appearance and taste of foods after a time
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-refrigeration units in morgues are used to cool HR to a temperature that retards microbial growth
-cold temperatures do not destroy all vegetative cells or endospores but inhibit the growth of microorganisms
-microorganisms can begin multiplying again when they are introduced to warm temperatures
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Radiation: has various effects on cells depending on its wavelength, intensity and duration
-radiation that kills microorganisms is of 2 types:
1) ionizing radiation: gamma rays, x-rays, high energy electron beams
-wavelengths are shorter than non-ionizing radiation and therefore has much more energy
-the food industry is recently using this time of radiation for food preservation
-low level ionizing radiation has recently been approved by the FDA for processing spices and certain meats and vegetables
- also used for the sterilization of pharmaceuticals and disposable dental and medical supplies
-post 9/11, the post office has used this radiation to sterilize certain classes of mail
2) nonionizing radiation: has a wavelength that is longer than ionizing radiation
-ultraviolet (UV) light is a form of nonionizing radiation that can effectively control the growth of microorganisms placed directly in its path
-it inhibits microbial growth by damaging the cell’s genetic material
- UV radiation is also used to control microbes in the air
-a UV or “germicidal” lamp is commonly found in hospital rooms, nurseries, operating rooms, and cafeterias
-UV light is also used to disinfect vaccines and other medical products
-a major disadvantage of UV light is that the radiation is not very penetrating
-this means that to be effective, the microorganism must be exposed directly to the UV light
-even paper prevents UV light from penetrating enough to kill microorganisms, and many microorganisms contain pigments resistant to the detrimental effects of UV light
-another problem with UV light is that it can damage human eyes, and prolonged exposure can cause burns and skin cancer in humans
-sunlight contains some UV radiation, but the shorter wavelengths…those most effective against bacteria….are screened out by the ozone layer of the atmosphere
Microwaves: do not have much direct effect on microorganisms
-bacteria can be easily cultured from the interior of recently operated microwave ovens
-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
- for this reason, pork cooked in a microwave oven has been responsible for outbreaks of trichinosis
Chemical Methods of Controlling Microorganisms
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-chemical agents are used to control the growth of microbes on both living tissue and inanimate objects
-unfortunately, few chemical agents achieve sterility
-most chemical agents reduce microbial populations to safe levels or they remove vegetative forms of pathogens from objects
-no single disinfectant is appropriate for all circumstances, so it is important to choose the agent that is best suited for the type of microbial population being treated
-chemical antimicrobial agents fall into one of two broad categories based on their suffix:
1) “-cide”: agents that will kill a particular type of microorganism
2) “-static”: agents that will prevent the growth of a particular type of microorganism
Germicides: “a substance that destroys microorganisms”
- kill a variety of microorganisms but not necessarily their spores
Bactericides: “an agent that destroys bacteria but not necessarily their spores”
Fungicides: “a substance that kills fungi”
- kills fungi and their spores
Viricides: (Virucide) “an agent destructive to viruses”
- kills viruses
Insecticides: “a substance that kills insects”
Larvicides: “a substance that kills insect larva”
Sporicides: kill bacterial and mold spores
-can be used during the terminal disinfection of embalming instruments and equipment
Factors influencing Chemical Agents:
-by reading the label, a lot can be learned about the disinfectant’s properties
1) nature of the disinfectant
-the label will usually indicate what groups of organisms the disinfectant will be effective against
2) concentration of the disinfectant
-higher concentrations of the antimicrobial agent are generally more efficient, however, sometimes adding more of the antimicrobial agent will induce the growth of other types of microbes
-the concentration of a disinfectant affects its action, so it should be diluted exactly as specified by the manufacturer
3) nature of the material to be disinfected
-are organic materials present that might interfere with the action of the disinfectant?
4) number of microorganisms present
-larger populations of microorganisms take longer to kill
5) type of microorganism present
-it is more difficult to control microbial growth when different species of microorganism are present on the object
6) length of exposure to disinfectant
-the longer the length of exposure of the microbe to the antimicrobial agent, the greater the number of microorganisms that will be killed
7) temperature of the disinfectant during exposure
-higher temperatures will usually increase the effectiveness of the microbial agent’s ability to kill the microorganism in question
8) disinfectant’s pH during exposure
-environmental factors such as pH, viscosity, and concentration of organic matter can also influence the effectiveness of a particular antimicrobial agent
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Halogens
Readings question #2: What are halogens and how do they work?
-widely used disinfectants that work by oxidizing the components of microbial cells
-some halogens also react with cellular proteins
-fluorine, chlorine, bromine, and iodine are extremely caustic and aggressive
-chlorine and iodine are used extensively as disinfectants
Chlorine: used to treat municipal drinking water and also swimming pools
-is a gas, so must be combined with water to form sodium hypochlorite
-household bleach contains 5% sodium hypochlorite
-this is several hundred times stronger than is needed to kill most disease- causing microorganisms
Hypochlorites: (bleaches)- “chlorine-containing compounds”