Control of Microorganisms
Page 300
-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?
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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
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- 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
Page 301
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
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-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
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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
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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
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- 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
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Chemical Methods of Controlling Microorganisms
Page 305
-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”
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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
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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 diseasecausing microorganisms
Hypochlorites: (bleaches)- “chlorine-containing compounds”
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-household bleach can be used in an emergency situation to treat water
that may not be safe for ingestion
-2 drops of bleach can be added to a liter of water (4 drops if water is
cloudy)
-allow the mixture to sit for 30 minutes and it should be safe
-US military forces are issued tablets that contain a form of chlorine that
coagulates materials in the water, which causes them to settle out and
clarifies the water
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Iodine: one of the oldest and most effective antiseptics
-effective against all kinds of bacteria, many endospores, various fungi, and
some viruses
- controls microbial growth by oxidizing certain molecules within the microbial cell
-can be used as a tincture (a solution of iodine and alcohol- antiseptic but does
not kill endospores- stain can be removed with rubbing alcohol) or an iodophore
Iodophore: “a compound consisting of iodine combined with a carrier, such as
polyvinylpyrrolidone, often used as a preoperative skin disinfectant”
-a compound of iodine and a surfactant such as detergent
-a common iodophore is providone-iodine, or Betadine (common
antiseptic)
-embalmers who are allergic to iodine must not use iodophores
-iodines are used mainly for skin disinfection and wound treatment
-many campers also use iodine for water treatment
-iodine tablets are added or the water is passed through iodine-treated
resin filters
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Alcohols
Readings question #3: How do alcohols control microbial growth?
- by denaturing proteins and dissolving lipids in the cell membrane of
microorganisms
-often added to other disinfectants to enhance their germicidal power
-are volatile, and may evaporate before their germicidal effect occurs
-do not kill bacterial endospores
-classified as intermediate-level disinfectants
-effectively kill bacteria and fungi but not endospores and nonenveloped viruses
-have the advantage of acting and then evaporating rapidly and leaving no
residue
-when the skin is swabbed before an injection, most of the microbial control
activity comes from simply wiping away dirt and microorganisms, along with
skin oils
-unsatisfactory antiseptics when applied to wounds
-cause coagulation of a layer of protein under which bacteria continue to
grow
-2 of the most commonly used alcohols are ethanol and isopropanol
Aldehydes
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Readings question #4: What are aldehydes, and how do they work?
-control microbial growth by reacting with the proteins in microorganisms and
altering their chemical structure
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-are among the most effective antimicrobials
-2 examples are formaldehyde and glutaraldehyde
Formalin: liquid form of formaldehyde, used as a disinfectant in which
formaldehyde gas is dissolve in water
-formaldehyde can cause irritation of the skin, eyes, nose, and throat
-ingestion can cause severe pain, vomiting, coma, and death
- potential cause of cancer
Glutaraldehyde: effective disinfectant, and is a cold chemical sterilant when used
in a 2 percent solution
-germicidal in 10 minutes and kills endospores in 3-12 hours
-inactivates the RNA and DNA of microorganisms
-cold chemical sterilants can be used on heat-sensitive objects and can also be
used to sterilize embalming instruments when an autoclave is not available
-less toxic than formaldehyde and is a common ingredient in hospital
disinfectants
-pH sensitive and is only active in an alkaline environment
-side effects: throat and lung irritation, headaches, difficulty breathing,
nosebleeds, burning eyes, skin rash, brownish staining of the hands, hives, or
nausea
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Phenolic Compounds
Readings question #5: Give two examples of phenolic compounds, and explain
how each control microbial growth.
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-control microbial growth by denaturing proteins and disrupting cell membranes
-not effective in killing bacterial endospores, so they do not make good sterilants
Carbolic Acid: (Phenol)
-Lister was the first to use it as a disinfectant for surgical wounds
-slightly acidic, “sweet and tarry” odor
-flammable and skin exposure can cause: chemical burns, liver damage, diarrhea,
dark urine, and hemolytic anemia
-breathed into the lungs when smoking tobacco
-often used in low concentrations (1%) in throat lozenges and throat sprays for
its local anesthetic effect, but has little antimicrobial effect at this low
concentration
Cresols: derived from a chemical called toluene
-3 different forms: otho-cresol, meta-cresol, para-cresol
-used to produce Lysol, deodorants, insecticides
-found in wood, tobacco, crude oil, and creosote used to manufacture telephone
poles and treated lumber
-possible side effects: irritation and burning of skin, eyes, mouth, and throat;
abdominal pain and vomiting; heart damage; anemia; liver and kidney damage;
facial paralysis; coma; and death
-commonly used in mortuary disinfectants because they work well in the
presence of other organic compounds
Hexachlorophene: 450 times more effective as a germicide than phenol
-effective antimicrobial agent
-now only available as a prescription due to its toxicity
-an ingredient in several commercial embalming chemicals
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Quaternary Ammonium Compounds
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Readings question #6: What are “quats”? How do surfactants effect cells?
-chemical disinfectants and antiseptics that damage cellular membranes and
denature microbial proteins
-these surface active agents, or surfactants are capable of altering the surface
tension of cell membranes causing their cellular contents to leak out, thus
destroying the cell
-are deactivated in the presence of soap and other organic matter found in items
like gauze
-e.g. benzalkonium chloride (Zephiran) and zethonium chloride which are topical
antiseptics (used to “prep” the skin for surgery, nasal sprays to reduce airborne
transmission, preservative in eye drops)
-e.g. ceepryn chloride (Cepacol) found in mouthwashes and throat lozenges
-hazards: skin and respiratory irritation, birth defects in pregnant women
-the most widely used surface-active agents (surfactants)
-strongly bactericidal against gram-positive bacteria and less active against
gram-negative bacteria
-are fungicidal, amoebicidal, virucidal against enveloped viruses
-do not kill endospores or mycobacteria
-strongly antimicrobial, colorless, odorless, tasteless, stable, easily diluted, and
nontoxic except in high concentrations
- if your mouthwash foams when you shake it, it probably contains a quat
-certain bacteria such as Pseudomonas not only survive in quats, but actually
grow in them
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