Islamic University of Gaza Faculty of Medicine Medical Microbiology 2008-2009 Prepared by: Sohaib M. El-Hams PRESENTED TO: Dr.Abdelraouf Ali El Manamma.
Post on 27-Dec-2015
213 Views
Preview:
Transcript
Islamic UniversityIslamic Universityof Gazaof Gaza
Faculty of Medicine Faculty of Medicine
Medical MicrobiologyMedical Microbiology
2008-20092008-2009
Prepared by:Prepared by:Sohaib M. El-HamsSohaib M. El-Hams
PRESENTED TO:PRESENTED TO: Dr.Abdelraouf Ali El Manamma Dr.Abdelraouf Ali El Manamma
Sterilization & DisinfectionSterilization & Disinfection Sterilization:Sterilization: is the killing or removal of all is the killing or removal of all
microorganisms, including bacterial spores, which are microorganisms, including bacterial spores, which are
highly resistant.highly resistant.
SterilizationSterilization is usually carried out by autoclaving, is usually carried out by autoclaving,
which consists of exposure to steam at which consists of exposure to steam at 121°C121°C under a under a
pressure of pressure of 15 lb/in 215 lb/in 2 for for 15 minutes15 minutes..
Surgical instruments that can be damaged by moist heat Surgical instruments that can be damaged by moist heat
are usually sterilized by exposure to ethylene oxide gas, are usually sterilized by exposure to ethylene oxide gas,
and most intravenous solutions are sterilized by and most intravenous solutions are sterilized by
filtration.filtration.
Sterilization & DisinfectionSterilization & Disinfection Disinfection:Disinfection: is the killing of many, but not all, is the killing of many, but not all,
microorganisms. microorganisms.
For adequate disinfection, pathogens must be killed, but For adequate disinfection, pathogens must be killed, but
some organisms and bacterial spores may survive. some organisms and bacterial spores may survive.
Disinfectants vary in their tissue damaging properties Disinfectants vary in their tissue damaging properties
from the corrosive phenol-containing compounds, which from the corrosive phenol-containing compounds, which
should be used only on inanimate objects, to less toxic should be used only on inanimate objects, to less toxic
materials such as ethanol and iodine, which can be used materials such as ethanol and iodine, which can be used
on skin surfaces. on skin surfaces.
Chemicals used to kill microorganisms on the surface of Chemicals used to kill microorganisms on the surface of
skin and mucous membranes are called antiseptics. skin and mucous membranes are called antiseptics.
RATE OF KILLING OF RATE OF KILLING OF MICROORGANISMSMICROORGANISMS
Death of microorganisms occurs at a certain rate dependent Death of microorganisms occurs at a certain rate dependent
primarily upon two variables: primarily upon two variables:
(1) The concentration of the killing agent.(1) The concentration of the killing agent.
(2) The length of time agent is applied.(2) The length of time agent is applied.
The rate of killing is defined by the relationship:The rate of killing is defined by the relationship:
N ∞1/CT N ∞1/CT
which shows that the number of survivors, N, is inversely which shows that the number of survivors, N, is inversely
proportionate to the concentration of the agent, C, and to the proportionate to the concentration of the agent, C, and to the
time of application of the agent. Collectively, CT is often time of application of the agent. Collectively, CT is often
referred to as the dose. referred to as the dose.
Stated alternatively, the number of microorganisms killed Stated alternatively, the number of microorganisms killed
is directly proportionate to CT. The relationship is usually is directly proportionate to CT. The relationship is usually
stated in terms of survivors, because they are easily stated in terms of survivors, because they are easily
measured by colony formation.measured by colony formation.
Death is defined as the inability to reproduce. In certain Death is defined as the inability to reproduce. In certain
circumstances, the physical remains of dead bacteria can circumstances, the physical remains of dead bacteria can
still cause problems.still cause problems.
CHEMICAL AGENTSCHEMICAL AGENTS
Chemicals vary greatly in their ability to kill Chemicals vary greatly in their ability to kill
microorganisms.microorganisms.
A quantitative measure of this variation is expressed as A quantitative measure of this variation is expressed as
the phenol coefficient, which is the ratio of the the phenol coefficient, which is the ratio of the
concentration of phenol to the concentration of the concentration of phenol to the concentration of the
agent required to cause the same amount of killing agent required to cause the same amount of killing
under the standard conditions of the test.under the standard conditions of the test.
Chemical agents act primarily by one of three Chemical agents act primarily by one of three
mechanisms: mechanisms:
(1) Disruption of the lipid-containing cell membrane. (1) Disruption of the lipid-containing cell membrane.
(2) Modification of proteins. (2) Modification of proteins.
(3) Modification of DNA.(3) Modification of DNA.
Each of the following chemical agents has been Each of the following chemical agents has been
classified into one of the three categories, but some of classified into one of the three categories, but some of
the chemicals act by more than one mechanism. the chemicals act by more than one mechanism.
DISRUPTION OF CELL DISRUPTION OF CELL MEMBRANESMEMBRANES
1.1. AlcoholAlcohol
2.2. DetergentsDetergents
3.3. PhenolsPhenols
1.1. Alcohol:-Alcohol:-
* Ethanol is widely used to clean the skin * Ethanol is widely used to clean the skin
before immunization or venipuncture. before immunization or venipuncture.
* It acts mainly by disorganizing the lipid * It acts mainly by disorganizing the lipid
structure in membranes, but it denatures structure in membranes, but it denatures
proteins as well. proteins as well.
* Ethanol requires the presence of water * Ethanol requires the presence of water
for maximal activity; i.e., it is far more for maximal activity; i.e., it is far more
effective at effective at 70%70% than at than at 100%.100%.
* Seventy percent ethanol is often used as an antiseptic * Seventy percent ethanol is often used as an antiseptic to clean the skin prior to venipuncture.to clean the skin prior to venipuncture.
* However, because it is not as effective as iodine-* However, because it is not as effective as iodine-
containing com- pounds, the latter should be used prior containing com- pounds, the latter should be used prior
to obtaining a blood culture and installing intravenous to obtaining a blood culture and installing intravenous
catheters.catheters.
2.2. DetergentsDetergents:-:-
* Detergents are "surface-active" agents composed of a * Detergents are "surface-active" agents composed of a
long-chain, lipid-soluble, hydrophobic portion and a long-chain, lipid-soluble, hydrophobic portion and a
polar hydrophilic group, which can be a cation, an polar hydrophilic group, which can be a cation, an
anion, or a nonionic group.anion, or a nonionic group.
* These surfactants interact with the lipid in the cell * These surfactants interact with the lipid in the cell
membrane through their hydrophobic chain and with membrane through their hydrophobic chain and with
the surrounding water through their polar group and the surrounding water through their polar group and
thus disrupt the membrane.thus disrupt the membrane.
* Quaternary ammonium compounds, e.g., * Quaternary ammonium compounds, e.g.,
benzalkonium chloride, are cationic detergents widely benzalkonium chloride, are cationic detergents widely
used for skin antisepsis.used for skin antisepsis.
3.3. PhenolsPhenols
* Phenol was the first disinfectant used in the * Phenol was the first disinfectant used in the
operating room (by Lister in the 1860s), but it is rarely operating room (by Lister in the 1860s), but it is rarely
used as a disinfectant today because it is too caustic. used as a disinfectant today because it is too caustic.
* Hexachlorophene, which is a biphenol with six * Hexachlorophene, which is a biphenol with six
chlorine atoms, is used in germicidal soaps, but concern chlorine atoms, is used in germicidal soaps, but concern
over possible neurotoxicity has limited its use. over possible neurotoxicity has limited its use.
* Another phenol derivative is cresol (methyl phenol), * Another phenol derivative is cresol (methyl phenol),
the active ingredient in Lysol. the active ingredient in Lysol.
* Phenols not only damage membranes but also * Phenols not only damage membranes but also
denature proteins. denature proteins.
MODIFICATION OF PROTEINSMODIFICATION OF PROTEINS
1.1. ChlorineChlorine
2.2. IodineIodine
3.3. Heavy MetalsHeavy Metals
4.4. Hydrogen PeroxideHydrogen Peroxide
5.5. Formaldehyde & GlutaraldehydeFormaldehyde & Glutaraldehyde
6.6. Ethylene OxideEthylene Oxide
7.7. Acids & AlkalisAcids & Alkalis
MODIFICATION OF PROTEINSMODIFICATION OF PROTEINS
1.1. Chlorine:-Chlorine:-
* Chlorine is used as a disinfectant to purify the * Chlorine is used as a disinfectant to purify the
water supply and to treat swimming pools.water supply and to treat swimming pools.
* It is also the active component of hypochlorite * It is also the active component of hypochlorite
(bleach, Clorox), which is used as a disinfectant in (bleach, Clorox), which is used as a disinfectant in
the home and in hospitals.the home and in hospitals.
* Chlorine is a powerful oxidizing agent that kills * Chlorine is a powerful oxidizing agent that kills
by cross-linking essential sulfhydryl groups in by cross-linking essential sulfhydryl groups in
enzymes to form the inactive disulfide. enzymes to form the inactive disulfide.
2. 2. Iodine:Iodine:
* Iodine is the most effective skin antiseptic used in * Iodine is the most effective skin antiseptic used in
medical practice and should be used prior to obtaining medical practice and should be used prior to obtaining
a blood culture and installing intravenous catheters a blood culture and installing intravenous catheters
because contamination with skin flora such as because contamination with skin flora such as
Staphylococcus epiderrnidis can be a problem.Staphylococcus epiderrnidis can be a problem.
* Iodine is supplied in two forms:* Iodine is supplied in two forms:
(1) Tincture of iodine ((1) Tincture of iodine (2% solution of iodine and 2% solution of iodine and
potassium iodide in ethanolpotassium iodide in ethanol) is used to prepare the ) is used to prepare the
skin prior to blood culture. Because tincture of iodine skin prior to blood culture. Because tincture of iodine
can be irritating to the skin, it should be removed with can be irritating to the skin, it should be removed with
alcohol. alcohol.
(2) lodophors are complexes of iodine with (2) lodophors are complexes of iodine with
detergents that are frequently used to prepare detergents that are frequently used to prepare
the skin prior to surgery because they are less the skin prior to surgery because they are less
irritating than tincture of iodine.irritating than tincture of iodine.
* Iodine, like chlorine, is an oxidant that * Iodine, like chlorine, is an oxidant that
inactivates sulfhydryl containing enzymes. It inactivates sulfhydryl containing enzymes. It
also binds specifically to tyrosine residues in also binds specifically to tyrosine residues in
proteins. proteins.
3.3. Heavy Metals:Heavy Metals:
* Metals Mercury and silver have the greatest * Metals Mercury and silver have the greatest
antibacterial activity of the heavy metals and are the antibacterial activity of the heavy metals and are the
most widely used in medicine.most widely used in medicine.
* They act by binding to sulfhydryl groups, thereby * They act by binding to sulfhydryl groups, thereby
blocking enzymatic activity. blocking enzymatic activity.
* Thimerosal (* Thimerosal (MerthiolateMerthiolate) and merbromin ) and merbromin
(Mercurochrome), which contain mercury, are used as (Mercurochrome), which contain mercury, are used as
skin antiseptics.skin antiseptics.
* Silver nitrate drops are useful in preventing * Silver nitrate drops are useful in preventing
gonococcal ophthalmia neonatorum.gonococcal ophthalmia neonatorum.
* Silver sulfadiazine is used to prevent infection of burn * Silver sulfadiazine is used to prevent infection of burn
wounds. wounds.
4.4. Hydrogen Peroxide:Hydrogen Peroxide:
* Hydrogen peroxide is used as an antiseptic to * Hydrogen peroxide is used as an antiseptic to
clean wounds and to disinfect contact lenses.clean wounds and to disinfect contact lenses.
* Its effectiveness is limited by the organism's ability * Its effectiveness is limited by the organism's ability
to produce catalase, an enzyme that degrades to produce catalase, an enzyme that degrades H202H202. .
* The bubbles produced when peroxide is used on * The bubbles produced when peroxide is used on
wounds are formed by oxygen arising from the wounds are formed by oxygen arising from the
breakdown of breakdown of H202H202 by tissue catalase. by tissue catalase.
* Hydrogen peroxide is an oxidizing agent that * Hydrogen peroxide is an oxidizing agent that
attacks sulflnydryl groups, thereby inhibiting attacks sulflnydryl groups, thereby inhibiting
enzymatic activity. enzymatic activity.
5. 5. Formaldehyde & Glutaraldehyde:Formaldehyde & Glutaraldehyde:
* Formaldehyde, which is available as a * Formaldehyde, which is available as a 37%37% solution solution
in water (in water (FormalinFormalin), denatures proteins and nucleic ), denatures proteins and nucleic
acids. acids.
* Both proteins and nucleic acids contain essential -* Both proteins and nucleic acids contain essential -
NH 2NH 2 and- and-OHOH groups, which are the main sites of groups, which are the main sites of
alkylation by the hydroxymethyl group of formaldehyde.alkylation by the hydroxymethyl group of formaldehyde.
* Glutaraldehyde, which has two reactive aldehyde * Glutaraldehyde, which has two reactive aldehyde
groups, is 10 times more effective than formaldehyde groups, is 10 times more effective than formaldehyde
and is less toxic. and is less toxic.
* In hospitals, it is used to sterilize respiratory therapy * In hospitals, it is used to sterilize respiratory therapy
equipment. equipment.
6. 6. Ethylene Oxide:Ethylene Oxide:
* Ethylene oxide gas is used extensively in hospitals for * Ethylene oxide gas is used extensively in hospitals for
the sterilization of heat-sensitive materials such as the sterilization of heat-sensitive materials such as
surgical instruments and plastics.surgical instruments and plastics.
* It kills by alkylating both proteins and nucleic acids; * It kills by alkylating both proteins and nucleic acids;
i.e., the hydroxyethyl group attacks the reactive hydrogen i.e., the hydroxyethyl group attacks the reactive hydrogen
atoms on essential amino and hydroxyl groups.atoms on essential amino and hydroxyl groups.
7.7. Acids & Alkalis:Acids & Alkalis:
* Strong acids and alkalis kill by denaturing proteins. * Strong acids and alkalis kill by denaturing proteins.
Although most bacteria are susceptible, it is important to Although most bacteria are susceptible, it is important to
note that Mycobacteriurn tuberculosis and other note that Mycobacteriurn tuberculosis and other
mycobacteria are relatively resistant to mycobacteria are relatively resistant to 2% NaOH2% NaOH, which , which
is used in the clinical laboratory to liquefy sputum prior to is used in the clinical laboratory to liquefy sputum prior to
culturing the organism.culturing the organism.
* Weak acids, such as benzoic, propionic, and citric * Weak acids, such as benzoic, propionic, and citric
acids, are frequency used as food preservatives because acids, are frequency used as food preservatives because
they are bacteriostatic. they are bacteriostatic.
* The action of these acids is partially a function of the * The action of these acids is partially a function of the
organic moiety, e.g., benzoate, as well as the low organic moiety, e.g., benzoate, as well as the low pHpH..
MODIFICATION OF NUCLEIC MODIFICATION OF NUCLEIC ACIDSACIDS
A variety of dyes not only stain microorganisms but also inhibit their A variety of dyes not only stain microorganisms but also inhibit their
growth.growth.
One of these is crystal violet (gentian violet), which is used as a skin One of these is crystal violet (gentian violet), which is used as a skin
antiseptic.antiseptic.
Its action is based on binding of the positively charged dye molecule Its action is based on binding of the positively charged dye molecule
to the negatively charged phosphate groups of the nucleic acids. to the negatively charged phosphate groups of the nucleic acids.
Malachite green, a triphenylamine dye like crystal violet, is a Malachite green, a triphenylamine dye like crystal violet, is a
component of Lowenstein- Jensen's medium, which is used to grow component of Lowenstein- Jensen's medium, which is used to grow
M. tuberculosis.M. tuberculosis.
The dye inhibits the growth of unwanted organisms in the sputum The dye inhibits the growth of unwanted organisms in the sputum
during the 6-week incubation period. during the 6-week incubation period.
PHYSICAL AGENTSPHYSICAL AGENTS
The physical agents act either by imparting The physical agents act either by imparting
energy in the form of heat or radiation or by energy in the form of heat or radiation or by
removing organisms through filtration.removing organisms through filtration.
(1) Heat(1) Heat
(2) Radiation(2) Radiation
(3) Filtration(3) Filtration
PHYSICAL AGENTSPHYSICAL AGENTS (1)(1) Heat:Heat: Heat energy can be applied in three ways: in the form ofHeat energy can be applied in three ways: in the form of
moist moist heat (heat (either boiling or autoclavingeither boiling or autoclaving) or ) or dry heatdry heat or or
by by pasteurizationpasteurization..
In general, heat kills by denaturing proteins, but In general, heat kills by denaturing proteins, but
membrane damage and enzymatic cleavage of DNA may membrane damage and enzymatic cleavage of DNA may
also be involved. also be involved.
Moist heatMoist heat sterilizes at a lower temperature than dry sterilizes at a lower temperature than dry
heat, because water aids in the disruption of non covalent heat, because water aids in the disruption of non covalent
bonds, e.g., hydrogen bonds, which hold protein chains bonds, e.g., hydrogen bonds, which hold protein chains
together in their secondary and tertiary structures. together in their secondary and tertiary structures.
Moist-heat sterilization, usually autoclaving, is the most Moist-heat sterilization, usually autoclaving, is the most
frequently used method of sterilization. frequently used method of sterilization.
Because bacterial spores are resistant to boiling (100°C Because bacterial spores are resistant to boiling (100°C
at sea level), they must be exposed to a higher at sea level), they must be exposed to a higher
temperature; this cannot be achieved unless the temperature; this cannot be achieved unless the
pressure is increased. pressure is increased.
For this purpose, an autoclave chamber is used in which For this purpose, an autoclave chamber is used in which
steam, at a pressure of 15 lb/in 2, reaches a steam, at a pressure of 15 lb/in 2, reaches a
temperature of 121°C and is held for 15-20 minutes.temperature of 121°C and is held for 15-20 minutes.
This kills even the highly heat-resistant spores of This kills even the highly heat-resistant spores of
Clostridium botulinum, the cause of botulism, with a Clostridium botulinum, the cause of botulism, with a
margin of safety. margin of safety.
Sterilization by Sterilization by dry heatdry heat, on the other hand, requires , on the other hand, requires
temperatures in the range of temperatures in the range of 180°C180°C for for 2 hours2 hours..
This process is used primarily for glassware and is used This process is used primarily for glassware and is used
less frequently than autoclaving.less frequently than autoclaving.
Pasteurization,Pasteurization, which is used primarily for milk, which is used primarily for milk,
consists of heating the milk to consists of heating the milk to 62°C62°C for for 30 minutes30 minutes
followed by rapid cooling. followed by rapid cooling. ("Flash" pasteurization at ("Flash" pasteurization at
72°C for 15 seconds is often used72°C for 15 seconds is often used) This is sufficient to ) This is sufficient to
kill the vegetative cells of the milk-borne pathogens, e.g., kill the vegetative cells of the milk-borne pathogens, e.g.,
Mycobacterium boris, Salmonella, Streptococcus, Mycobacterium boris, Salmonella, Streptococcus,
Listeria, and Brucella, but not to sterilize the milk. Listeria, and Brucella, but not to sterilize the milk.
Autoclaving:Autoclaving:
Figure of Autoclave:Figure of Autoclave:
(2)(2) Radiation: Radiation: The two types of radiation used to kill microorganisms are The two types of radiation used to kill microorganisms are
ultraviolet (UV) lightultraviolet (UV) light and and x-raysx-rays. .
The greatest an timicrobial activity of The greatest an timicrobial activity of UV lightUV light occurs at occurs at
250-260 nm250-260 nm, which is the wavelength region of , which is the wavelength region of
maximum absorption by the purine and pyrimidine bases maximum absorption by the purine and pyrimidine bases
of DNA. of DNA.
The most significant lesion caused by UV irradiation is the The most significant lesion caused by UV irradiation is the
formation of thymine dimers, but addition of hydroxyl formation of thymine dimers, but addition of hydroxyl
groups to the bases also occurs. groups to the bases also occurs.
As a result, DNA replication is inhibited and the organism As a result, DNA replication is inhibited and the organism
cannot grow. cannot grow.
Cells have repair mechanisms against UV-induced Cells have repair mechanisms against UV-induced
damage that involve either cleavage of dimers in the damage that involve either cleavage of dimers in the
presence of visible light (presence of visible light (photoreactivationphotoreactivation) or ) or
excision of damaged bases, which is not dependent excision of damaged bases, which is not dependent
upon visible light (upon visible light (dark repairdark repair). ).
Because UV radiation can damage the cornea and skin, Because UV radiation can damage the cornea and skin,
the use of UV irradiation in medicine is limited. the use of UV irradiation in medicine is limited.
However, it is used in hospitals to kill airborne However, it is used in hospitals to kill airborne
organisms, especially in operating rooms when they are organisms, especially in operating rooms when they are
not in use. Bacterial spores are quite resistant and not in use. Bacterial spores are quite resistant and
require a dose up to 10 times greater than do the require a dose up to 10 times greater than do the
vegetative bacteria. vegetative bacteria.
X-raysX-rays have higher energy and penetrating power than have higher energy and penetrating power than
UV radiation and kill mainly by the production of free UV radiation and kill mainly by the production of free
radicals, e.g., production of hydroxyl radicals by the radicals, e.g., production of hydroxyl radicals by the
hydrolysis of water. hydrolysis of water.
These highly reactive radicals can break covalent bonds These highly reactive radicals can break covalent bonds
in DNA, thereby killing the organism. Sulfhydryl-in DNA, thereby killing the organism. Sulfhydryl-
containing compounds, such as the amino acid cysteine, containing compounds, such as the amino acid cysteine,
can protect DNA from free-radical attack. can protect DNA from free-radical attack.
Another mechanism is a direct hit on a covalent bond in Another mechanism is a direct hit on a covalent bond in
DNA, resulting in chain breakage, but this is probably less DNA, resulting in chain breakage, but this is probably less
important than the mechanism involving free radicals. important than the mechanism involving free radicals.
X-rays kill vegetative cells readily, but spores are X-rays kill vegetative cells readily, but spores are
remarkably resistant, probably because of their lower remarkably resistant, probably because of their lower
water content.water content.
X-rays are used in medicine for sterilization of heat-X-rays are used in medicine for sterilization of heat-
sensitive items, such as sutures and surgical gloves, and sensitive items, such as sutures and surgical gloves, and
plastic items, such as syringes. plastic items, such as syringes.
(3) (3) Filtration: Filtration:
Filtration is the preferred method of sterilizing certain Filtration is the preferred method of sterilizing certain
solutions, e.g., those with heat-sensitive components. solutions, e.g., those with heat-sensitive components.
In the past, solutions for intravenous use were In the past, solutions for intravenous use were
autoclaved, but heat-resistant endotoxin in the cell walls autoclaved, but heat-resistant endotoxin in the cell walls
of the dead gram-negative bacteria caused fever in of the dead gram-negative bacteria caused fever in
recipients of the solutions. recipients of the solutions.
Therefore, solutions are now filtered to make them Therefore, solutions are now filtered to make them
pyrogen-free prior to autoclaving. pyrogen-free prior to autoclaving.
The most commonly used filter is composed of The most commonly used filter is composed of
nitrocellulose and has a pore size of nitrocellulose and has a pore size of 0.22 µm0.22 µm. .
This size will retain all bacteria and spores.This size will retain all bacteria and spores.
Filters work by physically trapping particles larger than Filters work by physically trapping particles larger than
the pore size and by retaining somewhat smaller the pore size and by retaining somewhat smaller
particles via electrostatic attraction of the particles to particles via electrostatic attraction of the particles to
the filters. the filters.
PEARLSPEARLS
SterilizationSterilization is the killing of all forms of microbial is the killing of all forms of microbial
life including bacterial spores.life including bacterial spores.
Spores are resistant to boiling, so sterilization of Spores are resistant to boiling, so sterilization of
medical equipment is typically achieved at medical equipment is typically achieved at 121°C121°C
for for 15 minutes15 minutes in an autoclave. in an autoclave.
Sterilization of heat-sensitive materials is achieved Sterilization of heat-sensitive materials is achieved
by exposure to ethylene oxide, and liquids can be by exposure to ethylene oxide, and liquids can be
sterilized by filtration.sterilized by filtration.
Spores and some bacteria will survive. Spores and some bacteria will survive.
DisinfectionDisinfection is reducing the number of bacteria to is reducing the number of bacteria to
a level low enough that disease is unlikely to occur.a level low enough that disease is unlikely to occur.
For example, disinfection of the water supply is For example, disinfection of the water supply is
achieved by treatment with chlorine.achieved by treatment with chlorine.
Disinfection of the skin prior to venipuncture is Disinfection of the skin prior to venipuncture is
achieved by treatment with achieved by treatment with 70%70% ethanol ethanol
Disinfectants that are mild enough to use on skin Disinfectants that are mild enough to use on skin
and other tissues, such as and other tissues, such as 70%70% ethanol, are called ethanol, are called
antiseptics. antiseptics.
The killing of microbes by either chemicals or The killing of microbes by either chemicals or
radiation is proportional to the dose, which is radiation is proportional to the dose, which is
defined as the product of the concentration defined as the product of the concentration
multiplied by the time of exposure. multiplied by the time of exposure.
Chemical agents kill bacteria by one of three Chemical agents kill bacteria by one of three
actions. actions.
Disruption of lipid in cell membranes, modification Disruption of lipid in cell membranes, modification
of proteins. of proteins.
Modification of DNA. Modification of DNA.
Physical agents kill (Physical agents kill (or removeor remove) bacteria by one of ) bacteria by one of
three processes: heat, radiation, or filtration.three processes: heat, radiation, or filtration.
Heat is usually applied at temperatures above boiling Heat is usually applied at temperatures above boiling
((121°C121°C) to kill spores, but heat-sensitive materials such ) to kill spores, but heat-sensitive materials such
as milk are exposed to temperatures below boiling as milk are exposed to temperatures below boiling
((pasteurizationpasteurization) that kills the pathogens in milk but ) that kills the pathogens in milk but
does not sterilize it.does not sterilize it.
Radiation, such as ultraviolet light and x-radiation, is Radiation, such as ultraviolet light and x-radiation, is
often used to sterilize heat-sensitive items. Ultraviolet often used to sterilize heat-sensitive items. Ultraviolet
light and x-radiation kill by damaging DIVA. light and x-radiation kill by damaging DIVA.
FiltrationFiltration can sterilize liquids if the pore size of can sterilize liquids if the pore size of
the filter is small enough to retain all bacteria and the filter is small enough to retain all bacteria and
spores. Heat sensitive liquids, e.g., intravenous spores. Heat sensitive liquids, e.g., intravenous
fluids, are often sterilized by filtration. fluids, are often sterilized by filtration.
Conclusion:Conclusion:
top related