Islamic University of Gaza Faculty of Medicine Medical Microbiology 2008-2009 Prepared by: Sohaib M. El-Hams PRESENTED TO: Dr.Abdelraouf Ali El Manamma.

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: