Sterilization and DisinfectionSterilization and Disinfection

SterilizationSterilization is the killing or removal of is the killing or removal of

all microorganisms, including bacterial all microorganisms, including bacterial

spores. It is an absolute germ free state.spores. It is an absolute germ free state.

DisinfectionDisinfection is the killing of many but is the killing of many but

not all, microorganisms. Specially not all, microorganisms. Specially

bacterial spores are not killed.bacterial spores are not killed.

DisinfectantDisinfectant is a chemical agent that is is a chemical agent that is

used for disinfection.used for disinfection.

Methods of sterilization:Methods of sterilization:

I. Heat I. Heat

II. Ionizing radiations II. Ionizing radiations

III. Filtration III. Filtration

IV. ChemicalsIV. Chemicals

I. I. HeatHeat::

It can be again It can be again

a. Dry heat a. Dry heat

b. Moist heat b. Moist heat

c. Pasteurizationc. Pasteurization

a.a. Dry Heat Dry Heat:: Sterilization by dry heat requires Sterilization by dry heat requires

temperatures in the range of 180°C for 2 temperatures in the range of 180°C for 2 hours. hours.

Used primarily for glassware.Used primarily for glassware. Used less frequently than autoclaving.Used less frequently than autoclaving. Dry heat can be applied by Dry heat can be applied by i. i. Red heat:Red heat: The article to be sterilized is directly held in the The article to be sterilized is directly held in the

flame and heated till it becomes red hot.flame and heated till it becomes red hot.ii. ii. Hot air oven:Hot air oven: Articles are sterilized in hot air oven at temp Articles are sterilized in hot air oven at temp

range of 160range of 16000C-180C-18000C.C.

16016000C is sterilization temperature.C is sterilization temperature. Uses: Glassware, sealed containers. etc Uses: Glassware, sealed containers. etc

are sterilized by this method.are sterilized by this method.

b. b. Moist heatMoist heat:: It can be applied byIt can be applied by1.1. BoilingBoiling2.2. SteamingSteaming

1. 1. BoilingBoiling:: Simple boiling is used to sterilize some Simple boiling is used to sterilize some

glassware. glassware.

Boiling done for 20-30 minutes for Boiling done for 20-30 minutes for

three consecutive days is called three consecutive days is called

Tyndalization. It is used for materials Tyndalization. It is used for materials

which can not withstand prolonged which can not withstand prolonged

boiling.boiling.

2. 2. SteamingSteaming

Most common method to be used. It is Most common method to be used. It is

normally applied above 100normally applied above 10000C under C under

high pressures. The instrument used high pressures. The instrument used

for it is called autoclave.for it is called autoclave.

Principle of autoclavingPrinciple of autoclaving::

In autoclave steam or moist heat is In autoclave steam or moist heat is

produced at a temp of 115produced at a temp of 11500C. C.

Water boils at 100Water boils at 10000C. At this temp vapour C. At this temp vapour

pressure equals the atmospheric pressure pressure equals the atmospheric pressure

i.e. 760 mm Hg. When water is heated in i.e. 760 mm Hg. When water is heated in

a closed vessel the vapour pressure rises a closed vessel the vapour pressure rises

with a subsequent rise in boiling point. with a subsequent rise in boiling point.

The boiling point rises to 115The boiling point rises to 11500C. C.

Thus steam produced at this temp is Thus steam produced at this temp is

super heated.super heated. This steam when condenses on the This steam when condenses on the

articles thermal energy is released from articles thermal energy is released from it and along with moisture this heat it and along with moisture this heat denatures the microbial proteins.denatures the microbial proteins.

Autoclave is used to sterilize most of the Autoclave is used to sterilize most of the instruments and culture media.instruments and culture media.

Different temperatures for autoclave at Different temperatures for autoclave at different pressures.different pressures.

11511500C at 10 psiC at 10 psi 12112100C at 15 psiC at 15 psi 13213200C at 27 psiC at 27 psi

Stovetop autoclaves—the simplest of autoclaves

Dental autoclave

c. c. PasteurizationPasteurization::

It is used primarily for milk.It is used primarily for milk.

It consists of heating the milk to 62°C It consists of heating the milk to 62°C

for 30 minutes followed by rapid cooling for 30 minutes followed by rapid cooling

OR heating it at 72OR heating it at 7200C for 20 seconds. C for 20 seconds.

This is sufficient to kill the vegetative This is sufficient to kill the vegetative

forms of the milk-borne pathogens, e.g. forms of the milk-borne pathogens, e.g.

Mycobacterium bovis, Salmonella, Mycobacterium bovis, Salmonella,

Streptococcus etcStreptococcus etc

II. II. Ionizing radiationsIonizing radiations:: The three types of radiation used to kill The three types of radiation used to kill

microorganisms microorganisms 1.Ultraviolet (UV) light and 2. X-rays. 3. 1.Ultraviolet (UV) light and 2. X-rays. 3.

Gamma rays Gamma rays Used in industry to sterilize disposable Used in industry to sterilize disposable

syringes, gloves, catheters etc.syringes, gloves, catheters etc.III. III. FiltrationFiltration:: Filtration is the preferred method of sterilizing Filtration is the preferred method of sterilizing

certain solutions, e.g. IV fluids. Antibiotic certain solutions, e.g. IV fluids. Antibiotic solutions.solutions.

Cellulose acetate membrane filter most Cellulose acetate membrane filter most common.common.

Pore size 0.02-1 µm. Removes bacteria.Pore size 0.02-1 µm. Removes bacteria.

High-efficiency particulate air (HEPA) High-efficiency particulate air (HEPA) filters remove almost all microorganisms filters remove almost all microorganisms larger than about 0.3 micron in diameter.larger than about 0.3 micron in diameter.

They are used to remove micro They are used to remove micro organisms from air. Used specially in TB organisms from air. Used specially in TB labs. labs.

Filter sterilization with a disposable, presterilizedFilter sterilization with a disposable, presterilizedplastic unit.plastic unit.

IV. IV. ChemicalsChemicals: They can be: They can be

a. Gases like Ethylene dioxide used in a. Gases like Ethylene dioxide used in plastic industry. Highly toxic plastic industry. Highly toxic inflammable ,potentially explosive inflammable ,potentially explosive gas .gas .

b. Liquids like Glutraldehyde used to b. Liquids like Glutraldehyde used to disinfect endoscopes.disinfect endoscopes.

Methods of DisinfectionMethods of Disinfection::

DisinfectantsDisinfectants are strong chemicals used are strong chemicals used

for disinfecting non living articles.for disinfecting non living articles.

They are toxic and corrosives for living They are toxic and corrosives for living

tissues.tissues.

AntisepticsAntiseptics::

Disinfectants which are less irritant and Disinfectants which are less irritant and

can be applied to living tissues are called can be applied to living tissues are called

antiseptics e.g. methylated spirit, Alcohol, antiseptics e.g. methylated spirit, Alcohol,

Iodine, Chloroxylenol (dettol) etc.Iodine, Chloroxylenol (dettol) etc.

Types of Disinfectants.Types of Disinfectants.

1.1.Phenol and Phenolic compoundsPhenol and Phenolic compounds. .

Phenol (carbolic acid) and phenolics are Phenol (carbolic acid) and phenolics are

good disinfectants. good disinfectants.

Phenolics are derivatives of Phenol. Phenolics are derivatives of Phenol.

Cresols is derived from coal tar form an Cresols is derived from coal tar form an

important group of phenolics.important group of phenolics.

2.2.BisphenolsBisphenols:: Bisphenols are derivatives of phenol.

Hexachlorophene and Triclosan are Hexachlorophene and Triclosan are

important bisphenols.important bisphenols.

3. 3. Biguanides:

The best known biguanide is

chlorhexidine used for microbial control

on skin and mucous membranes.

Hibiscrub (chlorhexidine + cetrimide ) Hibiscrub (chlorhexidine + cetrimide )

Hibisol (chlorhexidine + glycerine)Hibisol (chlorhexidine + glycerine)

4. 4. Halogen compoundsHalogen compounds. . The halogens, particularly iodine and The halogens, particularly iodine and

chlorine, are effective antimicrobial chlorine, are effective antimicrobial agents. agents.

TheThe most common commercial most common commercial preparation of Iodine is povidone-iodine preparation of Iodine is povidone-iodine (Pyodine). (Pyodine).

A liquid form of compressed chlorine gas A liquid form of compressed chlorine gas used extensively for disinfecting used extensively for disinfecting municipal drinking water, water in municipal drinking water, water in swimming pools, and sewage.swimming pools, and sewage.

3.3. Aldehydes: Aldehydes: Formaldehyde as gas used to sterilize Formaldehyde as gas used to sterilize

operation theatres and other spaces.operation theatres and other spaces. Glutaraldehyde a chemical relative of Glutaraldehyde a chemical relative of

formaldehyde less irritating and more formaldehyde less irritating and more effective than formaldehyde.effective than formaldehyde.

Glutaraldehyde used to disinfect hospital Glutaraldehyde used to disinfect hospital instruments, including endoscopes and instruments, including endoscopes and respiratory therapy equipmentrespiratory therapy equipment

4.4. Alcohol Alcohol:: Alcohols effectively kill bacteria and Alcohols effectively kill bacteria and

fungi but not spores and non enveloped fungi but not spores and non enveloped viruses.viruses.

Most commonly used alcohols are Most commonly used alcohols are ethanol and Isopropanol.ethanol and Isopropanol.

The recommended conc. of ethanol is The recommended conc. of ethanol is 70%70%

Isopropanol is slightly superior to Isopropanol is slightly superior to ethanol as an antiseptic and disinfectantethanol as an antiseptic and disinfectant

However, alcohols are unsatisfactory However, alcohols are unsatisfactory antiseptics when applied to wounds.antiseptics when applied to wounds.