disinfection by chemicals basics

DISINFECTIONby chemicals

basicsDr.T.V.Rao MD

Dr.T.V.Rao MD 1

Why we need Sterilization

• Microorganisms capable of causing infection are constantly present in the external environment and on the human body.

• Microorganisms are responsible for contamination and infection.

• The aim of sterilisation is to remove or destroy them from materials or from surfaces.

Dr.T.V.Rao MD 2

Uses of sterilisation

1. Sterilisation of materials, instruments used in surgical and diagnostic procedures.

2. Sterilisation of Media and reagents used in the microbiology laboratory.

3. Food and drug manufacturing to ensure safety from contaminating organisms.

Dr.T.V.Rao MD 3

How can microorganisms be killed?

1 Denaturation of proteins (e.g. wet heat, ethylene oxide)

2 Oxidation (e.g. dry heat, hydrogen peroxide)3 Filtration4 Interruption of DNA synthesis/repair (e.g.

radiation)5 Interference with protein synthesis (e.g. bleach)6 Disruption of cell membranes (e.g. phenols)

Dr.T.V.Rao MD 4

Factors that influence efficacy of disinfection/sterilization

1 Contact time2 Physico-chemical environment (e.g. pH)3 Presence of organic material4 Temperature5 Type of microorganism6 Number of microorganisms7 Material composition

Dr.T.V.Rao MD 5

Relative Resistance of Microbial Forms

Highest resistance Moderate resistance Least resistance

bacterial endospore (Bacillus & Clostridium)

protozoan cystsome fungal sporessome naked virusvegetative bacteria that have higher resistance ( M. tuberculosis, S.aureus, Pseudomonas)

most bacterial vegetative cellsordinary fungal spores & hypaeenveloped virusYeastsTrophozoites

Dr.T.V.Rao MD 6

Definitions: Sterilisation :

– It is a process by which an article, surface or medium is made free of all microorganisms either in vegetative or spore form.

Disinfection :– Destruction of all pathogens or organisms capable

of producing infections but not necessarily spores.– All organisms may not be killed but the number is

reduced to a level that is no longer harmful to health.

Dr.T.V.Rao MD 7

Antiseptics :

Antiseptics :– Chemical disinfectants which can safely applied to

living tissues and are used to prevent infection by inhibiting the growth of microorganisms.

Asepsis :– Technique by which the occurrence of infection

into an uninfected tissue is prevented.

Dr.T.V.Rao MD 8

Ideal sterilization/disinfection process

• Highly efficacious• Fast• Good penetrability• Compatible with all materials• Non-toxic• Effective despite presence of organic material• Difficult to make significant mistakes in process• Easily monitored

Dr.T.V.Rao MD 9

Figure 9.1 A plot of microbial death rate

Dr.T.V.Rao MD 10

90% die

1 min

90% die

1 min

Constant percentageof the extant populationis killed each minute

Time (min)

Nu

mb

er

of

livin

g m

icro

bes

Chemical Methods

Many matters, substances and objects cannot be sterilized with

Physical methods So Need for Disinfectants

Dr.T.V.Rao MD 11

Chemical methods • Alcohols• Aldehydes• Phenols• Halogens• Oxidizing agents• Salts• Surface active agents• Dyes• Vapour phase disinfectantsDr.T.V.Rao MD 12

Chemical agents • A variety of chemical agents are used as

antiseptics and disinfectants.• Factors influencing the potency of a disinfectant:

• Concentration• Time of action• pH • Temperature• Nature of organism• Presence of organic matter

Dr.T.V.Rao MD 13

Levels of Disinfection1. High level

disinfectants2. Intermediate

level disinfectants

3. low level disinfectants

Dr.T.V.Rao MD 14

High level disinfectants:

• Glutaraldehyde, Hydrogen peroxide, peracitic acid and chlorine compounds.

• Effectiveness may be equal to that of sterilisation.• Used for:

• Endoscopes• Cystoscopies• Surgical instruments with plastic components

Dr.T.V.Rao MD 15

Intermediate level disinfectants

• May not effective against spores

• Includes alcohols, iodophores and phenols

• Used for:– Laryngoscopes– Fiber optic

endoscopes

Dr.T.V.Rao MD 16

Low level disinfectants:

– Many organisms can survive on exposure to these disinfectants.

– Used for items which come in contact with the patients but they do not penetrate into tissues.

– Stethoscopes, ECG electrodes etc.

Dr.T.V.Rao MD 17

Alcohols :

– Ethyl alcohol and Isopropyl alcohol are commonly used.

– Act by denaturing of bacterial proteins.– No sporicidal and virucidal activity.– Used as skin antiseptics.– Isopropyl alcohol is preferred to Ethyl

alcohol as it is better fat solvent, more bactericidal and less volatile.

Dr.T.V.Rao MD 18

Aldehydes:2.

a) Formaldehydeb) Glutaraldehyde

Dr.T.V.Rao MD 19

Formaldehyde: Bactericidal, sporicidal and virucidal Used in both aqueous solution and gaseous forms A 10% aqueous solution is routinely used. Uses:

1) preservation of tissues for pathological examination2) To sterilize bacterial vaccines3) To prepare toxoid from toxin4) For killing of bacterial cultures and suspensions5) For destroying anthrax spores in hair and wool.

Dr.T.V.Rao MD 20

Glutaraldehyde :

• Effective against bacteria , fungi and viruses.• Less toxic and irritant to eyes and skin than

formaldehyde• Used as 2% buffered solution• Available commercially as CIDEX• Uses:

1. For sterilisation of cystoscopes, endoscopes and bronchoscopes

2. For sterilisation of plastic endotracheal tubes, face masks, rubber anesthetic tubes

Dr.T.V.Rao MD 21

Phenols:• Lister,the father of antiseptic surgery, first introduced

the use of phenol ( Carbolic acid) in surgery (1867).• Produced by distillation of coal tar between

temperatures of 170°C and 270°C.• Bactericidal action due to cell membrane damage.• Commonly used Phenol derivatives are

1. cresol 2. chlorhexidine 3. chloroxylenol 4. hexachlorophanes

Dr.T.V.Rao MD 22

Cresols :

• Lysol is a solution of cresols in soap.

• Active against a wide range of organisms.

• uses:1. For sterilisation of

infected glass ware2. Cleaning of floors3. Disinfection of excreta

Dr.T.V.Rao MD 23

Chlorhexidine:

–Eg.Savlon – (Chlorhexidine and Cetrimide)

–More active against Gram positive than Gram negative

–Good fungicidal activity.–No action on spores and little activity

against viruses

Dr.T.V.Rao MD 24

Chloroxylenol :

–Eg.dettol–Less toxic and

less irritant.–Readily

inactivated by organic matter

–Inactive against pseudomonas.

Dr.T.V.Rao MD 25

Hexachlorophanes:

:• More active against Gram positive than Gram

negative bacteria.• Bacteriostatic at high dilutions.• Applied on skin as prophylaxis against

staphylococcal infections.• Potentially toxic and should be used with care.

Dr.T.V.Rao MD 26

Halogens:

4.Halogens:i. Chlorine ii. Iodine

Commonly used disinfectants

Bactericidal, sporicidal and virucidal

Dr.T.V.Rao MD 27

Chlorine : In the form of

Bleaching powder, Sodium hypochlorite Chloramine

Disinfection is due to release of free chlorine. Reacts with water to form hypochlorus acid . Bactericidal, viricidal, fungicidal and sporicidal. Used in water supplies, swimming pools, food

and dairy industries.

Dr.T.V.Rao MD 28

Iodine :

• Used as skin disinfectant.

• Bactericidal and moderate action on spores.

• Betadine is one example.

Dr.T.V.Rao MD 29

5.Oxidising agents:

Hydrogen peroxide• Effective at concentration of 3-6%• Kills spores at 10- 25%• Used to disinfect

»Contact lenses»Surgical prostheses»Plastic implants

Dr.T.V.Rao MD 30

Salts:

• Salts of heavy metals have toxic effect on bacteria.

• Salts of copper, silver and mercury are used as disinfectants.

• Act by coagulation of bacterial proteins.• Mercuric chloride, once used as disinfectant is

highly toxic.• Thimersol and mercurochrome are less toxic • Copper salts are used as fungicides.

Dr.T.V.Rao MD 31

Surface active agents:

• Substances which alter energy relationships at interfaces , producing a reduction of surface tension, are known as surface active agents or surfactants.– Anionic– cationic– nonionic – amphoteric compounds.

Dr.T.V.Rao MD 32

The anionic compounds::

• e.g.:- common soaps, • Have strong detergent but weak

antimicrobial properties . • These agents are most active at acidic ph. • Effective against Gram positive

organisms but are relatively ineffective against Gram negative species.

Dr.T.V.Rao MD 33

Cationic surfactants::

• Quaternary ammonium compounds are the most important cationic surfactants.

• These compounds are bactericidal for a wide range of organisms, gram positive species are more susceptible.

• The common cationic compounds are acetyl trimethyl ammonium bromide (cetavalon or Cetrimide) and benzalkonium chloride.Dr.T.V.Rao MD 34

Amphoteric compounds:

Known as ‘Tego’ compounds possess detergent properties of anionic and antimicrobial activity of cationic compounds.

• They are active against a wide range of Gram positive and Gram negative organisms and some viruses.

Dr.T.V.Rao MD 35

Dyes ::• Two groups of dyes have been used extensively as

skin and wound antiseptics– aniline dyes – acridine dyes

• Both are bacteriostatic in high dilution but have low bactericidal action.

• Aniline dyes include crystal violet, brilliant green and malachite green.

• They are more active against Gram positive bacteria than Gram negative bacteria.

Dr.T.V.Rao MD 36

Dyes :

• Acridine dyes include acriflavine , euflavine, proflavine and aminacrine.

• They are more active against Gram positive bacteria than Gram negative bacteria.

• Gentian violet and acriflavine are two widely used dyes for skin disinfection especially in Gram positive bacterial infections.

Dr.T.V.Rao MD 37

Vapour phase disinfectants:

•Formaldehyde gas

•Ethylene oxide• Betapropiolactone

Dr.T.V.Rao MD 38

Formaldehyde gas:

• Used for fumigation of operation theatres, wards and laboratories etc.

• It is generated by adding 150 gm of KMnO4 to 280 ml of formalin for 1000 cu. Feet of room volume.

• The doors should be sealed and left unopened for 48 hours.

• The gas is toxic and irritant when inhaled.• After completion of sterilisation the irritant vapors

are nullified by exposure to ammonia vapor.

Dr.T.V.Rao MD 39

Ethylene oxide:

• It is a colorless liquid with a boiling point of 10.7°C.• Effective against all types of organisms including

viruses and spores.• It has a potential toxicity to human beings, including

mutagenicity and carcinogenicity .• It is highly inflammable.• Used for sterilizing plastic and rubber articles,

respirators, heart lung machines, sutures, dental equipment's etc.

Dr.T.V.Rao MD 40

Betapropiolactone :

• Condensation product of ketane and formaldehyde.

• It has a boiling point of 163°C.• Used in 0.2%.• Effective against all types of organisms

including viruses.• More efficient for fumigation than

formaldehyde.• Used for inactivation of vaccines.

Dr.T.V.Rao MD 41

• Programme Created by Dr.T.V.Rao MD for Medical and Paramedical Students in

the Developing World • Email.com

• doctortvrao@gmail.com

Dr.T.V.Rao MD 42