sterilization and disinfection

Sterilization and

Disinfection

Dr. Bharat Paul

Contents

• Historical background• Introduction• Factors Affecting Disinfection• Types of disinfection• Methods Of Disinfection & Sterilization

– Natural Methods– Physical Methods– Chemical Methods

• Some practical aspects• CSSD• References

Historical background

• The scientific use of disinfection and sterilization methods originated more than 100 years ago.

• Ignatz Semmelweis(1816-1865) and Joseph Lister(1827-1912) -important pioneers for the promotion of infection control.

Historical background

• More than 100 years ago, Semmelweis demonstrated that routine hand washing can prevent the spread of disease.

• He worked in a hospital in Vienna where maternity patients were dying at an alarming rate.

• He recognized that medical students worked on cadavers during an anatomy class and afterwards they went to the maternity ward.

Historical background

• Students did not wash their hands between touching the dead and the living!!!

• After administrating the hand washing before examining the maternity patients the mortality rate decreased.

Historical background

• Lister, for the first time, used carbolic

acid in operating theatres that significantly reduced mortality rates.

• In 1867, Lister introduced the use of phenol as antimicrobial agent for surgical wound dressings.

• His principles were gradually adopted in Britain and later in US.

• This was the beginning of infection control.

Introduction

Sterilization-• Destruction of all forms of life, including the

bacterial spores, viruses, prions• No degrees of sterilization: an all-or-nothing

process.• Physical or chemical methods.

Introduction

Disinfection -• Less lethal than sterilization. Destroys most

recognized pathogenic organisms but not necessarily all microbes (e.g. Spores)

• Purpose-prevent transmission of certain microorganisms with objects, hands or skin and prevent spreading the infection.

• Physical or chemical methods.

Introduction

• Disinfectant – usually a chemical agent that destroys disease causing pathogens or other harmful microorganisms, but might not kill bacterial spores. Refers to substances applied to inanimate objects.

• Antiseptic – Substance that prevents or arrests the growth of microorganisms. Preparations applied topically to living tissues.

Introduction

• Asepsis- prevention of contact with microorganisms.

• Sanitizer – Agent that reduces the number of bacterial contaminants to safe levels.

• Sterile – State of being free from all microorganisms.

Introduction

• Detergent – Surface cleaning agent that makes no antimicrobial claims. Acts by lowering surface tension.

• Cleaning – Removal of adherent visible soil, blood , and other debris from surfaces , crevices , serrations and lumens of instruments.

Factors that influence the degree of killing

• Types of organisms• Number of organisms• Concentration of disinfecting agent• Presence of organic material (e.g., serum, blood)• Nature (composition) of surface to be disinfected• Contact time• Temperature• pH• Biofilms• Compatibility of disinfectants and sterilants

Factors that influence the degree of killing

Type of organisms• Organisms vary in their ability to withstand

chemical and physical treatment, e.g.,• Spores–have coats rich in proteins, lipids and

carbohydrates• Mycobacteria–cell walls are rich in lipids• Prions–the most resistant known organisms to

the action of heat, chemicals, and radiation !!!

Factors that influence the degree of killing

Factors that influence the degree of killing

Number of organisms• Microbial load-the total number of organisms

which determine the exposure time of killing agent• organisms have varying degrees of susceptibility to

killing agents• not all organisms die at the same time• the death curve is logarithmic!!!• higher numbers of organisms require longer

exposure.

Factors that influence the degree of killing

Factors that influence the degree of killing

Concentration of disinfecting agent• a proper concentration of disinfecting agents

ensure the killing of target organisms, e.g.,• povidone-iodine should be diluted with water

before use because there is not enough free iodine to kill microorganisms in concentrated solution.

Factors that influence the degree of killing

• Presence of organic material(such as blood, mucus, pus) affects killing activity by inactivating the disinfecting agent, e.g,

• by coating the surface to be treated, prevents full contact between object and agent (Glutaraldehyde)

• For optimal killing activity, instruments and surfaces should be cleansed of excess organic material before disinfection !!!

Factors that influence the degree of killing

• Nature (composition) of surface to be disinfected

• some medical instruments are manufactured of biomaterials that exclude the use of certain disinfection and sterilization methods because of possible damage, e.g.,

• endoscopic instruments cannot be sterilized by the heat in an autoclave.

Factors that influence the degree of killing

Contact time• the amount of time a disinfectant or sterilant is

in contact with the object is critical e.g.,• Betadine must be in contact with object for at

least 1 to 2 min to kill microbes.• the spores of bacteria and fungi need a much

longer time• determine whether it is disinfecting or

sterilizing the object.

Factors that influence the degree of killing

Biofilms• communities of microorganisms.• can be on a surface of either inanimate or

animate objects, e.g, catheters , pipes that carry water.

• make disinfection more difficult.• the concentration of the disinfectant and the

contact time need to be increased.

Factors that influence the degree of killing

Compatibility of disinfectants• a common mistake is to believe that two

disinfectants are better than one !• some of them may inactivate other, e.g.,• the bleach and quaternary ammonium

compound together negate the activity of both.

Ideal disinfectant

• Highly efficacious• Fast• Good penetration• Compatible with most materials• Non-toxic• Effective despite presence of organic material.• Residual effect• Economical• Odourless

Types of disinfection

• Concurrent disinfection –– Application of disinfective measures as soon as

possible after the discharge of infectious material from the body of an infectious person.

– Consists of disinfection of urine ,faeces , vomit, clothes ,hands ,dressings, apron ,gloves.

• Terminal disinfection - – Application of disinfective measures after the

patient has died or has ceased to be a source of infection.

Types of disinfection

• Precurrent (prophylactic) disinfection – Disinfection of water by chlorine , pasteurization of milk ,hand washing.

Types of disinfectants

High-level disinfectants• activity against bacterial spores

Intermediate-level disinfectants• tuberculocidal activity but not sporocidal

Low-level disinfectants• a wide range of activity against

microorganisms but no sporocidal or tuberculocidal activity

Types of materials in healthcare

Critical materials• invade sterile tissues or enter the vascular

system.• most likely to produce infection if

contaminated and therefore require sterilization.

• E.g. Surgical instruments , cardiac catheters

Types of materials in healthcare

Semicriticial materials• have contact with mucous membranes• require high-level disinfection agents• E.g.cystoscope ,laryngoscope blade.

Noncriticial materials• have contact with intact skin• require intermediate-level to low-level disinfection• E.g. bedpans , BP Cuffs

Methods of disinfection

• Natural methods• Physical methods• Chemical methods

Natural agents

• Sunlight – – UV rays of sunlight lethal to bacteria and some

viruses.– Articles such as linen, bedding and furniture may

be disinfected.

• Air – Acts by drying or evaporation of moisture which is

lethal to most bacteria.

Physical agents

• Burning– Inexpensive articles such as contaminated

dressings , rags and swabs – disposed off by burning.

– Best done in an incinerator.– Addition of sawdust, paper ,kerosene or other

combustible material aid in burning.

Physical agents

• Hot air– Articles such as

glassware ,syringes , swabs , dressings and sharp instruments.

– Drawback – no penetrating power: not suitable for bulky materials.

– Hot air oven – temp 160-180 deg C for at least 1hour to kill spores.Hot air oven

Physical agents

• Thermal Death Point (TDP): Lowest temperature at which all of the microbes in a liquid suspension will be killed in ten minutes.

• Thermal Death Time (TDT): Minimal length of time in which all bacteria will be killed at a given temperature.

• Decimal Reduction Time (DRT): Time in minutes at which 90% of bacteria at a given temperature will be killed. Used in canning industry.

Physical agents

MOIST HEAT • Kills by denaturing proteins and destroying

cytoplasmic membranes. • More effective than dry heat; water better

conductor of heat than air.• Methods of microbial control using moist heat– Boiling – Autoclaving – Pasteurization

Physical agents

• Boiling– for 5-10 minutes :kill bacteria but not spores or

viruses.– Temp. above 100 deg C required for destruction of

spores.– Disinfection of small instruments , tools not used

for subcutaneous insertion , linen and rubber goods such as gloves.

– Slow process , unsuitable for thick beddings and it fixes albuminous stains.

Physical agents

• Autoclaving–Operate at high temperature and pressure.–Destroys all forms of life , including spores.–Sterilization of linen , dressings , gloves ,

syringes , instruments and culture media.–Not suitable for plastics and sharp

instruments.

Autoclave

Physical agents

Pasteurization• A process in which fluids are heated at

temperatures below boiling point to kill pathogenic microorganisms in the vegetative state without altering the fluid’s palatability.

• Conditions: 62 , 30min or 71.7 , 15sec ℃ ℃• Significance: kills vegetative pathogens.

Pasteurisation

Physical agents

• Radiation–Sterilization of bandages , dressings , catgut

and surgical instruments.–Great penetrating power with little or no

heating effect.–Most effective ,but very costly.–Normally carried out by gamma radiation.

Physical agents

• Filtration: Removal of microbes by passage of a liquid or gas through a screen like material with small pores. Used to sterilize heat sensitive materials like vaccines, enzymes, antibiotics, and some culture media.

• 0.22 and 0.45um Pores: Used to filter most bacteria. Don’t retain spirochetes, mycoplasma and viruses.

• 0.01 um Pores: Retain all viruses and some large proteins

Chemical agents

Phenol and related compounds• Intermediate- to low-level disinfectants • Denature proteins and disrupt cell membranes • Effective in presence of organic matter and

remain active for prolonged time. • Commonly used in health care settings, labs, and

homes (Lysol, triclosan) • Have disagreeable odor and possible side

effects.

Chemical agents

• Phenol(carbolic acid) – not an effective disinfectant

• Crude phenol- phenol and cresol. effective against gram +ve and –ve organisms.

• Cresol – used in 5 to10 % for disinfection of urine and faeces.

• Cresol emulsions – very powerful disinfectants

Chemical agents

• Chlorhexidine (hibitane ) – most useful skin antiseptic. 0.5% solution used as handlotion.1% creams used for burns

• Hexachlorphane – slow in action , but shows cumulative effect on skin and is compatible with soaps.

• Dettol (chloroxylenol) – relatively non toxic antiseptic.5 % dettol for disinfection of instruments and plastic equipments.

Chemical agents

Quaternary ammonium compounds– Cetrimide(cetavlon) – bactericidal against vegetative gram +ve

organisms , much less against gram -ve– Used in 1-2 % strength– Savlon – Combination of cetavlon and hibitane .– Plastic appliances may be disinfected in 20 min.– Disinfection of clinical thermometers in 3 minutes.

Chemical agents

Halogens and their compounds• Intermediate-level antimicrobial chemicals • Believed that they damage enzymes via

oxidation or by denaturing them. • Iodine tablets, iodophores (Betadine®), chlorine

treatment of drinking water, bleach, chloramines in wound dressings, and bromine disinfection of hot tubs.

Chemical agents

Alcohols• Intermediate-level disinfectants.• Denature proteins and disrupt cytoplasmic

membranes.• Evaporate rapidly.• Swabbing of skin with 70% ethanol prior to

injection.

Chemical agents

Isopropyl Alcohol (70%) • Powerful disinfectant and antiseptic • Mode of action: denatures proteins, dissolves

lipids and can lead to cell membrane disintegration

• Effectively kills bacteria and fungi • But does not inactivate spores!

Chemical agents

Aldehydes• Denature proteins and inactivate nucleic

acids. • Glutaraldehyde both disinfects (short

exposure) and sterilizes (long exposure) • Formalin used in embalming and disinfection

of rooms and instruments.

Chemical agents

Formaldehyde–Highly toxic and irritant gas–Effective against vegetative bacteria ,fungi

and many viruses.–Used as a 2-3 % solution for spraying rooms

, walls and furniture–Most effective at a high temperature and

relative humidity of 80-90%

Chemical agents

Oxidizing agents• Peroxides, ozone, and per acetic

acid kill by oxidation of microbial enzymes • High-level disinfectants and antiseptics • Hydrogen peroxide can disinfect and sterilize

surfaces of objects.• Ozone -treatment of drinking water. • Per acetic acid – effective sporocide used to

sterilize equipment.

Chemical agents

Surfactants• Surface active chemicals that reduce surface tension

of solvents to make them more effective at dissolving solutes

• Soaps and detergents • Colorless, tasteless, harmless to humans, and

antimicrobial; ideal for many medical and industrial uses.

• Low-level disinfectants.

Chemical agents

Metals-• Ions are antimicrobial because they alter the 3-D

shape of proteins, inhibiting or eliminating their function.

• Low-level bacteriostatic and fungistatic agents. • 1% silver nitrate to prevent blindness caused by N.

gonorrhoeae .• Thiomersal (mercury-containing compound) used

to preserve vaccines.

Chemical agents

Lime–Cheapest disinfectant–Used as fresh quick lime or 10-20 %

aqueous suspension known as milk of lime.–Faeces and urine disinfected by 10-20%

aqueous solution (in 2 hrs).–Used as a deodorant in public places where

toilets are located.

Chemical agents

Ethylene oxide– for heat sensitive articles – At 55- 60 deg C : kills bacteria ,spores and viruses.–Mixed with 12 % carbon dioxide (as it is

explosive)–Water vapor added to the mixture to increase

efficacy.– To sterilize fabrics, plastic equipment , cardiac

catheters , etc.

Some Newer agents

• Bacillocid® rasant – Formaldehyde-free disinfectant cleaner with low

use concentration

• Virkon– gaining importance as non Aldehyde compound– Disinfects medical devices and lab equipments.– Decontaminate spillages with Blood and body

fluids.

Gas plasma sterilization

• Gas plasma generated in an enclosed chamber under deep vacuum using Radio frequency or Microwave.

• Can be used for hand sterilization.• The mechanism of action of this device is the

production of free radicals within a plasma field that are capable of interacting with essential cell components

Sterilization Control

• To ensure that potentially infectious agents are destroyed by adequate sterilization regimes

• Three levels: • physical: measuring device control (temp.,

time, pressure)• Biological• Chemical

Sterilization Control

Biological:• Bacillus stearothermophilus spores(104-106

organisms) • survives steam heat at 121ºC for 5 min. and is killed at

121ºC in 13 min.• validate and determine the adequacy of steam or

chemical sterilization.• Bacillus subtilis/B.atrophaeus spores• validate and determine the adequacy of ethylene oxide

or dry heat sterilization.

CHEMICAL INDICATORS

• Browne's tubes are glass tubes that contain heat sensitive dyes. These change color after sufficient time at the desired temperature.

• Before heat exposure, the contents of the tube appear red.

• As heating progresses, the color changes to green.

CHEMICAL INDICATORS•Bowie Dick tape is applied to articles being autoclaved. Before heat exposure, the tape is uniformly buff in color. •After adequate heating, the tape develops dark brown stripes.

The pack on the left has been properly sterilized; that on the right has not.

SOME PRACTICAL ASPECTS

Disinfection of faeces & urine-• Collected in impervious container.• Add equal volume of disinfectant for 1-2 hrs.

Disinfectant Amount per litre Percent

Bleaching powder

50 gms 5

Crude phenol 100ml 10

Cresol 50 ml 5

Formalin 100 ml 10

Disinfection of faeces & urine-

• Quick lime or milk of lime can be used if above disinfectants not available.

• Bedpans and urinals – steam disinfected.

Disinfection of sputum

• Received in gauze or paper handkerchief .• Destroyed by burning.• Disinfected by boiling or autoclaving for 20

min at 20 lbs pressure.• Or 5 % cresol can be used.

• Disinfection of blood/body fluids spills– Clean the affected area with soap and water then

disinfect with a 1%Na hypochlorite solution for 15 minutes.

• HIV infected articles– Cleaning and 2% glutaraldehyde for 30 minutes.– 6% Hydrogen peroxide for 30 minutes.– 1% hypochlorite solution for 30 minutes.

Fumigation• To sterilize the operation theatre formaldehyde

gas (bactericidal & sporicidal, viricidal) is widely employed as it is cheaper for sterilization of huge areas like operation theatres.

• Formaldehyde is irritant to eye & nose; and it has been recognized as a potential carcinogen.

References

• K.Park Textbook of Preventive and Social medicine 23rd edition.

• CDC – Sterilization and disinfection guidelines• Hospital hygiene and infection control –WHO. • WHO Pharmacoepia Library- Methods of

Sterilization.• Occupation Safety and Health administration-

Disinfection guidelines.