STERILIZATION &

DISINFECTION

By

Dr. Riaz Ahmed

Objectives of sterilization & Disinfection

• TO BREAK THE CHAIN OF TRANSMISSION OF DISEASE SPREAD

• TO DECREASE MORBIDITY & MORTALITY OF DISEASE SPREAD

• TO PROLONG LIFE

• TO PROMOTE HEALTH

• TO PREVENT DISEASE

Definitions•Sterilization: It is a process whereby all living

organisms (both pathogenic & non-pathogenic) including their spores are either killed or removed.

•Dis-infection: A process, which destroys only vegetative form of pathogenic organisms, while leaving the spores

intact if any.•Infection: The entry & development OR mutliplication

of inf. Agent in the body of man or animal is called infection.

•Infestation: It is a state of having a parasite in OR on the body, which includes arthropods e.g.,

In- hook worm infestationOn- scabies / louse infestation

• DIS-INFESTATION: - • Removal OR destruction of these

parasites is called Disinfestations / PARASITOSIS.• TWO IMPORTANT METHODS: -• PHYSICAL: - • CHEMICAL: -• a) PHYSICAL: -• HEAT: -• It is certain, rapid and controllable. It has one

advantage over all chemical methods that when sterilization in complete, No harmful bacteria remain

• TYPES: -• DRY HEAT• WET HEAT / MOIST HEAT (▲)• 1- DRY HEAT:• INCINERATION / HEATING OVER FLAME: • It is the SUREST method of heat sterilization, which is most often

used by the bacteriologists when flaming a wire loop.

• → Certain- metals, Contaminated dressings, used swabs, disposable-plastics and culture- plates are BURNT in this way.

• This is in short the cheapest and safest arrangement. • HOT AIR OVEN: • HOT AIR OVEN IS NOT ONLY A POOR

CONDUCTOR OF HEAT BUT ALSO HAS A POOR PENETRATION.

• THEREFORE FANS ARE USED TO CIRCULATE THE AIR IN THE OVEN.

• A TEMP. OF 16OO C FOR ONE HOUR IS SUFFICIENT TO STERILIZE THE INSTRUMENTS.

• AT THIS HIGH TEMP; AS FABRICS WILL BE DESTROYED & RUBBER WILL MELT, SO THESE ARTICLES ARE NOT USED IN HOT AIR OVEN.

• ARTICLES STERILIZED IN H.A.O:• 1) GLASS-SYRINGES:

WHERE MOISTURE IS A PROBLEM & IT ALSO CREATS NUIASANCE.

• 2) OILY LIQUIDS: THESE BECOME SOLIDIFIED IN THE PRESENCE OF

MOISTURE.3) POWDERS: THESE BECOME SOLIDIFIED IN THE PRESENCE OF

MOISTURE IN HOT AIR OVEN.4) VERY FINE SHARPE INSTRUMENTS: SUCH AS THOSE USED IN EYE SURGERY. THEY

EITHER MAY BE DEMAGED OR GET BLUNTED BY MOIST ▲ & SO ARE PREFERABLY STERILIZED IN H.A.OVEN.

• MOIST-HEAT / WET ▲ ONE OF THE GREAT ADVANTAGES OF MOIST HEAT OVER DRY HEAT IS

THAT IT STERILIZES AT LOW TEMP & IN A SHORTER PERIOD OF TIME.• TYPES: PASTEURIZATION BOILING TYNDALLIZATION AUTOCLAVING• 1. PASTEURIZATION: -

– IN THIS PROCESS MILK IS HEATED TO A CERTAIN TEMP. BELOW ITS BOILING POINT.

– BY MAINTAINING AT THIS TEMP.FOR A CERTAIN PERIOD, IT IS SUFFICIENT TO KILL ALL THE PATHOGENIC & HARMFUL BACTERIA WITHOUT DESTROYING THE NUTRITIVE PROPERTIES OF MILK & THEN CHILLING IT RAPIDLY.

THIS METHOD Kills 99 % OF BACTERIA: – IT IS WELL KNOWN THAT HEATING MILK AT 140O F (60OC) FOR 30

MINUTES IS SUFFICIENT TO KILL THE BACTERIA OF– TUBERCULOSIS– TYPHOID– DYSENTRY– CHOLERA & OTHER NON-SPORE BEARING

• MILK BORNE INFECTIONS: WHICH AFFECT MAN e.g.– BRUCELLOSIS– SEPTIC SORE THROAT & INFANTILE PARALYSIS

• AFTER PASTEURIZATION, THE MILK IS IMMEDIATELY COOLED DOWN TO DISCOURAGE BACTERIAL GROWTH.

• THE ADVANTAGE OF PASTUERIZATION OVER BOILING IS THAT THE NUTRITIVE VALUE OF MILK IS PRESERVED.

• METHODS OF PASTEURIZATION:THERE ARE TWO METHODS OF PASTEURIZATION.1.CONTINUOUS FLOW FLASH PASTEURIZATION2.THE RETAINER PASTEURIZATION

• 1.CONTINUOUS FLOW FLASH PASTEURIZATION (C.F.F.P):IN THIS PROCESS MILK IS MADE TO PASS OVER A METALCOIL & A TEMP.OF 70-80O C IS MAINTAINED FOR ONE MINUTE, & THEN THE MILK IS RAPIDLY COOLED DOWN BY PASSING IT OVER COLD METAL

2.RETAINER PASTEURIZATION:

IN THIS METHOD MILK IS HEATED AT 60-65O C AND HELD AT THAT TEMP IN A SUITABLE TANK FOR 30 MINUTES THEN IS COOLED DOWN. THIS METHOD IS MOST SATISFACTORY AS THE PATHOGENIC BACTERIA ARE KILLED WITH CERTAINITY BUT IS EXPENSIVE.

2.BOILING:

IT IS EFFECTIVE METHOD OF DISINFECTION.

IT PROVIDES AN ATMOSPHERE OF BOILING AND STEAM.

• AN ADVANTAGE OF BOILING OVER PASTEURIZATION IS THAT IT IS EFFICACIOUS IN DESTROYING THE VIRUS OF HEPATIS.

• THESE ARE VERY RESISTANT TO ▲ BUT ARE SAID TO BE KILLED AFTER 3 MIN. BOILING AT 100O C WHILE BOILING WILL NOT KILL SPORES.

3.TYNDALLIZATION / INT.STEAMING:• THIS IS INT.STEAMING OF A SOLN AT 100O C FOR 30

MINUTES FOR THREE SUCCESSIVE DAYS.• AFTER THE FIRST STEAMING ONLY SPORES ARE LEFT

BEHIND. THEY GERMINATE IN THE MEDIUM & ARE DESTROYED IN THE NEXT STEAMING.

• ANY THAT SURVIVE, SHOULD BE KILLED AFTER THE THIRD STEAMING.

• IT IS TRUE STERILING PROCESS BUT IS APPLICABLE ONLY TO MEDIA IN WHICH THE SPORES CAN GERMINATE & GROW AS VEGETATIVE ORGANISMS. IT FAILS WHEN APPLIED TO DRUGS, SUTURE MATERIAL & INSTRUMENTS.

4. AUTOCLAVING (STEAMING UNDER PRESSURE) THIS IS MOST COMMONLY USED METHOD OF

STERILIZATION USED IN HOSPITAL, SO IT IS NECESSARY TO UNDER-STAND THE PRINCIPLE INVOLVED.

• PRINCIPAL: BECAUSE WATER BOILS WHEN ITS V.PRESSURE BECOMES EQUAL TO THAT

OF SURROUNDING AT PRESS, SO B.P OF WATER CAN BE RAISED BY INCREASING AT PRESSURE.

AT NORMAL (SEA-LEVEL); AT PRESS (760mm of Hg) OR 14.7LB/sq //

WATER BOILS AT 100O C, & THIS PRESSURE IS REFERED ZERO AT PRESSURE-GUAGE.

IF THE PRESSURE IS INCREASED BY 10 lb / sq // , THE WATER BOILS AT 115OC & IF THE ‘ P ’ IS 15 lb/sq // , THE B.P RISES TO 121O C.

• IF MATERIAL IS HELD UNDER PURE STEAM AT A TEMP. OF 121OC, FOR 15 MIN STERILIZATION CAN BE GUARANTED

• AT 126O C – 10 MIN ARE SUFFICIENT • AT 134O C STERILIZATION IS COMPLETED • WITH IN 3 MINUTES

• ADVANTAGES OF MOIST HEAT OVER DRY HEAT1) MOIST HEAT KILLS BY CO-AGULATING AND

DENATURING THE PROTEINS & ENZYMES WHILE DRY ▲ ACTS BY VITUE OF

• DESTRUCTIVE-OXIDATION OF CELL CONSTITUENTS.

2) MOIST ▲ KILLS AT LOWER TEMP.IN A SHOTER PERIOD OF TIME.

3) IT PRODUCESS NEGATIVE(-VE) PRESS. BY CONTRACTING IN ITS VOLUME WHEN IT CONDENCES BY COMING.IN CONTACT WITH COOLER SURFACE OR CABINET AND THE –VE PRESSURE BRINGS MORE STEAM

• TO THE SAME SITE• VERY SOON THE TEMP OF SURFACE IS

RAISED TO THAT OF SURROUNDING STEAM.

• THEREFORE STEAM ACTS MUCH MORE QUICKLY IN HEATING EXPOSED ARTICLES.

• 4) STEAM PENETRATES MUCH BETTER THAN DOES HOT AIR.

• THIS IS PARTIALLY DUE TO ITS DENSITY ONLY HALF THAT OF AIR AND PARTIALLY DUE TO NEGATIVE-PRESSURE PRODUCED BY ITS CONTRACTION IN VOLUME.

FACTORS RESPONSIBLE FOR FAILURE IN STERILIZATION

• IMPROPER PACKING OF LOAD IF DRESSINGS OF THEATRE GARMENTS ARE TO BE AUTO-CLAVED, THEY MUST BE ARRANGED SO LOSSLY THAT STEAM CAN CIRCULATE INTERNALLY AROUND THEM.

• DEFECTS IN AUTOCLAVE AIR SHOULD NOT ENTER THROUGH DOORS OR THROUGH CENTRAL SUPPLY.THERE SHOULD BE NO LEAKAGE.

• DEFECTS IN STEAM STEAM SHOULD NOT BE EITHER SUPER-HEATED OR OVER-SATURATED AS IT WILL NOT CONDENSE-EASILY. IF THE JACKET IS TOO WORMED, THE STEAM INSIDE CABINET WILL BECOME SUPER-HEATED.

• FAULTY OPERATION OF AUTOCLAVE• FULLY TRAINED STAFF SHOULD BE APPLIED.

• TEST OF EFFICIENCY FOR HEAT STERILIZATION / AUTOCLAVE-TAPE:

• THIS IS A TAPE PRINTED WITH A SENSTIVE INK WHICH UNDERGOES A COLOR CHANGE AT A SPECIFIC TEMP. IT FORMS THE BASIS OF BOWIE- DICK TEST FOR HIGH VACUUM AUTO CLAVES.

• IN THE MIDDLE OF TEST PACK OF TOWELS THERE IS PLACED A SQUARE SHAPED PAPER ON TO WHICH HAS BEEN STUCK TWO STRIPS OF SPECIFIED AUTO CLAVE TAPE (3M BRAND NO.1222) IN THE SHAPE OF DIAGONALLY.

• A TEMP OF 134O C IS APPLIED FOR 3 MINUTES.

• THERE SHOULD BE UNIFORM-DEVELOPMENT OF BARS THROUGH OUT THE LENGTH OF STRIPS.

• THIS INDICATES THAT STEAM HAS PASSED FREELY AND RAPIDLY TO THE CENTRE OF THE LOAD.

OTHER PHYSICAL METHODS

• FILTERATION: IT IS ALSO A VERY EFFECTIVE METHOD OF DIS-INFECTION.

• THIS METHOD CAN BE USED FOR PURIFYING WATER AND AIR.

• THE MATERIAL USED IN FILTER MAY BE PORCELAIN, SINTERED-GLASS, ASBESTOS, CELLULOSE ESTERS & OTHER INERT POLYMERS.

• MECHANISM IS MAINLY MECHANICAL BY STOPPING THE PASSING OF SUSPENDED MICROORGANISMS WHILE THEIR PASSAGE THROUGH THE PORES IN THE FILTERED MATERIAL.

• LIGHT: • DIRECT SUNSHINE KILLS

VEGETATIVE ORGANISM• FAIRLY RAPIDLY BUT SPORES ARE

MUCH MORE RESISTANT.• THE DIS-INFECTING PROPERTIES

RESIDE MAINLY IN THE ULTRA-VIOLET RANGE.

• U.V. LIGHT PRODUCED ARTIFICIALLY HAS POWERFUL GERMICIDAL-PROPERTIES & IS USED FOR DIS-INFECTING THE SURFACES AS WELL AS INSIDE OF THE INOCULATION CABINETS.

• 3) IONIZING-RADIATIONS:• TWO TYPES OF IONIZING RADIATIONS ARE IN

DAILY USE IN SPECIAL CENTRES.• 1.GAMMA-RADIATIONS• 2.HIGH ENERGY ELECTRONS• 1.GAMMA-RADIATIONS:• THESE ARE DERIVED FROM RADIO ACTIVE

ISOTOPES SUCH AS COBALT 60 AND CAESIUM-137.THEY POSESS GREATER PENETRATING POWER AND HENCE ARTICALS UPTO 0.5mm IN THICKNESS CAN BE STERILIZED.

• 2.HIGH ENERGY ELECTRONS• THE PENETRATING POWER OF ELECTRONS

DEPENDS UPON THE ENERGY BY WHICH THEY ARE ACCELERATED.

• USES OF IONIZING RADIATION:

THEY CAN BE USED TO STERILIZE A WIDE RANGE OF PRE-PACKED HEAT-SENSITIVE ARTICLES INCLUDING

• BONE-GRAFTS

• SURGICAL-SUTURES

• SYRINGES

• CATHETERS

• PETRI-DISHES

• RUBBER GLOVES

• CHEMICAL METHODS• A GOOD CHEMICAL DISINFECTANT• HAS THE FOLLOWING PROPERTIES• IT SHOULD BE ACTIVE AGAINST VIDE RANGE

OF ORGANISMS & SPORES.• IT SHOULD HAVE A RAPID ACTION.• ITS ACTION SHOULD HAVE NOT DECREASED

BY THE PRESENCE OF ORGANIC MATTER e.g. BLOOD, PUS OR FAECAL-MATTER.

• IT SHOULD NOT BE TOXIC, IRRITANT OR INDUCE HYPERSENSITIVITY-REACTION.

• TYPES: -• 1) IN-ORGANIC DIS-INFECTANTS: -• THE HALOGENS CHLORINE & IODINE ARE

MOST OFTEN IN COMMON USE; BEING TRUE STERILIZER AS THEIR ACTION IS RAPID AGAINST BOTH VEGETATIVE ORGANISMS & SPORES.

• a) IODINE: - THE BEST SKIN DIS-INFACTANT IS TINCT OF IODINE, WHICH CONTAINS.

• 2.5 % IODINE• 2.5 % POTASSIUM IODIDE (KI)• 90 % ETHANOL• 5 % WATER

• DIS-ADVANTAGE: THE DIS-ADVANTAGE IS THAT:

• IT IS IRRITATING TO THE RAW AREAS & MAY INDUCE AN ALLERGIC CONTACT-DERMATITIS

• OTHER COMPOUNDS ARE USED WHEN IODINE IS COMBINED WITH SURFACE-ACTIVE NON-TOXIC DETERGENT.

• ONE EXAMPLE IS • POLY-VINYL-IODINE OR BETADINE• THIS IS USED TO DIS INFECT FOMITES AS

WELL AS TO MOP (SWEEP) THE SURGICAL INTRUMENTS.

• CHLORINE: IT IS A POWERFUL DISINFACTANT & IS USED FOR CHLORINATION.

• HYPO-CHLORITE-SOLUTIONS ARE VERY USEFUL IN THE DIS-INFECTION OF HOSPITAL –ENVIRONMENT & THE FOMITES.

• THEY ARE ACTIVE PARTICULARLY AGAINST VIRUSES INCLUDING THOSE OF HEPATITIS.

• AMONG HYPOCHLORITE SOLNS.ONE IS CHLORUS THAT IS TOO TOXIC TOO CORROSIVE & ALSO STRONGER FOR GENERAL USE.

• MUCH WEAKER COMPOUNDS KNOWN AS MILTON (SOD-HYPOCHLORITE) MAY BE USED IN THE HOMES TO DISINFECTANT FEEDING BOTTLES OTHER COMP. CONTAINING HYPOCHLORITE SOLUTION ARE ‘VIM’& ‘AJAY’ WHICH ARE USED FOR THE DISINFECTION OF BATHS & SINKS.

• ORGANIC-DISINFECTANTS• (a) ALCOHOL: - 50—70 % ISO-PROPYLE ALCHOL IS

ALTHOUGH A CHEMICAL • DIS-INFECTANT YET IT IS NOT A TRUE STERILIZING

AGENT AS IT IS IN-EFFECTIVE AGAINST SPORES.• (b) ALDEHYDES: - THEY ARE TRUE STERILIZING

AGENTS• 37—41 % SOLN. OF FORMAL-DEHYDE GAS IN WATER

IS A COMMERICIAL FORMULA • DIS-ADVANTAGE: • ITS DIS-ADVANTAGE IS THAT IT IS IRRITATING TO

THE RAW AREAS & IN 2—4 % OF POPULATION, IT MAY INDUCE HYPERSENSITIVITY-REACTION.

• (c) PHENOLS (CARBOLIC-ACID) / LISTER (1827-1912)• (WOUND INFECTION) • THESE ARE ALSO DISINFECTANTS AND THEIR

GREAT ADVANTAGE IS THAT THEIR ACTION IS NOT DECREASED BY THE PRESENCE OF ORGANIC MATTER i.e. BLOOD, PUS OR FAECAL MATTER.

• PHENOL ITSELF IS TOO TOXIC & EXPENSIVE TO BE USED AS A DISINFECTANT.

• THEREFORE OTHER CLOSELY RELATED SUBSTANCES CAN BE USED e.g.

• (I) LYSOL: IT IS COMBINATION OF CRESOL SOLN IN EMULSION OF SOAP

• (II) CRESOL: IT IS ALSO EXTERMLY USED IS HOSP. PRACTCE.

• (III) SUDAL: IT IS ALSO A POWERFULPHENOLIC COMPOUND

• THESE ARE RELATIVELY CHEAP, LESS POISONOUS, THAN PURE PHENOL & ALSO ACTIVE IN THE PRESENCE OF ORGANIC MATTER.

• THEIR MAIN DIS-ADVANTAGE IS THEIR DISAGREEABLE DOUR OR IRRITATING EFFECT ON SKIN

• ANOTHER WIDELY, USED COMPOUND IS CHLORXYLENOL OR

• DETTOL:

THIS IS MUCH LESS IRRITANT & LESS TOXIC THAN ALL THE ABOVE MENTIONED COMPOUNDS, BUT HAS A LESS POTENT ACTION AS ITS ACTION IS ALSO ↓ed BY THE PRESENCE OF ORGANIC MATTER .

• 3) GASEOUS DISINFECTANTS:• 1) FORMAL –DEHYDE GAS: - COLD GAS HAS A

POOR PENETRATION POWER AND ALSO IS ADSORBED BY FABRICS.

• HOT GAS IS MUCH MORE USEFUL AS IT PENETRATES IN FABRICS EASILY.

• MAIN DRAWBACK: ITS MAIN D/B IS THAT AS 3—4 % OF POP.IS SENSITIVE TO PARAFORMAL-DEHYDE, SO IT IS NOT VERY COMMONLY USED AS COMMERCIAL PURPOSE.

• (II) ETHYLENE-OXIDE: - THIS IS COLOUR LESS FLUID, WHICH BOILS AT 120O C AND POWERFUL STERILIZATION AGENT.

• UNLIKE, FORMALIN, IT PENETRATES WELL EVEN THROUGH PLASTICS.

• IT CAN BE USED AT LOW TEMPERATURE, LEAVE NO RESIDUAL MATERIAL.

• IS A DEODOURISER & IS COMPARATIVELY NON-TOXIC.

• IT DOES NOT INDUCE HYPERSENSITIVITY REACTION WHEN USED AT A TEMP. B/W 50—60O C FOR 04 HOURS

• MOREOVER IT EFFECTIVELY STERILIZES THE HOSPITAL INTRUMENTS e.g. ENDOSCOPES, PLASTICS, FABRICS & ELECTRICAL INSTRUMENTS.

• METHODS OF STERILIZATION AND DISINFECTION OF VARIOUS ARTICLES

• 1) BOWLS: • THESE ARE AUTOCLAVED.• 2) BED-PANS: - THESE ARE DISINFACTANT WITH

HEAT / 2.5 % IN CRESOL SOLUTION. • 3) ROOMS: - FORMAL-DEHYDE GAS MAY BE USED

BUT IT IS BETTER TO USE A GOOD CHEMICAL DISINFACTANT e.g.

• POTASSIUM – PERMEGANATE (KMNO4) / (PINKY)• OR CHLORINATED LIME • 4) BED-SHEETS, COTTON-BLANKETS AND BED

COVERS: THESE ARE ALSO BOILED IN THE LAUNDARY-PROCESSING.

• 5) MATRESS & PILLOW- COVERS: - THESE SHOULD BE COVERED IN PLASTICS AND THEIR MEAR WASHING WITH SOAP IS SUFFICIENT ENOUGH.

• DISINFECTION OF SKIN: -• TINCT. OF IODINE IS USED AS

DISINFECTANT IN PRE-OPERATIVE TREATMENT OF SKIN.

• A PASTE- TEST IS PERFORMED BEFORE OPERATION TO DETACT HYPER SENSITIVE PATIENT.

• AN OTHER DISINFECTANT IS 0.5 % CHLORHEXIDINE IN 70 % ETHANOL, BUT POVIDONE –IODINE / BETADINE CONTAINING 1% IODINE IS BETTER.

• AFTER ATTENDING AN INFECTANT PERSON, HANDS SHOULD BE THOROUGHLY WASHED AND THEN IMMERSED IN AN ALCOHOLIC OR HYPOCHLORITE SOLUTION

LIST OF DISINFECTANTS

• (1) IN-ORGANIC DIS-INFECTANTS• POT-PERMEGANATE (KMNO4) / (PINKI)• BLEACHING POWDER (Caocl2)

• TINCT. IODINE

• (2) ORGANIC DIS-INFECTANTS• DETTOL (CHLORXYLENOLE) • PHENOL (CARBOLIC ACID)