1. STERILIZATION
&
DISINFECTION
By
Dr. Riaz Ahmed

2. 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

3. 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 infestation
On- scabies / louse infestation

4. • 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.

5. • → 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.

6. • 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.

7. • 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

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

9. 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.

10. • 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.

11. 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

12. • ADVANTAGES OF MOIST HEAT OVER DRY HEAT
1) 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

13. • 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.

14. 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.

15. • 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.

16. • 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.

17. 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.

18. • 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.

19. • 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.

20. • 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

21. • 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.

22. • 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

23. • 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.

24. • 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.

25. • 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.

26. • 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

27. • 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 .

28. • 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.

29. • 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.

30. • 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.

31. • 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.

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

33. 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)