Sterilization is a process that eliminates all microorganisms, while disinfection only eliminates pathogenic or disease-causing ones. Physical sterilization methods include heat, radiation, filtration and drying. Moist heat using an autoclave is the most reliable sterilization method. Chemical agents like alcohol, aldehydes, halogens and phenols are also used for sterilization and disinfection. Proper cleaning is important before sterilization or disinfection. Sterilized items are classified based on the risk of infection if contaminated.

1. Sterilisation &
Disinfection
PRESENTER: DR KRISHNA NAIK
MODERATOR: DR HEMANTH KUMAR

2. Sterilization:
Process by which an article, surface or medium is freed of all living
micro organisms either in vegetative or spore state
Disinfection:
The destruction or removal of all pathogenic organisms capable of
giving rise to infection
Rutala WA, Weber DJ. Guideline for disinfection and sterilization in healthcare facilities, 2008.

3. Antisepsis:
The term is used to indicate the prevention of infection , usually by
inhibiting the growth of bacteria in wound or tissues
Bactericidal agents: those who are able to kill
bacteria
Bacteriostatic agents: only prevention of multiplication of bacteria, but
they remain alive

4. Cleaning:
Important preparatory step before sterilisation or disinfection , by
removing soil and other dirty.
Decontamination:
The process of rendering an article or area free of contamination ,
including microbial, chemical, radioactive and other hazards

5. Sterilisation
Physical agents:
 Drying
 Dry heat: by flaming, incineration or hot air
 Moist heat: pasteurization , boiling, steam under pressure.
 Filtration: candle, asbestos pads, membranes
 Radiation
 Ultrasonic and sonic vibration

6. Chemical agents:
 Alcohol: Ethyl, isopropyl, trichlorobutanol
 Aldehydes: Formaldehyde, glutaraldehyde
 Dyes
 Halogenes
 Phenols
 Surface active agents
 Metallic salts
 Gases: Ethylene oxide, formaldehyde , beta propiolactone

7. Drying:
Moisture is essential for growth of bacteria
Drying in air has deleterious effects on many
bacteria
Spores are unaffected.

8. Heat:
Most reliable method of sterilization and should be the method of
choice.
The factors influencing sterilisation by heat:
Nature of heat dry or moist
Temperature and time
Number of microorganisms present
Type of material from which organism have to be eliminated

9. Mode of action
Dry heat : protein denaturation, oxidative damage and toxic
effects of elevated level of electrolytes.
Moist heat: denaturation and coagulation of proteins.

10. Dry heat
1. Flaming: inoculating loop/ wire , tip of forceps and searing
spatulas
2. Incineration: This is excellent method for terminal
sterilisation for biomedical waste. e,g; contaminated cloth,
animal waste and pathological materials

12. Hot air oven:
Holding time: 160°c for 2 hours
uses: glassware, forceps, scissors, scalpels, swab, liquid paraffin, and
fats.
Sterilisation control: spores of clostridium tetani

14. Moist heat:
Moist heat can be categorized into 3 groups
I. Temperature below 100°c
II. Temperature at 100°c
III. Temperature above 100°c

15. Temperature below 100°c
Pasteurisation of milk:
Holding period: 63°c, 30 min or 72°c, 15- 20 min
Target : all nonsporing pathogens
eg: mycobacteria, brucellae, salmonella

16. Temperature at 100°c
Boiling
Not recommended for sterilising but ok for disinfection.
Sterilisation may be promoted by addition of sodium bicarbonate
to the water
Holding period: 30 min

17. Temperature above 100°c
Autoclave (steam sterilizer):
Principle: water boils when its vapour pressure equals the
surrounding atmosphere.
Thus when pressure inside closed vessels increases the
temperature at which water boils increases too.
Flash autoclave: 134°c @ 30psi for 3min
High speed autoclave: 121°c @15psi for 15 min

18. uses: dressing, instruments, laboratory ware, media and
pharmaceutical products .

19. Sterilization control: spore of bacillus strearothermophillus is
used.

21. Filtration
Help to remove bacteria from heat labile liquids
uses : sera and solution of sugar or antibiotics
Principle: as viruses pass through the ordinary filters, filtration
can be used to obtain bacteria free filtration of clinical sample for
virus isolation.

22. Radiation
2 type of radiation
Ionising : gamma rays , high energy electrons
Non -ionising : infrared, UV rays
Gamma rays :
uses: Plastics, syringes, swabs, catheters, animal feeds, oils,
greases.

24. Infrared:
Used for rapid mass sterilisation of prepacked items; syringe,
catheters
UV rays:
Disinfect enclosed area such as entryways, operation theatres and
labs.

25. Ultrasonic and sonic vibration :
High frequency sound waves above 15000 cycle per second can
cause cavitation formation and denaturation of bacterial cell
membranes
Effective bactericidal and germicidal
Ultra sonic vibration act as cleaning agent also.

26. CHEMICALAGENTS
Ideal antiseptic or disinfectant:
Effective against all microorganisms
Be active in presence of organic matter
Effective in acidic as well as in alkaline media
Have speedy action
Be stable
Have high penetrating power
Rutala WA, Weber DJ. Guideline for disinfection and sterilization in healthcare facilities, 2008.

27. Mode of action:
Protein coagulation
Disruption of cell membrane resulting in exposure, damage/ loss
of content
Removal of sulfhydryl group which is essential for normal
functioning of enzyme
Substrate competition

28. Factors that determine the potency of disinfectants:
Concentration of substance
Time of action
pH of the medium
Temperature
Nature of organisms
Presence of extraneous material

29. Alcohol
Frequently used:
Ethyl alcohol
Isopropyl alcohol
Must be used at concentration 60-90%
Mode of action: protein denaturation and coagulation
Rapidly bactericidal rather than bacteriostatic against vegetative
forms of bacteria

30. Also tuberculocidal, fungicidal, and virucidal but do not destroy
bacterial spores
Bactericidal activity drops sharply when diluted below 50%
concentration
Alcohol is used effectively to disinfect oral and rectal
thermometers, scissors and stethoscopes
Isopropyl alcohol was slightly more bactericidal than ethyl
alcohol.
Jolivet et all . Surgical field and skin preparation. Orthopaedics & Traumatology: Surgery &
Research. 2019 ;105(1):S1-6.

32. Aldehyde
Formaldehyde:
Bactericidal , sporicidal and has lethal effect on viruses
Used to preserve anatomical specimens, destroying spores of
anthrax on hair and wool.
Potential carcinogen
Exposure to low level cause asthma like respiratory problems,
skin irritation.

33. Gluteraldehyde:
Effective against tubercle bacilli, fungi, viruses
Less toxic and irritant to eyes, skin
Used to treat corrugated rubber ,anaesthetic rubber , face masks,
plastic ET tube, metal instruments and polythene tubing.

34. Orthophthaladehyde(OPA)
Mode of action :
OPA and glutaraldehyde interact with amino acids, proteins, and
microorganisms
OPA appears to kill spore by blocking the spore germination
process
Microbicidal activity
Costly

35. Cidex: 2.4% glutaraldehyde or 0.55% orthophthaldehyde
Minimum time for immersion 12 min at 25°c
Reuse period is 14 days

36. Dyes
2 groups of dyes:
Aniline dye
Acridine dye
Both are bacteriostatic in high dilution but are of low bactericidal
activity.
Aniline dye is more active aganist gram +ve than gram –ve organisms
Used in microbiology labs as selective agents in culture media.

37. Halogens
Iodine:
Skin disinfectant
Povidone iodine releasing slowly and minimize toxicity
Time required for action iodine 30sec to 2 min
MOA: iodinates of lipids and oxidation of cellular componets.
Active bactericidal ,moderate action on spores.

39. Chlorine:(hypochlorite's)
The most widely used of the chlorine disinfectants
They have a broad spectrum of antimicrobial activity
Inexpensive and fast acting
Remove dried or fixed organisms and biofilms
Uses in floor, blood spills .
Bleaching powder for water supplies, swimming pools and food
and dairy industries.

40. Phenols
Obtained from distillation of coal tar between 170-270°c.
Lethal effect: capacity to cause cell membrane damage releasing
cell contents and causing lysis.
Carbolic acid is widely used in as disinfectants in hospital
Carbolization :5% carbolic acid for 20 min

41. Gases
Types of gases
Ethylene oxide
Formaldehyde gas
Beta propiolactone(BPL)
Ethylene oxide:
Action is due to its alkylating the amino, carboxyl, hydroxyl and
sulphydryl groups in protein molecules .also on DNA and RNA

42. Items: sutures , endoscopic devices, heart lung machines,
clothing

43. Formaldehyde gas:
Employed for fumigation of OT .
After fumigation, the doors should be sealed and left unopened
for 48 hours

44. Beta propiolactone:
Product of ketone and formaldehyde with a boiling point of 163°c.
Rapid biocidal activity but carcinogenic
Capable of killing all microorganisms and is very active against
viruses

45. Surface active agents
Substance that alter the energy relation relationship at interfaces,
producing a reduction in surgfacetension
Widely used as wetting agents, detergents and emulsifiers

46. Metallic salts
Salt of heavy metals have greater action
Eg: salt of sliver , copper and mercury
Protein coagulant and have capacity to combine with free
sulhydry group of cell enzymes.

47. Hydrogen peroxide
MOA: production of hydroxyl free radical that can attack
membrane lipid ,DNA and other essential cell componets.
Bactericidal, virucidal, sporicidal and fungicidal properties
Synergistic sporicidal effects of hydrogen peroxide (5.9%-23.6%)
and acetic acid
Use :effective disinfectant when used on inanimate surfaces

48. Hydrogen peroxide gas plasma:
Low temperature hydrogen peroxide plasma
Short duration time (45 min/cycle)
Low temperature and humidity , no toxic , no chemical residues
Items : laparoscopic instrument, plastic , sutures ets

50. Peracetic acid :
•MOA: Protein denaturation , disrupts cell wall
permeability and oxidizes sulfhydral bonds in protein
,enzymes and other metabolites
•Concentration 0.25% for 12 min at 50ºc.
•Reuse within 24 hr
•Uses: endoscopes and bronchoscopes

51. Spaulding classification :surgical/ medical instruments
based on risk of infection
Critical devices:
enter normally sterile body tissue or vascular system: e.g surgical
instruments, implants, cardiac and urinary catheters.
Sterilisation: ethyline oxide or hydrogen peroxide gas plasma
Semi critical devices:
contact mucous membranes or nonintact skin: e.g: endoscopes,
laryngoscope.
Sterilisation: glutaraldehyde, hydrogen peroxide, ortho phthaladehyde,
peracetic acid.

52. Non critical devices:
Contact intact skin: e.g; sethoscopes, sphygmomanometer
Sterilisation: alcohol, phenols, quaternary ammonium compounds.

55. Sterilization /disinfectant
method
Contact time Application
Alcohol
(chlorehexidine)
2% or 4%+ 70%
isopropyl alcohol(30 sec
to 2min)
Surgical scrub and skin
preparation, hand
hygiene and
thermometers,
sphygmomanometer
Gluteraldehyde 2.4% for minmum
12min at 25°c
Metal instruments
Povidone iodine 5%, 7.5% and 10%(30
sec to 2 min)
Skin preparation, scrub
and wound cleaning
Chlorine (hypochlorite) 5.25%- 6.15%. 12min Blood spillage, Floors,
ICU and wards
Carbolic acid(carbolization) 5% carbolic acid for 20
min
OT , ICU
Ethylene oxide Sutures, endoscopic
devices
Hydrogen peroxide gas
plasma
45 min Laparoscopic
instruments, plastic and
sutures

56. Sterilization /disinfectant
method
Contact time Application
Autoclave Flash:134°c@30 psi for
3min
High speed:121°@ 15psi
for 15 min
Metal instrument,
dressing pads
Gamma radiation Sutures, syringes,
catheters