sterilization and disinfection for 4th year MBBS

1. •‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬

2. Sterilization and Disinfection
Dr . Nadir Mehmood
Asstt Prof of Surgery
RMC

3. Learning Objectives
At the end of the discussion, a student will be able to;
• Define terms in relation to topic
• Classify methods of sterilization and disinfectives
• Enumerate the merits of different methods
• Indicate the choice of method for different
instruments and procedures
• Identify sequence followed in the CSSD
• Identify categories of critical and noncritical items

4. WHY NEEDED?
• Microorganisms are ubiquitous.
• Since they cause contamination,
infection and decay, it becomes
necessary to remove or destroy
them from materials or from
areas.
• This is the object of sterilization.

5.  The process of sterilization is used
• in microbiology for preventing contamination by extraneous
organisms,
• in surgery for maintaining asepsis,
• in food and drug manufacture for ensuring safety from
contaminating organisms, and
• in many other situations.
 The methods of sterilization employed depend on
• the purpose for which it is carried out,
• the material which has to be sterilized and
• the nature of the microorganisms that are to be removed or
destroyed.

6. Definition of terms
• Cleaning - the physical removal of organic
material or soil from objects, is usually done by
using water with or without detergents.
• Sterilization is the destruction of all forms of
microbial life; it is carried out in the hospital with
steam under pressure, liquid or gaseous
chemicals, or dry heat.
• Disinfection, defined as the intermediate
measures between physical cleaning and
sterilization, is carried out with pasteurization or
chemical germicides.

7. FUNCTIONS & ACTIVITIES of CSSD
CSSD
Rinsing
cleaning
Drying
checking
sterilizationLabelling
Storage
Issue &
Distribution
Receipt

8. Various Agents In Sterilization
PHYSICAL AGENTS CHEMICAL AGENTS
Sunlight
Alcohols:
Ethanol, isopropyl
Drying
Aldehydes:
Formaldehyde, Glutaraldehyde
Dry heat :
Hot air oven, Incineration, Flaming
Dyes
Moist heat:
Boiling, Pasteurization, tyndallisation,
Autoclaving
Halogens
Filtration Phenolic compounds
Radiation
Ionizing, Non Ionizing
Gases
Ethylene oxide, Formaldehyde, beta
propiolactone(BPL).
Ultrasonic vibration Metallic salts and surface active agents

9. Physical Agents:
Sunlight
•Direct sunlight is a natural method of sterilization of water in tanks, rivers and
lakes.
•Direct sunlight has an active germicidal effect due to the combined effect of
ultraviolet and heat rays.
Drying
•4/5 of the bacterial weight is due to water.
•Therefore drying in air has deleterious effect on many bacteria.
•This is unreliable method, spores are unaffected by drying.
Dry heat
Flaming:
Inoculating loop or wire, the tip of forceps are held in a Bunsen flame till they
become red hot.
Incineration:
This method is used to destroy contaminated cloth, animal carcasses and
pathological materials.

10. Physical Agents: cont..
Hot air oven
This method is applicable to metals, glassware, and some heat-
resistant oils and waxes that are immiscible in water.
Conditions
171ºc for at least one hour.
160ºc for at least two hour.
121ºc for at least sixteen hour.
Moist Heat:
Flash autoclaves use 134°C for 3 minutes.
Method Uses Comments
Water < 100°c (Pasteurization) For sterilization of serum, vaccines
and body fluids.
62°c for 15 min.
72°c for 30 sec.
Spores are not destroyed.
Water at 100°c For sterilization of glassware's, metal
and rubber items.
Some spores are not destroyed.
Arnold steamer:
Stream at atmospheric pressure
For sterilization of culture media
containing gelatin and sugar.
Preserves properties of media.
Autoclave :
Steam above atm pressure
For sterilization of culture media and
laboratory materials.
121°c at 15 psi for 15-20 minutes.
Almost Kills all the bacteria and spores.

11. Physical Agents: cont..
Filteration:
Filtration helps to remove bacteria from large volumes of
fluid, especially fluid containing heat-labile components such as
sera, solution of sugars and antibiotics.
A pore size of 0.2 m is effective because filters act not only
mechanically but by electrostatic adsorption of particles to their
surface.

12. Physical Agents: cont..
RADIATION
Non Ionisizing radiation:
Types Produced by Mode of action Uses Comments
Low energy
(Infrared and
ultraviolet rays)
UV lamps DNA damage Infrared rays:
Sterilization of prepacked
items such as syringes
and catheters.
Ultraviolet rays:
Used for disinfecting
operation threatres and
laboratories.
Use of UV light
is limited by
penetration and
hazardous.
Ionisizing radiation:
High energy
ionizing type
(Gamma rays and
high energy
electrons such as
X-rays and
cosmic rays)
Cobalt-60
based
instruments
DNA damage For the sterilization of
antibiotics, hormones
and other prepacked
disposable items such
as catheters, gloves,
syringes, infusion sets,
oils, animal feeds, etc.
They are
expensive.
They are very
effective due to
high penetrative
power.

13. Physical Agents: cont..
Ultrasonic and sonic vibration:
They have the property to disrupt the cells but the results have been variable.
 Gram negative rods are more sensitive to ultrasonic vibration whereas Gram
positive cocci, spores of fungi and bacteria are resistant to the vibration.
 Ultrasonic devices are used in dental.
 However, most sonic machines are not reliable for routine use.

14. Chemical Agents: cont..
Properties of Ideal antiseptics or disinfectants should
 Effective against all microorganisms and have a wide spectrum of
activity.
Have speedy action.
Be effective in presence of organic matter.
Be effective in varying pH(acidic and alkaline medium).
Be stable.
Also compatible with other antiseptics and disinfectants.
Have high penetrating power.
Not corrode metals.
Not cause local irritation or sensitization.
Not interfere with healing.
Not be toxic if absorbed into circulation.
Be cheap and safe.

15. The level of disinfection achieved depends on
several factors:
• contact time
• temperature
• type and concentration of the active
ingredients of the chemical germicide
• the nature of the microbial contamination.

16. Mechanisms of action of antiseptic
and disinfectants
• Oxidation of bacterial protoplasm
– Potassium permagnate, H202, Halogens
• Co-agulation (denaturation) of bacterial
proteins & disrupt cell membrane
– Phenols, chlorhexidine, alcohols, aldehydes
• Detergent like action ↑ permeability of
bacterial cell membrane
– Cetrimide, soaps

17. Types of disinfection
• High-level disinfection: can be expected to
destroy all microorganisms, with the exception of
large numbers of bacterial spores.
• Intermediate disinfection: inactivates
Mycobacterium tuberculosis, vegetative bacteria,
most viruses, and most fungi; does not
necessarily kill bacterial spores.
• Low-level disinfection: can kill most bacteria,
some viruses, and some fungi; cannot be relied
on to kill resistant microorganisms such as
tubercle bacilli or bacterial spores.

18. Medical devices, equipment, and surgical
materials are divided into three general
categories based on the potential risk of
infection involved in their use:
critical items
 semicritical items
 noncritical items

19. Critical items
• Critical items are instruments or objects that are
introduced directly into the bloodstream or into other
normally sterile areas of the body.
Examples of critical items are surgical instruments,
cardiac catheters, implants, pertinent components of
the heart-lung oxygenator, and the blood compartment
of a hemodialyzer.
Sterility at the time of use is required for these items;
consequently, one of several accepted sterilization
procedures is generally recommended.

20. Semicritical items
• These items come in contact with intact mucous membranes,
but they do not ordinarily penetrate body surfaces.
Examples are noninvasive flexible and rigid fiberoptic
endoscopes, endotracheal tubes, anesthesia breathing circuits,
and cystoscopes.
Sterilization is not absolutely essential; at a minimum, a high-
level disinfection procedure that can be expected to destroy
vegetative microorganisms, most fungal spores, tubercle
bacilli, and small nonlipid viruses is recommended. In most
cases, meticulous physical cleaning followed by an appropriate
high-level disinfection treatment gives the user a reasonable
degree of assurance that the items are free of pathogens.

21. Noncritical items
• Noncritical items are those that either do
not ordinarily touch the patient or touch
only intact skin.
Such items include crutches, bedboards,
blood pressure cuffs, and a variety of other
medical accessories.
These items rarely, if ever, transmit disease.
Consequently, washing with a detergent may
be sufficient.

22. • Items must be thoroughly cleaned before
processing, because organic material (e.g.,
blood and proteins) may contain high
concentrations of microorganisms. Also, such
organic material may inactivate chemical
germicides and protect microorganisms from
the disinfection or sterilization process.

23. For noncritical items
cleaning can consist only of
1) washing with a detergent or a disinfectant-
detergent,
2) rinsing,
3) thorough drying.

24. Steam sterilization
• Steam sterilization is the most inexpensive and
effective method for sterilization.
• Steam sterilization is unsuitable for processing
plastics with low melting points, powders, or
anhydrous oils.
• Items that are to be sterilized but not used
immediately need to be wrapped for storage.
• Sterility can be maintained in storage for various
lengths of time, depending on the type of wrapping
material, the conditions of storage, and the integrity
of the package.

28. Monitoring of steam sterilization processes
• to check the highest temperature that is
reached during sterilization and the length of
time that this temperature is maintained
• heat- and steam-sensitive chemical indicators
can be used on the outside of each pack
• a large pack might have a chemical indicator
both on the outside and the inside to verify
that steam has penetrated the pack

29. Microbiological monitoring
Microbiological monitoring of steam
sterilizers is recommended at least once a
week with commercial preparations of
spores of Bacillus stearothermophilus (a
microorganism having spores that are
particularly resistant to moist heat, thus
assuring a wide margin of safety).

30. Ethylene oxide gas sterilization
• It is a more complex and expensive
process than steam sterilization
• It is usually restricted to objects that
might be damaged by heat or excessive
moisture.
• Before sterilization, objects also need to
be cleaned thoroughly and wrapped in a
material that allows the gas to penetrate.

31. • Because ethylene oxide gas is toxic, precautions
(e.g., local exhaust ventilation) should be taken
to protect personnel. All objects processed by
gas sterilization also need special aeration
according to manufacturer's recommendations
before use to remove toxic residues of ethylene
oxide.
• Chemical indicators need to be used with each
package to show that it has been exposed to the
gas sterilization process.
• Moreover, it is recommended that gas sterilizers
be checked at least once a week with commercial
preparations of spores, usually Bacillus subtilis.

32. • Powders and anhydrous oils can be sterilized
by dry heat. Microbiological monitoring of dry
heat sterilizers usually provides a wide margin
of safety for dry heat sterilization.
• Liquid chemicals can be used for sterilization
and disinfection when steam, gas, or dry heat
sterilization is not indicated or available

33. Chloroxylenol (Dettol)
• Phenol derivative
• Does not co-agulate proteins,
• Non corrosive,Non irritating to skin
• Commercial 4.8 % solution used for surgical
antisepsis
• Skin cream and soap: 0.8%
• Mouth wash 1%

34. Oxidizing agents
• Potassium permagnate:
– Purple crystals, highly water soluble, liberates
oxygen which oxidizes bacterial protoplasm.
– Used for gargling, irrigating wounds, urethra
(condy`s lotion diluted solution of 1:4000 to
1:10,000 )
– High conc cause burns
– It is also used to disinfect water in ponds.
– Stomach wash in alkaloidal poisoning

35. Oxidizing agents
Hydrogen Peroxide
– liberates nascent oxygen which oxidizes necrotic
matter & bacteria.
– Helps in loosening & removing slough, ear wax
etc.
Benzoyl Peroxide
– Widely used drug for acne.
– liberates O2 in presence of water which kills
bacteria, specially anaerobes

36. Halogens
• Iodine,
• Iodophores,
• Chlorine,
• Chlorophores

37. Iodine
• Rapidly acting broad spectrum (bacteria,
fungi,virus)
• Acts by iodinating and oxidizing microbial
protoplasm.
• Used for cuts, degerming skin beforesurgery.
• Adverse effect: cause burns & blisters

38. Iodophores
• Known as povidine iodine.
• Non toxic, non staining prolonged action.
• Used on boils, furunculosis, burns, ulcers,
tinea, surgical srub, disinfecting surgical
instruments, non specific vaginitis.

39. Chlorine
• potent germicide. Kills pathogens in 30 sec.
used to disinfect urban water supplies.
• 0.1 to 0.25 ppm

40. Cholorophores
(1) Chlorinated lime (bleaching powder)
– obtained by action of chlorine on lime.
– used to disinfect drinking water
(2) Sodium hypochlorite
– Powerful disinfectant used in dairies for milk
cans.
– Too Irritant to be used as antiseptic.
– Root canal therapy in dentisry

41. Biguanides
Chlorhexidine: (Savlon)
– Acts by disrupting bacterial cell membrane &
denaturation of bacterial proteins
– Non irritant ,more active against gram +ve
bacteria.
– Used in for surgical scrub, neonatal bath, mouth
wash & general skin antiseptic.
– Most widely used antiseptic in dentisry 0.12-0.2%
oral rinse or 0.5 -1 % tooth paste

42. Quarternary ammonium antiseptics
cetrimide
• Detergents: Cidal to bacteria, fungi & viruses.
• Act by altering permeability of cell membrane
• Efficiently remove dirt and grease
• Widely used as antiseptics & disinfectants for
surgical instruments, gloves etc
• Combined with chlorhexidine (savlon)

43. Soaps
• Anionic detergents
• Weak antiseptics with cleansing action
• Washing with soap and warm water one of
the most effective methods of preventing
disease transmission
• Affect only Gm+ bacteria

44. Dyes
Gentian violet:
– Active against bacteria (gram + ve), fungi
– Used on chronic ulcers, furunculosis, bed sores,
ring worms.
Acriflavine
– Active against gram +ve bacteria & gonocci
– suitable for chronic ulcers & wounds
– Do not retard healing, non irritant

45. Microbial Characteristics and Microbial
Control
Figure 7.11

46. No Disinfectant is substitute for the
following Procedures
• 􀂾 Hand washing (hand hygiene);
• 􀂾 The use of personal protective equipment (e.g.
gloves) when handling blood, body
• substances, excretions and secretions;
• 􀂾 Appropriate handling of patient care equipment
and soiled linen;
• 􀂾 The prevention of needle stick/sharp injuries;
• 􀂾 Environmental cleaning
• 􀂾 Appropriate handling of waste and
• 􀂾 Taking care of yourself (e.g. immunization)