sterlization procedures and disinfection

7/31/2019 Sterlization Procedures and Disinfection

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deepika m



Decontamination

the process of removal of contaminatingpathogenic microorganisms from the

articles by a process of sterilization ordisinfection

use of physical or chemical means toremove, inactivate, or destroy living

organisms on a surface so that theorganisms are no longer infectious.



Decontamination steps

CLEANING

STERLIZATION

STEAM DRY CHEMICAL

DISINFECTION

HIGH LEVELINTERMEDIATE

LEVELLOW LEVEL



CLASSIFICATION OF INSTRUMENTSDEPINDING UPON ITS USE

CRITICAL

penetrate softtissue or bone,

enter thebloodstream ornormally sterile

tissue.

forceps, scalpels,bone chisels,scalers and

surgical burs

steam underpressure

(autoclaving), dryheat, or

heat/chemicalvapor

SEMICRITICALcontact mucousmembrane or

non-intact skin

mirrors,impression trays,amalgamcondensers,Endoscopes,Anesthesia

equipment

High leveldisinfection

NONCRITICALobjects thattouch onlyintact skin

x-ray heads,blood pressurecuffs and pulse

oximeters

Low leveldisinfection



DISINFECTION Process of elimination of most pathogenic

microorganisms (excluding bacterial spores) oninanimate objects

Achieved by :-physical methods

chemical methods

STERLIZATION process where all the living microorganisms,

including bacterial spores are killed.Achieved by :-physical

chemical

physiochemical methods



Classification of disinfectants:Based on consistency

Liquid (E.g., Alcohols, Phenols)

Gaseous (Formaldehyde vapor, Ethylene oxide)

Based on spectrum of activity

High level

Intermediate level Low level

Based on mechanism of action

Action on membrane (E.g., Alcohol, detergent)

Denaturation of cellular proteins (E.g., Alcohol, Phenol)

Oxidation of essential sulphydryl groups of enzymes (E.g.,H2O2, Halogens)

Alkylation of amino-, carboxyl- and hydroxyl group (E.g.,Ethylene Oxide, Formaldehyde)

Damage to nucleic acids (Ethylene Oxide, Formaldehyde)



Chemical methods of disinfection

chemicals are known as disinfectants.

Properties :-

Should have wide spectrum of activity

ƒShould be able to destroy microbes within practical periodof time

ƒShould be active in the presence of organic matter

ƒShould make effective contact and be wettable

ƒShould be active in any pH

ƒShould be stable

ƒShould have long shelf life, high penetrating power ƒShould be non-toxic, non-allergenic, non-irritative or non-

corrosive

ƒShould not have bad odour

ƒShould not leave non-volatile residue or stain

ƒShould not be expensive and must be available easily



High Level Disinfection (HLD)

There are three types of HLD:

Disinfection by boiling

Moist heat at 70-100°C

Chemical disinfection by:-Ethylene Oxide,

Gluteraldehyde,

Formaldehyde



Low level disinfection by:-

Alcohols,

quaternary ammonium compounds

Intermediate level disinfectionby:-

Phenolics

halogens



Mechanism of action

ALCOHOLS:

Mode of action: Alcohols dehydrate cells, disruptmembranes and cause coagulation of protein.

Examples: 70% Ethyl alcohol, isopropyl alcohol andmethyl alcohol

Uses:disinfect surfaces

clinical thermometers

methyl alc kills spores

Disadvantages: Skin irritant, volatile (evaporatesrapidly), inflammable



ALDEHYDES:

Mode of action: Acts through alkylation of amino-,carboxyl- or hydroxyl group, and probably

damages nucleic acids. It kills all microorganisms,

including spores.

Examples: Formaldehyde, Gluteraldehyde

Uses :40% Formaldehyde (formalin) is used for

surface disinfection and fumigation of rooms,

chambers, operation theatres, biological safety

cabinets, wards, sick rooms etc

Disadv : Vapors are irritating, has poor penetration,

leaves non-volatile residue, activity is reduced in

the presence of protein



PHENOLS

act as disinfectants at high concentration and as

antiseptics at low concentrations used to prevent infection of surgical wound

Disadv:toxic, corrosive and skin irritant.

HALOGENS

Iodophores permit slow release and reduce the irritationof the antiseptic.

For hand washing iodophores are diluted in 50%alcohol.

10% Povidone Iodine is used undiluted in pre andpostoperative skin disinfection

Disadv: Rapidly inactivated in the presence of organicmatter.

Iodine is corrosive and staining.



HYDROGEN PEROXIDE:

Mode of action: acts on the microorganisms

through its release of nascent oxygen.Produces

hydroxyl-free radical that damages proteins and

DNA.

Application: It is used at 6% concentration to

decontaminate the instrumentes for 20 – 30 min,

equipments such as ventilators. 3%

Hydrogen Peroxide Solution is used for skin

disinfection and deodorising wounds and ulcers.

Strong solutions are sporicidal.



HLD BY BOILING

best achieved by moist heat such as boiling in water

(100°C for one minute holding time)

kills all organisms

except for a few bacterial spores. note that boiling equipment items in water will not

achieve sterilization.



STERLIZATION METHODS

STERLIZATION

PHYSICAL

SUNLIGHT HEAT VIBRATION RADIATION FILTRTION

CHEMICALPHYSIOCHEM

ICAL



HEAT

DRY HEAT

RED HEAT

FLAMING

INCENERATION

HOT AIR OVEN

INFRARED

MOIST HEAT

BELOW 100DEGREE

AT 100

ABOVE 100



DRY HEAT: Red heat : Articles such as bacteriological

loops, straight wires, tips of forceps andsearing spatulas holding them inBunsen flame become red hot.

This is a simple method for effectivesterilization



Flaming:

Passing the article over a Bunsen flame, but notheating it to redness.

Articles such as scalpels, mouth of test tubes, flasks,glass slides and cover slips are passed through theflame a few times.

Most vegetative cells are killed, there is no guaranteethat spores too would die on such short exposure.

This method too is limited to those articles that can be

exposed to flame. Cracking of the glassware mayoccur.



Incineration:

Method of destroying contaminated material by

burning them in incinerator.

Articles such as soiled dressings; animal carcasses,

pathological material and bedding etc should be

subjected to incineration.

This technique results in the loss of the article, hence is

suitable only for those articles that have to be disposed.

Burning of polystyrene materials emits dense smoke,

and hence they should not be incinerated.



Hot air oven:

Introduced by Louis Pasteur.

Articles to be sterilized are exposed to high

temperature (160C) for duration of one hour in

an electrically heated oven.

Articles sterilized: Metallic instruments (like

forceps, scalpels, scissors), glasswares (such as

petri-dishes, pipettes, flasks, all-glass syringes),swabs, oils, grease, petroleum jelly and some

pharmaceutical products.



Sterilization process:

Articles to be sterilized must be perfectly dry before

placing them inside to avoid breakage. Articles must be placed at sufficient distance so as to

allow free circulation of air in between

Sterlization cycle

60 minutes at 160C 40 minutes at 170C

20 minutes at 180C.

Increasing temperature by 10 degrees shortens thesterilizing time by 50 percent.

The hot air oven must not be opened until thetemperature inside has fallen below 60C to preventbreakage of glasswares.



Advantages: It is an effective method of sterilization

of heat stable articles. The articles remain dry after

sterilization.

This is the only method of sterilizing oils and

powders.

Disadvantages:

ƒSince air is poor conductor of heat, hot air has

poor penetration.

ƒCotton wool and paper may get slightly charred. ƒGlasses may become smoky.

ƒTakes longer time compared to autoclave.



Infra red rays: Brings sterilization by generation of heat

Articles to be sterilized are placed in a movingconveyer belt and passed through a tunnel that isheated by infrared radiators to a temperature of 180C.

The articles are exposed to that temperature for aperiod of 7.5 minutes.

Articles sterilized included metallic instruments andglassware. It is mainly used in central sterile supplydepartment

Not applicable in diagnostic laboratory



Moist heat

Destroys through irreversible coagulationof proteins

Moist heat includes

BoilingPasteurization

Pressurized steam



Boiling (100 C)

Destroys most microorganisms and viruses

Not effective means of sterilization

Does not destroy endospores

Pasteurization(below 100deg)

Pasteur developed to avoid spoilage of wine

Does not sterilize but significantly reduces organisms

Used to increase shelf life of food

Most protocols employ HTST method,Heated to 72°C

and held for 15 seconds Other protocol UHT(ultra high temp)Heated to 140°C -

150°C, held for several seconds then rapidly cooled



Pressurized steam(above100deg)

Autoclave used to sterilize usingpressurized steam

Heated wate steamincreased pressure

Preferred method of sterilization Achieves sterilization at 121°C

and 15lbs in 15 minutes

Effective against endospores

Flash autoclaving sterilizes at

135°C and 15lbs in 3 minutes Prions destroyed at 132°C and

15lbs for 4.5 hours



Other Physical Methods

of ControlHeat sensitive materials require other methods of

microbial control

Filtration

Irradiation

High-pressure treatment



Filtration

Membrane filtration

used to remove microbes from fluids and air

Liquid filtration

Used for heat sensitive fluids

Membrane filters allow liquids to flow through

Traps microbes on filter Depth filters trap microbes using electrical charge

Filtration of air

High efficiency particulate air (HEPA) filter removenearly all microbes from air

Filter has 0.3µm pores to trap organisms



Radiation

Electromagnetic radiation

Energy released from waves Based on wavelength and frequency

Shorter wavelength, higher frequency = more

energy

Range of wavelength is electromagnetic spectrum Radiation can be ionizing or non-ionizing



Ionizing radiation

Radiation able to strip electrons from atoms

Three sources

Gamma radiation

X-rays

Electron accelerators

Causes damage to DNA and potentially to plasmamembrane

Used to sterilize heat resistant materials

Medical equipment, surgical supplies,

medications Some endospores can be resistant



Non-ionizing radiation

Ultraviolet radiation

Only type to destroy microbes directly

Damages DNA

Causes thymine dimersUsed to destroy microbes in air, drinking water

and surfaces

Limitation

Poor penetrating powerThin films or coverings can limit effect



High pressure processing

Used in pasteurization of commercial foods

Does not use high temperatures

Employs high pressureUp to 130,000 psi

Destroys microbes by denaturing proteins and

altering cell membrane permeability



Sterlization control

Three methods exist to check the efficacy of

sterilization process

Physical

Chemical Biological.



ƒPhysical: Temperature chart recorder andthermocouple.

ƒChemical: Browne’s tube No.3 (green spot,color changes from red to green)

ƒBiological: 10^6 spores of Bacillus subtilisvar niger or Clostridium tetani on paper stripsare placed inside

envelopes and then placed inside the hot airoven.Upon completion of sterilization cycle, the

strips are

removed and inoculated into thioglycollate brothor cooked meat medium and incubated at 37Cfor 3-5 days. Proper sterilization should kill the

spores and there should not be any growth.



SummaryDisinfection and sterilization guidelines must be

followed to prevent exposure to pathogens that

may lead to infection

Delivery of sterile products for use in patient care

depends not only on the effectiveness of the

sterilization process but also on cleaning,

disassembling and packaging of the device,

loading and monitoring the sterilizer

sterlization procedures and disinfection

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