Training Workshop on “Laboratory Risk Management”2-4 Oct, 2012, • Cairo, Egypt

Disinfection & Sterilization

Dr : Dina RamadanMicrobiologist In Central Health Laboratory

Ministry of HealthQuality Manager

DefinitionsDisinfection:

It is a procedure intended to reduce microorganisms as far as possible (but not bacterial spores) by physical and chemical means

Sterilization:

the complete removal or destruction of all forms of microbial life including bacterial spores

Remember :

No absolute assurance that there is 0 microorganism

Other Definitions

Disinfection

The use of a physical or chemical procedure to eliminate pathogenic microorganisms on inanimate objects

Sterilization

The use of a physical or chemical procedure to destroy all microbial life, including large numbers of highly resistant bacterial spores.

Chemical Disinfectant

Alcohols

• There are two water-soluble alcohol can be used in lab: ethyl alcohol and isopropyl alcohol.

• Concentration required : 60-90% in water• Mode of its action : it denaturing bacterial proteins• its Flammable, Can be removed from disinfected

articles by flaming.

Alcohols effect on bacteria

• they are bactericidal against for the vegetative forms of bacteria (Gram + and Gram -);

• also they are tuberculocidal, fungicidal, and virucidal against enveloped viruses (HIV, influenza ,herpes viruses).

• not effective against bacterial spores and have limited effectiveness against nonenveloped viruses ( adenovirus, rotavirus)

Alcohols

• Higher concentrations are less effective as the action of denaturing proteins is inhibited without the presence of water

Hypochlorite's

• it has broad spectrum antimicrobial effect

• inexpensive and fast acting,

• It is recommended for disinfection of counter tops and work surfaces,

Chlorine

• It is very effective against vegetative bacteria and viruses like HBV and HIV viruses, therefore its use is recommended at 1:10 dilution for disinfection of blood spills

• not much useful against spores

Phenol

• It effective against bacteria

(especially gram +ve bacteria)

and enveloped viruses.

• They are not effective against non

enveloped viruses and spores.

• This compounds is used for decontamination of the hospital environment, including laboratory surfaces.

No Disinfectant is substitute for the following Procedures

• Hand washing (hand hygiene);

• use of personal protective equipment

(PPE )in the lab

• Environmental cleaning

• Appropriate handling of waste and

• Taking care of yourself (e.g. immunization)

Yet no substitute for washing hands

Do not forget to Wash Your Hands

Immediately on arrival at workAfter handling specimensAfter removing glovesAfter using the toiletBefore leaving work

Sterilization

1. Heat sterilization

2. Chemical sterilization

3. Radiation sterilization

Heat Sterilization

It is the simplest, most effective and inexpensive method.

Types of heat sterilization :a) Steam sterilization (Autoclaving)

b) Dry heat sterilization

Mechanism of Action

• DRY HEAT

• protein denaturation

1. Oxidative damage

2. Toxic effects of increased levels of electrolytes

• MOIST HEAT

1. Protein denaturation & coagulation

2. Latent heat liberated when steam condenses on cooler surface

3. Hydrolysis & breakdown of bacterial proteins

Steam Sterilization (MOIST HEAT )

Advantages:– good penetration

– maintains integrity of liquids (e.g. Lubricants) due to the 100% humidity within the chamber.

Disadvantages:– Non stainless steel metal items corrode– may damage plastic and rubber items

Dry-Heat Sterilization• Heating at atmospheric pressure and often use a fan to

obtain uniform temperature by circulation.

• Heat at 180º for half hour , 170º for 1 hr., or 160º C for 2 hrs.

Temperature (°C) Time (minutes)

120 480

140 180

150 150

160 120

170 60

180 30

Dry-Heat Sterilization

• Advantages:• It is effective and safe for metal instruments because

the process does not dull instrument edges or rust/corrode the instruments.

• Disadvantages:– Less reliable than autoclaving

–Many materials do not tolerate

dry heat (as media)

Chemical Sterilization

• The chemical compounds used can be:a) Gas Sterilizationb) Liquid Sterilization

• Generally, chemical sterilization procedures have the disadvantages of presenting health hazards to users (e.g. poisonous, flammable, )

Gas Sterilization

• The gas used in this procedure is ethylene oxide.• Keep objects in constant atmospheric humidity. • Heat to temperatures between 30º and 60º C,for a

period of 10 hrs.• Residual ethylene oxide must be ventilated• It is used for sterilizing endoscopes and ansthetic

apparatus.

Liquid Sterilization

• Can be performed with buffered glutaric aldehyde.

• Procedure:– Immerse object in liquid for several hours.

– Rinse with sterile water after end of procedure.

– It used in hospitals for sterilization of surgical instruments, rubber or plastic equipment

which cannot be heat sterilized

Radiation Sterilization

• Provides effective way of sterilization when using non ionizing radiation in high doses (Gamma radiation ).

• it is clean process

• dry process

• the object full exposure from all directions

Non ionizing radiations• UV RAYS (ultra violet)

are used to sterilize internal Surfaces of safety cabinets, entry ways, Operation theaters etc.

• IR RAYS ( infra red)

are used for rapid mass sterilization of pre packed items such as syringes, catheters etc.

Sterilizing Filter

• Aqueous liquids sterilized by forced passage through filter of porosity small enough to retain any microorganism.

1) Membrane filters:• Manufactured from variety of polymeric material such as

cellulose diacetate, polycarbonate and polyester, as disc.

• Membrane made in 2 waysI. Labyrinthine pore membranes: Bacteria & yeastII. Capillary pore membranes: For viruses

Filters may be supplied with plastic holders pre sterilized for single use, or mounted in re-usable holders and fitted to filtration vessels.

Sterilizing Filter2)Syringe filters:

• Membrane 13-25mm diameter.• Fitted in syringe like holders of stainless steel or

polycarbonate.• Used for sterilization of small volumes of fluid.

3)Vacuum and in- line filters:

• Membranes of 25-45 mm diameter are used either with in line filter holders of Teflon or stainless steel and aluminum.

• Used for sterilization of large volumes of air and liquid.

In summary

• Sterilization and disinfection are costly and time consuming process

• However, it is an essential in all health care facilities to avoid infection.

• It depends the material and users of instrument.

• Staff should keep in mind that contaminated instrument present risk to the sample as well as the user himself.

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