number 6

Done by Narjes Alsammak

Corrected by Salsabeel Fleifel

Doctor Hamed Al Zoubi

Sterilization and disinfection

Terms:

-Sterilization: Elimination or deactivation of all forms of life (biological

entities: bacteria, viruses, prions)

باختصار عملية التعقيم هي القضاء على أي شكل من أشكال الحياة حيث تتم إبادة جميع

الميكروبات

-Disinfection: Reduction of pathogenic organisms to a level at which they

no longer constitute a risk (for non-living tissue/objects/ tools)

-Antisepsis: Same concept as disinfection but used on living tissue such as

wound (skin).

Methods of Sterilization:

1- Heat (dry – moist )

2- Radiation ( ionizing radiation – I.R rays – U.V rays )

3- Filtration

4- Chemical agents ( sterilization and disinfection)

1-Heat:

-Most reliable and widely applicated method.

-temperature above 100°C ensures that bacterial spores are killed,

cannot kill prions.

-Shorter applications of lower temperatures, such as in pasteurization,

can effectively remove specific infection hazards (Milk, Juice).

We have TWO kinds of heat: A-dry

B-moist

A-Dry heat:

-The most common method.

-Kills by sabotaging the oxidative process.

We have TWO kinds of dry heat: red – flaming

Red heat:

• Direct exposure to the flame until the item becomes red.

• Applications: sterilizing bacteriological loops, knives, blades...etc.

Flaming:

• Indirect exposure to the flame (killing of organisms present on the

surface of slides, mouth of culture tubes...etc.

Incinerator (:)محرقة Huge metal compartment used for burning objects that

cannot be cleaned. Also used for disposal of hospital waste.

Hot air oven: Expose the item to 160-170 °C for 1-2 hrs.

It has (electric element, source of heat, fan to distribute the heat).

Uses: sterilization of items which lack water (such as metals glassware).

B- Moist heat: (using water steam)

-steam is non-toxic, non-corrosive.

-the energy is considerable: 6 L (at temperature 134 °C, P= 3) condense to 10

ml gives 2162 J of heat energy.

- kills microorganisms by denature proteins

- for effective sterilization:

a. dry: does not contain water droplet.

b. saturated: hold all the water that can be in the form of vapor.

Note: when the dry saturated steam meets a cooler surface it condenses into

a small volume of water and the heat of vaporization is decreased.

moist heat could be : above 100, at 100, or below 100 °C.

• below 100°C: pasteurization, inspissation.

1- pasteurization:

o temp 72 °C, 20 secs, followed by rapid cooling (flash method).

o temp 63 °C, 30 min (holder method). Used to inactivate harmful

organisms in milk.

2- Inspissation: exposure of the media to humid heat at 75 °C on 3 days

(media contains protein : serum)

• At 100°C: boiling , Tyndallisation. 1- Boiling: 100°C, 5-10 min ( glass wares , forceps , scalpels )

2- Tyndallisation: 100°C, 20-30 min for 3 days ( metals that cannot

stand prolonged boiling (media containing sugar and gelatin).

• Above 100 C: autoclaving (standard : most efficient, reliable) o Though double walled chamber in which air is replaced by pure

saturated steam under pressure

o Same principle as pressure cooker (water boils at increased atm

pressure => boiling point below 100 )

o Equipment subjected high pressure ( saturated steam ) for 121C,

15-20 min depending on size of load and contents

o Uses : sterilize most of the instrument , culture media

• Monitoring autoclaves: the most used method in hospitals. 1- Chemical: sensitive chemicals which change in color at the right

temperature and time (autoclave tape, Browne's tube). 2- Biological: A spore-bearing organism is added during sterilization,

then cultured later to ensure that it has been killed. E.g: bacillus

stearothermophilus spores.

يتم وضع كائن يتحمل درجات حرارة عالية خالل عملية التعقيم وبعد االنتهاء يتم وضع

وسط لينمو. إذا لم ينمو هذا يعني أن ذلك الكائن مات، أي عملية التعقيم هذا الكائن في

.تمت بنجاح

2-Radiation:

• Not efficient for complete sterilization.

• Reduce number of bacteria in a certain area (operating theater).

o ionizing radiation:

-short wave length, high energy (gamma rays)

-moderate dose is lethal for microorganisms.

-Uses: pre-packed disposable plastic items that cannot stand

heat. (plastics syringes, catheters, gloves).

o Infra-red rays:

-heating, temperature reaches 180°C.

-Uses: mainly for glassware and syringes.

3-Filtration:

-Mechanism: Mechanically removes microorganisms by passage

liquid or gas through a screen (material with

pores)منخال done under negative or positive pressure.

-Application: Filtration is the preferred method of sterilizing certain

solutions which are more likely to be damaged by heat. E.g. IV fluids,

Antibiotic solutions, vaccines, enzymes, and some culture media.

-Membrane filter: (most common)

-Uniform pore size used in industry and researches

According to size:

a. 0.22-0.45 pores: most bacteria, cannot filter viruses,

mycoplasms or spirochetes.

b. 0.01 pores: can filter all viruses and some large proteins.

3-Chemicals agents:

a.Ethylene oxide:

o denature proteins and DNA by cross linking functional groups.

o Uses: sterilizing heat sensitive material (surgical instrument,

plastics, endoscopes, anesthetic apparatus).

o WARNING: highly inflammable, potentially explosive gas.

b.Aldehydes:

o denature proteins and inactivate nucleic acids.

o 1-Formaldehyde gas: operating theater and other spaces

o 2-Glutraldehyde (a chemical relative of formaldeyde):

less irritating, more effective than formaldehyde, used to

disinfect hospital instruments including endoscopes and

respiratory therapy equipment.

c.Halogens : denature or oxidize enzymes

(iodine, chlorine) --> effective antimicrobial agents.

Iodophores (Betadine) chlorine: treatment of drinking water, bleach.

d.Oxidizing agent :(peroxidase and ozone) --> kill by oxidation of

microbial enzymes.

1-hydrogen peroxidase: disinfects and sterilizes surfaces of objects.

2-ozone: treatment of drinking water.

e.Alcohol : denatures proteins, dissolves lipids which leads to cell

membrane disintegration.

-kills bacteria and fungi but does not kill spores.

-swabbing of skin with 70% ethanol prior to injection is preferred.

-most common: ethanol, isopropanol.

The choice between sterilization and disinfection depends on:

1- Nature of the item to be treated.

2- Likely microbial contamination.

3- Risk of transmitting infection.

Measurement of microbial death:

survivor curve, D value:dose required to inactivate 90% of the initial

population.

Resistance to sterilization and disinfection:

1- Vegetative bacteria and viruses are more susceptible.

2- Bacterial spores are the most resistant.

3- Within different species and strains of species, there may be wide

variation in intrinsic resistance (structure, growth conditions).

4- Prions: highly resistant, use disposable instrument.

يز هاكونا ماتاتا حكمة نغمها لز