Sterilization & Disinfection

INTRODUCTION

• Microorganisms can be found anywhere
• There must be a way to get ride of them

 

Sterilization:

Is the freeing of an article from all living organisms , including viable spores i.e Sterilization is killing or removal of all Microorganisms.

  

Disinfection:

Is partial  freeing of an article from harmful microorganisms.

i.e. is removal of many (not all), microorganism. e.g spores

Note…    

• Disinfection is done whenever we cant do sterilization, the best example is the human organs. 
• Disinfection decreases the chances of infection.

Methods of Sterilization & Disinfection

1. Physical Agents
2. Chemical Agents
3. Mechanical Removal  Methods

1. PHYSICAL METHOD

A. sterilization

1. physical methods,
2. chemical methods,
3. filtration
4. radiation.

1. Physical methods

• Dry heat
• Moist heat

 

Dry heat

Methods of dry heat:

1. Flaming
2. Hot air oven
3. Incineration

 

Red heat (flaming): Sterilize the metal objects 

like bacteriologic loops.

Hot air oven: 

Temperature used 

• 180 C for ½ hour or 
• 170º C for 1 hour 
• Or 160 C for 2 hours . 

Sterilize: The glass objects Metallic objects surgical instrument Powders Fatty oily material.

Incineration: Get rid of all disposal products in hospitals or factories

 B. Moist  heat:

• Autoclave: steam under pressure to raise the temperature to 121 C at 15-17 psi for at least 15 minutes.
•  At this elevated temperature all living cells, including endospores and viruses, are killed. 

 

• Saturated steam under pressure.
• Cheap & nontoxic
• Penetrates fabric
• Method of choice for all items except those which are moisture or heat sensitive.

4 parameters of importance

• Pressure
• Temperature
• Time
• Steam

Air must be removed and steam must reach the item for required time at required temperature

 

Mechanism of action:

• It acts by microbial death due to the denaturation of proteins.

Use to sterilize

• Textiles: This includes cotton, thread, synthetic fibers, etc.
• Metals: This includes instruments, sinks, kidney trays, drum trays, etc.
• Glass or crystal
• Liquids: This refers to distilled water and pharmacological solutions 
• Heat-resistant rubbers and plastics .

 

Sterilization is carried out mainly  at

• 121⁰C, 15 lb/in²  for  15-20 min
• Or 134⁰C, 30 lb/in² for 3 min

  Autoclave: Tests for efficiency 

A. Chemical tapes

B. Physical

• Digital
• Graphs

Notice the change of the colour of the tape

 

 

2. CHEMICAL METHOD

A. Fluids:

Formalin:

• Used for sterilization of theatres for 43 hours
• Can kill tetanus bacteria

3. FILTRATION

• The concept is to have filter with pores smaller than bacteria.
• Used for fluids (blood ,Plasma, serum, reagents , intravenous fluids ,hormones enz…etc) because they may be affected by heat.

 

Cellulose Membrane filter Most commonly used

4. RADIATION

Ionizing Radiation (g rays):

• Kills microbes by damaging DNA
• Used to sterilize plastic equipments like syringe & catheters

DISINFECTION

1. Physical methods (moist heat) 
2. Filtration 
3. Radiation. 
4. Chemical methods

1. Physical methods (moist heat)

• boiling
• Pasteurization

Boiling

At 100ºC is called Boiling, not efficient because it can’t kill the endospores & some bacterial toxins. e.g: boilers .

 

Pasteurization

• Below 100ºC to prevent denaturation of proteins .
• Heating followed by rapid cooling then heating again.
• used to get rid of organisms that transmitted by milk like :
• brucella sp ,coxiella sp ,mycobacterium bovis.

Done by 2 methods:

1. flash method:  72 c for 20 seconds
2. holder method:  63c for 30 minutes

 

 

FILTRATION

•  Some filter keep some organisms and allow others to pass through the filter
• HEPA FILTER:  high efficacy particulate air filter.

RADIATION

•  Ultra violet light

Reduce the number of micro organism to the minimum.

Sources:

• Natural: The Sun.
• Artificial: UV lamps

For disinfection of : operating theatre and theatre equipment's.

CHEMICAL METHODS 

 The most important method ,Used in different daily activities.

Disinfectants : are chemical solutions used to clean inanimate objects

Antiseptics : are chemical solutions used for application to living tissues.

 

  1- Alcohol

• Best Antiseptics for human skin. 
• It is volatile.
• Ethanol  70% is better than 100%. 
  

2- phenols

The famous one is Dettol 5%.

3- Iodine

• Iodine 1% is good for skin but it leaves stain
• Used in surgery 
  
  
  

 4-  Chlorine

• Hypochlorite salts.
• Used to disinfect water.
• Clorox is used to disinfect kitchen & bathrooms.
  
  
  

 

 5- peroxide

• Called oxygen in the market.
• Used to disinfect injuries
• Oral & ear  wash

 6- Formaldehyde & Glutaraldehyde

• Formaldehyde, which is available as a 37% solution in water (Formalin), denatures proteins and nucleic acids.
•  Glutaraldehyde is 10 times more effective than formaldehyde and is less toxic.
•  In hospitals, it is used to Disinfect endoscope , respiratory therapy equipment

 

7- Heavy Metals

• Mercury and silver
• Mercury is used as skin antiseptics.
• Silver nitrate drops
• Silver sulfadiazine is used to prevent infection of burn wounds.

 8- others

• Soap
• Chlorohexidine for oral wash to prevent infections
• Combinations