1. Microbiology &Immunology Course Associate Professor of Microbiology
NAJRAN UNIVERSITY
College of Medicine
Microbiology &Immunology Course
Lecture No. 8 By
Dr. Ahmed Morad Asaad
Associate Professor of Microbiology

2. STERILZATION AND DISINFECTION
DEFINITIONS
Sterilization is the complete inactivation of all forms of microbial life.
Antiseptics are compounds that are applied topically to human tissue. Antiseptics either inhibit the growth of microorganisms or they kill them, without adversely affecting the human tissue to which they are applied.
Disinfectants are compounds that kill microorganisms. (except bacterial endospores). Because they may be harmful to human tissue, disinfectants are usually reserved for use on inanimate objects

3. Disinfectants are either:
1‑ High‑level disinfectants kill mycobacteria, viruses, and all but the most resistant spores.
2‑ Low‑level disinfectants kill many vegetative bacteria and most viruses, but they are ineffective against mycobacteria or bacterial spores

4. Why we are in need for proper techniques of sterilization and disinfection?
1‑ Safety in the laboratory depends on using sterile or aseptic techniques in handing microorganisms.
2‑The patient's safety depends on using proper methods of sterilization to prepare instruments, intravenous solutions and needles.
3‑ The accuracy and validity of microbiological tests depend on the proper use of techniques for sterilization and disinfection.

5. Sterilization Physical means Chemical means Heat Radiation Filtration
Dry heat
Moistheat

6. Dry heat
a) Red heat: as in the sterilization of the bacteriological loop by heating in the Bunsen flame till it is red hot.
b) Hot air oven: It is the main means of sterilization by dry heat. The oven is an isolated double walled metal chamber that is heated by electricity, and has a thermostat that maintains the chamber air constantly at the chosen temperature. A temperature of 160ºC for 1 hr. is usually employed. This method is used for the sterilization of glassware such as, test tubes, Petri dishes, flasks, pipettes and all‑glass syringes.
c) Incineration : this used for the destruction of contaminated materials and bodies of dead animals.

7. Moist heat Moist heat at temperature < 100 ºC:
Pasteurization of Milk
The milk is heated either at 63ºC for 30 min. or at 72ºC for 20 sec. this process will destroy all the non‑spore forming pathogens such as Mycobacterium tuberculosis, Brucella abortus and various Salmonella that may be found in milk.

8. Moist heat at temperature of 100 ºC:
1- Boiling at 100ºC for10 min: is a method for the sterilization of glass or partly metal partly glass syringes and instruments such as, scalpels, forceps and scissors.
2- Steaming at 100ºC: This is done in the steamer or the Koch's sterilizer which is a vertical metal cylinder with a removable conical lid, having a small opening for the escaping steam. The articles to be sterilized are placed on a perforated tray situated above the water which is placed at the bottom of the cylinder. Water is boiled and the rising steam will sterilize the articles.

9. Moist heat at temperature above 100 ºC: Autoclave
120ºC {temperature}
20 – 30 minutes {time)
Double atmospheric pressure
The autoclave is used for the
sterilization of:
surgical instruments,
bed linen,
surgical dressing gowns,
cotton, gauze

10. Autoclave is the most efficient method for sterilization because:
1- The high temperature it attains.
2‑ The high penetrating power of steam under pressure.
3‑ When steam condenses on an article, it liberates a large amount of latent heat to its surface.

11. c) Ionizing radiation:
a) Ultraviolet (UV):
Bactericidal (but not total)
In operating rooms
b) Infrared (IR):
By heating effects (180C)
For syringes and glassware
c) Ionizing radiation:
Gamma rays
High penetrating power
Packed syringes - catheters

12. Filtration
This is a mechanical method for exclusion of bacteria from biological fluids which are destroyed by heat e.g. serum, plasma. hormones, vitamins and from fluid culturd media. Removal of bacteria is achieved by passing the fluid of air through a porous substance (e.g. asbestos, earthenware or milipore filters) that allow them to pass, but holds the bacteria back.

13. Chemical disinfectants
Type
Remarks
Alcohol (70%)
Skin disinfectant
Aldehydes (Formaldehyde)
Terminal room disinfection
Halogens
1- Hypochlorite:
Water treatment – surface disinfectants
2- Iodine:
Skin and wounds
Surface disinfectants

14. Type
Remarks
Hexachlorophane
Skin disinfectant (soap)
Replaced by chlorhexidine
Ethylene oxide
Sterilization of heat sensitive instruments