NAJRAN UNIVERSITY College of Medicine

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

2. STERILZATION AND DISINFECTION DEFINITIONS Sterilizationis the complete inactivation of all forms of microbial life. Antisepticsare 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. Disinfectantsare 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. Disinfectantsare either: 1‑ High‑level disinfectantskill mycobacteria, viruses, and all but the most resistant spores. 2‑ Low‑level disinfectantskill 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 Mycobacteriumtuberculosis, Brucellaabortusand 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. For testing efficiency of autoclave: a) Chemical indicator : It is a chemical substance which changes its colour when heated at 115ºC for 25 minutes (Browne's sterilizer‑control tube). b) Biological indicator : UesB.subtlisor B. Stearothermophiluswhich are spore‑ forming bacteria. The spores are destroyed when heated at 121ºC for 12 minutes.