Lecture 10-sterilization and
- 2. Learning Objectives At the end of this chapter, the student will be able to: • Define sterilization and disinfection. • Identify the various ways of sterilization techniques. • Explain why materials are sterilized in medical laboratory. • Describe how to disinfect and decontaminate laboratory waste.
- 3. Sterilization • Sterilization is the process of destruction or elimination of all forms of microorganisms by: – physical means (including heat, radiation, and filtration) – chemical agents (acids, alkalis, heavy metals, salts, halogens, etc). The equipment or material treated then becomes “Sterile”.
- 4. main purposes of Sterilization 1. In preparation for taking specimens, such as needles, syringes, test tubes, etc. 2. To sterilize contaminated materials and equipments. 3. To prepare apparatus used for bacteriologica cultures, such as petridishes, Pasteur pipettes, and others.
- 5. Methods of sterilization techniques.Methodsofsterilization techniques Physical method/Mechanical methods Chemical methods
- 6. Physical method/Mechanical methods Physical method Dry heat (hot air oven, flaming and red - hot) Moist heat (autoclave or steam under pressure and boiling Radiation
- 7. Mechanical methods • Hot Air oven • Owing to the low penetrating power of dry heat and great resistance of bacteria to it, higher temperatures are needed with a hot- air oven than with an autoclave. A temperature of 180c0 for 30 minutes will kill most resistant spores. • The material to be sterilized is placed in an oven and the temperature is raised and maintained at 180c0 for 30 minutes.
- 8. Mechanical methods • The sterilized material should not be removed until the oven is cold. • This is important particularly with pertidishes, as cold air will be sucked in to them, causing contamination, if they are removed before the oven is cold. • This is due to the contraction of hot air as it cools. This method is used only for glass or metal articles such as test tubes, petridishes, all glass syringes, and instruments.
- 9. Flaming • Metal spatula, glass slides, and cover slips may be sterilized by passing them through a Bunsen flame, with out letting them become red hot. • Red - hot • Wire loops and tips of forceps may be sterilized by heating them in a Bunsen flame until they become red hot and allow the materials (instruments) to cool before using them.
- 10. Moist heat • Boiling water • Moist heat may be applied by boiling water or steam. Boiling water is generally used for sterilizing instruments and syringes. These are boiled for 10 minuets in a water bath. • This will kill all non-sporing organisms but certain spore forming organisms can resist the temperature of boiling water for 1-2 hours.
- 11. • The addition of 2% sodium carbonate increases the disinfecting power of boiling water for 1-2 hours. Spores, which resist boiling water for 10 hours, have been killed within 30 minutes by the addition of sodium carbonate. Sodium carbonate also prevents the rusting of metal instruments. – This method is unsuitable if instruments are to be stored in a sterile condition.
- 12. Steam under pressure (autoclave) • Autoclave is an instrument that operates by creating high temperature under steam pressure. Autoclaving is the most common, effective, reliable and practical method of sterilizing laboratory materials.
- 13. Steam under pressure (autoclave) • The principle of autoclave is that steam is kept at a pressure of 15 pound (lb) per square inch to give a temperature of 121c0, which will kill spores with in 15 minutes. At this particular temperature, pressure and time, all forms of lives are destroyed.
- 14. Steam under pressure (autoclave) • Uses • Steam is more penetrating than hot air, and will give up its latent heat on striking a colder object; there by raising the temperature of the object rapidly It is used to sterilize: – syringes, – needles, – glasswares, – culture media, etc.
- 15. Autoclave