Lab Two - STERILISATION AND DISINFECTION

Lab Two:- ________________ Medical Microbiology
Prepared by: Luma J. Witwit




STERILISATION AND DISINFECTION
Microorganisms cause contamination, infection and decay, it becomes necessary to remove or destroy them from materials or from areas. This is the object of Sterilization.

STERILIZATION:-Sterilization is defined as the process by which an article, surface or medium is free of all living microorganisms either in the vegetative or spore state.

Advantages of sterilization
• 1-Prevent transmission of diseases.
• 2-Prevent contamination and growth of undesirable bacteria.
• 3-Prevent spoilage of material by microorganisms.
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DISINFECTION
• Disinfection means the destruction or removal of all pathogenic organisms or organisms capable of giving rise to infection.
• Disinfection can be done by chemicals
ANTISEPSIS
• Reduction of or inhibition of microbes found on living tissue.
• ANTISEPTICS:-Chemical disinfectants which can be safely applied to the skin or mucous membrane and are used to prevent infection by inhibiting the growth of bacteria are called antiseptics.

DIFFERENCES BETWEEN ANTISEPTICS AND DISINFECTION
1. All antiseptics are disinfectants. All disinfectants are not antiseptics.
2. It can be apply on the live tissues. It can be applied on inanimate object.
3. E.g.:- Skin or mucous membrane. E.g.:- Surface, lab working tables, floor or material.

METHODS OF STERILISATION AND DISINFECTION
The following methods are commonly used in the microbiology laboratory and hospital.

(I) PHYSICAL METHOD Sunlight, Drying,
-Dry heat: Red heat, Flaming, Incineration, Hot air oven.
-Moist heat: Pasteurization, Boiling, Autoclave (Steam under pressure).
-Filtration and Radiation etc.
(II) CHEMICAL METHOD Alcohols, Aldehydes, Halogens (Iodine, Chlorine etc.), Phenols, Gases and Surface - active agents (soap, detergent) etc.
HOT AIR OVEN
• This is the most widely used method of Sterilization by Dry heat.
• A holding period of 160°C for one hour is used to sterilize glassware, forceps, all-glass syringes, swabs etc.
• Glassware should be perfectly dry before being placed in the oven.
• Test tubes and flasks should be wrapped in paper.
• The material should arrange so as to allow free circulation of air in between the objects.
STERILIZATION BY MOIST HEAT
• Moist Heat is divided into 3 methods;
• 1) Temperature bellows 100°C e.g.: Pasteurization of milk.
• 2) Temperature at 100°C
e.g.: Boiling of water.
• 3) Temperature above 100°C (Steam under pressure) e.g.: Autoclave.
AUTOCLAVE
• The steam pressure rises inside and when it reaches the desired set level, the safety valve opens and the excess steam escapes.
• From this point, the holding period is calculated. The holding period is 121° C at 15 pound pressure for 15 minutes.
• When the holding period is over, the heater is turned off and the autoclave allowed to cool till the pressure inside is equal to the atmospheric pressure.
• The discharge tap is opened slowly and air is let into the autoclave.
• The domestic pressure cooker serves as a miniature autoclave and may be used for sterilizing small articles in clinics.
FILTRATION (Membrane filters)
• Membrane filters are widely used which is made of cellulose esters or other polymers.
• Their average pore diameters (APD) are 0.22 mm size.
• Filtration helps to remove bacteria from liquids such as sera and solutions of sugars or antibiotics used for preparation of culture media.
RADIATION Applications:-
Two types of radiation are used for Sterilization – Nonionizing & Ionizing.
IONISING RADIATION NONIONISING RADIATION Infrared and Ultraviolet rays are of the nonionizing low energy type.
Applications:-
• Clean surfaces like inoculation hoods, microbiology & other laboratories, hospital wards and operation theatres etc.
• X-rays, Gamma rays & Cosmic rays are highly lethal to all cells including bacteria.
• They have very high penetrative power. They damage DNA by various mechanisms.
Applications
Commercial plants use gamma radiation for sterilization of disposable items such as plastics syringes, swabs & animal feeds etc.
CHEMICAL AGENTS
• Several chemical agents are used as antiseptics and disinfectants used in the microbiology laboratory and hospital.
• However little is known about the mechanism of action of many of these agents.
• An ideal antiseptic or disinfectant should be:-
• Have a wide spectrum of activity and must be effective against all microorganisms, that is, bacteria including spores, viruses, protozoa and fungi;
• Have speedy action;
• Have high penetrating power;
Be stable
• Not corrode metals;
• Not cause local irritation or sensitization;
• Not interfere with healing;
• Not be toxic if absorbed into circulation;
• Be cheap and easily available;
• Be safe and easy to use.
• ( ethyl alcohol is used in concentration(50-70)%, phenol group(2-5%), Chlorine compounds 5% (added to water), Formaldehyde (gas), 37% Dettol or alcohol 70% are effective in vegetative cells(denaturation of protein and nucleic acids , solvents of lipid in cell membrane and active in reducing normal flora from the skin and clinical thermometers).