Agent: An agent that inhibits the growth of bacteria, but does not necessarily kill them. Bactericide: An agent that kills bacteria. Most do not kill Endospores.
An agent that kills spores.
The process of freeing an article from microorganisms including their spores.
By definition, it effects a reduction in the number of microorganisms (more than 99.9999% are killed).
Methods of Sterilisation
Microbial Control Methods
Mechanical Remova Methods
X Ray, Cathode, Gamma
Boiling Water/Hot Water
DRY HEAT :Incineration
Temp: 879-980 oC This is an excellent method of destroying materials such as contaminated cloth, animal carcasses and pathological materials.
DRY HEAT: Dry Oven
Sterilisation By Dry Heat:
by oxidation effects
•The oven utilizes dry heat to sterilize articles • Operated between 50oC to 250/300oC. •A holding period of 160oC for 1 hr is desirable.
• There is a thermostat controlling the temperature.
•Double walled insulation keeps the heat in and conserves energy, Hot Air Oven
DRY HEAT: FLAMING
250-300 °C Inoculation loop or Wire, the tip of Forceps and spatulas are held in a bunsen flame till they are red hot.
MOIST HEAT STERILIZATION
Kills microorganisms by coagulating their proteins. Types: Temp below 100oC: “Pasteurisation”,
Temperature at 100oC: Boiling. Temperature above 100oC : Autoclave.
Process of killing of pathogens in the milk but does not sterilize it .
Milk is heated at 63oC for 30 mins. (HOLDER METHOD)
At 72oC for 15-20 Sec. Rapid cooling to 13oC (FLASH PROCESS)
TEMPERATURE AT 100OC Boiling:
Kills vegetative forms of bacterial pathogens. Hepatitis virus: Can survive up to 30 minutes of boiling. Endospores: Can survive up to 20 hours or more of boiling
STEAM UNDER PRESSURE – AUTOCLAVE Temp > 100 OC
Works on the principle of Steam under pressure
Autoclave consists of a vertical or a horizontal cylinder. One end has an opening which is meant for keeping materials to be sterilised. Sterilisation is carried out under pressure at 121º for 15 mnts. J.Masri
Two types of radiations are used NON –IONISING IONISING
X- rays, gamma rays & cosmic rays.
High penetrative power No appreciable increase in the temperature – COLD STERILISATION Sterilise plastics Syringes, catheters, grease fabrics metal foils
Non- Ionising radiation:
Electromagnetic rays with longer wavelength Absorbed as heat Can be considered as hot air sterilisation
Used in rapid mass sterilisation of prepacked Syringes and catheters
Eg: UV rays
ULTRASONIC AND SONIC VIBRATION
Microorganisms vary in their sensitivity, hence no practical value in sterilisation and disinfection
Chemical agents act by Protein coagulation Disruption of the cell membrane Removal of Sulphydryl groups Substrate competition
Ethylene Oxide Colourless ,Highly penetrating gas with a sweet ethereal smell. Effective against all types of microorganisms including viruses and spores
Specially used for sterilising heart-lung machines,respirators,sutures,dental equipments, books and clothing. Also used to sterilise Glass, metal and paper surfaces ,plastics, oil,some foods and tobacco.