Sterilization

 

 Sterilization

Sterilization means freeing of any object or subject from all living organism either in vegetative  or spore that is known as to be sterilized.

Sterilization can be classified as:

        (i). Physical method

        (ii). Chemical method

v  Physical method of sterilization: Under physical method the physical agents acts either by giving energy in the form of heat or radiation or by removing organism through filteration various physical agent are:-

 (a). Heat: Heat energy can be applied in two ways.

                (i). Dry heat

                (ii). Moist heat

(i). Dry heat: It kills the micro organism by causing destructive oxidation of essential cell       constituents or by protein denaturation. Dry heat is done by:-

ü  Flaming: The articles are passed through the Bunsen flame for few minutes like  sterilization of scalpels, mouth of culture tubes, glass slide etc.

ü  Red heat: It is done by holding the article directly into flame of burner until it becomes red hot like sterilization of point of forceps, spatula, inoculation wire etc.

ü  Hot air oven: This is most common method of sterilization by dry heat. In this process the bacteria are killed by oxidation of cell constituency like sterilization of glassware like tubes, glass, bottles, flasks, petridishes or powders etc.

(ii). Moist heat: It kills micro-organism by denaturation and coagulation of protein and enzymes. It can be done by various method.

ü  Pasteurization: Sterilization of milk is called pasteurization the milk is pasteurized either at 63⁰ c-66⁰c for 30 minutes (holding method) and other method is flash method which is done by heating at 72⁰c for 24 sec. followed by rapid cooling to 13⁰c or low. It is called high temp short time method.

Eg:- M-boris, Salmonella, Streptococcus, Brucella.

ü  Boiling: The material to be sterilized is kept in a contains and boil for 10 minutes. It kills all form of vegetative bacteria.

ü  Tyndallization: An exposure to 100⁰c for 20 minutes followed by intermittent heating for three successive days is known as tydallization. It is generally used to kill the spore forming bacteria. First day kills vegetative form of bacteria. Second day kill spore vegelative third complete kill.

ü  Autoclaving: It is moist frequently used method of sterilization. This is very reliable  method and sterilize the suitable culture media bacteriotogical media having no egg or serum, rubber bag, dressing, instuments etc.

(b). Radiation:-

                They are of two types:-

                (i). Non-ionising Radiation

                (ii). Ionising Radiation

 (i). Non- Ionising Radiation: Infrared radiation act as a hot air sterilization. It is used in the sterilization of syrinjes and catheters before packing or radiation is operation theaters and laboratories.

 (ii). Ionising Radiation: It kill the micro organism by attacking on their DNA and breaking  covalents bonds in DNA-X-ray kills vegetative cell readily. It is used in medicines for sterilization of heat sensitive items, such as sutures and surgical gloves, plastic syringes, swab, catheters etc.

  (c). Filteration: Filteration is most officient method used for the sterilization of heat labile fluids such as serum, antibiotic solution and some culture media containing serum and egg etc. This method is not effective against viruses most commonly used filter is composed of nitrocellulose and has a pre size of 0.22um. The size retains all bacteria & spores. Some filter are Asbostos filter, sintered glass filter, membrane filter, chamber land filter, Earthen- ware filter.