Title 11. DETAILED STUDY OF DIFFERENT METHODS OF STERILIZATION INCLUDING THEIR MERITS AND DEMERITS.pdf ✅

PHARMD GURU Page 1 INTRODUCTION: Sterilization is an essential stage in the processing of any product used for parenteral administration, broken skin, mucosal surfaces or internal organs. Sterilization of microbiological materials, surgical dressings and equipments and other contaminated items is necessary to minimize the health hazard associated with these articles. The main reasons for controlling microorganisms are: 1) To prevent contamination in sterile products. 2) To prevent transmission of pathogenic microorganisms which are responsible for causing diseases in plants, animals and human beings. 3) To prevent decomposition and spoilage of food and food products. 4) To prevent the contamination of unwanted microbes in pure cultures and other microbiological experiments performed for research studies. 5) To prevent unwanted microbial contamination in antibiotic, enzyme, vitamin fermentation and other industrial processes. 6) To prevent contamination in aseptic areas which are used for the preparation of sterile dosage forms and sterility testing. Microorganisms can be killed, eliminated or inhibited by various physical and chemical agents. Several terms used to describe the physical processes and chemical agents employed in controlling microorganisms are:  Sterilization: Sterilization is a process by which an article, surface or medium is freed of all microorganisms either in the vegetative or spore state.  Disinfection: Disinfection means the destruction of all pathogenic organisms or organisms capable of giving rise to infections. In this process, vegetative cells are killed but not heat-resistant spores. Disinfection is usually accomplished by chemical agents called disinfectants. A disinfectant is normally applied to in- animate objects such as floors, buildings, equipment, laundry etc. DETAILED STUDY OF DIFFERENT METHODS OF STERILIZATION INCLUDING THEIR MERITS AND DEMERITS
PHARMD GURU Page 2  Sanitization: Sanitization is the process of disinfection including cleansing action. Sanitizers are commonly applied to inanimate objects.  Antiseptic: The term antiseptic is used to designate any substance which would prevent sepsis, either by killing microorganisms or by inhibiting their growth. An antiseptic can be applied to body tissues without causing injury to the tissue.  Germicide: A germicide is an agent that kills vegetative cells but not necessarily the resistant spore forms of germs. The terms bactericide, fungicide, virucide and sporicide refer to agents that kill bacteria, fungi, viruses and spores respectively.  Microbiostasis: Microbiostasis is the process of preventing the growth, reproduction and multiplication of microorganisms but not of killing them.  Preservative: A preservative is a substance that prevents the growth of microorganisms. These substances are mainly added in food and pharmaceuticals to prevent microbial growth. Preservatives are not harmful to living tissues. STERILIZATION METHODS: The various methods used in sterilization can be classified as follows: I. PHYSICAL METHODS: a) Dry heat sterilization: Ex: Incineration, direct flame, red heat, hot air etc. b) Moist heat sterilization/steam sterilization: Ex: Pasteurization, tyndallization, autoclave etc. c) Radiation/cold sterilization: 1) Use of ultra-violet rays: UV light 2) Ionising radiations: X-rays, gamma rays, beta rays. d) Filtration / mechanical methods: 1) Asbestos filter (seitz filter). 2) Sintered glass filter (martian filter). 3) Filter candles (ceramic/Berkefeld filter) 4) Membrane filter (millipore/ultra filter). II. CHEMICAL METHODS: a) Gaseous sterilization: Ex: Formaldehyde, ethylene oxide etc b) By using disinfectants: Ex: Cresol, phenol etc.
PHARMD GURU Page 3 PHYSICAL METHODS: These methods involve processes by the use of physical means. These may involve the utilization of heat in the presence or in the absence of moisture or the applications of radiations or mechanical filtration. 1) DRY HEAT STERILIZATION: Heat is the most reliable and rapid method of sterilization. The killing effect of dry heat is due to protein denaturation, oxidative damage and the toxic effect of elevated levels of electrolytes. The factors influencing sterilization by heat are nature of heat, number of microorganisms present, temperature and time, characteristics of the microorganisms etc. The time required for sterilization is inversely proportional to the temperature of exposure. This can be expressed as thermal death time, which is the minimum time required to kill a suspension of microorganisms at a prescribed temperature and under specific conditions. Sterilization time is directly related to the number of microorganisms in the suspension, presence and nature of spores, the strain and characteristics of the microorganisms. Microorganisms are more resistant to dry heat as compared to moist heat and therefore, this process requires higher temperatures and longer exposure times. 1) Sunlight and drying: Sunlight possesses ultraviolet rays which along with heat rays are responsible for appreciable germicidal activity. These rays cannot penetrate through glass. This is a natural method for sterilization of water in tanks, rivers and lakes. Drying in air has deleterious effect on many bacteria. Spores are unaffected by drying. Hence it is a very unreliable method. 2) Red heat: It is used to sterilize metallic objects by holding them on a flame till they are red hot e.g. inoculating wires, needles, forceps etc 3) Flaming: The article is passed over flame without allowing it to become red hot e.g. mouth of culture tubes, glass slides, scalpels, needles, coverslips etc. These items may be sometimes immersed in spirit in a tray and the spirit is then burnt off. However, it does not produce sufficient heat and destroys only vegetative microorganisms. 4) Incineration: This is an excellent method for rapidly destroying materials e.g. pathological material, bedding, animals carcasses, soiled dressing etc. Polystyrene
PHARMD GURU Page 4 type of materials emit clouds of dense black smoke and hence should be autoclaved in appropriate containers. 5) Hot air oven: This is the most widely used method of sterilization by dry heat. The modern hot air ovens consist of a double walled chamber of aluminium or stainless steel separated from the outer case by a thick layer of insulation made of fibreglass (Fig. 7.1). Insulation is also filled in the hollow flanged door, which carries an asbestos jacket that provides a tight seal. Heating is affected by electrical heating elements and thermostats automatically control temperature. The material should be arranged in a manner which allows free circulation of air between the objects and it should not be overloaded. Glassware should be perfectly dry and wrapped in kraft paper before being placed in the oven. The oven must be allowed to cool slowly for about two hours before the door is opened, since the glassware may get cracked by sudden cooling. Substances that are not heat-labile and can tolerate temperature upto 250°C may be sterilized by hot air oven. Normally the spores as well as the vegetative forms of all microorganisms are killed in two hours at a temperature of 160°C. The relation between the temperature and relative time required for sterilization in hot air oven is given in Table 7.1.