PHYSICAL AND CHEMICAL METHODS OF STERILIZATION Flashcards
- The effective UVL wavelength ranges from 200-280 nm with 260 nm as the most effective
- Microorganisms such as bacteria, viruses and yeast can be inactivated within seconds
- UVL is not sporicidal, and is more frequently used for surface disinfection.
- Example: Operating Rooms and T.B. laboratories, hospital wards
U.V. light/ Non Ionizing Radiation
- greater penetrance than UV rays
- Not routinely used because of its potential to harm human tissues
Ionizing radiation
o generate high speed electrons
o can be used to sterilize syringes, gloves, dressing packs, food, and some pharmaceuticals
o has lower penetrance and requires sophisticated instruments
Electron beams
o Produce nuclear disintegration of selected radioactive isotopes
o Have grater penetrance than electron beams but require longer exposure time
o Bactericidal, fungicidal, viricidal and sporicidal
o Used to sterilize disposable petri dishes, plastic syringes, vitamins, antibiotics, hormones, fabrics & glassware
Electromagnetic rays (Gamma rays)
- Mechanical sieving that does not kill microorganisms but merely separates them from liquid.
- removes most bacteria
- Does not filter viruses and some small bacteria like Chlamydia, Rickettsia & Mycoplasma
Filtration
- Most common method of physical sterilization
- The rate of killing is expressed in thermal death time
Sterilization by Heat
- For preservation of microorganisms in the process of lyophilization or freeze drying the organism is rapidly frozen then dehydrated in high vacuum and stored in vacuum- sealed container
Freezing
- Deprives microorganisms of moisture
- Mainly used for food preservation such as preparation of dried fish and fruits
- Destroys vegetative forms Endospores are resistant to drying
Dessication
- Preferred over dry heat because of its rapid killing action
- Cause coagulation and denaturation of proteins
Moist Heat
- Destroys disease-causing organisms in ilk and milk products as well beverages
- Uses heat at temperature sufficient to inactivate harmful organism in milk
- Does not achieve sterilization
Pasteurization
- Used to kill bacteria in vaccine
- destroy contaminating bacteria in vaccine preparations
- Done by heating in water bath at 60°C for 1 hour
- Not sporicidal
- Only vegetative forms of bacteria are destroyed
Vaccine bath
- Used to inactivate bacteria contaminating serum
- Done by heating in water bath at 56°C for several successive days
- Not sporicidal
- Only vegetative forms of bacteria are destroyed
- Higher temperature will cause coagulation of proteins present in the serum
Serum bath
- Used to solidify and disinfect egg-containing and serum containing media
- The culture medium is placed in an inspissator and is heated at 80-85°C for 30 mins for 3 successive days
Inspissation
- Involves utilizing water at boiling temperature of 100°C
- Not sporicidal, will destroy only the vegetative forms
- Killing action can be enhanced by addition of 2% sodium bicarbonate
- Certain metal articles & glass wares can be disinfected using this method for 10-20 mins without opening the lid of the boiler
Boiling
- AKA Steam under pressure
- Most efficient method of sterilization because it destroys all microbial forms
- It takes 15-20 mins to sterilize the materials
- Used to sterilize instruments, surgical bandages, culture media and other contaminated materials that can withstand high temp and pressure
Autoclave
- Temperature is > 100°C therefore spores are killed.
Autoclave
- AKA intermittent sterilization
- Involves exposing the material to be sterilized to live steam at 100°C for 30-90 mins for 3 consecutive days, depending on the material to be sterilized
- Can be used to sterilize culture media
- Vegetative forms are killed on the first day, spores that will germinate will be destroyed on the next successive days
Fractional sterilization (Tyndallization)
- Its effectiveness depends on the penetration of heat through the material to be sterilized
- Used to sterilize materials in enclosed tubes, oils, jellies, powders and glass such as test tubes and Petri dishes
Hot Air Oven/ Dry Heat
- Some bacteria can be killed after exposure to certain frequency of sound waves
- Exposure to sound waves at a frequency of approximately 20,000 cycles/second for 1 hour can kill some bacteria and viruses
- Used to disinfect & clean instruments & to reduce microbial load
Sonic & Ultrasonic Vibrations
o Used to sterilize bacteriological wire loops, straight wires, tips of forceps and searing spatula
o Materials are held over the Bunsen burner until they become red hot
o Limited only to articles that can be heated to redness flame
. Red flame
o Make used of Bunsen burner or alcohol lamp
o Not heated to redness
Open flame (Flaming)
- Based on the principle of osmosis
- When the concentration of the fluid surrounding the organism is altered, it will cause the bacterial cell to collapse
- Used for preservation of fruits in syrlups and meat in brine
Osmotic Pressure
- Useful for heat sensitive materials
- Example: plastics and lensed instruments endoscopes
Sterilization by Chemical Methods
o concentrate on the surface of membranes & disrupt membrane resulting in leakage of cell component
Surface active agents
detergents where fat soluble portion is positively charged due to combination with a quaternary nitrogen atom.
Example: cetrimide & benzalkonium chloride
Cationic agents
negatively charged agent that contain long chain hydrocarbons. Examples: soaps & bile salts. Removes dirt through the process of emulsification and are moist effective at acidic pH
Anionic agents
o Act by disrupting cell membranes as well as causing precipitation of proteins
o Inactivates enzymes
o Bactericidal & fungicidal
Phenolic Compounds
- Carbolic Acid
- no longer used today because it is toxic to human cells
- Used as gold standard in the chemical evaluation of new chemical agents using phenol coefficient test
Phenol
- phenol derivatives that are more potent and safer than phenol
- Example: Lysol
Cresols
- used as skin disinfectant
- Used for wound irrigation
- Main use is as antiseptic hand wash
Chlorhexidine
- pHisoHex, used in nurseries and for surgical and hospital
- microbial control procedures to control gram positive skin bacteria such as staphylococci and streptococci.
Hexachlorophene
- For topical purposes
- Effective against gram positive bacteria
Chlorohexylenols
- It has broad spectrum of activity, especially against gram positive bacteria.
- It is also effective against gram negative bacteria including Pseudomonas
- It has some activity on viruses and fungi
Triclosan
- disorganize lipid structure of the cell membrane , dehydrate cells and cause denaturation & coagulation of cellular proteins
- microbial killing property of alcohol is seen in 70% aqueous solution
- Disadvantage: skin irritant and flammable
Alcohol
- used a skin antiseptic
- Bactericidal
- Removes lipids from skin surfaces
Ethyl alcohol
- Has greater bactericidal activity than ethyl alcohol
- Less volatile
- Can disinfect surfaces
- Inhalation of its fumes can cause narcosis
Isoprophyl Alcohol
- used mainly as preservative
Benzyl alcohol
- fungicidal and sporicidal used in disinfecting inoculation hoods
Methyl alcohol
- cause damage to the enzyme activity bacteria
- Cause precipitation of proteins & oxidation of sulfhydryl groups
- Mostly bacteriostatic than bactericidal (Example: Mercurial, antiseptic)
- Silver Compounds: silver nitrate - for ophthalmia neonatorum
- Silver sulfadiazine: treats burns
Heavy Metals
- best antiseptic because it is sporicidal, bactericidal, fungicidal, viricidal and amoebicidal
- can be combined with neutral carrier polymers to produce iodophores (Example: povidone-iodine)
Iodine
- used as a gas or in combination with other chemicals to treat water (chlorine gas)
- Common household disinfectant
o Chlorine gas: used to disinfect swimming pools
o Sodium hypochlorite: sanitize dairy and food processing equipment
o Chlorine dioxide: kills endospores
Chlorine
- A weak antiseptic
- Used to clean wounds
- Disinfect surgical devices and soft plastic contact lenses
Hydrogen Peroxide
- Bactericidal oxidizing agents that can cause oxidation of essential sulfhydryl groups, inactivates enzymes
Halogens
- Damage nucleic acids by alkylation of amino- carboxyl- or hydroxyl groups
- It kills all microorganisms including spores
- Example: Formaldehyde (formalin)
- Used for surface disinfection
- Used to sterilize bedding and furniture
- can kill mycobacterium tuberculosis in sputum and fungi in athlete’s
Aldehydes
- sporicidal and used as a cold sterilant in sterilizing medical equipment such as respiratory therapy machines and other equipment
- More potent than aldehyde
- Requires alkaline pH for its action and exposure time of at least 3 hours to be effective
Glutaraldehyde
- Sporicidal and is used in the gaseous sterilization of heat sensitive materials or equipment like heart-lung machine, respiratory and dental equipment and polyethylene tubes in anesthesia machines
- More potent than glutaraldehyde but slower-acting
- Highly flammable & is usually combined with 10% Co2.
- It causes eye irritation and is mutagenic and carcinogenic
- Ethylene OXIDE Gas Chamber
Ethylene Oxide
