Sterlization Flashcards
(33 cards)
Define sterlization and disinfection
Sterlization: it is the process by which an article ,surface or medium is made free from all living micro organisms including spore.
Disinfection : it is the process that destroys most of the vegetative microbes or viruses but not spores in an inanimate surface.
Classify sterlization
Sterlization
1.physical agents
2. Chemical agents
Chemical agents : alcohol
Phenol, halogen, heavy metal, aldehydes
Physical agents
1. Heat:
a.moist heat -
At 100•C boiling ,
Steaming
Tyndalization
.above 100•C Autoclaving
.below 100•C pasteurization
Serum inspisator
b.dry heat:
red heat
Flaming
Hot air oven
- Radiation-
Ionizing
Non ionizing
3.filtration
Earthenware
Asbestos
Sintered glass membrane
Difference between antiseptic and disinfectant
Antiseptic are mild chemicals used in lower conc
Disinfectants are strong chemicals used in high conc
Antiseptic is used for living surfaces eg skin and MM
disinfectant is used for non living surface eg floor bed
Antiseptics are not irritant to living surface eg. Cresol savlon
Disinectants are harmful to living tissues
Eg. Acids and alkalis formaldehyde
Why moist heat is better than dry heat
- Moist heat has better penetrating power at lower temp
- It produces latent heat
- Kills the bacteria by denaturing their enzymes and structural proteins
4.Bacteria are more susceptiple to moist heat
2 examples of dry heat and moist heat
Dry heat: hot air oven
Red heat
Moist heat: autoclave
Pasteurization
What is autoclave
It is a process of sterlization by saturated steam under high pressure .
Needs a metallic cylindrical vessel
On the lid there is a guage, a safety valve and a stop clock
Uses: surgical blunt instrument
Dressing gown
Towels
Gauge
Culture media except heat sensitive
Principle of autoclave
- At atm pressure water boils at 100•C
- With rise in the pressure the boiling point of water also rises provided no air is present
- Steam under pressure unmixed with air has more temp than that of mixed with air
- Steam under pressure has more penetrating power. On contact with materials steam condenses to water. So there is lowering of pressure which draws more steam inside
- During condensation of steam to water a large amount of latent heat is liberated thus increasing the efficiency of sterlization
Appropriate time temp and pressure of autoclave
Time : 15 mins
Temp: 121•C
Pressure: 15 lb/ sq inch
Why dont we use autoclave for sharp objects . How are they sterlized
moist heat can make the sharp objects blunt making them less effective
It can also cause corrosion and rusting
We use 5% cresol for sharp instruments
How spores are destroyed ?
Physical methods
1.autoclave
2.hot air oven
3.tybdallization
4.ionizing radiation
Chemical methods
1.formaldehyde
2.gluteraldehyde
3.ethylene oxide
Temp of hot air oven
Holding time
180 C for 30 mins
170 C for 60 mins
160 C for 120 mins
Uses of hot air oven
Glassware
Oil
Oily injections
Swab sticks
Powder
Define tyndalization
Intermittent steaming with period of incubation in between
Method :
100° steaming it’s done for 30 minutes on 3 successive days and incubation in between for 37°C overnight.
principle:
1. 1st exposure on day one kills all vegetative forms.
2. spores which are not destroyed would germinate to form vegetative forms before second exposure.
3.second exposure on day 2 kills newly formed vegetative forms.
4. Spores if present germinate till the third exposure and would be killed on third exposure on third day.
5. this ensures complete 100% Removal of spores which might not be killed by a single exposure
Uses of tyndalisation
Sterlization of heat sensitive culture media eg. Loefflar serum
How is tyndalization done
100°C steaming is done for 30 minutes on 3 successive days and incubation in between for 37°C overnight.
40 to 45% of spores become vegetative. Spores can not be killed by 100°C so in incubation favourable environment is provided that is 37°C for the germination of spore to form a vegetative form then in 100°C that bacteria is killed thus spores are killed indirectly
What is pasteurization
Heating of milk to such temperature and for such period of time so as to kill the pathogenic bacteria that may be present in the milk without changing colour ,flavours and nutritive values of milk.
methods :
holding method - 63-66 •C for 30 mins followed by rapid cooling
flash method- 72•C for 20 secs immediate cooling at below 10•C
UHT method 131•C for 1 sec
Organisms :
m bovis
Brucella
Salmonella
E coli
Which products are pasteurized
Milk ,wine ,fruit juice
Beverages
Chemical sporicidal agents with clinical uses
Formaldehyde- blankets,
Operation theatre, hospital wards, disinfectant that kills bacterial spores
Gluteraldehyde- cytoscope , endoscope and other anaesthetic equipment
Disinfectant that kills bacterial spores
EO- heart lung machine
Cytoscope endoscope
Other chemical agents with use
Alcohol kills fungal spores
3 gaseous sterlizing agents
How to sterlize catheters
Formaldehyde gas
Ethylene oxide gas
Hydrogen peroxide- kills bacterial spores
Catheters- autoclave
Uses of ionizing radiation
1.In pharmacy and medicine.
2. catgut and nylon structure.
3. disposable surgical and medical supplies
gamma rays more used.
X rays less used because they induce radioactivity in exposed materials
Examples of antiseptic
Chlorhexidine( savlon)
Hexachlorophene
Iodophores
70% alcohol
