Sterilisation And Disinfec

Question 1

Sterilisation and disinfection def

Answer 1

Ster: the process by which a surface ,medium,article,is free of all viable MO’S either in vegetative or spore form

Disinfection: is the destruction of all pathogenic organisms

Question 2

Hot air oven

Answer 2

Most widely used method of dry heat.
Sterilisation is by conduction. Heat is absorbed by the item to be sterilised which then penetrates to the centre, until item reaches desired temp.
160°c for 2 hrs for scissors., Scalpels, glassware. Glass syringes.
Oven heated by electricity . A fan is fitted inside to ensure even distribution of air.
Shouldn’t be overloaded. Test tube & flasks wrapped by craft paper.
Rubber materials can’t withstand the temp.
At 180°c-cotton plugs are charred
150°C-sharp objects (ex: used in ophthalmic sungery)
Before door opened over cooled slowly for 2 hrs., as glassware may crack due to uneven heating.

Question 3

Pasteurisation of milk

Answer 3

Milk heated at 63°c for 30 min (Holder method) or 72°c for 15-20 sec, (flash method) followed by cooling to 13°c.
All non sporing pathogens like mycobact, brucellae, salmonellae are destroyed.

Question 4

Tyndallisation

Answer 4

. Intermittent sterilisation
. Heat at 100°c for 20min for 3 successive days.
. Principle- vegetative forms killed first then as favourable medium for spore germination , they are killed on subsequent exposure.
. Spores of thermophiles& anaerobes may not be killed.
.suitable for sugar and gelatin medium

Question 5

Autoclave (steam under pressure)

Answer 5

Principle- when water boils, its vapour pressure is equal to that of surrounding atmosphere. Hence when pressure inside a closed vessel increases the temperature at which the water boils increases; generating steam.
. The steam when condensed on a surface transmits latent heat. The large reduction in volume sucks more steam and process continues till temperature of that surface equals to steam.
. Temp 108°c-147°c. Materials like linen., laboratory ware., media & instruments sterlised.

Autoclaves used in health care: laboratory autoclave Instrument steriliser
Hospital dressing steriliser. Rapid cooling steriliser

. 2 types: gravity displacement, vacuum steriliser.

. Cylinder of stainless steel. Safety valve get to blow off if pressure rises over desired levels. Lid fastened by screw clamps made air tight. Exit tap for air & steam.heating by electricity.

. Mechanism: ① water added to cylinder & material to be sterilised on tray.
② lid screwed tight, discharge tap opened, autoclave heated
③ steam air mixture allowed to escape till air displaced.
④ when no more air present tap closed.
⑤ when steam pressure raises to desired set level, safety valve opens & steam escapes.
⑥ from this point holding period is calculated. When holding period is over heater is turned off & autoclave is allowed to cool till pressure reaches atmosp pressure.
⑦ discharge tap is opened to let air enter.
⑧ It tap opened when internal pressure high liquid media boils violently& explodes.
lf opened after reaching below atmo pressure the excess water evaporates.

Defects: method of air discharge is inefficient ( difficult to determine when it is complete)
Material remain moist after removal from autoclave.

Vacuum sterilisers: