MOIST HEAT STERILIZATION

Principle-Denaturation & coagulation of proteins due to the latent heat present in

steam

Advantages of steam –Latent heat liberated on condensing on a cooler

surface increases the temprature of that surface

What is Moist heat Sterilization?

Types of Moist heat Sterilization

•Pasteurization•Inspissation or Fractional Sterilization

Hot water below boiling point

•Tyndallization or Intermittent Sterilization

Boiling water /steam at atm pr

•AUTOCLAVE Saturated steam

Pasteurization

•63 C for 30 minutes

Holder Method

•72 C for 15-20 seconds

Flash Process

Heat labile fluids may be disinfected

It is the process of thickening

by dehydration

Inspissation

Media such as Lowenstein –Jensen media and Loeffler’s serum are rendered sterile by heating at 80-85 C for half an hour on three consecutive days

Tyndallisation

Principle: The first exposure kills all vegetative bacteria and the spores since they are in a favourable medium will germinate and be killed on subsequent occasions

Though generally adequate this method may fail with spores of certain anaerobes and thermophiles

The Autoclave was invented by Charles Chamberland in 1879

AUTOCLAVE

Definition

Autoclave is a pressurized device designed to heat aqueous solutions above their boiling point at normal atmospheric pressure to achieve sterilization

Reliable sterilization with moist heat requires temperatures above that of boiling water.

These high temperatures are most commonly achieved by steam under pressure in an autoclave. .

Need for autoclaving:

Autoclaving is the preferred method of sterilization unless the material to be sterilized can be damaged by heat

or moisture

Liquid H2O cannot be heated above 100°C in an open vessel

At 100°C boils

H2

O heated in a sealed vessel

Pressure rises

Boiling point of H2

O is raised

Air removal

Downward displacement

Steam pulsing

Vacuum pumps

Superatmospheric

Subatmospheric

Process

Biological indicators are the only process indicators that directly monitor the lethality of a given sterilization process. Spores used to monitor a sterilization process have demonstrated resistance to the sterilizing agent and are more resistant than the bioburden found on medical devices. 

Bacillus stearothermophilus Thermophilus aquaticus

Spore Test

If the autoclave does not reach the right temperature

the spores will germinate when incubated and their

metabolism will change the color of a pH –sensitive

chemical.

Any Questions???