The principle of autoclave is very simple. First, we learn about what is autoclave ?. Its definition is, it is a machine in a clinical laboratory that is used for the sterilization process. It (Autoclave) generates steam above100 C temperature.

There are three types of autoclaves. In the autoclave, steam passes through a cooler load resulting in the synthesis of heat with moisture. Both of these (Heat + Moisture) break the bacterial cell protein.

Most of the culture media are sterilized by autoclaves.

This sterilization technique completely destroys the endospore and vegetative form of bacteria.

Principle of autoclave

The principle of autoclave is that laboratory autoclave is equipment that gives moist heat or steam 121 C temperature. At this temperature vapor pressure, it and atmospheric pressure become the same. But due to the close vessel of the autoclave, the vapor pressure in the vessel increase resulting in raising the boiling point of water in a vessel.

this results in superheating steam in an autoclave.

2 Uses of autoclave in the clincal laboratory

Following are the proper uses of autoclaves in the microbiology section of the clinical laboratory.

  1. Autoclave used to sterilize surgical instruments.
  2. sterilization of culture media using autoclave

what are the Precautions of autoclaves during oprating?

  1. Load in the autoclave should be loosely arranged.
  2. Steam should be saturated and dry during autoclaving.
  3. Before starting sterilization, the air in the autoclave should be completely removed, so that the instruments are subjected to steam.

Autoclave temperature and time pressure chart microbiology

Steam Pressure IU/square inchesTemperature (C)Time (min)
Autoclave temperature and time pressure chart

what are the 3 Types of Autoclaves in microbiology?

There are three types of autoclaves.

Simple Non-Jacketed types of autoclave and principle

  • It is a simple pressure-cooker is the type of autoclave. It can be horizontal or vertical in shape. This type lacks the method of discharging air. It also lacks the mechanism of drying of articles after sterilization.

Steam Jacketed Autoclave types of autoclave

  • It is an advanced type of autoclave. It has an automatic air discharge system. There are a channel and a thermostat valve, which discharge air automatically. This type has an article drying system.

High Pre-vacuum types of autoclave

  • This type is highly equipped with an electrically driven pump. This pump creat vacuum in the chamber.

Autoclave testing methods in microbiology

There are three testing methods to check the sterilization of autoclaves. The purpose of using sterilization indicators for autoclaving is that ensure the sterilization process of all kinds of articles. Testing methods are also called control or indicator. Following are the indicator methods used in an autoclave.

  1. Physical method
  2. Chemical method
  3. Biological method

Physical Method for testing sterilization

We can check sterilization in three ways in the physical method.

Recording Temperature Thermometer.

It makes graphically time recording of the temperature in the autoclave.

Thermo-couple measurement of load temperature.

In this method, a thermocouple is inserted, the heating time of load is noted. This thermocouple is connected to the potentiometer outside the chamber. It indicates the temperature inside.

Automatic Process control

This is automatic as described by the name. In this process, every this like temperature, the time duration is pre. selected. After selection, articles are placed inside the chamber and the sterilization process starts. It has a monitoring system that monitors the temperature inside the body. If the temperature alters, this system restarts the sterilization process.

Chemical Method for testing autoclaves sterilization

There is two chemical method.

  1. Brown Control Tube
  2. Bowie Dick Tape

Brown Control Tube

The tube contains the RED solution. This solution turns green at 121 C for 25 minutes. This tube should be stored below 2o C. More temperature cause deterioration of it.

Bowie Dick Tape Principle

  • This a adhesible tab. Color of the tabe turn in to black on 121 C temperature.

Biological method for testing sterilization

Spore Indicator

This is a biological indicator or control for the conformation of the sterilization process. In this method spore of a bacteria name BACILLUS, Stereothermophillus was used. Spore requires 55 C to 66 C temperature for cultivation. But this spore was killed at 121 C temperature.

Before starting the sterilization, the spore is placed on the strip placed in the chamber. After autoclave spores are tested for viability.

What is the Biological method for testing autoclave sterilization?

The spore of BACILLUS, Stereothermophillus is used as a biological control for testing the sterilization process of autoclaves.

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