Methods for the sterilization effect verification of high-pressure steam sterilizer generally includes the chemical indicator method, the retention point thermometer method, the self-made temperature measurement tube method and the biological indicator method. The principles of each method are similar, mainly by verifying whether the temperature in the sterilizer can meet the requirements during sterilization. We can choose one or more of these methods for verification according to the specific conditions of our laboratory.
 
I. Chemical indicator method
Principle: The chemical indicator will be discolored or deformed by heat under a certain temperature and action time. This characteristic can be used to judge whether it reaches the required sterilization parameters.
 
Generally, 3M pressure sterilization indicator tape is commonly used in laboratories. This indicator tape uses the color change of the tape before and after sterilization to judge the sterilization effect. It is made by making inks from heat-sensitive chemical substances, color developers and paint accessories, and printing the inks in stripes on a special adhesive tape. The indicator tape can be directly pasted on the outside of the package, the length is not less than 5cm, and lightly press the tape to increase the viscosity and sealing effect. At 121℃ for 20min or 130℃ for 4min, the oblique white indicator lines printed on the tape will be completely black and become black lines. If the color is uneven or incomplete, it can be considered that the package does not meet the sterilization conditions.
 
II. Retention point thermometer method
Principle: The retention point thermometer method uses the non-reflux characteristic of a mercury thermometer. Its principle is similar to that of a traditional clinical thermometer, and it can indicate the maximum temperature reached by the sterilizer during the sterilization process.
 
When verifying, put the mercury thermometer in a large triangular flask containing water, and place the triangular flask on the upper and lower parts of the sterilizer during sterilization. After the sterilization, check whether the temperature of the mercury thermometer is consistent with the required temperature. This method can only verify the temperature and cannot indicate whether the sterilization time meets the requirements, so it is the minimum standard for sterilizer verification.
 
III. Self-made temperature measurement tube method
Principle: It use the feature of some chemicals that the shape of the crystal is different when they melt by heating and then cool down. The chemicals are sealed in a small glass tube and placed in a sterilizer during sterilization. After sterilization, you can observe the shape of the crystal to determine whether the temperature is up to standard.
 
The commonly used reagent is benzoic acid. The melting point of benzoic acid is 121-123°C, which is basically consistent with the sterilization temperature of the sterilizer we require. Therefore, the solid benzoic acid is sealed in a small glass tube and placed into the sterilizer during sterilization. After sterilization, the state of benzoic acid can be observed to verify whether the sterilizer has reached the required temperature. The limitation of this method is the same as the retention point thermometer method, that is, it can only indicate the temperature during sterilization, and it is impossible to judge whether the sterilization time meets the requirements.
 
VI. Biological indicator method
Principle: The spores of non-pathogenic Stearothermophilus are used as indicator bacteria to determine the effect of heat sterilization. The spores of Stearothermophilus are highly resistant to heat, and their heat resistance is similar to that of the pathogenic microorganism Clostridium botulinum spores. This is used as an indicator bacteria to verify whether the sterilizer can meet the sterilization requirements.
 
There are three types of biological indicators: spore suspension, spore flakes, flakes and medium mixed indicator tube. Generally they are placed in 5 points of the sterilization container: the front, middle and back of the lower layer and the central point of the upper and middle layers. After sterilization, take the indicator and inoculate it in bromocresol purple-glucose peptone water, culture at 55-60℃ for 2-7 days. If the medium is clear and the color does not change, it means that the spores have been killed and the sterilizer has a good sterilization effect. If the medium is yellow and turbid, it means that the spores have not been killed and the sterilization effect of the sterilizer is unqualified. The verification methods for spore suspension and spore flakes are the same.
 
For the effect verification of the sterilizer, there is currently no relevant standard that strictly requires the frequency, but the laboratory should formulate its own verification frequency regulations and perform it in strict accordance with the requirements.