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Knowledge of Biological Indicators

 Catalog

Definition of biological indicator
Composition of biological indicator
Preparation of biological indicator
Selection and use of biological indicators
Definition of biological indicator
 
Biological indicators, referred to as Bi (biological indicator), is a kind of microbial preparation which has certain tolerance to specific sterilization process and can quantitatively determine the efficacy. Most of the microorganisms suitable for the preparation of biological indicator are spore bacteria, because in addition to radiation sterilization, spore bacteria have stronger tolerance to sterilization process than conventional growing microorganisms. Biological indicator can be used not only to determine the sterilization effect of a given sterilization process condition, but also to determine whether it meets the requirements of sterility assurance.
 
Advantages of biological indicators
Biological indicator is made by combining a group of specific microorganisms and carrier, which has high resistance to the corresponding sterilization mode, indicating the death of microorganisms and reflecting the sterilization status truly and reliably. It can correctly reflect the relationship between time, temperature and humidity in the process of sterilization.
 
Composition of biological indicator
At present, there are three main forms of biological indicators commonly used in sterilization process validation, which are prepared from microbial spores with certain tolerance to specific sterilization process and known species. Some biological indicators may contain two different kinds of microorganisms, and the contents of the two microorganisms are not the same.
1 spore strip
2 spore suspension
3 self contained indicator
 
Spore strip
The spores are added to the carrier, such as inoculated on filter paper, glass / plastic and other thin or strip materials, and wrapped with specific materials to maintain its integrity and biological activity, commonly known as the spore strip. This kind of indicator is more suitable for verifying and monitoring the sterilization process of non solution items.
 
Spore suspension
 
The spore suspension can be inoculated into a representative product solution to be sterilized or a simulated product solution. The spore suspension is directly inoculated on the inner or outer surface of the product, so that the actual sterilization effect of the product can be more directly observed.
 
Self contained biological indicator
 
This kind of indicator is to add the spore strips (or pieces) into the medium package containing the indicator (e.g. in a small bottle). These medium are packaged separately and separated from the spore carrier. After sterilization, the medium bottle is crushed to immerse the spore strips (or pieces) in the medium. The spore strips (or pieces) are cultured at an appropriate temperature and time, and the color change of acid-base indicator in the medium is observed to judge The growth condition of the plant is very good.
 
Procurement sources and requirements of biological indicators
 
A qualified bioindicator supplier must meet the following conditions
 
(1) The manufacturer is responsible for determining the initial performance of the biological indicator. The manufacturer should attach a COA (analysis report) to each batch of biological indicators to explain the performance indicators of biological indicators.
 
(2) The manufacturer should indicate the purpose of the biological indicator, that is, to evaluate the type of sterilization process.

         The manufacturer shall also provide the following information: D value, method of D value determination, number of microorganisms, tolerance of biological indicator within the validity period, recommended storage conditions, use instructions, etc.

         The manufacturers of biological indicators should also provide the precautions for the disposal of biological indicators after use to ensure the safety of laboratory personnel and avoid damaging the environment 

Basic requirements of microorganism for preparation of biologic
Different sterilization methods use different biological indicators, and the microorganisms used to prepare biological indicators must have the following characteristics:al indicator
a:The tolerance of bacteria should be greater than that of all possible contaminated microorganisms in the products to be sterilized;
b: The strain should have no pathogenicity
c: The strain should be stable. It has a long survival period and is easy to preserve
d: It's easy to cultivate.
If dormant spores are used, the content of dormant seeds in biological indicator should be more than 90%.
 
Preparation of biological indicator
 
The preparation of biological indicators should be carried out according to certain procedures. Before preparation, the characteristics of microorganisms should be determined, such as D value (the heat resistance parameter of microorganisms, which is the time required to kill 90% of microorganisms at the specified temperature, expressed in minutes), etc. The strain should be cultured in suitable medium. The culture should be made into suspension, in which the number of spores should be dominant, and the spores should be kept in a non nutritive liquid.
 
Biological indicators contain a certain number of one or more spores, which can be made into various forms. Usually, a certain number of spores are put on the carrier, such as filter paper, glass slide, stainless steel, plastic products, etc.; spore suspension can also be sealed in ampoules; some biological indicators are also equipped with medium system. The biological indicator should be packed with suitable materials and set the validity period. The carrier and packaging materials should not only protect the biological indicator from pollution and loss, but also ensure that the sterilization agent can penetrate and fully contact with the biological indicator. Carrier and packaging should be designed to facilitate storage, transportation, sampling, transfer and inoculation.
 
Some biological indicators can directly inoculate spores into liquid sterilized products or substitutes with similar physical and chemical properties. When substitutes are used, the data are used to prove their equivalence
 
Selection and use of biological indicators
 
Biological indicator for damp heat sterilization
 
Spores of Bacillus stearothermophilus are the most commonly used biological indicator for hygrothermal sterilization. D value is 15-30 minutes, the number of living spores per piece is 5 × 10͇ ~ 5 × 10 ⁶, and it should be completely killed at 121c and 19 minutes. In addition, Clostridium sporogenes can be used with D value of 0.4-0.8 minutes.
 
Biological indicator for dry heat sterilization
 
Bacillus subtilis spore is the most commonly used biological indicator for dry heat sterilization. The number of living spores per piece was 5 × 10͇ ~ 5 × 10 ⁶. Endotoxin challenge pyrogen removal process verification is often used to replace biological indicator verification, because endotoxin is more difficult to kill than microbial spores.
 
Biological indicator for ion radiation
 
The most commonly used biological indicator for radiation sterilization is Bacillus pumilus spores. The number of living spores per piece was 10, and the D value was 3 kGy under the radiation dose of 25 kGy. However, it should be noted that the microorganisms loaded in the sterilized articles may show stronger radiation resistance than the spores of Bacillus pumilus. Therefore, the spores of Bacillus pumilus can be used to monitor the sterilization process, but can not be used as the basis for the establishment of sterilization radiation dose.
 
 Biological indicator for ethylene oxide sterilization
 
In ethylene oxide sterilization process, the spores of Bacillus subtilis var Niger are often used as biological indicators to control the process. In ethylene oxide sterilization, spore D value of Bacillus subtilis was more than 2.5 minutes. When ethylene oxide concentration was 600 mg / L, relative humidity was 60%, and temperature was 54 ℃, Bacillus subtilis should be killed in 60 minutes.
 
Biological indicator for liquid hydrogen peroxide sterilization
 
In liquid hydrogen peroxide sterilization process, Bacillus stearothermophilus spores are often used, but Clostridium or Bacillus subtilis spores can also be used, and other types of microbial spores can be used, as long as the tolerance to hydrogen peroxide is not less than that of the above three kinds of spores.
 
Summary
 
To ensure the sterility of sterile products is the core issue of product quality assurance. Aseptic production process is the key means to ensure the sterility of products. Only the fully validated sterilization (aseptic) production process can ensure the production of aseptic products. Dust challenge test is an important part of aseptic production process validation. The selection of appropriate biological indicators is the key to the recognition of microbial challenge test results

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