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Factors affecting the sterilizing effect of culture medium

Whether the culture medium is thoroughly sterilized directly affects the scientific research test data. There are many factors that affect the culture medium sterilization. In addition to the type and number of miscellaneous bacteria in the culture medium, the length of sterilization time and the temperature, it also depends on the following points:

Maintenance of nutrients

When sterilized by humidity and heat, the microorganisms are killed, and the nutrient composition of the culture medium is also destroyed to a certain extent, especially the amino acids and vitamins. For example, 59% of lysine, arginine and other basic amino acids were destroyed at 121℃ only for 20min, and a considerable amount of methionine and tryptophan were also destroyed. Under the action of heat, some nutrients may react with each other, resulting in changes in the quantity of original nutrients in the medium, thus affecting the quality of the medium.

Heat resistance of microorganisms

The thermal resistance of bacterial spores is high, and the time required for sterilization depends on the time required to reduce bacterial spores to a specified number.

PH value

The PH value has a great influence on the heat resistance of microorganisms. Microorganisms are least likely to die when PH is between 6.0 and 8.0. When PH <6.0, microorganisms are relatively easy to die. At this time, PH is easy to penetrate into the cells of microorganisms, thus changing the physiological response of cells and promoting their death. So the lower the PH of the medium, the shorter the time required.

Nutrients of culture medium

High concentration of organic matter, such as fats, sugars and proteins, will wrap around the cell and form a thin film, affecting heat conduction. The high concentration of salt and pigment weakens its heat resistance and makes it easier to sterilize. For example: Escherichia coli in water heated to 60-65℃ will die, in 10% sugar solution need 70℃ heated 4-6 minutes to die, in 30% sugar solution need 30 minutes to die. When the general sugar content is more, the best choice is 115℃, 30 minutes; The general medium can be selected at 121℃ for 20 minutes.


The air in the foam forms an insulating layer, making it hard for heat to penetrate and killing bacteria.


Small particles, easy to sterilize, large particles, it is difficult to sterilize. Medium containing a small number of larger particles and crude fibers can be removed by coarse filtration (which should not affect the quality of the medium), as medium agglomeration will cause incomplete sterilization of the medium.

Whether the air in the sterilizer is cleared

This is the key point that affects the ratio of temperature and pressure in sterilization. Under the same pressure, if the air fails to be discharged, that is to say, it is not pure steam sterilization, the temperature may not meet the purpose requirements at this time, which will seriously affect the effect of sterilization.

Our PQS series medium sterilizer adopts saturated steam as sterilization medium, which is specifically used for the high temperature sterilization of medium loaded by non-sealed container. Its temperature is adjustable,and temperature detect method is flexible。It has reliable sterilization effect for the culture medium in varieties of standard and volume.Temperature time and F0 dual control meet national pharmacopoeia requirements.

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