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Precautions for microbiological testing

2024-01-11 14:03

Inspection personnel

(1) Microbial testing cannot rely solely on fully automated identification instruments. Each step in the testing process requires a high degree of subjective analysis and judgment ability, which is closely related to personal experience, skills, and basic knowledge of microbial testing.

(2) In addition to requiring microbiological testing personnel to have a serious and serious work attitude, precise and meticulous observation and operation habits, and pay attention to personal hygiene, it is also necessary to train and master microbiological testing techniques.

(3) Inspectors should implement a pre job training system, and only those who pass the pre job training can start working. They should also actively participate in learning, training, lectures, and learning new technologies, master microbiological testing methods, standards, and relevant laws and regulations.

(4) Participate in writing testing programs and instrument operation programs, learn quality assurance system knowledge and basic metrology knowledge.

(5) Participate in various level tests and blind sample tests to improve detection level and ability to analyze and solve problems.

(6) The person in charge of microbiology should regularly assess the professional knowledge and proficiency of the inspectors, in order to improve their quality.

2. Instruments and equipment

Main instruments and equipment for microbiological testing

Refrigerator, biosafety cabinet, ultra clean workbench, refrigerator, biosafety cabinet, ultra clean workbench, high-pressure sterilizer, incubator, water bath, pH meter, microscope, oven, etc.


All instruments and equipment are required to be used correctly according to the manufacturer's methods and relevant regulations.

Instruments and equipment that require mandatory periodic calibration must be calibrated by qualified metrology departments before they can be used.

For commonly used valuable instruments and equipment, they should be inspected before use, registered after use, and regularly maintained to ensure that the instruments are in good working condition.

(1) Autoclave sterilizer

A. Operators should understand the principle of high-pressure sterilizers and follow operating rules.

B. The sterilized items should not be placed too tightly.

C. Place a biological or chemical indicator strip during use; Calibrate daily with a mercury retention thermometer.

D. Monitor quarterly using biological indicators.

Attention: The sterile instruments required for laboratory use should be able to be sterilized correctly, and sterile instruments and vessels should be clearly labeled.

(2) Incubator

A. Items that are too hot or too cold should not be placed inside the box. When taking and placing items, the box door should be closed at will to maintain a constant temperature.

B. If the culture is accidentally spilled into the box, it should be cleaned immediately and necessary disinfection measures should be taken.

C. The culture should not come into direct contact with the surroundings and lowest layer of the incubator.

D. Record temperature changes daily and correct any deviations immediately

3. Culture medium and reagents

The culture medium used for microbiological testing must be produced by professional manufacturers, and the product quality must comply with relevant quality standards. Storage should also meet the requirements to prevent deliquescence, clumping, etc. Once the culture medium deteriorates, it cannot be used again.

(1) The preparation of the culture medium should be strictly carried out in accordance with the methods specified in the standards, and preparation records should be kept.

(2) To ensure the quality of the culture medium, attention should be paid during preparation: the preparation of the culture medium must be carried out in a glass container or enamel jar, and using metal vessels such as copper and iron may have a toxic effect on microbial growth.

(3) Use a dedicated corner spoon to take samples and avoid cross contamination.

(4) Distilled water or deionized water must be used for preparation, and tap water must not be used.

(5) Different types of microorganisms have different requirements for pH values, and pH values should be measured during preparation. If the measurement results do not meet the required requirements, NaOH or HCL solution should be used for adjustment.

(6) The prepared culture medium should be used in a timely manner. If there are no special requirements, it can be stored at room temperature or 2-8 degrees Celsius.

4. Inspection environment

Microbial testing is conducted in the laboratory, which means that microorganisms must not be allowed to spread out, samples must not be contaminated, and pathogenic bacteria must not be allowed to infect testing personnel. Therefore, the environmental requirements and hygiene management system of the laboratory are very important.

(1) The microbiological testing room requires a clean internal and external environment, a reasonable layout, and a separate operating area from the office area.

(2) The washing room, culture room, disinfection room, and sterile room should be separated and equipped with dedicated rooms.

(3) The microbiology room should be equipped with automatic or foot operated hand sinks and fixed disinfection facilities.

(4) The sterile room is equipped with a buffer room.

(5) Regularly disinfect the operating environment

(6) Conduct daily air colony tests.

5. Sampling

(1) Sampling tools and containers should be made of materials that are resistant to disinfection and sterilization. Sampling tools should not be disinfected with disinfectants, and preservatives should not be added to the samples to avoid affecting the accuracy of the test results.

(2) Under strict aseptic operation conditions, collect samples uniformly and accurately according to the national standard for sample collection, and seal them in a timely manner to ensure the accuracy and representativeness of the samples.

(3) After sealing each sample, label it and keep a record. Generally, the sample can be stored in an environment of 2-8 degrees Celsius. If it is frozen food, it should be kept in a frozen state and sent in a timely manner.

(4) The sampling quantity shall not be less than three times the required quantity for all inspections, for inspection, retesting, and future reference.

6. Inspection quality

In addition to testing the required inspection items according to national standard methods, attention should also be paid to the following aspects in practical work, otherwise it will affect the accuracy of the inspection results:

(1) When using the weight method or the volume method in quantitative testing, there may be errors in the test results because for samples with a specific gravity not equal to 1, the test results of 1ml and lg will never be equal. Generally, the weight method is suitable for solid samples, and the volume method is suitable for liquid samples. However, for viscous liquids (such as yogurt), if the volume method is used, a certain amount of sample will adhere to the straw, so it is best to use the weight method for such samples.

(2) If the sample needs to be diluted with sterile water or sterile physiological saline, it is best to use a homogenizer to prepare a uniform bacterial suspension.

(3) Sample dilution often results in a small amount of sample being retained inside and outside the pipette. It should be noted that the depth of the pipette inserted into the sample or diluent should be consistent, otherwise it will affect the test results. After inhaling the liquid, it should be slowly injected into the increasing diluent along the tube wall. Special attention should be paid not to the tip of the pipette touching the diluent at this time.

(4) When pouring the culture medium into the sample and bacterial suspension, it is important to note that the temperature of the culture medium should be between 45 and 50 degrees Celsius, and to thoroughly mix the culture medium with the sample bacterial suspension.

(5) When cultivating microorganisms, the correct cultivation temperature and time should be selected according to the requirements.

(6) A blank control should be performed. If bacteria are detected in the blank control, it can be considered that there is a problem with the quality of the culture medium and there is contamination during the operation process. In addition, standard bacterial strains were used as positive controls to observe the quality of the culture medium.

(7) The entire inspection process should strictly adhere to sterile operations.

(8) Timely check the results and keep good records of the original data.

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