Electrical impedance technology

Electrical impedance technology

Ur, A. is equal to the early 1970s. It was found that there was a change in electrical impedance in the vigorous bacterial culture, and its change decreased with the growth of the culture time. Therefore, the application of electrical impedance technology to identify bacteria in the specimen was proposed.

(1) Basic principles of electrical impedance technology

Electrical impedance refers to the obstruction and resistance of conductive materials to current in AC circuits. It is a composite energy composed of resistive (reactive) and reactive (reactive) components. In general, bacteria can decompose electrically inert substrates such as proteins, carbohydrates, and lipids in the medium into electroactive metabolites such as ammonia, lactate, acetate, and bicarbonate. When bacteria grow vigorously, a large number of electrically inert molecules in the culture medium can be converted into many electroactive molecules and ions, thereby increasing the conductivity in the culture medium, and the electrical impedance of the culture is reduced accordingly. Therefore, the electrical impedance measurement technique is actually a method for measuring the metabolic activity of bacteria. Due to the different types of bacteria, the activities of the metabolites produced on the culture medium are also different, thus becoming the basis for the identification of bacteria using electrical impedance technology.

(2) Application of electrical impedance technology

Since this measurement technique was proposed by Ur, A. and others in 1975, it is currently considered to be meaningful in the following two aspects:

1. Bacterial identification Using electrical impedance technology to measure the growth of many bacteria in a special culture medium, you can quickly get a variety of bacterial characteristic curves. So far, the use of this method has initially tested the bacteria of the genus Enterobacteriaceae, Pseudomonas, Bacillus, Clostridium, Staphylococcus and Lactobacillus. The results show that the cultivation of these bacteria Things can produce a characteristic change in electrical impedance, thereby identifying bacteria.

2. Bacteremia detection timely and accurately detects pathogenic bacteria from animals with bacteremia, which can provide an effective treatment basis for clinical, but it is still difficult to report the test results within 48 hours using conventional methods, so it provides a fast, Sensitive and simple blood sample culture detection technology is also one of the problems that the microbiology laboratory needs to solve. Hadiy et al. Used Bactometer32 research to find that this method can detect at least 0.1CFU (colony forming unit) per ml of blood.

In addition, the electrical impedance technology can also quickly determine the content of E. coli and bacteria in various water sources such as drinking water, treated sewage effluent, contaminated river water, and wastewater.

(3) Characteristics of electrical impedance technology

There are four main points:

1. Specificity When this technique is used to measure changes in the electrical impedance of bacterial cultures, so-called "fingerprints" of various bacteria or characteristic graphs can be obtained. According to the currently reported materials, many bacteria have their own unique curves, so it is accurate to identify certain bacteria with this method.

2. Sensitivity When 103 bacteria per milliliter, the activity of its metabolites can be detected within 2 hours. For example, when the number of bacteria per milliliter reaches 105, the metabolic activity of its bacteria can be within a few minutes. Check out. Because the actual measurement sample volume is 0.1ml, the actual sensitivity of this method is to detect the activity of 100 bacteria per ml.

3. Repeatability This method has high repeatability, and does not report different experimental results due to the replacement of the operator or the different batches of specimens being tested.

4. The speed of reporting the results quickly depends on the number of live bacteria in the culture to be tested and is proportional to the inoculated amount of bacteria, that is, the greater the inoculated amount, the faster the rate of positive reactions. For example, when this method is used to detect Escherichia coli, Pseudomonas aeruginosa, Streptococcus faecalis and Staphylococcus aureus, when the inoculation amount is 103 to 105 bacteria per milliliter, it is generally measured within 2 hours. If 10 to 15 bacteria are inoculated per milliliter of culture medium, the detection time will take 48 hours. This method is usually 4-6 times faster than the radiation method and 10 times faster than the conventional method.

The disadvantage of this method is that it is sometimes inconsistent with the results obtained by the conventional method, and it is impossible to completely distinguish the contaminated bacteria present in the specimen from the pathogenic bacteria being tested.