Types of cell contamination

In cell laboratories, cell contamination is generally classified into microbial contamination and eukaryotic contamination. Among them, microbial contamination includes fungi and yeasts, bacteria, mycoplasma, etc. Eukaryotes usually have cross-contamination between cell lines.

Contamination by bacteria, fungi or yeast is easy to identify. It can be directly judged through the color change of the culture medium or by observing under a microscope. If the cell culture medium turns yellow after bacterial contamination and there are small black dots under the microscope, and they move regularly. After yeast contamination, the culture medium turns purple, and transparent, continuous circles can be seen under the microscope. However, if it is mycoplasma contamination, since mycoplasma grows slowly at the beginning of Z and is difficult to detect under a microscope, it is very hard to detect.

Eukaryotic cell contamination refers to the contamination of one type of cell by another, mainly occurring during improper operation, especially when certain cell lines are studied for a long time and subcultured. At present, more and more scientific researchers have discovered the overlooked problem of intercellular contamination. According to incomplete statistics, approximately 15-20% of cells have intercellular contamination.

2. The influence of cell contamination on the experiment

No matter what type of pollution occurs, it will cause the same result, that is, the experiment must be redone, thus wasting working time, increasing the experimental cost and reducing the repeatability of the experiment. Moreover, when conducting experiments based on contaminated cells and uncontaminated cells, it is possible to obtain completely different experimental results. What is more serious is that if the cells you are studying are of another type, all the work you have done will be in vain.

At present, there are more and more reports on cell contamination in the academic circle. An article titled A case of mistaken identity by Megan Scudellari was published in The journal The Scientist on September 16, 2008. The article points out that the breast cancer cells used in the more than 650 studies that have been published so far may not be true breast cancer cells.

Christopher Korch, a geneticist at the University of Colorado, discovered that over the past 15 years, 78 widely used cell lines in his published articles have been proven to be contaminated. Among them, there are two "star" cell lines with severe contamination. One is the HEp-2 cell line. The HEP-2 used in 5,789 articles was contaminated by HELA cells. Another one is the INT 407 cell line. The cell line used in 1,336 articles was also contaminated by HELA cells. This article titled "Line of Attack" was published in the journal Science in 2015.

3. How to prevent cell contamination

For a cell culture laboratory, the most important thing is to eliminate all possible sources of contamination. The sources of pollution can be divided into direct and indirect categories. Direct contamination refers to the contamination caused by the use of reagents or the cells being cultured have already been contaminated. Indirect pollution may come from laboratories, experimental equipment or ourselves. Therefore, how to prevent the occurrence of cell contamination is the top priority in the daily work of a cell laboratory.

If a new type of cell is introduced to the laboratory or a cell that has been cultivated and preserved for a long time but has never been tested on the preserved cells, it may cause contamination to the laboratory. Therefore, before use, it is necessary to test the newly introduced cell lines or check whether the preserved cells are pure and free from contamination.

2. For the selection of reagents such as culture media, they must be produced in factories that comply with GMP/GLP regulations. Moreover, routine contamination tests for serum are required, and good packaging habits and systems must be established.

Whether the laboratory is kept clean, whether the experimental equipment is kept sterile, and whether the operation procedures are carried out correctly can all prevent contamination. Therefore, strict aseptic operation norms and management must be followed.