Why is it that when it comes to cell culture, what is the little black sand grain???

Black gum worm contamination.

Black gum worm Open Category: Biology.

1. Overview of black rubber insects: When cell culture, sometimes small black dots are seen moving under the 400 times microscope, small black spots are sometimes dotted, sometimes small flakes, and the form of movement is vibration in situ (similar to Brownian motion), this small black spot is neither bacteria, mold, nor mycoplasma (we once asked Zhou Shouchang to culture with blood plates, and no colonies appeared), and the industry currently calls it "black gum worm". Are black gum bugs living things?

This has always been a doubt in the industry. Black gum worms are generally found in serum, and serum is usually filtered through a filter membrane, so there can be no microorganisms such as bacteria, molds and mycoplasma in serum. If the black gum worm is not a living organism, it will continue to increase, and when it reaches a certain number, it will compete with the cells for nutrients in the culture medium, thus making the cells die due to insufficient nutrition.

Grows competitively with cells and has a detrimental effect on cell growth.

"Black gum worms" will multiply, and when they multiply for a long time, a large area under the field of vision will be "black gum worms". "Black gum worms" are related to serum and have a lot to do with serum quality.

Small black dots: It does not multiply with cell growth, it may be calcium phosphate precipitation, on the contrary, it may be black charella, which will move under the microscope, which will affect cell growth or recombinant cell protein expression.

Adherent black fragments may be cell lysis fragments.

Mold contamination: Adherent culture has filamentous white, severe mildew, flocculent, if in the fermenter, white balls, like crushed styrofoam.

Colorectal cells are flocculent and floating, and the culture medium is cloudy.

Streptococcus: round, bright, three-three-two-two.

If the cells are contaminated with bacteria, the most common are gram-positive bacteria, such as Bacillus subtilis. and gram-negative bacteria such as Escherichia coli and Pseudomonas, among which Staphylococcus albicans is more common. When cultured cells are contaminated with bacteria, the culture medium will soon become cloudy and the pH will change.

There are also a few cultures that do not change much with the naked eye, and contamination can only be known when the bacteria are found under the microscope. Therefore, it should be carefully observed every day. After pollution, the cells underwent pathological changes, and the intracellular granules increased, thickened, and finally became rounded and fell off and died, resulting in the failure of the experiment and the loss of cell lines (lines).

How to judge contamination: If it is bacterial contamination, the substrate should be cloudy soon. If it is a fungal infection, especially in the initial stage, small black dots can be seen under low magnification, especially small black dots in clusters, so special attention should be taken.

If it is uncertain, change to high magnification, if it is a dead cell, it can be resolved under high magnification, while the fungus is still a small black dot under high magnification. Some (e.g., mycoplasma) contamination is not visible on microscopic examination, but the cells are abnormally growing.