The liquid in the sampling tube turns yellow.

The liquid in the sampling tube turned yellow because the preservation solution was contaminated by bacteria.

The liquid in the sampling tube is actually a virus nucleic acid preservation solution. The reason why the preservation solution is pink is that the acid-base indicator "phenol red" may be added, which can help us quickly judge whether the virus preservation solution has deteriorated. Phenol red is red in alkaline environment and yellow in acidic environment. If the preservation solution is contaminated by miscellaneous bacteria, the metabolism of bacteria will make the culture medium acidic and the preservation solution will turn yellow.

Introduction of virus preservation solution in nucleic acid detection

At present, common sample preservation solutions are generally divided into inactivated type and non-inactivated type, and inactivated sample preservation solution is commonly used in COVID-19 nucleic acid detection. As the name implies, inactivated sample preservation solution can quickly inactivate pathogens. High concentration of guanidine salt can make it lose infectivity, crack the virus, release nucleic acid, and keep the sample at room temperature for a long time, reducing the cost of transportation and preservation.

The use of inactivated preservation solution not only ensures the safety of inspectors, but also makes preliminary preparations for subsequent nucleic acid amplification detection. Colored preservation solution is also helpful to observe whether the preservation solution leaks or not, and to judge the liquid level when sucking samples. The virus preserved in the non-inactivated sample preservation solution is more complete, which is beneficial to increase the survival time and infection stability of the virus in vitro and improve the detection rate.

Therefore, non-inactivated specimen preservation solution is more commonly used for the collection and transportation of clinical specimens. In addition to the indicator, guanidine salt, bisimidazolidine and other substances will be added to the virus preservation solution, which is mainly responsible for inactivating the virus and inhibiting bacteria.

Reference to the above content: Sohu. Composite nucleic acid detection sampling tube