What is the liquid in the virus transport medium? Why is it red?

Nucleic acid test, as the name suggests, is the collection of nucleic acids (by using nasal swabs or oropharyngeal swabs) and then amplification by PCR to detect the presence of a target sequence to determine whether a species is present. Since the outbreak of the Covid-19, this technology has gradually been in the public eye.

Once the biological sample is collected, it is vital to ensure that the nucleic acid is intactly preserved. However, like bacteria, exfoliated cells, and other secretory components may have active ingredients that catalyze nucleic acid cleavage. In particular, the genetic material of Covid-19 is RNA, which is weaker than DNA and is easier to lyse.

Therefore, the viral transport medium(VTM) has only one mission – to keep the genetic material in the test sample intact. Depending on whether it is inactivated, it can be divided into two transport media.

Inactivated Transport Medium

Killing all viruses and cells and also inhibit all potential RNA hydrolases is the simplest method. For example, surfactants/lysis salts are used to destroy the membrane structure of virus/cells, so that viral proteins lose physiological activity. The enzymes are inhibited with guanidine salts (e.g., guanidine isothiocyanate) to protect the nucleic acid, similar to the nucleic acid extraction lysate (TRIzol reagent). It is commonly used for routine biological testing to avoid the risk of aerosol infection by transmissible viruses.

Guanidine-free lysis inactivation type: A non-guanidine salt protein denaturing agent is added, which lyses the virus in order to inactivate it and release nucleic acids into the solution. There is no need of nucleic acid extraction, suitable for direct PCR amplification (but its solubility and denaturation capacity is relatively weak compared to guanidine salts)

Non-inactivated Transport Medium

Non-inactivating transport media are made of organic solvent and inert materials that are designed to maintain the viability of clinical specimens that contain viruses. They suppress microbial contamination and provide protection for samples during transport and processing. The main components of an inactivated viral transport medium are basal Hank’s balanced salt solution. Gentamicin and amphotericin B are added to inhibit competing bacteria and yeast. The HEPES buffer is used to maintain the proper pH level.

Personal protection should be given top priority because the non-inactivating VTM contains viable viruses/bacteria. There is a risk that the researcher would become infected. At the same time, costly cold-chain transportation is required for efficient preservation. It can be utilized for the field of virus isolation, cultivation, and development of vaccines.

Summary

Although the two transport media serve similar purposes, there are still some fundamental distinctions. While non-inactivated VTM stabilizes cell/viral viability and prevents bacterial reproduction, inactivated VTM protects nucleic acids by viruses and cells decease.

A pH indicator is typically added to the solution in order to visually observe the status of the solution (under different pH values, the colors alter).

 Phenol Red sodium salt (CAS:34487-61-1) is widely used as pH indicator. The solution is red in neutral, yellow in acidic, and purple in alkaline. The solution will turn yellow if the solution is tainted with bacteria and the pH declines.If you add vinegar to this fuchsia red solution, it should become yellow, so friends with conditions can test it.

Anthocyanins in fruits function as an indicator; they turn cyan (alkaline) when unripe and purple (purple) when mature (acidic).