Viral Transport Medium 

In modern microbiology transport media is one of the most important things used in the transport of specimens from one place to another. For a successful analysis, The samples need to be in a stable environment that is not detrimental to the organisms or the environment. Transport media have diverse functions depending on the type of organism they are used for, and the time organism has to spend in it. A VTM is a non-nutritive ready to use media that contains various antibiotics and antimycotics to prevent the growth of bacteria and fungi. These mixtures can stabilize the sample for 2 to 3 days under normal conditions and even when proper refrigeration is not available. However, the specimen must not be exposed to environmental extremes. Transport media are called so because they have special ingredients that keep the clinical specimen to be transported in a stable condition and prevent degradation.

 Widespread Uses of VTM

As mentioned above VTM is used for the transport of clinical specimens and viral clinical samples that are to be tested. During this COVID-19 pandemic, VTM has been one of the most widely used and demanded chemical mixtures. Nasal swabs were taken from the CVID-19 patients are saved in the VTM solutions for stability until the testing is done. As the VTM prevents temperature-related degradation, drying of the sample, and also discourages the growth of the bacteria and fungi that comes with the sample so it is an essential requirement also prescribed by WHO and CDC.

viral transport medium

Many variants are developed over time by laboratories yet the composition of the VTM is so adjusted that it does not hinder the analysis to be performed on it. There are so many factors that determine what should go into the VTM, such as a complete understanding of the pathogenesis of the suspected agent, stage of infection, as well as age and immunocompetence of the infected individual. It is important to select the appropriate specimens, collect the specimen carefully to optimize the recovery of the infectious agent, and transport the specimens as directed to maintain viability, and minimize overgrowth with contaminating organisms.

How VTM works for the protection of Viral Samples

As a virus is a very simple cellular organism thus any changes in the environment may change the viral nucleic acid size. Most of the viral transport media contain some of the essential components such as PH stabilizing agents that ensure that the viral proteins remain intact. Similarly, antibiotics and antifungals are added depending on the need to prevent contaminants from degrading the sample. Some VTMs are isotonic to prevent the lysis of viral however this requirement is not necessary as there are many commercially available viral transport media that are popular and are hypertonic in nature. Some  VTMs also contains glycerine that acts as a temperature absorber and gives viral specimen more stability under higher temperatures, this is especially important in areas where samples collected are not refrigerated.

Types

Viral Transport Media has various types depending on the concentration and the ingredients used. Some of the ingredients are consistent throughout the media types such as fetal bovine serum and buffer solutions are the same but the amount varies. The variable ingredient is antibiotic types. But the bottom line is that the VTM composition is variable to a very little extent.

There are however studies that show that VTM can be exchanged with Phosphate buffer saline solution (PBS) but VTM performs well under higher temperatures and can stabilize the specimen for a longer period of time while PBS is only effective for 12- 18 hours. This makes VTM a better choice.

 There are following types of VTM that can be used for the transport of Viral specimens,

  1. Cell culture media
    Usually used for specimens such as Herpes Simplex Virus (HSV). and usually suitable for inhouse transport of the sample it can stabilize the virus for 0.6- 4 days.  So much suitable for short transport. It contains a 10% fetal bovine serum as well that create isotonic conditions for the virus.
  2. BSS charcoal media VTM
    It is much like Phosphate buffer saline solution but has additive charcoal that acts as a PH stabilizer. Used for the specimens that are more acidic. Stabilize acid-base conditions at the near-physiological PH of the virus so that it can survive a long time.
  3. Broth-based media
    It contains bacteriological Broth and is much suitable for the long term and long journey transport of the specimen. It is usually used for the transport of all Influenza, parainfluenza, and HSV virus. Mostly throat samples are collected in the Broth-based media. The contamination chances are less than 1% and temperature requirements are also not stringent.
  4. Bentonite
    This media was developed in the 80s to overcome all the limitations of Phosphate Buffer Saline or BSS solution. It has ability to increase the stability of the virus up to 3 weeks and that even with simplest change in broth own composition.
  5. Sucrose based media
    Sucrose based media is more hypertonic in nature as compared to all other media developed so far for the transport of the virus. It can withstand -70c temperature so is ideal for the samples that are to be transported on dry ice. The stability time is 10 to 15 days.

Conclusion:

A virus is a sensitive A cellular organism with very defining stability conditions. For the successful analysis of the specimen, the virus concentration is important. Over a period of time after collection of the specimen, the virus starts to degrade and results in lower toter of the virus in the specimen. Virus Transport Media are the solutions that help stabilize the virus titer and prevent degradation. Different media are used for the transport of the samples depending on the nature of the virus and specimen type. Other variables such as contamination hazard, temperature, and days that are needed for the transport of the specimen are plays a role. VTM is an essential part of microbiology related work and analysis.