Introduction:
In the world of microbiology, the effective and safe transfer of viral specimens is critical for accurate diagnostic tests and research. Viral Transport Media (VTM) is essential for protecting the viability of viral samples throughout transportation, ensuring the stability of genetic material, and aiding virus isolation. This comprehensive overview looks into the significance of VTM, its composition, and the critical considerations for its use in a variety of laboratory settings.
Also Read:Transport media | Its types, uses, with 19 Examples
Viral Transport Media (VTM) serves as the primary guardian in the tiny world of microbiology, where we reveal the mysteries of microscopic objects. VTM is like a perfectly prepared mixture of buffers having germ-fighting talents, and stability magic. Its job is to protect viruses from time and the environment.
Definition:
Viral Transport Media (VTM) is a specialized nutrient medium that keeps viral specimens stable and viable during their travel from the collection site to the laboratory. Its major function is to prevent desiccation, preserve virus genetic material, and aid in downstream diagnostic procedures.
Figure: Viral transport medium VTM
Principle of Viral transport medium:
The principle of Viral Transport Media (VTM) is to provide an environment that keeps viral specimens intact and viable during their transfer from the collection site to the laboratory. This is accomplished through the VTM’s precisely adjusted combination of components. The following are the key principles:
Viral Integrity Preservation: VTM aims to safeguard viruses’ genetic material, ensuring that it remains stable and intact during transmission. This is critical for precise and accurate laboratory testing.
Prevention of Microbial Contamination: Antimicrobial compounds in VTM inhibit the growth of bacteria and fungi that could contaminate viral specimens. This helps to keep the sample pure for exact analysis.
Viability Preservation: The buffering components in VTM assist in maintaining an ideal pH level, preventing virus particle destruction. This is necessary to maintain the viruses alive and viable for diagnostic purposes.
Viral Adaptability: VTM formulations are viral tolerant to a variety of viruses, including respiratory, intestinal, and other viruses. Because of its adaptability, it is a commonly used and standardized approach for transferring diverse viral species. The components of a suitable viral transport medium are chosen to produce an isotonic solution including proteins to protect the viral structure, antibiotics to control microbial contamination, and one or more buffers to control the pH. Viral transport media are created to preserve the vitality of viral cultures or specimens for tests such as the nucleic acid amplification test (NAAT) while preventing sample drying.
In short, the VTM approach is around providing a protective and supporting environment for viral specimens, allowing them to withstand transportation hurdles and maintaining their relevancy for laboratory diagnoses and study.
Composition of viral transport medium:
Liquid medium
- Buffered solution: Buffered solutions within Viral Transport Media (VTM) play an important function in ensuring a stable pH environment. The pH of the medium is crucial in maintaining the integrity of the viral genetic material throughout transportation. Fluctuations in pH could compromise the virus’s structural stability, making buffered solutions a vital component.
- Saline solutions: Saline solutions are critical in maintaining an isotonic environment within VTM. This isotonicity is critical for preventing virus particle osmotic stress during transit. Saline solutions aid in the overall preservation of the virus ensuring that it arrives at the laboratory in a state suitable for examination.
Stabilizing agent
- Protease inhibitor: Protease inhibitors are included in VTM and provide a defense mechanism against enzymatic degradation. Proteases are enzymes that can degrade proteins, and protease inhibitors protect viral proteins from destruction by reducing their action. This protection is vital for preserving the structural integrity of the viral particles throughout transmission.
- Antibiotics: Antibiotics are added to VTM formulations to prevent bacterial contamination during viral specimen transit. Antibiotics guarantee the purity of viral samples by preventing bacterial development and protecting them from undesired microbial interactions that could affect the accuracy of future diagnostic tests.
PH buffering system:
- Importance of pH control: Because many viruses are pH sensitive, pH buffering in VTM is essential. When viruses are exposed to severe pH conditions, they may undergo structural alterations or lose viability. The pH buffering system in VTM helps to maintain a steady and appropriate pH level, providing a stable environment for viral particle preservation.
- Common PH buffers in VTM: Common buffers, such as HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) and phosphate, have a vital role in maintaining VTM’s pH. These buffers operate as chemical agents that withstand pH fluctuations, ensuring that the viral transport medium maintains the required acidity or alkalinity for good viral specimen preservation.
Many of the following properties would be present in an ideal viral transport medium:
- Even at room temperature, it would keep the virus active.
- It would be nontoxic for cell cultures and would not hide the appearance of viral cytopathic effects.
- It would have a long shelf life (whether frozen or not frozen).
- It could be used for culture isolations as well as direct diagnostics such as enzyme immunoassays or immunofluorescence.
Preparation of Viral transport media VTM:
Many viral transport media (VTM), such as COPAN Universal Transport Media and Eagle Minimum Essential Medium (E-MEM), are commercially available for immediate usage. However, VTMs can be prepared locally, and the formulation differs depending on whether the samples are taken from humans or other animals.
Viral transport medium for human specimens:
Simple version:
- In 400ml sterile distilled water, combine 10g veal infusion broth and 2g bovine albumin fraction V.
- Add 0.8 mL of gentamicin sulphate solution (50 mg/mL) and 3.2 mL of amphotericin B solution (250 g/mL).
- Filtration is used for sterilization.
Elaborated version:
- Heat 500ml fetal bovine serum (FBS) at 56.0°C for 30 minutes.
- Mix 50ml amphotericin B and 50ml gentamicin with inactivated FBS and then filter sterilize it.
- To 500ml Hanks Balanced Salt Solution (HBSS), add 10ml of the FBS mixture.
- To the HBSS containing FBS, add 2ml of the Gentamicin/Amphotericin B mixture.
- Fill bottles, label with the production date and expiration date, and aliquot 3ml into sterile tubes.
- Keep at 2-8°C.
Viral transport medium for animal specimens:
Transport medium 199:
- Take 1 liter of tissue culture medium 199 containing 0.5% bovine serum albumin.
- Add the following ingredients: benzylpenicillin, streptomycin, polymyxin B, gentamicin, nystatin, ofloxacin hydrochloride, and sulfamethoxazole.
- Filter sterilize and dispense in screw-capped tubes.
PBS Glycerol-transport medium:
- Phosphate-buffer saline (PBS) should be prepared and mixed 1:1 with sterile glycerol.
- Add the following ingredients: benzylpenicillin, streptomycin, polymyxin B, gentamicin, nystatin, ofloxacin hydrochloride, and sulfamethoxazole.
- Dispense into sterile plastic vials and store for brief periods (1-2days) at -20 °C or room temperature.
Examples of viruses preserved by VTM ( viral transport medium):
Viral transfer Media (VTM) is a medium used to transfer different types of viruses for diagnostic testing and research. The VTM used is frequently determined by the type of virus and the specimen being collected. Here are some viruses that could be transported using various forms of VTMs:
Respiratory Viruses:
- Examples: Influenza viruses (flu), respiratory syncytial virus (RSV), and coronaviruses (including SARS-CoV-2, which causes COVID-19).
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Herpesviruses:
- Examples: Herpes simplex virus (HSV), and varicella-zoster virus (VZV).
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Enteric Viruses:
- Examples: Norovirus, rotavirus, enteric adenoviruses.
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Vector-Borne Viruses:
- Examples: Zika virus, Dengue virus, West Nile virus.
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Bloodborne Viruses:
- Examples: Hepatitis B virus (HBV), Hepatitis C virus (HCV), Human Immunodeficiency Virus (HIV).
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Gastrointestinal Viruses:
- Examples: Adenovirus, astrovirus, sapovirus.
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Genital Viruses:
- Examples: Human papillomavirus (HPV), herpes simplex virus (HSV), and human immunodeficiency virus (HIV).
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Neurotropic Viruses:
- Examples: Rabies virus, herpes simplex virus (HSV), and enteroviruses.
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Vector Control:
- Examples: Mosquito-borne viruses like Zika virus, Dengue virus, and chikungunya virus.
- VTM Type: Universal Viral Transport Media, Liquid-based VTMs.
Uses of Viral Transport Media:
- Viral transport media are used to collect and transport virus-infected specimens.
- These are also employed to keep other organisms alive, such as mycoplasma, chlamydiae, and ureaplasma.
- VTMs also aid in increasing the amount of viral particles in a sample.
- Liquid transport media are typically used to carry swabs or materials that have been released into the medium from a collection swab.
- It allows for the collection and transportation of samples in regions where refrigeration is not available.
Limitations of Viral Transport Media:
- Contaminant growth may be detected during the long term of travel.
- The specimen should be injected in the appropriate medium as soon as feasible after shipment. The time between sample collection and inoculation onto the culture medium should be kept to a minimum for the best outcomes.
- Some viruses may be more labile than others, and VTMs may be equally effective.
- Some antibiotics and chemicals used in VTMs may alter the pH of the fluid, affecting the organism’s survival
References and sources:
- Johnson, F. B. (1990). Transport of viral specimens. Clinical microbiology reviews, 3(2), 120–131. https://doi.org/10.1128/cmr.3.2.120
- https://www.who.int/ihr/publications/Annex8.pdf?ua=1
- https://www.cdc.gov/coronavirus/2019-ncov/downloads/Viral-Transport-Medium.pdf
