With an increasing need for extensive research on SARS-CoV2 biology, the diagnosis of COVID-19 infections by cell culture relies heavily on the careful and aseptic collection of specimens. This is where specialized Viral Transport Medium (VTM) is required to protect the virus from environmental damage and maintain its activity with adequate sustainable transport system.
Over the years, a variety of transport media have been formulated including the early bacterial transport media. Although some swab-tube combinations have proven to be both effective and convenient, swabs which are toxic to the virus or culture should be avoided. Among liquid transport media, sucrose-based and broth-based media appear to be the most popular whereas some labs even use E-MEM media with sterile PBS.
Viral Transport Medium Guidelines by WHO and CDC
In the light of COVID-19 pandemic, specialized transport media allow more effective usage of the virus culture prior to diagnosis. Word Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) have recently brought out certain guidelines for VTM preparation to encourage more labs in preparation of efficient transport medium for viruses.
According to WHO, suitable Viral Transport Medium in collecting nasal and throat swabs from human patients is prepared with the following reagents: 10g veal infusion broth and 2g bovine albumin fraction in sterile distilled water (400 ml). For avoiding contamination, 0.8 ml gentamicin sulfate solution (50 mg/ml) and 3.2 ml amphotericin B (250 µg/ml) should also be added.
As per CDC guidelines, VTM reagents can be the following: HBSS with Calcium and magnesium ions, 2% heat inactivated FBS, 100µg/ml Gentamicin sulfate, and 0.5µg/ml Amphotericin B. In order to do sterility checks, CDC recommends the use of blood agar plate for checking microbial growth upon incubation.
In case of VTM aliquot storage, the temperature depends on time of storage. For an optimal storage period of 48 hours-96 hours, the sterile media should be stored at 2 to 8 degree Celsius without freezing. For a greater period of storage, the vials can be stored at -20 degree Celsius until used but one should prevent freeze-thaw cycles at any cost.
How is VTM effective for SARS-CoV-2 Transport?
The Viral Transport Medium’s nutritional components and pH makes it the ideal culture medium for transporting viral specimen from a patient’s body to the lab. HBSS, modified and enriched with BSA, cysteine, gelatin, sucrose and glutamic acid, help in maintaining the viability of the coronavirus during its transport. The VTM is also made selective to inhibit bacterial or fungal growth by adding Vancomycin, Amphotericin B and gentamycin.
The medium is designed to be biocompatible with primary cell cultures. Sucrose in the media further facilitates virus viability when stored at lower temperatures for longer period of time. Generally, VTM comes with nasopharyngeal and/or oropharyngeal swabs for collection which is followed by an immediate placing of the swabs into the sterile tubes containing the medium for maintaining optimal viral load.
AdvancellsTM VTM kit
Approved by ICMR and Validated by National Institute of Virology, AdvancellsTM Viral Transport Medium are specially manufactured based on WHO and CDC guidelines. The kit comes with three swab options: Cotton, Polyester, and Nylon, with customized plastic or wooden sticks. Furthermore, besides leak proof packaging, AdvancellsTM VTM guarantees standardized production and QC with minimized lot to lot variation. For enquiries on VTM kits, fill the form below or visit http://www.vaidyaglobal.com/advancellsgroup/vtm.php