Shell Vial Cell Culture: Principle, Procedure and Uses

Shell vial cell culture, a centrifuge-enhanced tissue culture assay, is a modification of conventional cell culture for the rapid detection of viruses in vitro. Rapid shell vial cultures are used to detect many viruses.

Principle of Shell Vial Cell Culture

The technique involves inoculation of the clinical specimen on to cell monolayer grown on a coverslip in the culture tube, followed by low-speed centrifugation and incubation.

It is thought that minor trauma caused by low-speed centrifugation into the susceptible cell surface enhances viral infectivity by enhancing viral entry.

The infected cell monolayer is then stained for the presence of viral antigens by direct fluorescent antibody (DFA) or indirect fluorescent antibody (IFA) staining within hours or days of inoculation. In this way, viruses that normally take days to weeks to produce a cytopathic effect (CPE) can be detected within 1 to 2 days by this culture technique.

Preparation of Shell Vials

Shell vials (15 mm X 45 mm 1-dram vials) are prepared by adding a round coverslip to the bottom of the shell vial, covering them with a normal growth medium, and adding appropriate cells. During incubation, a cell monolayer forms on top of the coverslip. Shell vials should be used 5 to 9 days after the cells have been added.

Shell vials with the already-formed monolayer can be purchased from various suppliers. MRC-5 (Human Fibroblast cells) is used as a cell line in shell vial culture.

Uses of Shell Vial Cell Culture

Rapidity achieved without compromising sensitivity has made shell vial cell culture an important technique in diagnostic virology. This technique can detect most viruses that grow in conventional cell culture and is especially useful for viruses that require relatively long incubation for producing cytopathic effects (CPE).

It is used to identify medically important viruses such as;

1. Cytomegalovirus (CMV),
2. Varicella-zoster Virus (VZV),
3. Herpes Simplex Virus (HSV),
4. Adenovirus,
5. Influenza A&B virus
6. Parainfluenza 1,2,3 virus and
7. Respiratory Syncytial Virus (RSV)

It is also used to culture obligate intracellular bacteria such as Chlamydia trachomatis.

Advantage

The advantage of a shell vial is its speed; most viruses are detected within 24 hours.

Limitations

1. Only one type of virus can be detected per shell vial. For example, a specimen that might contain influenza A and B, or adenovirus, would need to be inoculated to three separate virus-specific conjugates. This limitation can be overcome by using pooled antibodies followed by staining with individual antibody conjugates if positive in pool antibody testing.

References and further readings

1. Jayakeerthi, R. S., Potula, R. V., Srinivasan, S., & Badrinath, S. (2006). Shell Vial culture Assay for the rapid diagnosis of Japanese encephalitis, West Nile and Dengue-2 viral encephalitis. Virology Journal, 3(1), 2.
2. Tille, P. (2017). Bailey & Scott’s Diagnostic Microbiology (14 edition). Mosby.