Impedance-based method for the quantification of infectious SARS-CoV-2.

Area of Science:

• Virology
• Cell Biology
• Infectious Disease Research

Background:

• Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19, necessitating accurate methods for quantifying infectious viral loads.
• Traditional titration methods for infectious viruses often have low throughput, limiting large-scale sample screening.
• Understanding transmission and validating inactivation treatments require robust infectious titration assays.

Purpose of the Study:

• To develop and validate a Real-Time Cell Analysis (RTCA) assay for quantifying infectious SARS-CoV-2.
• To establish a correlation between cell impedance measurements and viral concentration.
• To provide a simplified and high-throughput method for infectious SARS-CoV-2 titration.

Main Methods:

• Utilized Real-Time Cell Analysis (RTCA) to measure cell impedance changes upon SARS-CoV-2 infection.
• Monitored virus-specific Cell Index (CI) drop kinetics.
• Correlated the time to a 50% drop in CI values (tCI50) with viral concentration to create a standard curve.
• Employed an improved Spearman and Kärber method for infectious titer quantification, correlating CI drop with Cytopathic Effect.

Main Results:

• The RTCA assay demonstrated virus-specific kinetics in cell impedance, showing a distinct Cell Index (CI) drop.
• A reliable standard curve was established by correlating viral concentrations with the time to a 50% CI drop (tCI50).
• The assay achieved reduced uncertainty in titer estimation (0.26 log10 with 16 wells/dilution), indicating high precision.

Conclusions:

• The developed RTCA assay is a powerful and simplified tool for quantifying infectious SARS-CoV-2.
• This method facilitates effective risk assessment in food and environmental virology.
• RTCA offers a high-throughput alternative to traditional low-throughput titration methods.