Monitoring Influenza Virus Survival Outside the Host Using Real-Time Cell Analysis

Summary

Reported here is a protocol for the quantification of infectious viral particles using real-time monitoring of electrical impedance of infected cells. A practical application of this method is presented by quantifying influenza A virus decay under different physicochemical parameters mimicking environmental conditions.

Abstract

Methods for virus particle quantification represent a critical aspect of many virology studies. Although several reliable techniques exist, they are either time-consuming or unable to detect small variations. Presented here is a protocol for the precise quantification of viral titer by analyzing electrical impedance variations of infected cells in real-time. Cellular impedance is measured through gold microelectrode biosensors located under the cells in microplates, in which magnitude depends on the number of cells as well as their size and shape. This protocol allows real-time analysis of cell proliferation, viability, morphology and migration with enhanced sensitivity. Also provided is an example of a practical application by quantifying the decay of influenza A virus (IAV) submitted to various physicochemical parameters affecting viral infectivity over time (i.e., temperature, salinity, and pH). For such applications, the protocol reduces the workload needed while also generating precise quantification data of infectious virus particles. It allows the comparison of inactivation slopes among different IAV, which reflects their capacity to persist in given environment. This protocol is easy to perform, is highly reproducible, and can be applied to any virus producing cytopathic effects in cell culture.

Introduction

The transmission of a virus relies on the combination of several factors. For a virus secreted in the environment, its transmission also depends on the ability to persist in conditions outside of the host. Studying viral inactivation in general is, therefore, a crucial step in helping national health authorities and policy makers implement control and biosafety measures.

Knowledge about virus persistence in natural and laboratory settings has increased considerably over the last decade. In the case of influenza A viruses (IAV), their transmission routes submit viral particles to a wide range of environmental conditions. Specifically, they c....

Protocol

Handle all influenza viruses according to appropriate biosafety level requirements (BSL-2 or higher depending on the subtype). Use IAV strains with a low passage history (less than 5x on MDCK cells) to insure low variation between experiments.

1. Preparation of reagents and starting materials

1. Preparation of MDCK cells and sterile cell culture medium
   1. Cultivate Madin-Darby Canine Kidney (MDCK) cells in modified Eagle’s medium (MEM) supplemented with 10% heat inactiv.......

Discussion

RTCA is an impedance-based technology that is increasingly used for real-time monitoring of cell properties, such as cell adherence, proliferation, migration and cytotoxicity. In this study, the capacity of this technology to assess IAV survival outside the host is demonstrated by measuring virus inactivation slope. Fastidious techniques such as TCID₅₀ and plaque assays are replaced by objective real-time assessment of cell viability, thus reflecting cytopathic effects induced by the virus. Similar to the TCID.......

Materials

Name	Company	Catalog Number	Comments
0.25%Trypsin	ThermoFisher	25200056
75 cm2 tissue culture flask	Falcon	430641U
E-Plate 16 (6 plates)	ACEA Biosciences, Inc	5469830001	E-plates are avalible in different packaging
FCS	Life technologies (gibco)	10270-106
MEM 1X	Life technologies (gibco)	31095029
PBS 1X	Life technologies (gibco)	14040091
Penicillin-Streptomycin	Life technologies (gibco)	11548876
TPCK-Trypsin	Worthington	LS003740
xCELLigence Real-Time Cell Analysis Instrument S16	ACEA Biosciences, Inc	380601310	The xCELLigence RTCA S16 instruments are available in different formats (16-well, 96-well, single or multi-plate)