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The stress of infected cells is visible

Researchers from the Cancer Biology and Infection laboratory have observed that cell nuclei infected by bacteria are getting brighter. They developed a method to study the virulence of bacteria and to identify future antibiotics or anti-virulants from this property they have automated.

Published on 20 February 2018
Antibiotic resistance is a public health threat. It is therefore necessary to search for new antibiotics and/or means to specifically block the virulence of pathogenic bacteria. In this context, it would be strategically advantageous to develop a simple and rapid method for measuring the pathogenicity of these bacteria.

By observing cells infected by bacteria, researchers from the Bacterial Pathogenesis and Cellular Responses team [Cancer Biology and Infection laboratory] noticed that the nuclei of damaged cells became brighter (Figure). On the basis of this observation, they quantified the intensity of the fluorescence emitted by the nuclei (collaboration with the Center for the screening for BioActive Molecules plateform of the Large Scale Biology laboratory), and then showed that the percentage of cells having a bright nucleus is a very good indicator of the progress of the infection. This analysis now makes it possible to obtain kinetics that are all potential "signatures" of bacterial virulence.

Nuclei coloration (Hoechst) are performed on living cells which are then brought into contact with the bacteria. A fluorescence microscope observation is performed andimages are taken every 15 minutes to monitor the effect of bacteria in real time. Automated microscopes can take images in plates containing 96 or 384 wells, so that many different conditions can be tested in parallel.
Inset photo: trimming nuclei that appear more and more brilliant as the bacterial infection progresses.

The researchers then applied this approach to other types of host cells or bacteria using different mechanisms of intoxication (implementation of retraction or death of cells, for example). The researchers were also able to demonstrate that this imaging method was perfectly adapted to library screening strategies (CRISPR-Cas9, siRNA, mutant bacteria, clinical strains, etc.) with the aim of identifying bacteria or modified cells that would present particular properties with respect to infection. This technique finally proves to be usable for the screening of chemical molecules or antibodies that protect cells from damage caused by bacteria; knowing that the possible deleterious effects (side effects) for the cells and bacteria of such potential therapeutic candidates can also be measured.
The method called CLIQ-BID for "Cell Live Imaging Quantification of Bacteria Induced Damage" is a simple and accessible tool that allows to study the virulence of bacteria and identify future antibiotics or anti-virulent in order to disarm the bacteria without killing them.

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