Our team studies the long-term impact of pathogenic bacteria on health. In particular, we are interested in understanding the molecular basis of persistent bacterial infections and determine mechanistic details underlying bacterial dormancy. We use the facultative intracellular pathogen Listeria monocytogenes as a bacterial model to tackle these questions. In the long run, we hope our research will help to find new treatments to limit recurrent infections and provide new strategies to eradicate persistent pathogens.
The pathogenicity of L. monocytogenes is linked to the bacterium’s ability to invade different cell types, such as the epithelial cells of the intestine, liver, brain and placenta. When it reaches the cytoplasm of these cells, L. monocytogenes proliferates and uses the force of actin polymerization to move into the cytosol and spread to neighboring cells. Although L. monocytogenes has been considered for long time a cytosolic bacterium, we have shown that after 2-3 days of infection in epithelial cells, bacteria stop producing ActA (the protein that triggers actin polymerisation on the bacterial surface) and are engulfed in vacuoles with lysosomal features (“Listeria-containing vacuoles”, LisCVs). Inside LisCVs, a bacterial subpopulations survive the acidic lysosomal milieu and enter in a slow/ non-replicative form. In the absence of ActA, bacteria can even parasitize host cells in a viable but non-culturable (VBNC) state, rendering L. monocytogenes undetectable on agar plates, classically used in clinical microbiology (Kortebi et al., 2017). We propose that intravacuolar L. monocytogenes could contribute to the asymptomatic carriage of this pathogen and render it tolerant to antibiotic therapy.
In this project of our team, currently funded by the ANR (French National Research Agency), by combining a high-content siRNA-based screening with transposon insertion sequencing (Tn-Seq) and transcriptomics, we aim at identifying host and bacterial features required for LisCVs biogenesis and L. monocytogenes long-term survival in epithelial cells.
L. monocytogenes is a non-spore-forming bacterium able to survive in a variety of stressful environments. One of its survival strategies is entry into a so-called viable but non-culturable (VBNC) state, where bacterial cells retain a slowed metabolism but are unable to grow on conventional culture media. VBNC pathogens pose a significant risk for human and animal health as they are not detected by standard growth-based techniques and can “wake up” back into a vegetative and virulent state. We have recently developed in the lab a robust protocol to induce VBNC transition of L. monocytogenes under condition of nutrient starvation. We discovered that during VBNC transition, L. monocytogenes bacilli progressively transform into coccoidal forms, after shedding their cell wall in a moult-like process to generate cell wall deficient bacteria . Our data shake the longstanding assumption of the cell wall as a hallmark of microbes. By combining cell microscopy, biochemistry and integrative multi-OMICS (transcriptomics, proteomics and metabolomics), we aim at characterizing the fundamental mechanisms required for the transition from a vegetative state to a dormant VBNC state.
Many bacterial pathogens manipulate host epigenome for efficient and long-term colonization. This is achieved by releasing virulence factors that directly target host chromatin or hijacks its epigenetic machinery. In this collaborative project which gathers 5 different teams from Pasteur Institute and Paris Diderot University, we propose to fight bacterial pathogens by chemically targeting host-induced epigenetic modifications. By targeting the host machinery, this innovative strategy should minimize the emergence of microbial resistance.
