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Département Microbiologie

Séminaires Microbiologie

Les événements Microbiologie sont affichés en bleu dans l’agenda I2BC...

La prochaine journée du département aura lieu le 28 avril 2017.
Contact : Nathalie Dautin

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  • Mardi 4 décembre 11:00-12:30 - Muriel Masi - « Membranes et Cibles Thérapeutiques », UMR_MD1, Inserm U1261 & IRBA, Aix-Marseille Université

    Envelope permeability, antibiotic accumulation and resistance in Gram-negative bacteria : New insights from the European IMI-TRANSLOCATION program

    Résumé : The alarming threat of multidrug resistant bacteria is leaving clinicians with very limited options to combat infections especially those caused by Gram-negative pathogens. As part of the European IMI antimicrobial resistance programme New Drugs for Bad Bugs, TRANSLOCATION aimed to increase the overall understanding of how Gram-negative bacteria accumulate antibiotics and come up with new solutions to fight against these pathogens ( During the last 5 years, my research projects focused on the bacterial cell envelope of clinically relevant Enterobacteriaceae as a permeability barrier that control antibiotic translocation, a key compartment that senses and responds to external antibiotic stresses, and a target for the development of new antimicrobials.
    In the first part of my talk, I will illustrate progress in WGS in linking bacterial genotypes and phenotypes, with the recent example of Enterobacter aerogenes. In this work, we report the evolution of antibiotic resistance of E. aerogenes strains that were sequentially isolated during the clinical course of two patients with imipenem. Comparative genomics of these isolates revealed a number of mutations, some of which located in genes encoding sensor kinases of regulatory two-component systems (TCS) — namely CpxA, PhoQ and PmrB. Cpx is an envelope stress response pathway that monitor and defend the bacterial cell envelope integrity against harmful conditions. It is constituted by the canonical CpxAR TCS and the periplasmic auxiliary protein CpxP. The CpxA mutation then was fully characterized in Escherichia coli K12 as a gain-of-function mutation that constitutively activates the Cpx stress response and confers a high level of resistance to various classes of antibiotics including β-lactams and aminoglycosides. This was mainly due to downregulation of outer membrane porins, upregulation of AmpC β-lactamase and AcrD efflux pump. In addition, the identified mutation that yielded to a Y144N substitution in the periplasmic sensing domain of the CpxA displaced interactions with CpxP in bacterial two-hybrid assay. Altogether our results clearly show the complex and intimate connection between β-lactam therapy, cell wall homeostasis and activation envelope stress response systems. This work also points to the major role of TCS in antibiotic-mediated stress adaptation and resistance, and validates TCS as new targets for antibiotic adjuvants.
    In the second part of my talk, I will discuss some of the conceptual and experimental challenges to understand rules for permeation through general porins and improve antibiotic accumulation. Reduced influx through outer membrane porins and increased efflux activity both mainly contribute to inadequate intracellular drug concentrations and times of residence close to their target. In this context, I will first present (micro)spectrofluorimetric approaches that allow quantification of the intracellular antibiotic content in intact cells. I will then present the recent development of a scoring function based on structural and physical properties of general porins and series of antibiotics β-lactam antibiotics. This scoring function correlated with in vitro permeation assays and in vivo antibacterial activity. Ultimately, we seek to use these approaches to identify physicochemical properties to improve the drug translocation, investigate the activity of permeability adjuvants, and screen for antibiotic accumulation defects in clinical strains.

    Lieu : Salle Kalogeropoulos - Bâtiment 400, Campus d’Orsay

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