The Unité des Agents Antibactériens studies the genetic basis, biochemical mechanisms, heterologous expression, evolution, and dissemination of antibiotic resistance in bacteria pathogenic for humans

Antibiotic resistance by modulation of gene expression. Acquired inducible vancomycin resistance by remodeling of peptidoglycan synthesis in Gram-positive cocciand intrinsic multidrug-resistance in Acinetobacterby efflux are under the control of two-component regulatory systems. We have shown that constitutively resistant Enterococcusselected under therapy have suffered mutations in the sensor, in the regulator, or in a transcription terminator. We have also detected a three-component regulatory system in Enterococcuswhich is currently under study. Multidrug resistance in Acinetobactercan also be due to overexpression of efflux systems due to mutations in two component systems. We have developed a biochip for detection of resistance in Acinetobacter by efflux or acquisition of foreign DNA.

Biological cost and dissemination of vancomycin resistance. We have evaluated, in vitro and in vivo, the biological cost of vancomycin resistance in Enterococcusand Staphylococcusand the consequence on its dissemination. A dual bioluminescence system has been engineered that allows comparison of the isogenic strains constructed. A high fitness cost was observed only when resistance was induced, i.e.in the presence of the antibiotic. This finding may account for the impressive dissemination of vancomycin resistance and its transfer to Methicillin Resistant S. aureus (MRSA).

Aminoglycoside resistance by ribosomal 16S rRNA methylation. We have detected high-level resistance to all clinically available aminoglycosides in enterobacteria and demonstrated that this new phenotype was due to methylation of the N7 position of nucleotide G1405 in the 16S rRNA that blocks aminoglycoside binding by ribosomes. The three-dimensional structure of two methylases has been determined. These high-resolution structures should underpin the design of potential inhibitors of these enzymes which could be used to restore the activity of aminoglycosides against resistant pathogens.

Resistance island in Pseudomonas aeruginosa. Study of clinical isolates led to the characterization of multidrug resistance transposon Tn6061and the description of ISCR6. It also indicated that IS6100, present at one end of the transposon, can mediate large chromosomal inversions contributing to genetic adaptability of the host.

Gene and protein transfer from an E. coli derived bacterial vector to mammalian cells. Recent development has dealt with cell delivery of large (> 150 kb) bacterial artificial chromosomes and the construction of second generation vectors with the genes of interest integrated in the chromosome that have been patented. Protein delivery is exploited for stimulation of mucosal immunity in vaccines delivered by the nasal or the intragastric route.

Centre National de Référence des Antibiotiques (CRAB). The public health missions of the CRAB, assigned by the French Health Ministry, consist in the maintenance of strain collections, evaluation of the in vitro activity of new antibiotics, the development of reference techniques for antibioticsusceptibility testing, and the contribution to surveillance of resistance.

Keywords: bacteriology, antibiotics, resistance, gene transfer, infectious diseases

Liou, F.G., S. Yoshizawa, P. Courvalin, and M. Galimand. 2006. Aminoglycoside resistance by ArmA-mediated ribosomal 16S methylation in human bacterial pathogens. J. Mol. Biol. 359 : 358-364.

Périchon, B., P. Courvalin, and M. Galimand. 2007. Transferable resistance to aminoglycosides by methylation of G1405 in 16S rRNA and to hydrophilic fluoroquinolones by QepA-mediated efflux in Escherichia coli. Antimicrob. Agents Chemother. 51 : 2464-2469.

Périchon, B., P. Bogaerts, T. Lambert, P. Courvalin, and M. Galimand. 2008. Sequence of conjugative plasmid pIP1206 mediating resistance to aminoglycosides by rRNA methylation and to hydrophilic fluoroquinolones by efflux. Antimicrob. Agents Chemother. 52 : 2581-2592.

Schmitt, E., M. Galimand, M. Panvert, P. Courvalin, and Y. Mechulam. 2009. Structural bases for 16S rRNA methylation catalyzed by ArmA and RmtB methyltransferases. J. Mol. Biol. 388 : 570-582.

Weber, P., D. Meziane-Cherif, A. Haouz, F. A. Saul, and P. Courvalin. 2009. Crystallization and preliminary X-ray analysis of d-Ala:d-Ser ligase associated with VanG-type vancomycin resistance in Enterococcus faecalis BM4518. Acta Cryst. Section F65 :1024-1026.