Par des méthodes de nature probabiliste, nous démontrons des nouveaux résultats de rigidité pour des groupes et des pseudo-groupes de difféomorphismes de variétés unidimensionnelles dont la classe de différentiabilité est intermédiaire (i.e. entre C 1 et C 2). En particulier, nous prouvons des généralisations du théorème de Denjoy et d'un lemme classique de Kopell pour des groupes abéliens. Ensuite, nous appliquons les techniques introduites à l'étude des feuilletages de codimension 1 dont la régularité transverse est intermédiaire. Nous obtenons notamment des versions généralisées du théorème de Sacksteder en classe C 1. Nous finissons par quelques remarques à propos de la mesure stationnaire

Pseudomonas aeruginosa, a major cause of nosocomial and chronic infections, is considered a paradigm of antimicrobial resistance development. However, the evolutionary trajectories of antimicrobial resistance and the impact of mutator phenotypes remain mostly unexplored. Therefore, whole-genome sequencing (WGS) was performed in lineages of wild-type and mutator (⌬mutS) strains exposed to increasing concentrations of relevant antipseudomonal agents. WGS provided a privileged perspective of the dramatic effect of mutator phenotypes on the accumulation of random mutations, most of which were transitions, as expected. Moreover, a frameshift mutagenic signature, consistent with error-prone DNA polymerase activity as a consequence of SOS system induction, was also seen. This effect was evidenced for all antibiotics tested, but it was higher for fluoroquinolones than for cephalosporins or carbapenems. Analysis of genotype versus phenotype confirmed expected resistance evolution trajectories but also revealed new pathways. Classical mechanisms included multiple mutations leading to AmpC overexpression (ceftazidime), quinolone resistance-determining region (QRDR) mutations (ciprofloxacin), oprD inactivation (meropenem), and efflux pump overexpression (ciprofloxacin and meropenem). Groundbreaking findings included gain-of-function mutations leading to the structural modification of AmpC (ceftazidime), novel DNA gyrase (GyrA) modification (ciprofloxacin), and the alteration of the ␤-lactam binding site of penicillin-binding protein 3 (PBP3) (meropenem). A further striking finding was seen in the evolution of meropenem resistance, selecting for specific extremely large (>250 kb) genomic deletions providing a growth advantage in the presence of the antibiotic. Finally, fitness and virulence varied within and across evolved antibiotic-resistant populations, but mutator lineages showed a lower biological cost for some antibiotics.

Abstract. We develop dynamical methods for studying left-orderable groups as well as the spaces of orderings associated to them. We give new and elementary proofs of theorems by Linnell (if a left-orderable group has infinitely many orderings, then it has uncountably many) and McCleary (the space of orderings of the free group is a Cantor set). We show that this last result also holds for countable torsion-free nilpotent groups which are not rank-one Abelian. Finally, we apply our methods to the case of braid groups. In particular, we show that the positive cone of the Dehornoy ordering is not finitely generated as a semigroup. To do this, we define the Conradian soul of an ordering as the maximal convex subgroup restricted to which the ordering is Conradian, and we elaborate on this notion.Résumé. Nous développons des méthodes dynamiques pourétudier les groupes ordonnables ainsi que leurs espaces d'ordres associés. Nous donnons des preuves nouvelles etélémentaires de théorèmes dûsà Linnell (si un groupe ordonnable possède une infinité d'ordres, alors il possède une infinité non dénombrable) et McCleary (l'espace des ordres du groupe libre est un Cantor). Nous montrons que ce dernier résultat est valable aussi pour les groupes nilpotents dénombrables et sans torsion qui ne sont pas abéliens de rang un. Finalement, nous appliquons nos méthodes au cas des groupes de tresses. En particulier, nous démontrons que le cone positif de l'ordre de Dehornoy n'est pas de type fini en tant que semi-groupe. Pour ce faire, nous définissons le noyau conradien d'un ordre commeétant le plus grand sous-groupe convexe sur lequel la relation est conradienne, et nous travaillons avec cette notion.

The original version (in Spanish) of this text was prepared for a mini-course in Antofagasta, Chile. Subsequently, enlarged and revised versions were published in the series Monografías del IMCA (Perú) and Ensaios Matemáticos (Brasil). This translation arose from the necessity of making this text accessible to a larger audience. I would like to thank Juan Rivera-Letelier for his invitation to the II Workshop on Dynamical Systems ( 2001), for which the original version was prepared, and Roger Metzger for his invitation to IMCA (2006), where part of this material was presented. I would also like to thank both Étienne Ghys and Maria Eulália Vares for motivating me and allowing me to publish the revised Spanish version in Brasil, as well as all the people who strongly encouraged me to conclude this English version.This work was partially supported by CONICYT and PBCT via the Research Network on Low Dimensional Dynamics. I would also to acknowledge the support of both the UMPA Department of the École Normale Supérieure de Lyon, where the idea of writing this text was born during my PhD thesis, and the Institut des Hautes Études Scientifiques, where the original notes started taking its definite form while I benefited from a one-year postdoctoral position.This work owes a lot to many of my colleges. Several remarks spread throughout the text and the content of some examples and exercises were born during fruitful and quite stimulating discussions. It is then a pleasure to thank Sylvain Crovisier (Proposition 4.2.25),

Overproduction of multidrug resistance (MDR) efflux pumps is involved in the resistance to a wide range of compounds in bacteria. These determinants extrude antibiotics, but also bacterial metabolites like quorum-sensing signals. Non-regulated extrusion of bacterial metabolites might produce a metabolic burden, so that MDR-overproducing mutants could have a reduced fitness when compared with their parental strains. To test such a possibility, we have compared the behaviour of two MDR Pseudomonas aeruginosa in vitro selected mutants (nalB and nfxB) with their isogenic parental strain with respect to some properties with potential relevance for the survival in the environment and the virulence of this bacterial species. Overproduction of the MDR determinants MexABOprM (nalB mutant) and MexCDOprJ (nfxB mutant) decreased the survival in water, the production of phenazines and proteases, and the virulence (using a Caenorhabditis elegans model system) of the P. aeruginosa mutants. In contrast, the capability of forming biofilms was not impaired. The simple models tested in the present work can enable the analysis of the fitness of large numbers of antibiotic-resistant bacteria by using more realistic approaches than the in vitro competition assays currently used.

No abstract

This work is devoted to the study of minimal, smooth actions of finitely generated groups on the circle. We provide a sufficient condition for such an action to be ergodic (with respect to the Lebesgue measure), and we illustrate this condition by studying two relevant examples. Under an analogous hypothesis, we also deal with the problem of the zero Lebesgue measure for exceptional minimal sets. This hypothesis leads to many other interesting conclusions, mainly concerning the stationary and conformal measures. Moreover, several questions are left open. The methods work as well for codimension-one foliations, though the results for this case are not explicitly stated.

Nous démontrons que tout homomorphisme d'un groupe de Kazhdan discret dans le groupe des difféomorphismes directs du cercle de classe C 1+α (α > 1/2) a une image finie.  2002 Éditions scientifiques et médicales Elsevier SAS ABSTRACT.-We prove that every homomorphism from a discrete Kazhdan group to the group of orientation-preserving diffeomorphisms of the circle of class C 1+α (α > 1/2) has a finite image.