Mechanisms of Bacterial Resistance to Antibiotics


The evolution of bacterial resistance to antimicrobials poses nowadays a major thread to global human health and food security. In our group we are interested in revealing the molecular basis of the resistance mechanisms to last generation beta-lactam antibiotics, in particular the carbapenems, and the evolution and dissemination of the genes involved. The growing resistance to carbapenems among non-fermentative Gram-negative bacilli represents a major global challenge. Members of the Acinetobacter genus in particular, such as A. baumannii, possess clinical relevance due to their incidence in nosocomial infections and associated mortality, conforming one of our study models. In turn, Pseudomonas (P. putida group) and Acinetobacter bereziniae provide environmental reservoirs of resistance genes, representing other of our study models with the aim to elucidate their role in the transfer of resistance between pathogen and environmental bacteria.

Research Lines

Antimicrobial multiresistance in Acinetobacter baumannii analyzed from a multifactorial perspective. Evolution and dissemination of plasmids carrying OXA-type carbapenemase genes in clinical strains of local origin. Biogenesis of these enzymes

Antimicrobial resistance in A. baumannii has a multifactorial basis and includes the production of oxacillinases (OXA) endowed with carbapenemase activity, mainly acquired from horizontal gene transfer (HGT). Our objective is elucidating the molecular basis of evolution and dissemination of blaOXA genes among multiresistant clones of A. baumannii. The blaOXA gene is the main responsible of carbapenem resistance among local strains and is bounded with recognition sites for the XerC/D site-specific recombinases. Our hypothesis is that these sites participate in the mobilization of blaOXA genes to other genomic locations or plasmids by recombination events. We study the role of plasmidic XerC/D sites in the evolution of resistance plasmids and HGT mechanisms involved in their dissemination among the clinical A. baumannii population. The carbapenemase OXA-58 is exported to the bacterial periplasm as a lipoprotein in the form of cargo of outer membrane vesicles, thus contributing to bacterial multiresistance. The biogenesis mechanism of these vesicles and their role in multiresistance are also subjects of our study.  Principal investigators: J. Morán Barrio – A. Limansky – A. Viale.

Pseudomonas (P. putida group) and Acinetobacter bereziniae as environmental reservoirs of blaVIM-2 y blaNDM-1 metallo-beta-lactamase genes conferring carbapenem resistance. Genetic platforms responsable of the dissemination and clinical impact

The emergence of nosocomial strains resistant carbapenem antibiotics is mainly due to intragenomic events involving the mobilization of carbapenemase genes including metallo-beta-lactamase (MBL) genes, added to horizontal gene transfer (HGT). It is therefore relevant to elucidate the contribution of each of these events to the evolution of this resistance. In this context, and under the hypothesis that resistance genes emerge in bacteria subjected to antimicrobial selective pressure, it is essential to characterize genetic platforms carrying MBL genes of both ample dissemination (blaVIM-2), as well as recently occurring (blaNDM-1). We study with this objective the molecular basis of dissemination of these MBL genes in microbial organisms that constitute environmental reservoirs, with special emphasis in the genus Pseudomonas and Acinetobacter, including Pseudomonas putida group species and A. bereziniae. An increase knowledge of the evolution and dissemination of these genes from these reservoirs to pathogenic and multiresistant opportunistic species will certainly contribute to the control of nosocomial infections.  Principal investigators: A. Limansky - A. Viale - J. Morán Barrio.

Role of proteins secreted in association to outer membrane vesicles to the physiopathology of Acinetobacter barumannii

baumannii pathogenesis is associated to antimicrobial multiresistance (MR) and to virulence factors still poorly characterized. There is a growing evidence that the outer membrane vesicles (OMV) are vehicles to transport bacterial proteins that contribute to the establishment of the infection. Our goal is to study the contribution of secretion proteins with special emphasis in lipoproteins, to the pathogen survival under stress conditions that mimic the contact with the host. We focus in particular in proteins secreted in association with A. baumannii OMV, with the aim to increase significantly our understanding of their role in the physiopathology of this organism. This, in turn, will reveal new targets for the development of therapeutic drugs. Principal investigator: J. Morán Barrio.

Selected Publications

  • Pseudomonas putida group species as reservoirs of mobilizable Tn402-like class 1 integrons carrying blaVIM-2 metallo-β-lactamase genes. Infect Genet Evol. 2021 Dec;96:105131. Brovedan MA, Marchiaro PM, Díaz MS, Faccone D, Corso D, Pasteran F, Viale AM, Limansky AS. (2021). doi: 10.1016/j.meegid.2021.105080.
  • What do we know about plasmids carried by members of the Acinetobacter genus? World J Microbiol Biotechnol. Jul 13;36(8):109. Brovedan MA, Cameranesi MM, Limansky AS, Morán-Barrio J, Marchiaro P, Repizo GD. (2020). doi: 10.1007/s11274-020-02890-7.
  • Microevolution in the major outer membrane protein OmpA of Acinetobacter baumanniiViale AM, Evans BA.   Microb Genom. 6(6):e000381. (2020) doi: 10.1099/mgen.0.000381.
  • Acinetobacter baumannii NCIMB8209: a Rare Environmental Strain Displaying Extensive Insertion Sequence-Mediated Genome Remodeling Resulting in the Loss of Exposed Cell Structures and Defensive Mechanisms. Repizo GD, Espariz M, Seravalle JL, Díaz Miloslavich JI, Steimbrüch BA, Shuman HA, Viale AM. mSphere 5(4):e00404-20. (2020) doi: 10.1128/mSphere.00404-20.
  • Acquisition of plasmids conferring carbapenem and aminoglycoside resistance and loss of surface-exposed macromolecule structures as strategies for the adaptation of Acinetobacter baumannii CC104O/CC15P strains to the clinical setting. Cameranesi MM, Paganini J, Limansky AS, Moran-Barrio J, Salcedo SP, Viale AM, Repizo GD. Microb Genom. Mar 26. (2020) doi: 10.1099/mgen.0.000360.
  • Characterization of the diverse plasmid pool harbored by the blaNDM-1-containing Acinetobacter bereziniae HPC229 clinical strain. Brovedan M, Repizo GD, Marchiaro P, Viale AM, Limansky A. (2019) PLoS One. 14(11):e0220584. doi: 10.1371/journal.pone.0220584.
  • Site-specific recombination at XerC/D sites mediates the formation and resolution of plasmid co-integrates carrying a blaOXA-58- and TnaphA6-resistance module in Acinetobacter baumanniiCameranesi MM, Morán-Barrio J, Limansky AS, Repizo GD, Viale AM. Front Microbiol. 9:66. (2018) doi: 10.3389/fmicb.2018.00066.6.0.
  • The Acinetobacter Outer Membrane Contains Multiple Specific Channels for Carbapenem β-Lactams as Revealed by Kinetic Characterization Analyses of Imipenem Permeation into Acinetobacter baylyi Cells. Morán-Barrio J, Cameranesi MM, Relling V, Limansky AS, Brambilla L, Viale AM. Antimicrob Agents Chemother. Feb 23;61(3):e01737-16. (2017) doi: 10.1128/AAC.01737-16.
  • Complete Sequence of a blaNDM-1-Harboring Plasmid in an Acinetobacter bereziniae Clinical Strain Isolated in Argentina. Brovedan M, Marchiaro PM, Morán-Barrio J, Cameranesi M, Cera G, Rinaudo M, Viale AM, Limansky AS. Antimicrob Agents Chemother. Oct;59(10):6667-9. (2015) doi: 10.1128/AAC.00367-15.
  • The complete nucleotide sequence of the carbapenem resistance-conferring conjugative plasmid pLD209 from a Pseudomonas putida clinical strain reveals a chimeric design formed by modules derived from both environmental and clinical bacteria. Marchiaro PM, Brambilla L, Morán-Barrio J, Revale S, Pasteran F, Vila AJ, Viale AM, Limansky AS. Antimicrob Agents Chemother. 58(3):1816-21. (2014) doi: 10.1128/AAC.02494-13.