Project description:Colistin is a crucial last-line drug used for the treatment of life-threatening infections caused by multi-drug resistant strains of the Gram-negative bacteria, Acinetobacter baumannii. However, colistin resistant A. baumannii isolates can be isolated following failed colistin therapy. Resistance is most often mediated by the addition of phosphoethanolamine (pEtN) to lipid A by PmrC, following missense mutations in the pmrCAB operon encoding PmrC and the two-component signal transduction system PmrA/PmrB. We recovered an isogenic pair of A. baumannii isolates from a single patient before (6009-1) and after (6009-2) failed colistin treatment that displayed low/intermediate and high levels of colistin resistance, respectively. To understand how increased colistin-resistance arose, we genome sequenced each isolate which revealed that 6009-2 had an extra copy of the insertion sequence element ISAba125 within a gene encoding an H-NS-family transcriptional regulator. Consequently, transcriptomic analysis of the clinical isolates identified was performed and more than 150 genes as differentially expressed in the colistin-resistant, hns mutant, 6009-2. Importantly, the expression of eptA, encoding a second lipid A-specific pEtN transferase, but not pmrC, was significantly increased in the hns mutant. This is the first time an H-NS-family transcriptional regulator has been associated with a pEtN transferase and colistin resistance.
Project description:Guanidine DNA quadruplex (G4-DNA) structures convey a distinctive layer of epigenetic information that is critical for the regulation of key biological activities and processes as genome transcription regulation, replication and repair. Despite several works that have been published recently, the information regarding their role and possible use as therapeutic drug targets in bacteria is still scarce. Here, we tested the biological activity of a small G4-DNA ligand library based on the naphthalene diimide (NDI) pharmacophore, against both Gram-positive and Gram-negative bacteria. For the best compound identified, NDI-10, the action mechanism was further characterized. Gram-negative bacteria were more resistant altogether due to the presence of the outer membrane, although the activity of the G4-Ligand was generally bactericidal, while it was bacteriostatic for Gram-positive bacteria. This asymmetric activity could be related to the different prevalence of putative G4-DNA structures in each group, the influence that they can exert on the gene expression (which was found more severe for the Gram-negative bacteria) and the role of the G4 structures in these bacteria, that seems to be more related to promote transcription in Gram-positive bacteria and repress transcription in Gram-negative.