The ability of Pseudomonas aeruginosa to cause difficult-to-treat infections relies on its capacity to fine-tune the expression of multiple virulence traits via the las , rhl , and pqs QS systems. Both the pqs effector protein PqsE and the rhl transcriptional regulator RhlR are required for full production of key virulence factors in vitro and pathogenicity in vivo .

Summary: The stringent response regulator DksA plays a key role in Gram negative bacteria adaptation to challenging environments. Intriguingly, the plant and human pathogen Pseudomonas aeruginosa is unique as it expresses two functional DksA paralogs: DksA1 and DksA2. However, the role of DksA2 in P . aeruginosa adaptive strategies has been poorly investigated so far. Here, RNA‐Seq analysis and phenotypic assays showed that P . aeruginosa DksA1 and DksA2 proteins are largely interchangeable. Relative to wild type P . aeruginosa , transcription of 1779 genes was altered in a dksA1 dksA2 double mutant, and the wild type expression level of ≥90% of these genes was restored by in trans complementation with either dksA1 or dksA2 . Interestingly, the expression of a small sub‐set of genes seems to be preferentially or exclusively complemented by either dksA1 or dksA2 . In addition, evidence has been provided that the DksA‐dependent regulation of virulence genes expression is independent and hierarchically dominant over two major P . aeruginosa regulatory circuits, i.e ., quorum sensing and cyclic‐di‐GMP signalling systems. Our findings support the prominent role of both DksA paralogs in P . aeruginosa environmental adaptation.

Colistin is used as a last-resort antibiotic against extensively drug-resistant Gram-negative pathogens. However, colistin resistance is on the rise.

Background: Bacterial resistance to antibiotics continues to rise globally, posing a significant public health challenge and incurring substantial social and economic burdens. In response, the World Health Organization (WHO) has published a list of priority pathogens for which effective treatment options are critically limited. Several antibiotics are categorized as Gram-positive-only (GPO) agents due to their lack of activity against Gram-negative species. Although these compounds often target conserved bacterial processes, their limited spectrum is largely attributed to poor penetration of the Gram-negative outer membrane (OM). Results: In this study, we designed and synthesized a series of adarotene-derived compounds to evaluate the impact of introducing positively charged groups on their interaction with the Gram-negative OM. One of the newly synthesized derivatives, SPL 207, displayed minimum inhibitory concentration (MIC) values ranging from 8 to 64 µM against a panel of Gram-positive and Gram-negative bacteria. The ability of SPL207 to disrupt outer and inner membrane permeability was evaluated using fluorescence assays and confocal microscopy, revealing that the compound compromises membrane integrity across all tested Gram-negative bacteria. Strong synergistic activity was observed in combination with colistin against three P. aeruginosa colistin-resistant strains. Atomistic details of membrane interference were elucidated by molecular dynamics (MD) simulations, with SPL207 clearly acting as a membrane destabilizer by enhancing Ca²⁺ ions diffusion and lipids destabilization. Conclusions: Although the observed MIC values remain above clinically acceptable thresholds, these findings provide a promising proof of concept. The further structural optimization of adarotene derivatives may yield novel broad-spectrum agents with improved antimicrobial potency against MDR pathogens.