Bacterial cell division requires precise regulation of septal peptidoglycan (PG) synthesis by the essential SEDS-bPBP synthase FtsWI. Activation of FtsWI is thought to occur through an allosteric cascade initiated by the late-arriving divisome protein FtsN and transmitted via the FtsQ-FtsL-FtsB (FtsQLB) complex, but the molecular details of this process remain incompletely defined and differ across species. Here, using the conditional essentiality of ftsN in Pseudomonas aeruginosa, we identify substitutions in the non-enzymatic pedestal domain of FtsI that bypass the requirement for FtsN. These mutations restore cell division in ΔftsN cells, suppress dominant-negative phenotypes of activation-defective ftsL alleles, and reduce cell length in an otherwise wild-type background, demonstrating that they alter FtsWI regulation to overcome the requirement for stimulation by both FtsN and FtsQLB. Mapping these mutations onto the P. aeruginosa FtsQLBWI structure reveals that they cluster on distinct surfaces of the pedestal domain. Because some of these substitutions have been identified in clinical P. aeruginosa isolates with increased aztreonam resistance, we next asked whether these regulatory substitutions alter β-lactam susceptibility. Variants at the FtsI-FtsL interface modestly reduce susceptibility to multiple β-lactam antibiotics, whereas a variant on the opposite face of the pedestal domain produces striking FtsN-dependent hypersusceptibility to the same molecules. These findings show that the FtsI pedestal domain plays a central role in the regulation of FtsWI and reveal a previously unrecognized relationship between divisome regulation and β-lactam susceptibility. More broadly, our work identifies the pedestal domain as a regulatory hub that integrates multiple inputs controlling septal PG synthesis and highlights its potential relevance to β-lactam resistance in clinical P. aeruginosa isolates.

Bloodstream infections (BSIs) caused by carbapenemase-producing Enterobacterales (CPE) carry a high mortality, and comparative real-world data remain limited, particularly for metallo-β-lactamase (MBL) and dual-carbapenemase producers. We conducted a single-centre, six-year (2020-2025) retrospective study of 308 adults with CPE BSIs at a Romanian tertiary hospital, applying multivariable logistic regression, Cox proportional-hazards models with a 72 h landmark analysis, and inverse-probability-of-treatment-weighted (IPTW) regression to examine 30-day mortality and microbiological recurrence. Pre-specified sensitivity analyses addressed calendar period, carbapenemase class and incomplete outcome ascertainment. Klebsiella pneumoniae accounted for 92.5% of isolates, MBL determinants for 44.1% and dual carbapenemases for 31.8%. Thirty-day mortality was 72% among 275 patients with documented day-30 status. Vasopressor requirement, viral pneumonia and bacterial respiratory infection were independently associated with death, whereas definitive ceftazidime/avibactam with or without aztreonam (C/AVI ± AZT) was associated with lower mortality (adjusted OR 0.38; 95% CI 0.17-0.83). Mortality was 66.3% with C/AVI ± AZT, 79.3% with colistin and 67.1% with other regimens. After IPTW, C/AVI ± AZT was associated with lower 30-day mortality than colistin (OR 0.48; 95% CI 0.26-0.93); in the OXA-48/KPC subgroup, the estimate was unchanged but less precise (OR 0.49; 95% CI 0.20-1.19). The association was attenuated and no longer significant after adjustment for calendar period (OR 0.72; 95% CI 0.37-1.42), with epoch-stratified estimates of 1.14, 0.75 and 0.44 for 2020-2021, 2022-2023 and 2024-2025, respectively; crude mortality under colistin was stable across epochs (81.1%, 76.6%, and 81.2%, respectively), whereas mortality under C/AVI ± AZT fell (83.3%, 72.2%, and 60.7%, respectively). Weighted estimates were near-identical in isolates with and without an MBL determinant (0.46 and 0.48, respectively). Recurrence (10.1%) was more frequent with single OXA-48 or MBL producers. C/AVI ± AZT was associated with lower 30-day mortality than colistin, but the association was concentrated in the period when the agent was routinely available and did not survive adjustment for calendar time. These findings describe an association, not a causal survival advantage.

Healthcare-associated infections (HAIs) caused by multidrug-resistant Klebsiella spp. represent a critical and escalating global public health threat. Carbapenem-resistant Klebsiella pneumoniae (CRKP) has been designated a critical-priority pathogen by the World Health Organization, and in the 2024 WHO Bacterial Priority Pathogens List, it was the top-ranked pathogen overall. The convergence of carbapenem resistance with hypervirulence in emerging strains has further complicated therapeutic decision-making. This review provides a narrative synthesis of the evidence published between 2020 and 2025 on the prevalence, resistance mechanisms, molecular epidemiology, clinical outcomes, and therapeutic strategies for Klebsiella pneumoniae infections acquired in healthcare settings, with particular attention to the Eastern European and Romanian context. PubMed/MEDLINE, Embase, Web of Science, and the Cochrane Library were searched for relevant publications from January 2020 to June 2025, supplemented by WHO and ECDC surveillance reports. Studies were selected narratively for their relevance to the themes addressed. No new quantitative pooling was undertaken; all summary estimates reported below are cited from the published meta-analyses and surveillance reports that generated them. In the most recent global meta-analysis of hospital-acquired CRKP infection, which pooled 61 studies and 513,307 patients from 14 countries, the global prevalence of CRKP among nosocomial K. pneumoniae infections was 28.69% (95% CI: 26.53-30.86%), with pronounced regional variation from 14.29% in high-income North America to 66.04% in South Asia, and 42.05% in Western Europe. Pooled mortality among patients infected with CRKP has been estimated in a separate meta-analysis at 42.14%, compared with 21.16% among patients infected with carbapenem-susceptible strains, rising to 54.30% in bloodstream infections. Surveillance data place Romania third in Europe for carbapenem resistance among invasive K. pneumoniae isolates, at 50.30%, with a distinctive predominance of NDM plus OXA-48-like co-producers. Ceftazidime-avibactam is recommended for KPC- and OXA-48-producing strains, whereas metallo-beta-lactamase producers require aztreonam-containing combinations. CRKP in HAIs constitutes a global epidemiological emergency characterised by marked regional heterogeneity in carbapenemase distribution, high attributable mortality and rapidly evolving molecular profiles. Locally adapted surveillance, rapid molecular diagnostics, and stewardship programmes are required since empirical therapy cannot be standardised across regions.

Multidrug-resistant Gram-negative bacteria pose a significant threat to global public health, with resistance mediated by metallo-β-lactamases being particularly prominent. Aztreonam/avibactam (AZA), a novel β-lactam/β-lactamase inhibitor combination, had been approved in China and the European Union for treating complicated intra-abdominal infections and hospital-acquired pneumonia (including ventilator-associated pneumonia) in adults. The combination exhibits broad-spectrum antimicrobial activity against carbapenemase-producing Enterobacterales. It inhibits KPC and OXA-48, and importantly, aztreonam (ATM) is stable against metallo-β-lactamases. Current in vitro activity studies strongly support the use of AZA against MBL-producing Enterobacterales, while its activity against non-fermenting bacteria appears to vary depending on the species and isolate, requiring further clinical confirmation. As a prime example of "repurposing existing drugs," its pharmacokinetics and pharmacodynamics have been thoroughly studied, and phase III studies have provided supportive safety and efficacy data, but the clinical evidence specifically concerning microbiologically confirmed MBL-producing infections remains limited and exploratory because of very small subgroup sizes. It is important to note that the combination of ceftazidime/avibactam (CZA) with ATM differs significantly from AZA in pharmacokinetic properties. Therefore, CZA plus ATM (CZA + ATM) cannot be considered an equivalent substitute for AZA. Currently, the resistance rate for AZA is low, with most cases being isolated events. The primary mechanisms of resistance involve mutations in the PBP3 gene, mutations and overexpression of β-lactamases, reduced outer membrane permeability, and overexpression of efflux pumps. Available data suggest that AZA is an important treatment option for severe infections caused by multidrug-resistant Enterobacterales, including MBL-producing strains, although pharmacoeconomic conclusions remain context-dependent.

Multidrug-resistant (MDR) Gram-negative bacteria pose significant therapeutic challenges due to their protective outer membranes and evolving resistance mechanisms. Exploiting bacterial iron uptake pathways via siderophore-antibiotic conjugates offers a promising strategy to enhance antibiotic efficacy. Here we synthesized siderophore-aztreonam, and siderophore-daptomycin conjugates and compared their activity to that of cefiderocol against select Gram-negative pathogens, including MDR Acinetobacter baumannii and Pseudomonas aeruginosa. Our in vitro studies demonstrated that siderophore conjugates exhibit comparable or superior antimicrobial activity to, with daptomycin conjugates notably retaining efficacy over extended periods. These findings suggest that conjugation with iron chelators that closely mimic natural siderophores can improve antibiotic delivery and activity, providing complementary options to existing therapies for multidrug-resistant Gram-negative infections.

Newer antibiotics have expanded treatment options for drug-resistant Gram-negative infections, but registration evidence is dominated by syndrome-based trials and post-approval evidence by heterogeneous observational cohorts. Translation to immunocompromised patients remains uncertain because profound neutropenia, transplantation, cell-targeted therapy, organ dysfunction, impaired source control, and limited immune-mediated clearance change both the probability and consequences of treatment failure. This critical narrative Review integrates 27 pivotal-trial protocol identifiers included in a predefined evidence map, immune-phenotype-specific cohorts, contemporary guidance, pharmacokinetic/pharmacodynamic evidence, and treatment-emergent resistance reports for a bounded core set of newer agents first authorized in the United States or European Union between 2014 and 2025, including newer β-lactam/β-lactamase-inhibitor combinations, cefiderocol, sulbactam-durlobactam, aztreonam-avibactam, and selected non-β-lactams. Fifteen of 27 pivotal protocols explicitly excluded at least one major immune phenotype or threshold; 11 had unresolved immune-host enrollment, and one enrolled immunocompromised patients but pooled distinct immune phenotypes. None reported comparative outcomes resolved to a defined immune phenotype. Phenotype-specific post-approval evidence was concentrated in hematological malignancy/profound neutropenia and solid-organ transplantation, whereas direct treatment-outcome evidence was sparse or absent for solid tumors, cellular therapies including CAR-T, advanced HIV infection, inborn errors of immunity/primary immunodeficiencies, and pediatric immunocompromised patients. We therefore separate phenotype-specific transportability from methodological credibility rather than treating directness as an overall certainty grade. The Review then synthesizes treatment by resistance mechanism and applies a host-pathogen-drug-context framework to empirical selection, diagnostics, exposure optimization, source control, de-escalation, relapse, and resistance. The resulting evidence map supports mechanism-active therapy while making the limits of transfer auditable and defining priorities for standardized phenotype reporting and pragmatic enrollment.