Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 18 5 2026 10 05 637 654 Prashant Joshi Laboratory of Applied Microbiology and Cancer Remedies, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India; Department of Chemistry, S. B. E. S’s. Science College, Chhatrapati Sambhajinagar, Maharashtra, India Nilesh Makwana Laboratory of Applied Microbiology and Cancer Remedies, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India Devang Barot Laboratory of Applied Microbiology and Cancer Remedies, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India Dhanraj Kamble Department of Chemistry, S. B. E. S’s. Science College, Chhatrapati Sambhajinagar, Maharashtra, India Bipin Yadav Department of Biosciences and Bioengineering, Indian Institute of Technology, Roorkee, Uttarakhand, India Arun Kharat Laboratory of Applied Microbiology and Cancer Remedies, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India 2025 11 23 2026 08 06 The continuous evolutionary race between antibacterial innovation and antimicrobial resistance (AMR) has become one of the greatest challenges in the management of Gram-negative bacterial infections. Although numerous antibiotics and β-lactam–β-lactamase inhibitor combinations have been introduced since 2000, their clinical utility has been progressively eroded by the rapid emergence and global dissemination of resistance mechanisms, including carbapenemase production, reduced outer membrane permeability, multidrug efflux, target modification, and antibiotic-inactivating enzymes. This review provides a chronological and mechanistic overview of anti-Gram-negative antibiotic development over the past two decades while examining the parallel evolution of bacterial resistance that has limited the therapeutic lifespan of both established and newly approved agents. We critically discuss the mechanisms of action, antibacterial spectrum, pharmacological characteristics, clinical utility, and resistance determinants of recently approved antibiotics, with particular emphasis on therapeutic innovations that overcome conventional resistance barriers, including advanced β-lactam–β-lactamase inhibitor combinations, the siderophore cephalosporin cefiderocol, next-generation tetracyclines, aminoglycosides, and novel bacterial topoisomerase inhibitors. Emerging therapeutic strategies, including investigational antibacterial agents, artificial intelligence-assisted antibiotic discovery, bacteriophage therapy, and CRISPR-based antimicrobial approaches, are also reviewed as potential solutions to the growing challenge of multidrug-resistant Gram-negative pathogens. Collectively, these advances illustrate that successful antibiotic development increasingly depends on innovative target engagement, improved bacterial uptake, and resistance-informed drug design rather than incremental modification of existing scaffolds alone. Ultimately, preserving the clinical effectiveness of new antibiotics will require the integration of antimicrobial stewardship, rapid diagnostics, genomic surveillance, and mechanism-guided drug development to slow the continuing evolutionary arms race between bacterial adaptation and therapeutic innovation. https://ijm.tums.ac.ir/index.php/ijm/article/view/5959 https://ijm.tums.ac.ir/index.php/ijm/article/download/5959/1925