Peptidoglycan Remodeling in Gram-Negative Bacteria: From Stress Adaptation to Antibiotic Tolerance and Therapeutic Targeting

The peptidoglycan (PG) sacculus of Gram-negative bacteria is continuously reorganized by a diverse enzymatic repertoire, including lytic transglycosylases, endopeptidases, carboxypeptidases, amidases and LD-transpeptidases, that operate alongside PG synthases to maintain envelope integrity throughout the cell cycle. This remodeling machinery has been extensively characterized in the context of growth and division and it is now emerging also as a key determinant of bacterial survival under non-growing and stress conditions. This review summarizes current knowledge on PG remodeling in Gram-negative bacteria, with emphasis on its regulation during stationary phase, environmental stress, and outer membrane perturbation. How these remodeling pathways, characterized by increased 3–3 cross-linking and enhanced PG–outer membrane coupling, contribute to survival under β-lactam exposure and how related enzymatic configurations can give rise to antibiotic tolerance and resistance is also discussed. Finally, recent progress in targeting PG remodeling enzymes, particularly lytic transglycosylases and peptidases, as adjuvant strategies to potentiate existing antibiotics are reviewed. In summary, PG remodeling represents a mechanistically validated but still underexploited target for addressing antibiotic tolerance and resistance in Gram-negative pathogens.