coli, 3− is recognized by the OM receptors FepA and IroN, and is transported into the periplasm utilizing the energy provided by the TonB–ExbB–ExbD complex (Fig. 37,38 The high Fe 3+-binding affinity of Ent ( K a ∼ 10 49 M −1) 39,40 allows bacteria to scavenge Fe 3+ from the host environment in the form of 3−. 34–36Įnterobactin (Ent) is a tris-catecholate siderophore produced by Gram-negative species including Escherichia coli, Salmonella enterica and Klebsiella pneumoniae. β-lactams and fluoroquinolones) can be narrowed by targeting select species or a group of strains within a species through covalent attachment to a siderophore. 15,24–33 Recent examples demonstrated that the activity of broad-spectrum antibiotics ( e.g. 20–23 Several decades of work showed that the siderophores and siderophore uptake machinery of Gram-negative bacteria can be leveraged to deliver toxic cargos into the bacterial periplasm and cytoplasm. These secondary metabolites are biosynthesized in the cytoplasm, exported to the extracellular space to coordinate Fe 3+ and then returned to the bacterial cell via specialized OM receptors. 17–19 To scavenge iron from the host, many bacteria biosynthesize small-molecule Fe 3+ chelators called siderophores.
15,16 Iron is an essential nutrient for the vast majority of bacterial species thus, acquiring adequate levels of iron is important for survival and host colonization.
9,12–14 In this regard, essential nutrient transporters located in the OM of Gram-negative bacteria provide opportunities for selective recognition and intracellular delivery of antibacterial molecules. To date, various strategies of narrowing the activity spectrum of antibiotics in clinical use have been explored. 8–11 Such pathogen-selective antibiotics are predicted to reduce the occurrence of antibiotic resistance in microbial populations and have smaller impact on the host microbiome. 7 To address this emerging public health crisis, novel therapies that exhibit narrow-spectrum activity must be developed and implemented in combination with rapid diagnostics. 5,6 Coupled with the scarcity of new antibiotics in the drug pipeline, society is faced with the reality that bacterial infections that were once of minor concern can become lethal. 3,4 Moreover, broad-spectrum antibiotics can damage the commensal microbiota and trigger life-threatening secondary infections such as those caused by Clostridioides difficile. 1,2 The overuse of broad-spectrum antibiotics in the treatment of such bacterial infections facilitates the selection of resistant strains, which causes antibiotics to lose effectiveness over time. Introduction Infections caused by Gram-negative bacteria can be difficult to treat due to the semipermeable outer-membrane (OM) that serves as an efficient barrier against most antibiotics. coli and supports that native siderophore scaffolds provide the opportunity for narrowing the activity spectrum of antibiotics in clinical use and targeting pathogenicity. Overall, this work illuminates the uptake and cell-killing activity of Ent- and DGE-β-lactam conjugates against E. coli treated with the siderophore-β-lactam conjugates revealed cellular morphologies consistent with the inhibition of penicillin-binding proteins PBP3 (Ent/DGE-Amp/Lex) and PBP2 (Ent/DGE-Mem).
Phase-contrast and fluorescence imaging of E. A comparative analysis of siderophore-β-lactams harboring ampicillin (Amp), Lex and Mem indicated that the DGE-Mem conjugate is advantageous because it targets IroN and exhibits low minimum inhibitory concentrations, fast time-kill kinetics, and enhanced stability to serine β-lactamases. coli CFT073 demonstrated that the DGE-β-lactams target the pathogen-associated catecholate siderophore receptor IroN. These siderophore-β-lactam conjugates showed enhanced minimum inhibitory concentrations against Escherichia coli compared to the parent antibiotics. In this work, we report the synthesis and evaluation of four new siderophore-β-lactam conjugates where the broad-spectrum β-lactam antibiotics cephalexin (Lex) and meropenem (Mem) are covalently attached to either enterobactin (Ent) or diglucosylated Ent (DGE) via a stable polyethylene glycol (PEG 3) linker. The design and synthesis of narrow-spectrum antibiotics that target a specific bacterial strain, species, or group of species is a promising strategy for treating bacterial infections when the causative agent is known.