visualization-bacterial-resistance-using-fluorescent-antibiotic

Visualization of Bacterial Resistance using Fluorescent Antibiotic Probes

Fluorescent antibiotics are multipurpose research tools that are readily used for the study of antimicrobial resistance, due to their significant ...

An azide-functionalised analogue of the oxazolidinone antibiotic linezolid was synthesised and shown to retain antimicrobial activity. Using facile 'click' chemistry, this versatile intermediate can be further functionalised to explore antimicrobial structure-activity relationships or conjugated to fluorophores to generate fluorescent probes. Such probes can report bacteria and their location in a sample in real time. Modelling of the structures bound to the cognate 50S ribosome target demonstrates binding to the same site as linezolid is possible. The fluorescent probes were successfully used to image Gram-positive bacteria using confocal microscopy. 

An azido-oxazolidinone antibiotic for live bacterial cell imaging and generation of antibiotic variants.

The polymyxin lipodecapeptides colistin and polymyxin B have become last resort therapies for infections caused by highly drug-resistant Gram-negative bacteria. Unfortunately, their utility is compromised by significant nephrotoxicity and polymyxin-resistant bacterial strains. We have conducted a systematic activity-toxicity investigation by varying eight of the nine polymyxin amino acid free side chains, preparing over 30 analogues using a novel solid-phase synthetic route. Compounds were tested against a panel of Gram-negative bacteria and counter-screened for in vitro cell toxicity. Promising compounds underwent additional testing against primary kidney cells isolated from human kidneys to better predict their nephrotoxic potential. Many of the new compounds possessed equal or better antimicrobial potency compared to polymyxin B, and some were less toxic than polymyxin B and colistin against mammalian HepG2 cells and human primary kidney cells. These initial structure-activity and structure-toxicity studies set the stage for further improvements to the polymyxin class of antibiotics. 

Activity and Predicted Nephrotoxicity of Synthetic Antibiotics Based on Polymyxin B.

Reduced susceptibility to antimicrobials in Gram-negative bacteria may result from multiple resistance mechanisms, including increased efflux pump activity or reduced porin protein expression. Up-regulation of the efflux pump system is closely associated with multidrug resistance (MDR). To help investigate the role of efflux pumps on compound accumulation, a fluorescence-based assay was developed using fluorescent derivatives of trimethoprim (TMP), a broad-spectrum synthetic antibiotic that inhibits an intracellular target, dihydrofolate reductase (DHFR). Novel fluorescent TMP probes inhibited eDHFR activity with comparable potency to TMP, but did not kill or inhibit growth of wild type Escherichia coli. However, bactericidal activity was observed against an efflux pump deficient E. coli mutant strain (ΔtolC). A simple and quick fluorescence assay was developed to measure cellular accumulation of the TMP probe using either fluorescence spectroscopy or flow cytometry, with validation by LC-MS/MS. This fluorescence assay may provide a simple method to assess efflux pump activity with standard laboratory equipment.

Fluorescent Trimethoprim Conjugate Probes To Assess Drug Accumulation in Wild Type and Mutant Escherichia coli.

Many bacterial pathogens have now acquired resistance toward commonly used antibiotics, such as the glycopeptide antibiotic vancomycin. In this study, we show that immobilization of vancomycin onto a nanometer-scale solid surface with controlled local density can potentiate antibiotic action and increase target affinity of the drug. Magnetic nanoparticles were conjugated with vancomycin and used as a model system to investigate the relationship between surface density and drug potency. We showed remarkable improvement in minimum inhibitory concentration against vancomycin-resistant strains with values of 13-28 μg/mL for conjugated vancomycin compared to 250-4000 μg/mL for unconjugated vancomycin. Higher surface densities resulted in enhanced affinity toward the bacterial target compared to that of unconjugated vancomycin, as measured by a competition experiment using a surrogate ligand for bacterial Lipid II, N-Acetyl-l-Lys-d-Ala-d-Ala. High density vancomycin nanoparticles required >64 times molar excess of ligand (relative to the vancomycin surface density) to abrogate antibacterial activity compared to only 2 molar excess for unconjugated vancomycin. Further, the drug-nanoparticle conjugates caused rapid permeabilization of the bacterial cell wall within 2 h, whereas no effect was seen with unconjugated vancomycin, suggesting additional modes of action for the nanoparticle-conjugated drug. Hence, immobilization of readily available antibiotics on nanocarriers may present a general strategy for repotentiating drugs that act on bacterial membranes or membrane-bound targets but have lost effectiveness against resistant bacterial strains.

Surface Ligand Density of Antibiotic-Nanoparticle Conjugates Enhances Target Avidity and Membrane Permeabilization of Vancomycin-Resistant Bacteria.

The public health threat posed by a looming 'post-antibiotic' era necessitates new approaches to antibiotic discovery. Drug development has typically avoided exploitation of membrane-binding properties, in contrast to nature's control of biological pathways via modulation of membrane-associated proteins and membrane lipid composition. Here, we describe the rejuvenation of the glycopeptide antibiotic vancomycin via selective targeting of bacterial membranes. Peptide libraries based on positively charged electrostatic effector sequences are ligated to N-terminal lipophilic membrane-insertive elements and then conjugated to vancomycin. These modified lipoglycopeptides, the 'vancapticins', possess enhanced membrane affinity and activity against methicillin-resistant Staphylococcus aureus (MRSA) and other Gram-positive bacteria, and retain activity against glycopeptide-resistant strains. Optimised antibiotics show in vivo efficacy in multiple models of bacterial infection. This membrane-targeting strategy has potential to 'revitalise' antibiotics that have lost effectiveness against recalcitrant bacteria, or enhance the activity of other intravenous-administered drugs that target membrane-associated receptors.

Protein-inspired antibiotics active against vancomycin- and daptomycin-resistant bacteria.

Better understanding how multidrug-resistant (MDR) bacteria can evade current and novel antibiotics requires a better understanding of the chemical biology of antibiotic action. This necessitates using new tools and techniques to advance our knowledge of bacterial responses to antibiotics, ideally in live cells in real time, to selectively investigate bacterial growth, division, metabolism, and resistance in response to antibiotic challenge. In this review, we discuss the preparation and biological evaluation of fluorescent antibiotics, focussing on how these reporters and assay methods can help elucidate resistance mechanisms. We also examine the potential utility of such probes for real-time in vivo diagnosis of infections.

Fluorescent Antibiotics: New Research Tools to Fight Antibiotic Resistance.

Fluorescent probes derived from the fluoroquinolone antibiotic ciprofloxacin were synthesised using a Cu(i)-catalysed azide-alkyne cycloaddition (CuAAC) to link a ciprofloxacin azide derivative with alkyne-substituted green and blue fluorophores. The azide () and fluorophore ( and ) derivatives retained antimicrobial activity against Gram-positive and Gram-negative bacteria. The use of confocal fluorescent microscopy showed intracellular penetration, which was substantially enhanced in the presence of carbonyl cyanide 3-chlorophenylhydrazone as an efflux pump inhibitor in .

Fluoroquinolone-derived fluorescent probes for studies of bacterial penetration and efflux.

The  dihydrofolate reductase (DHFR) destabilizing domain (DD), which shows promise as a biologic tool and potential gene therapy approach, can be utilized to achieve spatial and temporal control of protein abundance  simply by administration of its stabilizing ligand, the routinely prescribed antibiotic trimethoprim (TMP). However, chronic TMP use drives development of antibiotic resistance (increasing likelihood of subsequent infections) and disrupts the gut microbiota (linked to autoimmune and neurodegenerative diseases), tempering translational excitement of this approach in model systems and for treating human diseases. Herein, we identified a TMP-based, non-antibiotic small molecule, termed 14a (MCC8529), and tested its ability to control multiple DHFR-based reporters and signaling proteins. We found that 14a is non-toxic and can effectively stabilize DHFR DDs expressed in mammalian cells. Furthermore, 14a crosses the blood-retinal barrier and stabilizes DHFR DDs expressed in the mouse eye with kinetics comparable to that of TMP (≤6 h). Surprisingly, 14a stabilized a DHFR DD in the liver significantly better than TMP did, while having no effect on the mouse gut microbiota. Our results suggest that alternative small-molecule DHFR DD stabilizers (such as 14a) may be ideal substitutes for TMP in instances when conditional, non-antibiotic control of protein abundance is desired in the eye and beyond.

Article	Year
An azido-oxazolidinone antibiotic for live bacterial cell imaging and generation of antibiotic variants. Bioorganic & medicinal chemistry\| PubMed ID: 25023540	2014
Activity and Predicted Nephrotoxicity of Synthetic Antibiotics Based on Polymyxin B. Journal of medicinal chemistry\| PubMed ID: 26734854	2016
Fluorescent Trimethoprim Conjugate Probes To Assess Drug Accumulation in Wild Type and Mutant Escherichia coli. ACS infectious diseases\| PubMed ID: 27737551	2016
Surface Ligand Density of Antibiotic-Nanoparticle Conjugates Enhances Target Avidity and Membrane Permeabilization of Vancomycin-Resistant Bacteria. Bioconjugate chemistry\| PubMed ID: 27959504	2017
Protein-inspired antibiotics active against vancomycin- and daptomycin-resistant bacteria. Nature communications\| PubMed ID: 29295973	2018
Fluorescent Antibiotics: New Research Tools to Fight Antibiotic Resistance. Trends in biotechnology\| PubMed ID: 29478675	2018
Fluoroquinolone-derived fluorescent probes for studies of bacterial penetration and efflux. MedChemComm\| PubMed ID: 31303987	2019
Non-antibiotic Small-Molecule Regulation of DHFR-Based Destabilizing Domains . Molecular therapy. Methods & clinical development\| PubMed ID: 31649953	2019

Wanida Phetsang

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