Monitoring bacterial resistance to chloramphenicol and other antibiotics by liquid chromatography electrospray ionization tandem mass spectrometry using selected reaction monitoring

Antibiotic resistance is a growing problem worldwide. For this reason, clinical laboratories often determine the susceptibility of the bacterial isolate to a number of different antibiotics in order to establish the most effective antibiotic for treatment. Unfortunately, current susceptibility assays are time consuming. Antibiotic resistance often involves the chemical modification of an antibiotic to an inactive form by an enzyme expressed by the bacterium. Selected reaction monitoring (SRM) has the ability to quickly monitor and identify these chemical changes in an unprecedented time scale. In this work, we used SRM as a technique to determine the susceptibility of several different antibiotics to the chemically modifying enzymes β‐lactamase and chloramphenicol acetyltransferase, enzymes used by bacteria to confer resistance to major classes of commonly used antibiotics. We also used this technique to directly monitor the effects of resistant bacteria grown in a broth containing a specific antibiotic. Because SRM is highly selective and can also identify chemical changes in a multitude of antibiotics in a single assay, SRM has the ability to detect organisms that are resistant to multiple antibiotics in a single assay. For these reasons, the use of SRM greatly reduces the time it takes to determine the susceptibility or resistance of an organism to a multitude of antibiotics by eliminating the time‐consuming process found in other currently used methods. Copyright © 2013 John Wiley & Sons, Ltd.     

Mucin-Inspired Single-Chain Polymer (MIP) Fibers as Potent SARS-CoV-2 Inhibitors

Mucins are the key component of the defensive mucus barrier. They are extended fibers of very high molecular weight with diverse biological functions depending strongly on their specific structural parameters. Here, we present a mucin-inspired nanostructure, produced via a synthetic methodology to prepare methacrylate-based dendronized polysulfates ( MIP-1 ) on a multi gram-scale with high molecular weight (MW=450 kDa) and thiol end-functionalized mucin-inspired polymer ( MIP ) via RAFT polymerization. Cryo-electron tomography (Cryo-ET) analysis of MIP-1 confirmed a mucin-mimetic wormlike single-chain fiber structure (length=144±59 nm) in aqueous solution. This biocompatible fiber showed promising activity against SARS-CoV-2 and its mutant strain, with a remarkable low half maximal (IC₅₀) inhibitory concentration (IC₅₀=10.0 nM). Additionally, we investigate the impact of fiber length on SARS-CoV-2 inhibition by testing other functional polymers ( MIPs ) of varying fiber lengths.     

Selective side-chain oxidation of peralkylated pyrromethene?BF2 complexes

Treatment with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) oxidized 2,6-diethyl-1,3,5,7,8-pentamethylpyrromethene–BF₂ complex 1 , 13,14-trimethyl-2, 3, 4, 5,9,10,11,12-octahydroindomethene–BF₂ complex 5 , and 1,3,5,7,8-pentamethyl-1,2,3,5,6,7-hexahydropyromethene–BF₂ complex 8 to the weakly fluorescent 3-formyl, 5-oxo, and 8-formyl derivatives 4 , 6 , and 9 , respectively. The dye 1 was oxidized by lead tetraacetate to 1,7,8-trimethyl-2,6-diethyl-3,5-diacetoxymethylpyrromethene–BF₂ complex 12 [λ_f (ethanol) 538 nm, Φ 0.62, λ_las (ethanol) 555–570 nm]. Catalytic reduction (Pd/C) converted the aldehyde 4 to 2,6-diethyl-3-hydroxymethyl-1,5,7,8-tetramethylpyrromethene–BF₂ complex 10 [λ_f (ethanol) 537 nm, Φ 0.70, λ_las (ethanol) 547–575 nm].     

Controlled Grafting Expansion Microscopy

Expansion microscopy (ExM) is a recently developed technique that allows for the resolution of structures below the diffraction limit by physically enlarging a hydrogel-embedded facsimile of the biological sample. The target structure is labeled and this label must be retained in a relative position true to the original, smaller state before expansion by linking it into the gel. However, gel formation and digestion lead to a significant loss in target-delivered label, resulting in weak signal. To overcome this problem, we have here developed an agent combining targeting, fluorescent labeling and gel linkage in a single small molecule. Similar approaches in the past have still suffered from significant loss of label. Here we show that this loss is due to insufficient surface grafting of fluorophores into the hydrogel and develop a solution by increasing the amount of target-bound monomers. Overall, we obtain a significant improvement in fluorescence signal retention and our new dye allows the resolution of nuclear pores as ring-like structures, similar to STED microscopy. We furthermore provide mechanistic insight into dye retention in ExM.