ABSTRACT
The increasing prevalence of multidrug-resistant (MDR) pathogens has promoted the development of innovative approaches, such as drug repurposing, synergy, and efficient delivery, in complement to traditional antibiotics. In this study, we present an approach based on biocompatible nanocarriers containing antimicrobial cations and known antibiotics. The matrices were prepared by coordinating GaIII or InIII to formulations of chitosan/tripolyphosphate or catechol-functionalized chitosan with or without encapsulated antibiotics, yielding particles of 100-200 nm in hydrodynamic diameter. MDR clinical isolates of Pseudomonas aeruginosa were found to be effectively inhibited by the nanocarriers under nutrient-limiting conditions. Fractional inhibitory concentration (FIC) indices revealed that cation- and antibiotic-encapsulated nanomatrices were effective against both Gram-negative and Gram-positive pathogens. Metallophores, such as deferoxamine (DFO), were probed to facilitate the sequestration and transport of the antimicrobial cations GaIII or InIII. Although the antimicrobial activities were less significant with DFO, the eradication of biofilm-associated bacteria showed promising trends against P. aeruginosa and Staphylococcus epidermidis. Interestingly, indium-containing compounds showed enhanced activity on biofilm formation and eradication, neutralizing P. aeruginosa under Fe-limiting conditions. In particular, InIII-cross-linked catechol-modified chitosan matrices were able to inhibit pathogenic growth together with DFO. The nanocarriers showed low cytotoxicity toward A549 cells and improvable CC50 values with NIH/3T3 cells.
ABSTRACT
A fluorescence turn-on probe, an azide-masked and trehalose-derivatized carbazole (Tre-Cz), was developed to image mycobacteria. The fluorescence turn-on is achieved by photoactivation of the azide, which generates a fluorescent product through an efficient intramolecular C-H insertion reaction. The probe is highly specific for mycobacteria and could image mycobacteria in the presence of other Gram-positive and Gram-negative bacteria. Both the photoactivation and detection can be accomplished using a handheld UV lamp, giving a limit of detection of 103 CFU/mL, which can be visualized by the naked eye. The probe was also able to image mycobacteria spiked in sputum samples, although the detection sensitivity was lower. Studies using heat-killed, stationary-phase, and isoniazid-treated mycobacteria showed that metabolically active bacteria are required for the uptake of Tre-Cz. The uptake decreased in the presence of trehalose in a concentration-dependent manner, indicating that Tre-Cz hijacked the trehalose uptake pathway. Mechanistic studies demonstrated that the trehalose transporter LpqY-SugABC was the primary pathway for the uptake of Tre-Cz. The uptake decreased in the LpqY-SugABC deletion mutants ΔlpqY, ΔsugA, ΔsugB, and ΔsugC and fully recovered in the complemented strain of ΔsugC. For the mycolyl transferase antigen 85 complex (Ag85), however, only a slight reduction of uptake was observed in the Ag85 deletion mutant ΔAg85C, and no incorporation of Tre-Cz into the outer membrane was observed. The unique intracellular incorporation mechanism of Tre-Cz through the LpqY-SugABC transporter, which differs from other trehalose-based fluorescence probes, unlocks potential opportunities to bring molecular cargoes to mycobacteria for both fundamental studies and theranostic applications.
ABSTRACT
Auranofin, a gold(I)-complex with tetraacetylated thioglucose (Ac4 GlcSH) and triethylphosphine ligands, is an FDA-approved drug used as an anti-inflammatory aid in the treatment of rheumatoid arthritis. In repurposing auranofin for other diseases, it was found that the drug showed significant activity against Gram-positive but was inactive against Gram-negative bacteria. Herein, the design and synthesis of gold nanoclusters (AuNCs) based on the structural motif of auranofin are reported. Phosphine-capped AuNCs are synthesized and glycosylated, yielding auranofin analogues with mixed triphenylphosphine monosulfonate (TPPMS)/Ac4 GlcSH ligand shells. These AuNCs are active against both Gram-negative and Gram-positive bacteria, including multidrug-resistant pathogens. Notably, an auranofin analogue, a mixed-ligand 1.6 nm AuNC 4b, is more active than auranofin against Pseudomonas aeruginosa, while exhibiting lower toxicity against human A549 cells. The enhanced antibacterial activity of these AuNCs is characterized by a greater uptake of Au by the bacteria compared to AuI complexes. Additional factors include increased oxidative stress, moderate inhibition of thioredoxin reductase (TrxR), and DNA damage. Most intriguingly, the uptake of AuNCs are not affected by the bacterial outer membrane (OM) barrier or by binding with the extracellular proteins. This contrasts with AuI complexes like auranofin that are susceptible to protein binding and hindered by the OM barrier.
