Ring-fused 2-pyridones effective against multidrug-resistant Gram-positive pathogens and synergistic with standard-of-care antibiotics

Structural and functional analysis reveals the catalytic mechanism and substrate binding mode of the broad-spectrum endolysin Ply2741

The emergence of antibiotic-resistant bacteria has attracted interest in the field of endolysins. Here, we analyzed the diversity of Streptococcus endolysins and identified a new endolysin, Ply2741, that exhibited broad-spectrum bactericidal activity. Our results demonstrated that Ply2741 could effectively eradicate multidrug-resistant gram-positive pathogens in vitro and in vivo. Structural analysis revealed that the bactericidal activity of Ply2741 depends on the classic "Cys-His-Asn" catalytic triad. Site-directed mutagenesis results further identified that the conserved residue Gln29, located near the catalytic triad, also contributes to the lytic activity of Ply2741. Furthermore, the key residues (R189 and W250) in the Ply2741 cell wall binding domain (CBD) responsible for binding to peptidoglycan were revealed by molecular docking and fluorescence-activated cell sorting (FACS) analysis. Ply2741 demonstrates a broad lytic spectrum, with significant bactericidal activity against Enterococcus, Staphylococcus, and Streptococcus and species. To the best of our knowledge, we found that residue Gln29 participated in the lytic activity of endolysin for the first time. Additionally, we systematically elucidate the binding mode and key residues of the Ply2741CBD. This study proposes Ply2741 as a potential antibiotic substitute and provides a structural basis for the modification and design of endolysins.

Plant Diversity Reduces the Risk of Antibiotic Resistance Genes in Agroecosystems

Despite advances in dispersal mechanisms and risk assessment of antibiotic resistance genes (ARGs), how plants influence ARG contamination in agricultural soils remains underexplored. Here, the impacts of plant species and diversity on ARGs and mobile genetic elements (MGEs) in three agricultural soils are comprehensively investigated in a pot experiment. The results indicate that increased plant diversity reduces ARGs and MGEs abundance by 19.2%-51.2%, whereas plant species exhibit inconsistent and soil-dependent effects. Potential bacterial hosts harboring abundant ARGs have greater relative abundance than nonhosts, and both their richness and cumulative relative abundance are reduced by plant diversity. Notably, hosts inhibited by plant diversity present a greater relative abundance than the other hosts. The enriched compounds in root exudates due to plant diversity play a more important role in the metabolic network and contribute to rebalancing of the abundance of potential hosts and nonhosts. An independent test using pure organics reveals that higher resource diversity, resulting from increased plant diversity, reduces the relative abundance and mobility of abundant and high-risk ARGs. This study highlights the resource-mediated mitigation of the risks posed by ARG contamination and indicates that ensuring plant and resource diversity is a promising strategy for controlling ARGs in agroecosystems.

Vancomycin-Resistant Enterococcus faecium: A current perspective on resilience, adaptation, and the urgent need for novel strategies

Vancomycin-resistant Enterococcus faecium (VREfm) has become a critical opportunistic pathogen, urgently requiring new antimicrobial strategies due to its rising prevalence and significant impact on patient safety and healthcare costs. VREfm continues to evolve through mutations and the acquisition of new genes via horizontal gene transfer, contributing to resistance against several last-resort antibiotics. Although primarily hospital-associated, VREfm is also detected in the community, food chain, livestock, and environmental sources like wastewater, indicating diverse transmission pathways and the need for a One Health approach. Advances in genomics have shed light on VREfm's persistence in hospital settings, particularly its adaptation to the gastrointestinal tract of hospitalized patients, recent clonal shifts, and the dominance of specific clonal lineages. Despite extensive research, significant gaps remain in understanding the molecular mechanisms behind VREfm's unique adaptation to clinical environments. In this review, we aim to present an overview of VREfm current prevalence, mechanisms of resistance, and unveil the adaptive traits that have facilitated VREfm's rise and global success. A particular focus is given to key plasmids, namely linear plasmids, virulence factors, and bacteriocins as potential drivers in the global emergence of the ST78 clonal lineage. We also address diagnostic challenges and the limited treatment options available for VREfm, as well as emerging antibiotic alternatives aimed at restoring gut microbiota balance and curbing VREfm proliferation. A multifaceted approach combining research, clinical practices, and public health policies is crucial to mitigate the impact of this superbug and preserve antimicrobial effectiveness for future generations.

Exploring Acyl Thiotriazinoindole Based Pharmacophores: Design, Synthesis, and SAR Studies with Molecular Docking and Biological Activity Profiling against Urease, α-amylase, α-glucosidase, Antimicrobial, and Antioxidant Targets

A diminutive chemical library of acyl thiotriazinoindole (ATTI) based bioactive scaffolds was synthesized, instigated by taking the economical starting material Isatin, through a series of five steps. Isatin was first nitrated followed by the attachment of pentyl moiety via nucleophilic substitution reaction. The obtained compound was reacted with thiosemicarbazide to obtain thiosemicarbazone derivative, which was eventually cyclized using basic conditions in water as solvent. Finally, the reported series was obtained through reaction of nitrated thiotriazinoindole moiety with differently substituted phenacyl bromides. The synthesized compounds were characterized using NMR spectroscopy and elemental analysis. Finally, the synthesized motifs were scrutinized for their potential to impede urease, α-glucosidase, DPPH, and α-amylase. Compound 5 h with para cyano group manifested the most pivotal biological activity among all, displaying IC50 values of 29.7 ± 0.8, 20.5 ± 0.5 and 36.8 ± 3.9 µM against urease, α-glucosidase, and DPPH assay, respectively. Simultaneously, for α-amylase compound 5 g possessing a p-CH3 at phenyl ring unfolded as most active, with calculated IC50 values 90.3 ± 1.1 µM. The scaffolds were additionally gauged for their antifungal and antibacterial activity. Among the tested strains, 5d having bromo as substituent exhibited the most potent antibacterial activity, while it also demonstrated the highest potency against Aspergillus fumigatus. Other derivatives 5b, 5e, 5i, and 5j also exhibited dual inhibition against both antibacterial and antifungal strains. The interaction pattern of derivatives clearly displayed their SAR, and their docking scores were correlated with their IC50 values. In molecular docking studies, the importance of interactions like hydrogen bonding was further asserted. The electronic factors of various substituents engendered variety of interactions between the ligands and targets implying their importance in the structures of the synthesized heterocyclic scaffolds. To conclude, the synthesized compounds had satisfactory biological activity against various important targets. Further studies are therefore encouraged by attachment of different substitutions in the structure at various positions to enhance the activity of these compounds.

6-Methoxyldihydrochelerythrine Chloride Inhibiting Intra and Extracellular Drug-Resistant Bacteria

Vancomycin-resistant enterococcus (VRE) is a major nosocomial pathogen that exhibits enhanced infectivity due to its robust virulence and biofilm-forming capabilities. In this study, 6-methoxyldihydrochelerythrine chloride (6-MDC) inhibited the growth of exponential-phase VRE and restored VRE's sensitivity to vancomycin. 6-MDC predominantly suppressed the de novo biosynthetic pathway of pyrimidine and purine in VRE by the RNA-Seq analysis, resulting in obstructed DNA synthesis, which subsequently weakened bacterial virulence and impeded intracellular survival. Furthermore, 6-MDC inhibited biofilm formation, eradicated established biofilms, reduced virulence, and enhanced the host immune response to prevent intracellular survival and replication of VRE. Finally, 6-MDC reduced the VRE load in peritoneal fluid and cells significantly in a murine peritoneal infection model. This paper provides insight into the potential antimicrobial target of benzophenanthridine alkaloids for the first time.

Photoredox-Catalyzed Radical Coupling of C7-Chloromethyl-Substituted Thiazolino Ring-Fused 2-Pyridones with Quinoxalinones

We have developed an Ir(PPy)3 photoredox-catalyzed cross-coupling reaction that allows installation of quinoxalinones at the C7 position of thiazolino ring-fused 2-pyridones (TRPs) under mild conditions. The methodology tolerates various substituted quinoxalinones and biologically relevant substituents on the C8 position of the TRP. The TRP scaffold has large potential in the development of lead compounds, and while the coupled products are interesting from a drug-development perspective, the methodology will be useful for developing more potent and drug-like TRP-based candidates.

Dihydrothiazolo ring-fused 2-pyridone antimicrobial compounds treat Streptococcus pyogenes skin and soft tissue infection

We have developed GmPcides from a peptidomimetic dihydrothiazolo ring-fused 2-pyridone scaffold that has antimicrobial activities against a broad spectrum of Gram-positive pathogens. Here, we examine the treatment efficacy of GmPcides using skin and soft tissue infection (SSTI) and biofilm formation models by Streptococcus pyogenes. Screening our compound library for minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations identified GmPcide PS757 as highly active against S. pyogenes. Treatment of S. pyogenes biofilm with PS757 revealed robust efficacy against all phases of biofilm formation by preventing initial biofilm development, ceasing biofilm maturation and eradicating mature biofilm. In a murine model of S. pyogenes SSTI, subcutaneous delivery of PS757 resulted in reduced levels of tissue damage, decreased bacterial burdens, and accelerated rates of wound healing, which were associated with down-regulation of key virulence factors, including M protein and the SpeB cysteine protease. These data demonstrate that GmPcides show considerable promise for treating S. pyogenes infections.

Biofilm inhibition/eradication: exploring strategies and confronting challenges in combatting biofilm

Biofilms are complex communities of microorganisms enclosed in a self-produced extracellular matrix, posing a significant threat to different sectors, including healthcare and industry. This review provides an overview of the challenges faced due to biofilm formation and different novel strategies that can combat biofilm formation. Bacteria inside the biofilm exhibit increased resistance against different antimicrobial agents, including conventional antibiotics, which can lead to severe problems in livestock and animals, including humans. In addition, biofilm formation also imposes heavy economic pressure on industries. Hence it becomes necessary to explore newer alternatives to eradicate biofilms effectively without applying selection pressure on the bacteria. Excessive usage of antibiotics may also lead to an increase in the number of resistant strains as bacteria employ an advanced antimicrobial resistance mechanism. This review provides insight into multifaceted technologies like quorum sensing inhibition, enzymes, antimicrobial peptides, bacteriophage, phytocompounds, and nanotechnology to neutralize biofilms without developing antimicrobial resistance (AMR). Furthermore, it will pave the way for developing newer therapeutic agents to deal with biofilms more efficiently.

Synthesis of Three-Dimensional Ring Fused Heterocycles by a Selective [4 + 2] Cycloaddition Between Bicyclic Thiazolo 2-Pyridones and Arynes

A selective [4 + 2] cycloaddition reaction of thiazolo-2-pyridones with arynes has been demonstrated. The developed protocol allows rapid access to highly functionalized, structurally complex thiazolo-fused bridged isoquinolones in high yields, which are susceptible to further late-stage functionalization.

Dihydrothiazolo ring-fused 2-pyridone antimicrobial compounds treat Streptococcus pyogenes skin and soft tissue infection

We have developed GmPcides from a peptidomimetic dihydrothiazolo ring-fused 2-pyridone scaffold that have antimicrobial activities against a broad-spectrum of Gram-positive pathogens. Here we examine the treatment efficacy of GmPcides using skin and soft tissue infection (SSTI) and biofilm formation models by Streptococcus pyogenes. Screening our compound library for minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations identified GmPcide PS757 as highly active against S. pyogenes. Treatment of S. pyogenes biofilm with PS757 revealed robust efficacy against all phases of biofilm formation by preventing initial biofilm development, ceasing biofilm maturation and eradicating mature biofilm. In a murine model of S. pyogenes SSTI, subcutaneous delivery of PS757 resulted in reduced levels of tissue damage, decreased bacterial burdens and accelerated rates of wound-healing, which were associated with down-regulation of key virulence factors, including M protein and the SpeB cysteine protease. These data demonstrate that GmPcides show considerable promise for treating S. pyogenes infections.

A Highly Substituted Ring-Fused 2-Pyridone Compound Targeting PrfA and the Efflux Regulator BrtA in Listeria monocytogenes

Listeria monocytogenes is a facultative Gram-positive bacterium that causes listeriosis, a severe foodborne disease. We previously discovered that ring-fused 2-pyridone compounds can decrease virulence factor expression in Listeria by binding and inactivating the PrfA virulence activator. In this study, we tested PS900, a highly substituted 2-pyridone that was recently discovered to be bactericidal to other Gram-positive pathogenic bacteria, such as Staphylococcus aureus and Enterococcus faecalis. We show that PS900 can interact with PrfA and reduce the expression of virulence factors. Unlike previous ring-fused 2-pyridones shown to inactivate PrfA, PS900 had an additional antibacterial activity and was found to potentiate sensitivity toward cholic acid. Two PS900-tolerant mutants able to grow in the presence of PS900 carried mutations in the brtA gene, encoding the BrtA repressor. In wild-type (WT) bacteria, cholic acid binds and inactivates BrtA, thereby alleviating the expression of the multidrug transporter MdrT. Interestingly, we found that PS900 also binds to BrtA and that this interaction causes BrtA to dissociate from its binding site in front of the mdrT gene. In addition, we observed that PS900 potentiated the effect of different osmolytes. We suggest that the increased potency of cholic acid and osmolytes to kill bacteria in the presence of PS900 is due to the ability of the latter to inhibit general efflux, through a yet-unknown mechanism. Our data indicate that thiazolino 2-pyridones constitute an attractive scaffold when designing new types of antibacterial agents. IMPORTANCE Bacteria resistant to one or several antibiotics are a very large problem, threatening not only treatment of infections but also surgery and cancer treatments. Thus, new types of antibacterial drugs are desperately needed. In this work, we show that a new generation of substituted ring-fused 2-pyridones not only inhibit Listeria monocytogenes virulence gene expression, presumably by inactivating the PrfA virulence regulator, but also potentiate the bactericidal effects of cholic acid and different osmolytes. We identified a multidrug repressor as a second target of 2-pyridones. The repressor-2-pyridone interaction displaces the repressor from DNA, thus increasing the expression of a multidrug transporter. In addition, our data suggest that the new class of ring-fused 2-pyridones are efficient efflux inhibitors, possibly explaining why the simultaneous addition of 2-pyridones together with cholic acid or osmolytes is detrimental for the bacterium. This work proves conclusively that 2-pyridones constitute a promising scaffold to build on for future antibacterial drug design.

Therapeutics for Vancomycin-Resistant Enterococcal Bloodstream Infections

Vancomycin-resistant enterococci (VRE) are common causes of bloodstream infections (BSIs) with high morbidity and mortality rates. They are pathogens of global concern with a limited treatment pipeline. Significant challenges exist in the management of VRE BSI, including drug dosing, the emergence of resistance, and the optimal treatment for persistent bacteremia and infective endocarditis. Therapeutic drug monitoring (TDM) for antimicrobial therapy is evolving for VRE-active agents; however, there are significant gaps in the literature for predicting antimicrobial efficacy for VRE BSIs. To date, TDM has the greatest evidence for predicting drug toxicity for the three main VRE-active antimicrobial agents daptomycin, linezolid, and teicoplanin. This article presents an overview of the treatment options for VRE BSIs, the role of antimicrobial dose optimization through TDM in supporting clinical infection management, and challenges and perspectives for the future.