Possible drugs for the treatment of bacterial infections in the future: anti-virulence drugs

Multifaceted quorum-sensing inhibiting activity of 3-(Benzo[d][1,3]dioxol-4-yl)oxazolidin-2-one mitigates Pseudomonas aeruginosa virulence

As antibiotic resistance escalates into a global health crisis, novel therapeutic approaches against infectious diseases are in urgent need. Pseudomonas aeruginosa, an adaptable opportunistic pathogen, poses substantial challenges in treating a range of infections. The quorum-sensing (QS) system plays a pivotal role in orchestrating the production of a large set of virulence factors in a cell density-dependent manner, and the anti-virulence strategy targeting QS may show huge potential. Here, we present a comprehensive investigation into the potential of the synthesized compound 3-(benzo[d][1,3]dioxol-4-yl)oxazolidin-2-one (OZDO, C10H9NO4) as a QS inhibitor to curb the virulence of P. aeruginosa. By employing an integrated approach encompassing in silico screening, in vitro and in vivo functional identification, we elucidated the multifaceted effects of OZDO. Molecular docking predicted that OZDO interfered with three core regulatory proteins of P. aeruginosa QS system. Notably, OZDO exhibited significant inhibition on the production of pyocyanin, rhamnolipid and extracellular proteases, biofilm formation, and cell motilities of P. aeruginosa. Transcriptomic analysis and quantitative real-time PCR displayed the down-regulation of QS-controlled genes in OZDO-treated PAO1, reaffirming the QS-inhibition activity of OZDO. In vivo assessments using a Caenorhabditis elegans-infection model demonstrated OZDO mitigated P. aeruginosa pathogenicity, particularly against the hypervirulent strain PA14. Moreover, OZDO in combination with polymyxin B and aztreonam presented a promising avenue for innovative anti-infective therapy. Our study sheds light on the multifaceted potential of OZDO as an anti-virulence agent and its significance in combating P. aeruginosa-associated infections.

Nanoenabling MbtI Inhibitors for Next-Generation Tuberculosis Therapy

The urgent need for safer and innovative antitubercular agents remains a priority for the scientific community. In pursuit of this goal, we designed and evaluated novel 5-phenylfuran-2-carboxylic acid derivatives targeting Mycobacterium tuberculosis (Mtb) salicylate synthase (MbtI), a key enzyme, absent in humans, that plays a crucial role in Mtb virulence. Several potent MbtI inhibitors demonstrating significant antitubercular activity and a favorable safety profile were identified. Structure-guided optimization yielded 5-(3-cyano-5-isobutoxyphenyl)furan-2-carboxylic acid (1e), which exhibited strong MbtI inhibition (IC50 = 11.2 μM) and a promising in vitro antitubercular activity (MIC99 = 32 μM against M. bovis BCG). Esters of 1e were effectively loaded into poly(2-methacryloyloxyethyl phosphorylcholine)-poly(2-(diisopropylamino)ethyl methacrylate) (PMPC-PDPA) polymersomes (POs) and delivered to intracellular mycobacteria, resulting in reduced Mtb viability. This study provides a foundation for the use of POs in the development of future MbtI-targeted therapies for tuberculosis.

Chemical-mediated virulence: the effects of host chemicals on microbial virulence and potential new antivirulence strategies

The rising antimicrobial resistance rates and declining antimicrobial discovery necessitate alternative strategies to combat multidrug-resistant pathogens. Targeting microbial virulence is an emerging area of interest. Traditionally, virulence factors were largely restricted to bacteria-derived toxins, adhesins, capsules, quorum sensing systems, secretion systems, factors required to sense, respond to, acquire, or synthesize, and utilize trace elements (such as iron and other metals) and micronutrients (such as vitamins), and other factors bacteria use to establish infection, form biofilms, or damage the host tissues and regulatory elements thereof. However, this traditional definition overlooks bacterial virulence that may be induced or influenced by host-produced metabolites or other chemicals that bacteria may encounter at the infection site. This review will discuss virulence from a non-traditional perspective, shedding light on chemical-mediated host-pathogen interactions and outlining currently available mechanistic insight into increased bacterial virulence in response to host factors. This review aims to define a possibly underestimated theme of chemically mediated host-pathogen interactions and encourage future validation and characterization of the contribution of host chemicals to microbial virulence in vivo. From this perspective, we discuss proposed antivirulence compounds and suggest new potential targets for antimicrobials that prevent chemical-mediated virulence. We also explore proposed host-targeting therapeutics reducing the level of host chemicals that induce microbial virulence, serving as virulence attenuators. Understanding the host chemical-mediated virulence may enable new antimicrobial solutions to fight multidrug-resistant pathogens.

Development of a transcription factor decoy-nanocarrier system as a successful inhibitor of Enterococcus faecalis virulence in vitro and in vivo

Enterococcus faecalis is a troublesome nosocomial pathogen that acquired resistance to most available antimicrobial agents. Antivirulence agents represent an unconventional treatment approach. Here, transcription factor decoy (TFD)-loaded cationic liposomes (TLL) were developed as an inhibitor of the Fsr quorum-sensing system and its associated virulence traits, in E. faecalis. The consensus sequence of the FsrA binding site was found conserved among 651 E. faecalis annotated genomes. The TFD was synthesized as an 82 bp DNA duplex, containing the conserved binding sequence, and loaded onto cationic liposomes. The optimum loading capacity, mean particle size, and zeta potential of the TLL were characterized. The developed TLL lacked any effect on E. faecalis growth and significantly inhibited the in vitro production of the proteolytic enzymes controlled by the Fsr system; gelatinase and serine protease, in a concentration-dependent manner. This inhibition was accompanied by a significant reduction in the transcription levels of FsrA-regulated genes (fsrB, gelE, and sprE). The developed TLL were safe as evidenced by the nonhemolytic effect on human RBCs and the negligible cytotoxicity on human skin fibroblast cells. Moreover, in the larvae infection model, TLL displayed a significant abolish in the mortality rates of Galleria mellonella larvae infected with E. faecalis. In conclusion, the developed TLL offer a new safe strategy for combating E. faecalis infection through the inhibition of quorum-sensing-mediated virulence; providing a platform for the development of similar agents to combat many other pathogens.

Harmine acts as a quorum sensing inhibitor decreasing the virulence and antibiotic resistance of Pseudomonas aeruginosa

BACKGROUND

As antimicrobial resistance (AMR) has become a global health crisis, new strategies against AMR infection are urgently needed. Quorum sensing (QS), responsible for bacterial communication and pathogenicity, is among the targets for anti-virulence drugs that thrive as one of the promising treatments against AMR infection.

METHODS

We identified a natural compound, Harmine, through virtual screening based on three QS receptors of Pseudomonas aeruginosa (P. aeruginosa) and explored the effect of Harmine on QS-controlled and pathogenicity-related phenotypes including pyocyanin production, exocellular protease excretion, biofilm formation, and twitching motility of P. aeruginosa PA14. The protective effect of Harmine on Caenorhabditis elegans (C. elegans) and mice infection models was determined and the synergistic effect of Harmine combined with common antibiotics was explored. The underlaying mechanism of Harmine's QS inhibitory effect was illustrated by molecular docking analysis, transcriptomic analysis, and target verification assay.

RESULTS

In vitro results suggested that Harmine possessed QS inhibitory effects on pyocyanin production, exocellular protease excretion, biofilm formation, and twitching motility of P. aeruginosa PA14, and in vivo results displayed Harmine's protective effect on C. elegans and mice infection models. Intriguingly, Harmine increased susceptibility of both PA14 and clinical isolates of P. aeruginosa to polymyxin B and kanamycin when used in combination. Moreover, Harmine down-regulated a series of QS controlled genes associated with pathogenicity and the underlying mechanism may have involved competitively antagonizing autoinducers' receptors LasR, RhlR, and PqsR.

CONCLUSIONS

This study shed light on the anti-virulence potential of Harmine against QS targets, suggesting the possible use of Harmine and its derivates as anti-virulence compounds.

A New "Non-Traditional" Antibacterial Drug Fluorothiazinone-Clinical Research in Patients with Complicated Urinary Tract Infections

In order to combat resistance, it is necessary to develop antimicrobial agents that act differently from conventional antibiotics. Fluorothiazinone, 300 mg tablet (The Gamaleya National Research Center), is an original antibacterial drug based on a new small molecule T3SS and flagellum inhibitor. A total of 357 patients with complicated urinary tract infections (UTIs) were divided into two groups and given Fluorothiazinone 1200 mg/day or a placebo for 7 days to evaluate the efficacy and safety of the drug. Additionally, all patients were given Cefepime 2000 mg/day. Fluorothiazinone with Cefepime showed superiority over placebo/Cefepime based on the assessment of the proportion of patients with an overall outcome in the form of a cure after 21 days post-therapy (primary outcome), overall outcome in cure rates, clinical cure rates, and microbiological efficacy at the end of therapy and after 21 days post-therapy (secondary outcomes). In patients who received Fluorothiazinone, the rate of infection recurrences 53 and 83 days after the end of the therapy was lower by 18.9%, compared with patients who received placebo. Fluorothiazinone demonstrated a favorable safety profile with no serious unexpected adverse events reported. The results showed superiority of the therapy with Fluorothiazinone in combination with Cefepime compared with placebo/Cefepime in patients with cUTIs.

Nucleus-forming jumbophage PhiKZ therapeutically outcompetes non-nucleus-forming jumbophage Callisto

With the recent resurgence of phage therapy in modern medicine, jumbophages are currently under the spotlight due to their numerous advantages as anti-infective agents. However, most significant discoveries to date have primarily focused on nucleus-forming jumbophages, not their non-nucleus-forming counterparts. In this study, we compare the biological characteristics exhibited by two genetically diverse jumbophages: 1) the well-studied nucleus-forming jumbophage, PhiKZ; and 2) the newly discovered non-nucleus-forming jumbophage, Callisto. Single-cell infection studies further show that Callisto possesses different replication machinery, resulting in a delay in phage maturation compared to that of PhiKZ. The therapeutic potency of both phages was examined in vitro and in vivo, demonstrating that PhiKZ holds certain superior characteristics over Callisto. This research sheds light on the importance of the subcellular infection machinery and the organized progeny maturation process, which could potentially provide valuable insight in the future development of jumbophage-based therapeutics.

Evaluation of novel compounds as anti-bacterial or anti-virulence agents

Antimicrobial resistance is a global threat, leading to an alarming increase in the prevalence of bacterial infections that can no longer be treated with available antibiotics. The World Health Organization estimates that by 2050 up to 10 million deaths per year could be associated with antimicrobial resistance, which would equal the annual number of cancer deaths worldwide. To overcome this emerging crisis, novel anti-bacterial compounds are urgently needed. There are two possible approaches in the fight against bacterial infections: a) targeting structures within bacterial cells, similar to existing antibiotics; and/or b) targeting virulence factors rather than bacterial growth. Here, for the first time, we provide a comprehensive overview of the key steps in the evaluation of potential new anti-bacterial and/or anti-virulence compounds. The methods described in this review include: a) in silico methods for the evaluation of novel compounds; b) anti-bacterial assays (MIC, MBC, Time-kill); b) anti-virulence assays (anti-biofilm, anti-quorum sensing, anti-adhesion); and c) evaluation of safety aspects (cytotoxicity assay and Ames test). Overall, we provide a detailed description of the methods that are an essential tool for chemists, computational chemists, microbiologists, and toxicologists in the evaluation of potential novel antimicrobial compounds. These methods are cost-effective and have high predictive value. They are widely used in preclinical studies to identify new molecular candidates, for further investigation in animal and human trials.

Sulisobenzone is a potent inhibitor of the global transcription factor Cra

Transcription is carried out by the RNA polymerase and is regulated through a series of interactions with transcription factors. Catabolite activator repressor (Cra), a LacI family transcription factor regulates the virulence gene expression in Enterohaemorrhagic Escherichia coli (EHEC) and thus is a promising drug target for the discovery of antivirulence molecules. Here, we report the crystal structure of the effector molecule binding domain of Cra from E. coli (EcCra) in complex with HEPES molecule. Based on the EcCra-HEPES complex structure, ligand screening was performed that identified sulisobenzone as an potential inhibitor of EcCra. The electrophoretic mobility shift assay (EMSA) and in vitro transcription assay validated the sulisobenzone binding to EcCra. Moreover, the isothermal titration calorimetry (ITC) experiments demonstrated a 40-fold higher binding affinity of sulisobenzone (KD 360 nM) compared to the HEPES molecule. Finally, the sulisobenzone bound EcCra complex crystal structure was determined to elucidate the binding mechanism of sulisobenzone to the effector binding pocket of EcCra. Together, this study suggests that sulisobenzone may be a promising candidate that can be studied and developed as an effective antivirulence agent against EHEC.

Pharmacokinetics, quorum-sensing signal molecules and tryptophan-related metabolomics of the novel anti-virulence drug Fluorothiazinon in a Pseudomonas aeruginosa-induced pneumonia murine model

Pseudomonas aeruginosa (PA) infection is commonly associated with hospital-acquired infections in patients with immune deficiency and/or severe lung diseases. Managing this bacterium is complex due to drug resistance and high adaptability. Fluorothiazinon (FT) is an anti-virulence drug developed to suppress the virulence of bacteria as opposed to bacterial death increasing host's immune response to infection and improving treatment to inhibit drug resistant bacteria. We aimed to evaluate FT pharmacokinetics, quorum sensing signal molecules profiling and tryptophan-related metabolomics in blood, liver, kidneys, and lungs of mice. Study comprised three groups: a group infected with PA that was treated with 400 mg/kg FT ("infected treated group"); a non-infected group, but also treated with the same single drug dose ("non-infected treated group"); and an infected group that received a vehicle ("infected non-treated group"). PA-mediated infection blood pharmacokinetics profiling was indicative of increased drug concentrations as shown by increased Cmax and AUCs. Tissue distribution in liver, kidneys, and lungs, showed that liver presented the most consistently higher concentrations of FT in the infected versus non-infected mice. FT showed that HHQ levels were decreased at 1 h after dosing in lungs while PQS levels were lower across time in lungs of infected treated mice in comparison to infected non-treated mice. Metabolomics profiling performed in lungs and blood of infected treated versus infected non-treated mice revealed drug-associated metabolite alterations, especially in the kynurenic and indole pathways.

Bacteriophage steering of Burkholderia cenocepacia toward reduced virulence and increased antibiotic sensitivity

Antibiotic resistance in bacteria is a growing global concern and has spurred increasing efforts to find alternative therapeutics, such as the use of bacterial viruses, or bacteriophages. One promising approach is to use phages that not only kill pathogenic bacteria but also select phage-resistant survivors that are newly sensitized to traditional antibiotics, in a process called "phage steering." Members of the bacterial genus Burkholderia, which includes various human pathogens, are highly resistant to most antimicrobial agents, including serum immune components, antimicrobial peptides, and polymixin-class antibiotics. However, the application of phages in combination with certain antibiotics can produce synergistic effects that more effectively kill pathogenic bacteria. Herein, we demonstrate that Burkholderia cenocepacia serum resistance is due to intact lipopolysaccharide (LPS) and membranes, and phage-induced resistance altering LPS structure can enhance bacterial sensitivity not only to immune components in serum but also to membrane-associated antibiotics such as colistin. IMPORTANCE Bacteria frequently encounter selection pressure from both antibiotics and lytic phages, but little is known about the interactions between antibiotics and phages. This study provides new insights into the evolutionary trade-offs between phage resistance and antibiotic sensitivity. The creation of phage resistance through changes in membrane structure or lipopolysaccharide composition can simultaneously be a major cause of antibiotic sensitivity. Our results provide evidence of synergistic therapeutic efficacy in phage-antibiotic interactions and have implications for the future clinical use of phage steering in phage therapy applications.

Anti-Biofilm Activity of Carnosic Acid from Salvia rosmarinus against Methicillin-Resistant Staphylococcus aureus

The Salvia rosmarinus "Eretto Liguria" ecotype was studied as a source of valuable bioactive compounds. LC-MS analysis of the methanolic extract underlined the presence of diterpenoids, triterpenoids, polyphenolic acids, and flavonoids. The anti-virulence activity of carnosic acid along with the other most abundant compounds against methicillin-resistant Staphylococcus aureus (MRSA) was evaluated. Only carnosic acid induced a significant reduction in the expression of agrA and rnaIII genes, which encode the key components of quorum sensing (QS), an intracellular signaling mechanism controlling the virulence of MRSA. At a concentration of 0.05 mg/mL, carnosic acid inhibited biofilm formation by MRSA and the expression of genes involved in toxin production and made MRSA more susceptible to intracellular killing, with no toxic effects on eukaryotic cells. Carnosic acid did not affect biofilm formation by Pseudomonas aeruginosa, a human pathogen that often coexists with MRSA in complex infections. The selected ecotype showed a carnosic acid content of 94.3 ± 4.3 mg/g. In silico analysis highlighted that carnosic acid potentially interacts with the S. aureus AgrA response regulator. Our findings suggest that carnosic acid could be an anti-virulence agent against MRSA infections endowed with a species-specific activity useful in multi-microbial infections.

Eradication of Bacterial Persister Cells By Leveraging Their Low Metabolic Activity Using Adenosine Triphosphate Coated Gold Nanoclusters

Bacteria first develop tolerance after antibiotic exposure; later genetic resistance emerges through the population of tolerant bacteria. Bacterial persister cells are the multidrug-tolerant subpopulation within an isogenic bacteria culture that maintains genetic susceptibility to antibiotics. Because of this link between antibiotic tolerance and resistance and the rise of antibiotic resistance, there is a pressing need to develop treatments to eradicate persister cells. Current anti persister cell strategies are based on the paradigm of "awakening" them from their low metabolic state before attempting eradication with traditional antibiotics. Herein, we demonstrate that the low metabolic activity of persister cells can be exploited for eradication over their metabolically active counterparts. We engineered gold nanoclusters coated with adenosine triphosphate (AuNC@ATP) as a benchmark nanocluster that kills persister cells over exponential growth bacterial cells and prove the feasibility of this new concept. Finally, using AuNC@ATP as a new research tool, we demonstrated that it is possible to prevent the emergence of antibiotic-resistant superbugs with an anti-persister compound. Eradicating persister cells with AuNC@ATP in an isogenic culture of bacteria stops the emergence of superbug bacteria mediated by the sub-lethal dose of conventional antibiotics. Our findings lay the groundwork for developing novel nano-antibiotics targeting persister cells, which promise to prevent the emergence of superbugs and prolong the lifespan of currently available antibiotics.

Carbon dots: Types, preparation, and their boosted antibacterial activity by photoactivation. Current status and future perspectives

Carbon dots (CDs) correspond to carbon-based materials (CBM) with sizes usually below 10 nm. These nanomaterials exhibit attractive properties such us low toxicity, good stability, and high conductivity, which have promoted their thorough study over the past two decades. The current review describes four types of CDs: carbon quantum dots (CQDs), graphene quantum dots (GQDs), carbon nanodots (CNDs), and carbonized polymers dots (CPDs), together with the state of the art of the main routes for their preparation, either by "top-down" or "bottom-up" approaches. Moreover, among the various usages of CDs within biomedicine, we have focused on their application as a novel class of broad-spectrum antibacterial agents, concretely, owing their photoactivation capability that triggers an enhanced antibacterial property. Our work presents the recent advances in this field addressing CDs, their composites and hybrids, applied as photosensitizers (PS), and photothermal agents (PA) within antibacterial strategies such as photodynamic therapy (PDT), photothermal therapy (PTT), and synchronic PDT/PTT. Furthermore, we discuss the prospects for the possible future development of large-scale preparation of CDs, and the potential for these nanomaterials to be employed in applications to combat other pathogens harmful to human health. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Click Triazole as a Linker for Pretargeting Strategies: Synthesis, Docking Investigations, Fluorescence Diagnosis, and Antibacterial Action Studies

In this study, three compounds A1, A2, and A3 and fluorescent probes T1, T2, T3, and T4 were designed and synthesized. ¹H NMR, ¹³C NMR, and MS characterization and elemental analysis were used to confirm A1-A3 and T1-T4. A1-A3 and T1-T4 formed diagnostic molecules by "click" reactions. A1-A3 and T1-T4 did not significantly increase cell death at concentrations of 80 μmol/L. Preliminary screening of the compounds for antibacterial activity revealed that A2 has better antibacterial activity against Agrobacterium tumefaciens. The synthesized compounds and fluorescent probes can be targeted and combined in the physiological condition to form diagnostic molecules for fluorescence detection of Agrobacterium tumefaciens. The binding sites of A1-A3 were deduced theoretically using the AutoDock Vina software docking tool. Further study of the mechanism of the antibacterial action of these compounds is likely to identify new agents against resistant bacterial strains.

Bacterial virulence regulation through soluble peptidoglycan fragments sensing and response: knowledge gaps and therapeutic potential

Given the growing clinical-epidemiological threat posed by the phenomenon of antibiotic resistance, new therapeutic options are urgently needed, especially against top nosocomial pathogens such as those within the ESKAPE group. In this scenario, research is pushed to explore therapeutic alternatives and, among these, those oriented toward reducing bacterial pathogenic power could pose encouraging options. However, the first step in developing these antivirulence weapons is to find weak points in the bacterial biology to be attacked with the goal of dampening pathogenesis. In this regard, during the last decades some studies have directly/indirectly suggested that certain soluble peptidoglycan-derived fragments display virulence-regulatory capacities, likely through similar mechanisms to those followed to regulate the production of several β-lactamases: binding to specific transcriptional regulators and/or sensing/activation of two-component systems. These data suggest the existence of intra- and also intercellular peptidoglycan-derived signaling capable of impacting bacterial behavior, and hence likely exploitable from the therapeutic perspective. Using the well-known phenomenon of peptidoglycan metabolism-linked β-lactamase regulation as a starting point, we gather and integrate the studies connecting soluble peptidoglycan sensing with fitness/virulence regulation in Gram-negatives, dissecting the gaps in current knowledge that need filling to enable potential therapeutic strategy development, a topic which is also finally discussed.

Research Progress on Small Molecular Inhibitors of the Type 3 Secretion System

The overuse of antibiotics has led to severe bacterial drug resistance. Blocking pathogen virulence devices is a highly effective approach to combating bacterial resistance worldwide. Type three secretion systems (T3SSs) are significant virulence factors in Gram-negative pathogens. Inhibition of these systems can effectively weaken infection whilst having no significant effect on bacterial growth. Therefore, T3SS inhibitors may be a powerful weapon against resistance in Gram-negative bacteria, and there has been increasing interest in the research and development of T3SS inhibitors. This review outlines several reported small-molecule inhibitors of the T3SS, covering those of synthetic and natural origin, including their sources, structures, and mechanisms of action.

The biogenesis of β-lactamase enzymes

The discovery of penicillin by Alexander Fleming marked a new era for modern medicine, allowing not only the treatment of infectious diseases, but also the safe performance of life-saving interventions, like surgery and chemotherapy. Unfortunately, resistance against penicillin, as well as more complex β-lactam antibiotics, has rapidly emerged since the introduction of these drugs in the clinic, and is largely driven by a single type of extra-cytoplasmic proteins, hydrolytic enzymes called β-lactamases. While the structures, biochemistry and epidemiology of these resistance determinants have been extensively characterized, their biogenesis, a complex process including multiple steps and involving several fundamental biochemical pathways, is rarely discussed. In this review, we provide a comprehensive overview of the journey of β-lactamases, from the moment they exit the ribosomal channel until they reach their final cellular destination as folded and active enzymes.

Chemically Tuning Resveratrol for the Effective Killing of Gram-Positive Pathogens

In the era of antimicrobial resistance, the identification of new compounds with strong antimicrobial activity and the development of alternative therapies to fight drug-resistant bacteria are urgently needed. Here, we have used resveratrol, a safe and well-known plant-derived stilbene with poor antimicrobial properties, as a scaffold to design several new families of antimicrobials by adding different chemical entities at specific positions. We have characterized the mode of action of the most active compounds prepared and have examined their synergistic antibacterial activity in combination with traditional antibiotics. Some alkyl- and silyl-resveratrol derivatives show bactericidal activity against Gram-positive bacteria in the same low micromolar range of traditional antibiotics, with an original mechanism of action that combines membrane permeability activity with ionophore-related activities. No cross-resistance or antagonistic effect was observed with traditional antibiotics. Synergism was observed for some specific general-use antibiotics, such as aminoglycosides and cationic antimicrobial peptide antibiotics. No hemolytic activity was observed at the active concentrations or above, although some low toxicity against an MRC-5 cell line was noted.

Targeting the Pseudomonas aeruginosa Virulence Factor Phospholipase C With Engineered Liposomes

Engineered liposomes composed of the naturally occurring lipids sphingomyelin (Sm) and cholesterol (Ch) have been demonstrated to efficiently neutralize toxins secreted by Gram-positive bacteria such as Streptococcus pneumoniae and Staphylococcus aureus. Here, we hypothesized that liposomes are capable of neutralizing cytolytic virulence factors secreted by the Gram-negative pathogen Pseudomonas aeruginosa. We used the highly virulent cystic fibrosis P. aeruginosa Liverpool Epidemic Strain LESB58 and showed that sphingomyelin (Sm) and a combination of sphingomyelin with cholesterol (Ch:Sm; 66 mol/% Ch and 34 mol/% Sm) liposomes reduced lysis of human bronchial and red blood cells upon challenge with the Pseudomonas secretome. Mass spectrometry of liposome-sequestered Pseudomonas proteins identified the virulence-promoting hemolytic phospholipase C (PlcH) as having been neutralized. Pseudomonas aeruginosa supernatants incubated with liposomes demonstrated reduced PlcH activity as assessed by the p-nitrophenylphosphorylcholine (NPPC) assay. Testing the in vivo efficacy of the liposomes in a murine cutaneous abscess model revealed that Sm and Ch:Sm, as single dose treatments, attenuated abscesses by >30%, demonstrating a similar effect to that of a mutant lacking plcH in this infection model. Thus, sphingomyelin-containing liposome therapy offers an interesting approach to treat and reduce virulence of complex infections caused by P. aeruginosa and potentially other Gram-negative pathogens expressing PlcH.

Candidates for Repurposing as Anti-Virulence Agents Based on the Structural Profile Analysis of Microbial Collagenase Inhibitors

The pharmacological inhibition of the bacterial collagenases (BC) enzymes is considered a promising strategy to block the virulence of the bacteria without targeting the selection mechanism leading to drug resistance. The chemical structures of the Clostridium perfringens collagenase A (ColA) inhibitors were analyzed using Bemis-Murcko skeletons, Murcko frameworks, the type of plain rings, and docking studies. The inhibitors were classified based on their structural architecture and various scoring methods were implemented to predict the probability of new compounds to inhibit ColA and other BC. The analyses indicated that all compounds contain at least one aromatic ring, which is often a nitrobenzene fragment. 2-Nitrobenzene based compounds are, on average, more potent BC inhibitors compared to those derived from 4-nitrobenzene. The molecular descriptors MDEO-11, AATS0s, ASP-0, and MAXDN were determined as filters to identify new BC inhibitors and highlighted the necessity for a compound to contain at least three primary oxygen atoms. The DrugBank database was virtually screened using the developed methods. A total of 100 compounds were identified as potential BC inhibitors, of which, 10 are human approved drugs. Benzthiazide, entacapone, and lodoxamide were chosen as the best candidates for in vitro testing based on their pharmaco-toxicological profile.

Evaluation of the Antibacterial Activity of Crude Extracts Obtained From Cultivation of Native Endophytic Fungi Belonging to a Tropical Montane Rainforest in Colombia

Bioactive secondary metabolite production from endophytic fungi has gained a recurring research focus in recent decades as these microorganisms represent an unexplored biological niche for their diverse biotechnological potential. Despite this focus, studies involving tropical endophytes remain scarce, particularly those isolated from medicinal plants of these ecosystems. In addition, the state of the art of the pharmaceutical industry has experienced stagnation in the past 30years, which has pushed pathogenic infections to get one step ahead, resulting in the development of resistance to existing treatments. Here, five fungal endophytes were isolated from the medicinal plant Otoba gracilipes (Myristicaceae), which corresponded to the genera Xylaria and Diaporthe, and screened to demonstrate the promissory potential of these microorganisms for producing bioactive secondary metabolites with broad-spectrum antibacterial activities. Thus, the evaluation of crude organic extracts obtained from the mycelia and exhaust medium allowed the elucidation of Xylaria sp. and Diaporthe endophytica potential toward providing crude extracellular extracts with promising bioactivities against reference strains of Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923), according to the determined half-maximum inhibitory concentration (IC₅₀) with values down to 3.91 and 10.50mg/ml against each pathogen, respectively. Follow-up studies provided insights into the polarity nature of bioactive compounds in the crude extracts through bioactivity guided fractionation using a polymeric resin absorbent alternative extraction procedure. In addition, evaluation of the co-culturing methods demonstrated how this strategy can enhance endophytes biosynthetic capacity and improve their antibacterial potential with a 10-fold decrease in the IC₅₀ values against both pathogens compared to the obtained values in the preliminary evaluations of Xylaria sp. and D. endophytica crude extracts. These results support the potential of Colombian native biodiversity to provide new approaches concerning the global emergence of antibiotics resistance and future production of undiscovered compounds different from the currently used antibiotics classes and simultaneously call for the value of preserving native habitats due to their promising ecosystemic applications in the biotechnological and pharmaceutical industries.

Repurposing epigenetic inhibitors to target the Clostridioides difficile-specific DNA adenine methyltransferase and sporulation regulator CamA

Epigenetically targeted therapeutic development, particularly for SAM-dependent methylations of DNA, mRNA and histones has been proceeding rapidly for cancer treatments over the past few years. However, this approach has barely begun to be exploited for developing new antibiotics, despite an overwhelming global need to counter antimicrobial resistance. Here, we explore whether SAM analogues, some of which are in (pre)clinical studies as inhibitors of human epigenetic enzymes, can also inhibit Clostridioides difficile-specific DNA adenine methyltransferase (CamA), a sporulation regulator present in all C. difficile genomes sequenced to date, but found in almost no other bacteria. We found that SGC0946 (an inhibitor of DOT1L), JNJ-64619178 (an inhibitor of PRMT5) and SGC8158 (an inhibitor of PRMT7) inhibit CamA enzymatic activity in vitro at low micromolar concentrations. Structural investigation of the ternary complexes of CamA-DNA in the presence of SGC0946 or SGC8158 revealed conformational rearrangements of the N-terminal arm, with no apparent disturbance of the active site. This N-terminal arm and its modulation of exchanges between SAM (the methyl donor) and SAH (the reaction product) during catalysis of methyl transfer are, to date, unique to CamA. Our work presents a substantial first step in generating potent and selective inhibitors of CamA that would serve in the near term as chemical probes to investigate the cellular mechanism(s) of CamA in controlling spore formation and colonization, and eventually as therapeutic antivirulence agents useful in treating C. difficile infection.

Polymyxins, the last-resort antibiotics: Mode of action, resistance emergence, and potential solutions

Infections caused by multi-drug resistant (MDR) bacterial pathogens are a leading cause of mortality and morbidity across the world. Indiscriminate use of broad-spectrum antibiotics has seriously affected this situation. With the diminishing discovery of novel antibiotics, new treatment methods are urgently required to combat MDR pathogens. Polymyxins, the cationic lipopeptide antibiotics, discovered more than half a century ago, are considered to be the last-line of antibiotics available at the moment. This antibiotic shows a great bactericidal effect against Gram-negative bacteria. Polymyxins primarily target the bacterial membrane and disrupt them, causing lethality. Because of their membrane interacting mode of action, polymyxins cause nephrotoxicity and neurotoxicity in humans, limiting their usability. However, recent modifications in their chemical structure have been able to reduce the toxic effects. The development of better dosing regimens has also helped in getting better clinical outcomes in the infections caused by MDR pathogens. Since the mid-1990s the use of polymyxins has increased manifold in clinical settings, resulting in the emergence of polymyxin-resistant strains. The risk posed by the polymyxin-resistant nosocomial pathogens such as the Enterobacteriaceae group, Pseudomonas aeruginosa, and Acinetobacter baumannii, etc. is very serious considering these pathogens are resistant to almost all available antibacterial drugs. In this review article, the mode of action of the polymyxins and the genetic regulatory mechanism responsible for the emergence of resistance are discussed. Specifically, this review aims to update our current understanding in the field and suggest possible solutions that can be pursued for future antibiotic development. As polymyxins primarily target the bacterial membranes, resistance to polymyxins arises primarily by the modification of the lipopolysaccharides (LPS) in the outer membrane (OM). The LPS modification pathways are largely regulated by the bacterial two-component signal transduction (TCS) systems. Therefore, targeting or modulating the TCS signalling mechanisms can be pursued as an alternative to treat the infections caused by polymyxin-resistant MDR pathogens. In this review article, this aspect is also highlighted.

Metabolite Profiling of Malaysian Gracilaria edulis Reveals Eplerenone as Novel Antibacterial Compound for Drug Repurposing Against MDR Bacteria

With a continuous threat of antimicrobial resistance on human health worldwide, efforts for new alternatives are ongoing for the management of bacterial infectious diseases. Natural products of land and sea, being conceived to be having fewer side effects, pose themselves as a welcome relief. In this respect, we have taken a scaffolded approach to unearthing the almost unexplored chemical constituents of Malaysian red seaweed, Gracilaria edulis. Essentially, a preliminary evaluation of the ethyl acetate and acetone solvent extracts, among a series of six such, revealed potential antibacterial activity against six MDR species namely, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enterica, methicillin-resistant Staphylococcus aureus (MRSA), Streptococcus pyogenes, and Bacillus subtilis. Detailed analyses of the inlying chemical constituents, through LC-MS and GC-MS chromatographic separation, revealed a library of metabolic compounds. These were led for further virtual screening against selected key role playing proteins in the virulence of the aforesaid bacteria. To this end, detailed predictive pharmacological analyses added up to reinforce Eplerenone as a natural alternative from the plethora of plausible bioactives. Our work adds the ongoing effort to re-discover and repurpose biochemical compounds to combat the antimicrobial resistance offered by the Gram-positive and the -negative bacterial species.

A phage protein-derived antipathogenic peptide that targets type IV pilus assembly

Phage-inspired antibacterial discovery is a new approach that recruits phages in search for antibacterials with new molecular targets, in that phages are the biological entities well adapted to hijack host bacterial physiology in favor of their own thrive. We previously observed that phage-mediated twitching motility inhibition was effective to control the acute infections caused by Pseudomonas aeruginosa and that the motility inhibition was attributed to the delocalization of PilB, the type IV pilus (TFP) assembly ATPase by binding of the 136-amino acid (aa) phage protein, Tip. Here, we created a series of truncated and point-mutant Tip proteins to identify the critical residues in the Tip bioactivity: N-terminal 80-aa residues were dispensable for the Tip activity; we identified that Asp82, Leu84, and Arg85 are crucial in the Tip function. Furthermore, a synthetic 15-aa peptide (P1) that corresponds to Leu73 to Ala87 is shown to suffice for PilB delocalization, twitching inhibition, and virulence attenuation upon exogenous administration. The transgenic flies expressing the 15-aa peptide were resistant to P. aeruginosa infections as well. Taken together, this proof-of-concept study reveals a new antipathogenic peptide hit targeting bacterial motility and provides an insight into antibacterial discovery targeting TFP assembly.

Antibiotic Therapy of Plague: A Review

Plague-a deadly disease caused by the bacterium Yersinia pestis-is still an international public health concern. There are three main clinical forms: bubonic plague, septicemic plague, and pulmonary plague. In all three forms, the symptoms appear suddenly and progress very rapidly. Early antibiotic therapy is essential for countering the disease. Several classes of antibiotics (e.g., tetracyclines, fluoroquinolones, aminoglycosides, sulfonamides, chloramphenicol, rifamycin, and β-lactams) are active in vitro against the majority of Y. pestis strains and have demonstrated efficacy in various animal models. However, some discrepancies have been reported. Hence, health authorities have approved and recommended several drugs for prophylactic or curative use. Only monotherapy is currently recommended; combination therapy has not shown any benefits in preclinical studies or case reports. Concerns about the emergence of multidrug-resistant strains of Y. pestis have led to the development of new classes of antibiotics and other therapeutics (e.g., LpxC inhibitors, cationic peptides, antivirulence drugs, predatory bacteria, phages, immunotherapy, host-directed therapy, and nutritional immunity). It is difficult to know which of the currently available treatments or therapeutics in development will be most effective for a given form of plague. This is due to the lack of standardization in preclinical studies, conflicting data from case reports, and the small number of clinical trials performed to date.

Polymyxins, the last-resort antibiotics: Mode of action, resistance emergence, and potential solutions

Infections caused by multi-drug resistant (MDR) bacterial pathogens are a leading cause of mortality and morbidity across the world. Indiscriminate use of broad-spectrum antibiotics has seriously affected this situation. With the diminishing discovery of novel antibiotics, new treatment methods are urgently required to combat MDR pathogens. Polymyxins, the cationic lipopeptide antibiotics, discovered more than half a century ago, are considered to be the last-line of antibiotics available at the moment. This antibiotic shows a great bactericidal effect against Gram-negative bacteria. Polymyxins primarily target the bacterial membrane and disrupt them, causing lethality. Because of their membrane interacting mode of action, polymyxins cause nephrotoxicity and neurotoxicity in humans, limiting their usability. However, recent modifications in their chemical structure have been able to reduce the toxic effects. The development of better dosing regimens has also helped in getting better clinical outcomes in the infections caused by MDR pathogens. Since the mid1990s the use of polymyxins has increased manifold in clinical settings, resulting in the emergence of polymyxin-resistant strains. The risk posed by the polymyxin-resistant nosocomial pathogens such as the Enterobacteriaceae group, Pseudomonas aeruginosa, and Acinetobacter baumannii, etc. is very serious considering these pathogens are resistant to almost all available antibacterial drugs. In this review article, the mode of action of the polymyxins and the genetic regulatory mechanism responsible for the emergence of resistance are discussed. Specifically, this review aims to update our current understanding in the field and suggest possible solutions that can be pursued for future antibiotic development. As polymyxins primarily target the bacterial membranes, resistance to polymyxins arises primarily by the modification of the lipopolysaccharides (LPS) in the outer membrane (OM). The LPS modification pathways are largely regulated by the bacterial two-component signal transduction (TCS) systems. Therefore, targeting or modulating the TCS signalling mechanisms can be pursued as an alternative to treat the infections caused by polymyxin-resistant MDR pathogens. In this review article, this aspect is also highlighted.

African Plant-Based Natural Products with Antivirulence Activities to the Rescue of Antibiotics

The worldwide emergence of antibiotic-resistant bacteria and the thread of widespread superbug infections have led researchers to constantly look for novel effective antimicrobial agents. Within the past two decades, there has been an increase in studies attempting to discover molecules with innovative properties against pathogenic bacteria, notably by disrupting mechanisms of bacterial virulence and/or biofilm formation which are both regulated by the cell-to-cell communication mechanism called ‘quorum sensing’ (QS). Certainly, targeting the virulence of bacteria and their capacity to form biofilms, without affecting their viability, may contribute to reduce their pathogenicity, allowing sufficient time for an immune response to infection and a reduction in the use of antibiotics. African plants, through their huge biodiversity, present a considerable reservoir of secondary metabolites with a very broad spectrum of biological activities, a potential source of natural products targeting such non-microbicidal mechanisms. The present paper aims to provide an overview on two main aspects: (i) succinct presentation of bacterial virulence and biofilm formation as well as their entanglement through QS mechanisms and (ii) detailed reports on African plant extracts and isolated compounds with antivirulence properties against particular pathogenic bacteria.