Antibiotics for emerging pathogens

Synthetic Mimics of Antimicrobial Peptides for the Targeted Therapy of Multidrug-Resistant Bacterial Infection

Antibacterial materials are highly demanded in treatment of bacterial infection, especially severe ones with multidrug-resistance. Herein, pH-responsive polypeptide, i.e., poly-L-lysine modified by 1-(propylthio)acetic acid-3-octylimidazolium and citraconic anhydride (PLL-POIM-CA), is synthesized by post-polymerization modification of poly-L-lysine (PLL) with 1-(propylthio)acetic acid-3-octylimidazolium (POIM) and citraconic anhydride (CA). It is observed that PLL-POIM-CA is stable under normal physiological condition, while CA cleaves rapidly at weakly acidic environment like bacterial infectious sites. The hydrolyzed PLL-POIM-CA exhibits excellent broad-spectrum antibacterial activities against Gram-negative bacteria of Escherichia coli and Gram-positive bacteria of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA). In particular, the minimum inhibitory concentration (MIC) against multidrug-resistant bacteria like MRSA is as low as 7.8 µg mL^-1 . Moreover, PLL-POIM-CA exhibits good biocompatibility with mouse fibroblast cells (L929) in vitro and improved hemocompatibility with an HC₅₀ exceeding 5000 µg mL^-1 . Therefore, PLL-POIM-CA displays an excellent bacteria versus cells selectivity (HC₅₀ /MIC) over 534, which is 53 times higher than natural antimicrobial peptide of indolicidin. It is further demonstrated in vivo that the antimicrobial polypeptide effectively accelerates MRSA-infected wound healing by relieving local inflammatory response. Therefore, this targeted antimicrobial polypeptide has broad application prospects for the treatment of multidrug-resistant bacterial infection.

Polymyxin B-Triggered Assembly of Peptide Hydrogels for Localized and Sustained Release of Combined Antimicrobial Therapy

Repurposing old antibiotics into more effective and safer formulations is an emergent approach to tackle the growing threat of antimicrobial resistance. Herein, a peptide hydrogel is reported for the localized and sustained release of polymyxin B (PMB), a decade-old antibiotic with increasing clinical utility for treating multidrug-resistant Gram-negative bacterial infections. The hydrogel is assembled by additing PMB solution into a rationally designed peptide amphiphile (PA) solution and its mechanical properties can be adjusted through the addition of counterions, envisioning its application in diverse infection scenarios. Sustained release of PMB from the hydrogel over a 5-day period and prolonged antimicrobial activities against Gram-negative bacteria are observed. The localized release of active PMB from the hydrogel is shown to be effective in vivo for treating Pseudomonas aeruginosa infection in the Galleria mellonella burn wound infection model, dramatically reducing the mortality from 93% to 13%. Complementary antimicrobial activity against Gram-positive Staphylococcus aureus and enhanced antimicrobial effect against the Gram-negative Acinetobacter baumannii are observed when an additional antibiotic fusidic acid is incorporated into the hydrogen network. These results demonstrate the potential of the PMB-triggered PA hydrogel as a versatile platform for the localized and sustained delivery of combined antimicrobial therapies.

Polymer Composite Sponges with Inherent Antibacterial, Hemostatic, Inflammation-Modulating and Proregenerative Performances for Methicillin-Resistant Staphylococcus aureus-Infected Wound Healing

Clinical wound management remains a major challenge due to massive bleeding, bacterial infection, and difficult wound healing after tissue trauma. To simultaneously address these issues, composite polymer sponges for accelerating drug-resistant bacterial infected wound healing are fabricated by facilely mixing sodium polyacrylate (PAAS), double quaternary ammonium salts-conjugated chitosan (QAS-CS), and collagen (COL) in aqueous solution, followed by lyophilization. Composite sponges (PAAS/QAS-CS/COL, PQC) show highly porous microstructures (porosity ≈90%) with moderate compress modulus (≈0.3 MPa), tensile strength (0.004 MPa), and high swelling ratio (≈3500%). Importantly, PQC sponge demonstrates superior hemostasis ability over commercially available CS sponge by inducing rapid hemagglutination, and exhibits significantly better antibacterial activity against both methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli by destroying cell membrane and causing the leakage of bioactive components such as potassium ion and β-galactosidase from treated bacterial. Furthermore, PQC sponge can efficiently promote cell proliferation. Significantly, the sponge greatly expedites the regeneration of MRSA-infected full-thickness skin wound in rabbit by successfully eradicating bacterial infection, and reducing inflammation. PQC sponge also improves both early angiogenesis and blood vessel maturation at the wound site. Overall, this multifunctional sponge is a promising wound dressing for clinical use and holds great potential for rapid clinical translation.

Anti-Inflammatory and Antimicrobial Volatile Oils: Fennel and Cumin Inhibit Neutrophilic Inflammation via Regulating Calcium and MAPKs

Neutrophilic inflammatory diseases, such as chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), or psoriasis, exert a huge burden on the global health system due to the lack of safe and effective treatments. Volatile oils from terrestrial plants showed impressive therapeutic effects against disorders of the skin, digestive system, lungs, liver, metabolism, and nervous system. However, their effect on the immune system and neutrophil function is still elusive. Fennel, cumin, marjoram, lavender, caraway, and anise are the common nutraceuticals that are widely used in the Mediterranean diet. The volatile oils of these herbs were screened for various biological activities, including anti-inflammatory, anti-allergic, antimicrobial, and antiviral effects. Several oils showed anti-inflammatory and antimicrobial potential. Fennel (Foeniculum vulgare) and cumin (Cuminum cyminum) fruits' volatile oils significantly suppressed the activation of human neutrophils, including respiratory burst and the degranulation induced by formyl peptide receptor agonists fMLF/CB and MMK1 in the human neutrophils (IC₅₀, 3.8–17.2 µg/ml). The cytotoxic effect and free-radical scavenging effects (ABTS, DPPH) of these oils did not account for the observed effects. Both fennel and cumin volatile oils significantly shortened calcium influx recovery time and inhibited phosphorylation of mitogen-activated protein kinases (p38, JNK, and ERK) expression. The gas chromatography–mass spectrometry analysis of these oils revealed the presence of estragole and cuminaldehyde as the major components of fennel and cumin volatile oils, respectively. Our findings suggested that cumin and fennel, common in the Mediterranean diet, hold the potential to be applied for the treatment of neutrophilic inflammatory diseases.

Total flavonoids from Potentilla kleiniana Wight et Arn inhibits biofilm formation and virulence factors production in methicillin-resistant Staphylococcus aureus (MRSA)

ETHANOPHARMACOLOGICAL RELEVANCE

Potentilla kleiniana Wight et Arn is a wide-spread wild plant in the mountainous areas in southern China. The whole herb has been used as a traditional herbal medicine to treat fever, arthritis, malaria, insect and snake bites, hepatitis, and traumatic injury. In vitro studies have reported the antibacterial activity use of the plant in traditional medicinal systems.

AIM OF THE STUDY

The aim of this study was to investigate the inhibitory activity of total flavonoid from Potentilla kleiniana Wight et Arn (TFP) on methicillin-resistant Staphylococcus aureus (MRSA) in planktonic state and biofilm state.

MATERIALS AND METHODS

Antibacterial activities of TFP on planktonic MRSA were determined by agar diffusion method, microtiter plate assay and time-kill curve assay. Electrical conductivity, membrane permeability, membrane potential and autoaggregation were analyzed to study TFP effects on planktonic MRSA growth. Crystal violet (CV) staining and confocal laser scanning microscopy (CLSM) were analyzed to study TFP effects on aggregation and maturation of MRSA biofilm. After TFP treatment, extracellular polymeric substances (EPS) production were examined. Morphological changes in planktonic and MRSA biofilm following TFP treatment were determined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, α-Toxin protein expression and adhesion-related gene expression were also determined.

RESULTS

The minimum inhibitory concentration (MIC) of TFP against MRSA was 20 μg/mL. The agar diffusion method and time-kill curve assay results indicated that TFP inhibited planktonic MRSA growth. TFP treatment significantly inhibited planktonic MRSA growth by inhibiting autoaggregation, α-hemolysin activity, α-Toxin protein expression, but increasing electrolyte leakage, membrane permeability and membrane potential and impacting cell structure. Moreover, TFP treatment significantly inhibited aggregation and maturation on MRSA biofilm by decreasing surface hydrophobicity, EPS production and adhesion-related gene expression.

CONCLUSION

The results of this trial provide scientific experimental data on the traditional use of Potentilla Kleiniana Wight et Arn for traumatic injury treatment and further demonstrate the potential of TFP to be developed as a novel anti-biofilm drug.

Polymyxin B-modified conjugated oligomer nanoparticle for targeted identification and enhanced photodynamic antimicrobial therapy

We report a photosensitive polymyxin B-modified conjugated oligomer nanoparticle that integrates the targeted identification and synergistic photodynamic therapy in one treatment against resistant Gram-negative bacteria. The study expands the application of antibiotics and opens a new avenue for enhancing photodynamic antimicrobial therapy and fighting bacterial resistance.

Development of Amphiphilic Coumarin Derivatives as Membrane-Active Antimicrobial Agents with Potent In Vivo Efficacy against Gram-Positive Pathogenic Bacteria

Increases in drug-resistant pathogens are becoming a serious detriment to human health. To combat pathogen infections, a new series of amphiphilic coumarin derivatives were designed and synthesized as antimicrobial agents with membrane-targeting action. We herein report a lead compound, 25, that displayed potent antibacterial activity against Gram-positive bacteria, including MRSA. Compound 25 exhibited weak hemolytic activity and low toxicity to mammalian cells and can kill Gram-positive bacteria quickly (within 0.5 h) by directly disrupting the bacterial cell membranes. Additionally, compound 25 demonstrated excellent efficacy in a murine corneal infection caused by Staphylococcus aureus. These results suggest that 25 has great potential to be a potent antimicrobial agent for treating drug-resistant Gram-positive bacterial infections.

Drugs That Changed Society: History and Current Status of the Early Antibiotics: Salvarsan, Sulfonamides, and β-Lactams

The appearance of antibiotic drugs revolutionized the possibilities for treatment of diseases with high mortality such as pneumonia, sepsis, plaque, diphtheria, tetanus, typhoid fever, and tuberculosis. Today fewer than 1% of mortalities in high income countries are caused by diseases caused by bacteria. However, it should be recalled that the antibiotics were introduced in parallel with sanitation including sewerage, piped drinking water, high standard of living and improved understanding of the connection between food and health. Development of salvarsan, sulfonamides, and β-lactams into efficient drugs is described. The effects on life expectancy and life quality of these new drugs are indicated.

Residual Helicity at the Active Site of the Histidine Phosphocarrier, HPr, Modulates Binding Affinity to Its Natural Partners

The phosphoenolpyruvate-dependent phosphotransferase system (PTS) modulates the preferential use of sugars in bacteria. The first proteins in the cascade are common to all organisms (EI and HPr). The active site of HPr involves a histidine (His15) located immediately before the beginning of the first α-helix. The regulator of sigma D (Rsd) protein also binds to HPr. The region of HPr comprising residues Gly9-Ala30 (HPr^9–30), involving the first α-helix (Ala16-Thr27) and the preceding active site loop, binds to both the N-terminal region of EI and intact Rsd. HPr^9–30 is mainly disordered. We attempted to improve the affinity of HPr^9–30 to both proteins by mutating its sequence to increase its helicity. We designed peptides that led to a marginally larger population in solution of the helical structure of HPr^9–30. Molecular simulations also suggested a modest increment in the helical population of mutants, when compared to the wild-type. The mutants, however, were bound with a less favorable affinity than the wild-type to both the N-terminal of EI (EIN) or Rsd, as tested by isothermal titration calorimetry and fluorescence. Furthermore, mutants showed lower antibacterial properties against Staphylococcus aureus than the wild-type peptide. Therefore, we concluded that in HPr, a compromise between binding to its partners and residual structure at the active site must exist to carry out its function.

Photodegradable antimicrobial agents - synthesis, photodegradation, and biological evaluation

Multi-drug resistant (MDR) bacteria are already a significant health-care problem and are making the combat of infections quite challenging. Here we report the synthesis of several new compounds containing an ethanolamine moiety, of which two exhibit promising antimicrobial activity (at the 6 μM level). All the compounds are degraded when exposed to light and form inactive products.

Progress in the Application of Carbon Dots-Based Nanozymes

As functional nanomaterials with simulating enzyme-like properties, nanozymes can not only overcome the inherent limitations of natural enzymes in terms of stability and preparation cost but also possess design, versatility, maneuverability, and applicability of nanomaterials. Therefore, they can be combined with other materials to form composite nanomaterials with superior performance, which has garnered considerable attention. Carbon dots (CDs) are an ideal choice for these composite materials due to their unique physical and chemical properties, such as excellent water dispersion, stable chemical inertness, high photobleaching resistance, and superior surface engineering. With the continuous emergence of various CDs-based nanozymes, it is vital to thoroughly understand their working principle, performance evaluation, and application scope. This review comprehensively discusses the recent advantages and disadvantages of CDs-based nanozymes in biomedicine, catalysis, sensing, detection aspects. It is expected to provide valuable insights into developing novel CDs-based nanozymes.

Characterization of Macro- and Microalgae Extracts Bioactive Compounds and Micro- and Macroelements Transition from Algae to Extract

The aim of this study was to evaluate the characteristics of macroalgae (Cladophora rupestris, Furcellaria lumbricalis, Ulva intestinalis) and microalgae (Arthrospira platensis (Sp1, Sp2), Chlorella vulgaris) extracts, including micro- and macroelement transition to extract, antioxidant, antimicrobial properties, the concentrations of chlorophyll (-a, -b), and the total carotenoid concentration (TCC). In macroalgae, the highest TCC and chlorophyll content were found in C. rupestris. In microalgae, the TCC was 10.1-times higher in C. vulgaris than in Sp1, Sp2; however, the chlorophyll contents in C. vulgaris samples were lower. A moderate negative correlation was found between the chlorophyll-a and TCC contents (r = -0.4644). In macroalgae extract samples, C. rupestris and F. lumbricalis showed the highest total phenolic compound content (TPCC). DPPH antioxidant activity and TPCC in microalgae was related to the TCC (r = 0.6191, r = 0.6439, respectively). Sp2 extracts inhibited Staphylococcus haemolyticus; C. rupestris, F. lumbricalis, U. intestinalis, and Sp2 extracts inhibited Bacillus subtilis; and U. intestinalis extracts inhibited Streptococcus mutans strains. This study showed that extraction is a suitable technology for toxic metal decontamination in algae; however, some of the desirable microelements are reduced during the extraction, and only the final products, could be applied in food, feed, and others.

A ruthenium nanoframe/enzyme composite system as a self-activating cascade agent for the treatment of bacterial infections

The cascade catalytic strategy could effectively enhance the antibacterial activity by regulating the production of hydroxyl radicals (˙OH) in the sites of bacterial infection. In this work, a ruthenium metal nanoframe (Ru NF) was successfully synthesized via the palladium template method. The cascade catalysis in the bacterial infection microenvironment was achieved by physically adsorbed natural glucose oxidase (GOx), and hyaluronic acid (HA) was coated on the outer layer of the system for locating the infection sites accurately. Eventually, a composite nano-catalyst (HA-Ru NFs/GOx) based on the ruthenium nanoframe was constructed, which exhibited excellent cascade catalytic activity and good biocompatibility. The prepared HA-Ru NFs/GOx enhances the antibacterial activity and inhibits bacterial regeneration through the outbreak of reactive oxygen species (ROS) caused by self-activating cascade reactions. In addition, in vivo experiments indicate that HA-Ru NFs/GOx could efficiently cause bacterial death and significantly promote wound healing/skin regeneration. Accordingly, ruthenium metal framework nanozymes could be used as an effective cascade catalytic platform to inhibit bacterial regeneration and promote wound healing, and have great potential as new antibacterial agents against antibiotic-resistant bacteria.

Elucidating the mechanism by which synthetic helper peptides sensitize Pseudomonas aeruginosa to multiple antibiotics

The emergence and rapid spread of multi-drug resistant (MDR) bacteria pose a serious threat to the global healthcare. There is an urgent need for new antibacterial substances or new treatment strategies to deal with the infections by MDR bacterial pathogens, especially the Gram-negative pathogens. In this study, we show that a number of synthetic cationic peptides display strong synergistic antimicrobial effects with multiple antibiotics against the Gram-negative pathogen Pseudomonas aeruginosa. We found that an all-D amino acid containing peptide called D-11 increases membrane permeability by attaching to LPS and membrane phospholipids, thereby facilitating the uptake of antibiotics. Subsequently, the peptide can dissipate the proton motive force (PMF) (reducing ATP production and inhibiting the activity of efflux pumps), impairs the respiration chain, promotes the production of reactive oxygen species (ROS) in bacterial cells and induces intracellular antibiotics accumulation, ultimately resulting in cell death. By using a P. aeruginosa abscess infection model, we demonstrate enhanced therapeutic efficacies of the combination of D-11 with various antibiotics. In addition, we found that the combination of D-11 and azithromycin enhanced the inhibition of biofilm formation and the elimination of established biofilms. Our study provides a realistic treatment option for combining close-to-nature synthetic peptide adjuvants with existing antibiotics to combat infections caused by P. aeruginosa.

Nanotargeting of Resistant Infections with a Special Emphasis on the Biofilm Landscape

Bacterial resistance to antimicrobial compounds is a growing concern in medical and public health circles. Overcoming the adaptable and duplicative resistance mechanisms of bacteria requires chemistry-based approaches. Engineered nanoparticles (NPs) now offer unique advantages toward this effort. However, most in situ infections (in humans) occur as attached biofilms enveloped in a protective surrounding matrix of extracellular polymers, where survival of microbial cells is enhanced. This presents special considerations in the design and deployment of antimicrobials. Here, we review recent efforts to combat resistant bacterial strains using NPs and, then, explore how NP surfaces may be specifically engineered to enhance the potency and delivery of antimicrobial compounds. Special NP-engineering challenges in the design of NPs must be overcome to penetrate the inherent protective barriers of the biofilm and to successfully deliver antimicrobials to bacterial cells. Future challenges are discussed in the development of new antibiotics and their mechanisms of action and targeted delivery via NPs.

Sustainable triazine-derived quaternary ammonium salts as antimicrobial agents

The first examples of highly efficient antimicrobial triazine-derived bis imidazolium quaternary ammonium salts (TQAS) are reported. TQAS have been prepared with an easy, atom efficient, economically sustainable strategy and tested as antimicrobial agents, reaching MIC values below 10 mg L-1. Distinctively, TQAS have low MIC and low cytotoxicity.

Antibacterial Potential of a Novel Peptide from the Consensus Sequence of Dermaseptin Related Peptides Secreted by Agalychnis annae

BACKGROUND

The consistently increasing reports of bacterial resistance and the reemergence of bacterial epidemics have inspired the health and scientific community to discover new molecules with antibacterial potential continuously. Frog-skin secretions constitute bioactive compounds essential for finding new biopharmaceuticals. The exact antibacterial characterization of dermaseptin related peptides derived from Agalychnis annae, is limited. The resemblance in their conserved and functionally linked genomes indicates an unprecedented opportunity to obtain novel bioactive compounds.

OBJECTIVE

In this study, we derived a novel peptide sequence and determined its antibacterial potentials.

METHODS

Consensus sequence strategy was used to design the novel and active antibacterial peptide named 'AGAAN' from skin secretions of Agalychnis annae. The in-vitro activities of the novel peptide against some bacterial strains were investigated. Time kill studies, DNA retardation, cytotoxicity, betagalactosidase, and molecular computational studies were conducted.

RESULTS

AGAAN inhibited P. aeruginosa, E. faecalis, and S. typhimurium at 20 μM concentration. E. coli and S. aureus were inhibited at 25 μM, and lastly, B. subtilis at 50 μM. Kinetics of inactivation against exponential and stationary growing bacteria was found to be rapid within 1-5 hours of peptide exposure, depending on time and concentration. The peptide displayed weak hemolytic activity between 0.01%-7.31% at the antibacterial concentrations. AGAAN efficiently induced bacterial membrane damage with subsequent cell lysis. The peptide's DNA binding shows that it also targets intracellular DNA by retarding its movement. Our in-silico molecular docking analysis displayed a strong affinity to the bacterial cytoplasmic membrane.

CONCLUSION

AGAAN exhibits potential antibacterial properties that could be used to combat bacterial resistance.

The Polymeric Matrix Composition of Vibrio cholerae Biofilms Modulate Resistance to Silver Nanoparticles Prepared by Hydrothermal Synthesis

Biofilms represent the dominant microbial lifestyle in nature. These complex microbial communities in which bacteria are embedded in a self-produced protective polymeric extracellular matrix, display an enhanced resistance to antimicrobials and thus represent a major health challenge. Although nanoparticles have proven to be effective against bacteria, the interactions between nanoparticles and the polymeric biofilm matrix are still unclear. In this work, silver nanoparticles (AgNPs) were used on mature biofilms formed by the pathogen Vibrio cholerae, and their effects on the biofilm microstructure were evaluated. Bacteria cells within mature biofilms showed an increased tolerance to AgNPs, with their elimination requiring a concentration nine times higher than planktonic cells. Mutant strains not able to form a pellicle biofilm were four times more susceptible to AgNPs than the wild-type strain forming a strong biofilm. Moreover, electron microscopy analysis revealed that AgNPs interacted with the extracellular matrix components and disrupted its microstructure. Finally, two major proteins, Bap1 and RbmA, appeared to mediate the biofilm bacterial resistance to AgNPs. This work highlights the role of the polymeric biofilm matrix composition in resistance to AgNPs. It underlines how crucial it is to understand and characterize the interactions between nanoparticles and the biofilm matrix, in order to design appropriate metallic nanoparticles efficient against bacterial biofilms.

New insights into the structure and function of an emerging drug target CysE

The antimicrobial resistant strains of several pathogens are major culprits of hospital-acquired nosocomial infections. An active and urgent action is necessary against these pathogens for the development of unique therapeutics. The cysteine biosynthetic pathway or genes (that are absent in humans) involved in the production of L-cysteine appear to be an attractive target for developing novel antibiotics. CysE, a Serine Acetyltransferase (SAT), catalyzes the first step of cysteine synthesis and is reported to be essential for the survival of persistence in several microbes including Mycobacterium tuberculosis. Structure determination provides fundamental insight into structure and function of protein and aid in drug design/discovery efforts. This review focuses on the overview of current knowledge of structure function, regulatory mechanism, and potential inhibitors (active site as well as allosteric site) of CysE. Despite having conserved structure, slight modification in CysE structure lead to altered the regulatory mechanism and hence affects the cysteine production. Due to its possible role in virulence and vital metabolism of pathogens makes it a potential target in the quest to develop novel therapeutics to treat multi-drug-resistant bacteria.

Ceftizoxime loaded ZnO/L-cysteine based an advanced nanocarrier drug for growth inhibition of Salmonella typhimurium

l-Cysteine coated zinc oxide (ZnO) nano hollow spheres were prepared as a potent drug delivery agent to eradicate Salmonella enterica serovar Typhimurium (S. typhimurium). The ZnO nano hollow spheres were synthesized by following the environmentally-friendly trisodium citrate assisted method and l-cysteine (L-Cys) conjugate with its surface. ZnO/L-Cys@CFX nanocarrier drug has been fabricated by incorporating ceftizoxime with L-Cys coated ZnO nano hollow spheres and characterized using different techniques such as scanning electron microscope (SEM), attenuated total reflection Fourier transform infrared (ATR-FTIR), and X-ray diffraction (XRD) etc. Furthermore, the drug-loading and encapsulation efficiency at different pH levels was measured using UV–vis spectrometer and optimized. A control and gradual manner of pH-sensitive release profile was found after investigating the release profile of CFX from the carrier drug. The antibacterial activity of ZnO/L-Cys@CFX and CFX were evaluated through the agar disc diffusion method and the broth dilution method, which indicate the antibacterial properties of antibiotics enhance after conjugating. Surprisingly, the ZnO/L-Cys@CFX exhibits a minimum inhibitory concentration (MIC) of 5 µg/ml against S. typhimurium is lower than CFX (20 µg/ml) itself. These results indicate the nanocarrier can reduce the amount of CFX dosed to eradicate S. typhimurium.

The role and mechanism of polydopamine and cuttlefish ink melanin carrying copper ion nanoparticles in antibacterial properties and promoting wound healing

Melanin and its analogue polydopamine (PDA) have attracted considerable attention in biomedical science due to their surface-rich metal binding sites, excellent adhesion and good biocompatibility. Bacterial infections at the wound site and uncontrolled bleeding are associated with a high risk of death, and the prevention of wound infections remains a major challenge. On this basis, the four nanoparticles (NPs) of melanin, PDA, copper ion-loaded melanin (Cu(ii) loaded melanin) and copper ion-loaded PDA (Cu(ii) loaded PDA) were studied in terms of antibacterial and wound healing capabilities. The in vitro experiments showed that Cu(ii) loaded PDA NPs had good blood compatibility and low cytotoxicity, showing the best antibacterial effect in comparison with other samples. Not only could the slow release of copper ions from the nanoparticles kill bacteria, but also the phenolic hydroxyl group and amine groups of PDA NPs played a synergistic role in bacterial death. In wound healing experiments, the Cu(ii) loaded PDA NPs could easily and tightly bind with biological tissue, demonstrating excellent hemostasis, antibacterial and wound healing capabilities. In summary, the excellent properties of Cu(ii) loaded PDA NPs made them a safe and effective drug for preventing wound infection and promoting healing.

Development of Drug-Resistant Klebsiella pneumoniae Vaccine via Novel Vesicle Production Technology

Drug resistance of Klebsiella pneumoniae severely threatens human health. Overcoming the mechanisms of K. pneumoniae resistance to develop novel vaccines against drug-resistant K. pneumoniae is highly desired. Here, we report a technology platform that uses high pressure to drive drug-resistant K. pneumoniae to pass through a gap, inducing the formation of stable artificial bacterial biomimetic vesicles (BBVs). These BBVs had little to no bacterial intracellular protein or nucleic acid and had high yields. BBVs were efficiently taken up by dendritic cells to stimulate their maturation. BBVs as K. pneumoniae vaccines had the dual functions of inducing bacteria-specific humoral and cellular immune responses to increase animals' survival rate and reduce pulmonary inflammation and bacterial loads. We believe that BBVs are new-generation technology for bacterial vesicle preparation. Establishment of this BBV vaccine platform can maximally expand preparation technology for vaccines against drug-resistant K. pneumoniae.

Exploring Phytochemicals for Combating Antibiotic Resistance in Microbial Pathogens

Antibiotic resistance or microbial drug resistance is emerging as a serious threat to human healthcare globally, and the multidrug-resistant (MDR) strains are imposing major hurdles to the progression of drug discovery programs. Newer antibiotic-resistance mechanisms in microbes contribute to the inefficacy of the existing drugs along with the prolonged illness and escalating expenditures. The injudicious usage of the conventional and commonly available antibiotics in human health, hygiene, veterinary and agricultural practices is proving to be a major driver for evolution, persistence and spread of antibiotic-resistance at a frightening rate. The drying pipeline of new and potent antibiotics is adding to the severity. Therefore, novel and effective new drugs and innovative therapies to treat MDR infections are urgently needed. Apart from the different natural and synthetic drugs being tested, plant secondary metabolites or phytochemicals are proving efficient in combating the drug-resistant strains. Various phytochemicals from classes including alkaloids, phenols, coumarins, terpenes have been successfully demonstrated their inhibitory potential against the drug-resistant pathogens. Several phytochemicals have proved effective against the molecular determinants responsible for attaining the drug resistance in pathogens like membrane proteins, biofilms, efflux pumps and bacterial cell communications. However, translational success rate needs to be improved, but the trends are encouraging. This review highlights current knowledge and developments associated challenges and future prospects for the successful application of phytochemicals in combating antibiotic resistance and the resistant microbial pathogens.

Functionalization of an Electroactive Self-Healing Polypyrrole-Grafted Gelatin-Based Hydrogel by Incorporating a Polydopamine@AgNP Nanocomposite

Hydrogels are considered a promising wound dressing owing to their ability to absorb wound exudates and their moist network structure for skin regeneration. It is of great significance to give added multiple functions to hydrogels for wound healing. In this paper, we present a gelatin-based hydrogel with self-healing ability, conductivity, and antibacterial and antioxidant activities. Dopamine was added into an alkaline solution to polymerize into polydopamine (PDA), which was used to reduce AgNO₃ into Ag nanoparticles (AgNPs) to gain a PDA@AgNP composite. Polypyrrole-grafted gelatin (PPyGel) was dissolved in a PDA@AgNP solution and ferric ions were used as a cross-linking agent to form PDA@AgNPs-PPyGel-Fe hydrogels. The as-prepared hydrogels are soft and ductile and exhibit porous structures with pore sizes from 20 to 50 μm. The hydrogels have high water absorption ability, indicating the potential to absorb wound exudates. PPy and Fe³⁺ endow the hydrogels with slightly higher conductivity than that of skin tissue, indicating the ability to effectively transmit bioelectric signals for skin regeneration. The ionic interactions and hydrogen bonding in hydrogels make them possess self-healing ability, and the self-healing process can be completed in 30 min. PDA confers hydrogels with effective antioxidant activities, while AgNPs endow hydrogels with good antibacterial activities. Moreover, the hydrogels possess good blood compatibility and cytocompatibility. In sum, the developed hydrogel has potential applications as wound dressings.

Benzimidazole analogues as efficient arsenals in war against methicillin-resistance staphylococcus aureus (MRSA) and its SAR studies

Small molecule based inhibitors development is a growing field in medicinal chemistry. In recent years, different heterocyclic derivatives have been designed to counter the infections caused by multi-drug resistant bacteria. Indeed, small molecule inhibitors can be employed as an efficient antibacterial agents with different mechanism of action. Methicillin-resistant Staphylococcus aureus (MRSA) is becoming lethal to mankind due to easy transmission mode, rapid resistance development to existing antibiotics and affect difficult-to-treat skin and filmsy diseases. Benzimidazoles are a class of heterocyclic compounds which have capability to fight against MRSA. High biocompatibility of benzimidazoles, synergistic behaviour with antibiotics and their tunable physico-chemical properties attracted the researchers to develop new benzimidazole based antibacterial agents. The present review focus on recent developments of benzimidazole-hybrid molecules as anti MRSA agents and the results of in-vitro and in-vivo studies with possible mechanism of action and discussing structure-activity relationship (SAR) in different directions. Benzimdazoles act as DNA binding agents, enzyme inhibitors, anti-biofilm agents and showed synergistic effect with available antibiotics to achieve antibacterial activity against MRSA. This cumulative figures would help to design new benzimidazole-based MRSA growth inhibitors.

Synthetic cajaninstilbene acid derivatives eradicate methicillin-resistant Staphylococcus aureus persisters and biofilms

The Staphylococcus aureus can switch to a transient genotype-invariant dormancy, known as a persister, to survive treatment with high doses of antibiotics. This transient persister is an important reason underlying its resistance. There is an urgent need to find new antibacterial agents capable of eradicating methicillin-resistant S. aureus (MRSA) persisters. In this study, 37 new derivatives of cajaninstilbene acid (CSA) were designed and synthesized, and their biological activity against MRSA persisters was evaluated. Most of the newly synthesized derivatives exhibit more potent antimicrobial properties against S. aureus and MRSA than CSA itself, and 23 of the 37 derivatives show a tendency to eradicate MRSA persisters. A representative compound (A6) was demonstrated to target bacterial cell membranes. It eradicated the adherent biofilm of MRSA in a concentration dependent manner, and showed a synergistic antibacterial effect with piperacilin. In a model mouse abscess caused by MRSA persisters, A6 effectively reduced the bacterial load in vivo. These results indicate that A6 is a potential candidate for treatment of MRSA persister infections.

Triazolo Based-Thiadiazole Derivatives. Synthesis, Biological Evaluation and Molecular Docking Studies

The goal of this research is to investigate the antimicrobial activity of nineteen previously synthesized 3,6-disubstituted-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole derivatives. The compounds were tested against a panel of three Gram-positive and three Gram-negative bacteria, three resistant strains, and six fungi. Minimal inhibitory, bactericidal, and fungicidal concentrations were determined by a microdilution method. All of the compounds showed antibacterial activity that was more potent than both reference drugs, ampicillin and streptomycin, against all bacteria tested. Similarly, they were also more active against resistant bacterial strains. The antifungal activity of the compounds was up to 80-fold higher than ketoconazole and from 3 to 40 times higher than bifonazole, both of which were used as reference drugs. The most active compounds (2, 3, 6, 7, and 19) were tested for their inhibition of P. aeruginosa biofilm formation. Among them, compound 3 showed significantly higher antibiofilm activity and appeared to be equipotent with ampicillin. The prediction of the probable mechanism by docking on antibacterial targets revealed that E. coli MurB is the most suitable enzyme, while docking studies on antifungal targets indicated a probable involvement of CYP51 in the mechanism of antifungal activity. Finally, the toxicity testing in human cells confirmed their low toxicity both in cancerous cell line MCF7 and non-cancerous cell line HK-2.

Suppression of hyphal formation and virulence of Candida albicans by natural and synthetic compounds

Candida albicans undergoes a morphological yeast-to-hyphal transition during infection, which plays a significant role in its pathogenesis. The filamentous morphology of the hyphal form has been identified as a virulence factor as it facilitates surface adherence, intertwining with biofilm, invasion, and damage to host tissues and organs. Hence, inhibition of filamentation in addition to biofilm formation is considered a viable strategy against C. albicans infections. Furthermore, a good understanding of the signaling pathways involved in response to environmental cues driving hyphal growth is also critical to an understanding of C. albicans pathogenicity and to develop novel therapies. In this review, first the clinical significance and transcriptional control of C. albicans hyphal morphogenesis are addressed. Then, various strategies employed to suppress filamentation, prevent biofilm formation, and reduce virulence are discussed. These strategies include the inhibition of C. albicans filament formation using natural or synthetic compounds, and their combination with other agents or nanoformulations.

Benzohydrazide and Phenylacetamide Scaffolds: New Putative ParE Inhibitors

Antibacterial resistance (ABR) is a major life-threatening problem worldwide. Rampant dissemination of ABR always exemplified the need for the discovery of novel compounds. However, to circumvent the disease, a molecular target is required, which will lead to the death of the bacteria when acted upon by a compound. One group of enzymes that have proved to be an effective target for druggable candidates is bacterial DNA topoisomerases (DNA gyrase and ParE). In our present work, phenylacetamide and benzohydrazides derivatives were screened for their antibacterial activity against a selected panel of pathogens. The tested compounds displayed significant antibacterial activity with MIC values ranging from 0.64 to 5.65 μg/mL. Amongst 29 title compounds, compounds 5 and 21 exhibited more potent and selective inhibitory activity against Escherichia coli with MIC values at 0.64 and 0.67 μg/mL, respectively, and MBC at onefold MIC. Furthermore, compounds exhibited a post-antibiotic effect of 2 h at 1× MIC in comparison to ciprofloxacin and gentamicin. These compounds also demonstrated the concentration-dependent bactericidal activity against E. coli and synergized with FDA-approved drugs. The compounds are screened for their enzyme inhibitory activity against E. coli ParE, whose IC₅₀ values range from 0.27 to 2.80 μg/mL. Gratifyingly, compounds, namely 8 and 25 belonging to the phenylacetamide series, were found to inhibit ParE enzyme with IC₅₀ values of 0.27 and 0.28 μg/mL, respectively. In addition, compounds were benign to Vero cells and displayed a promising selectivity index (169.0629-951.7240). Moreover, compounds 1, 7, 8, 21, 24, and 25 (IC₅₀: <1 and Selectivity index: >200) exhibited potent activity in reducing the E. coli biofilm in comparison with ciprofloxacin, erythromycin, and ampicillin. These astonishing results suggest the potential utilization of phenylacetamide and benzohydrazides derivatives as promising ParE inhibitors for treating bacterial infections.

Hyaluronidase-responsive phototheranostic nanoagents for fluorescence imaging and photothermal/photodynamic therapy of methicillin-resistant Staphylococcus aureus infections

Infectious diseases associated with antibiotic-resistant bacteria are ever-growing threats to public health. Effective treatment and detection methods of bacterial infections are in urgent demand. Herein, novel phototheranostic nanoagents (MoS2@HA-Ce6 nanosheets, MHC NSs) with hyaluronidase (HAase)-responsive fluorescence imaging (FLI) and photothermal/photodynamic therapy (PTT/PDT) functions were prepared. In this design, Ce6 is used as both a photosensitizer and a fluorescent probe, while MoS2 nanosheets (MoS2 NSs) serve as both a fluorescence quencher and a photothermal agent. Hyaluronic acid conjugated with Ce6 (HA-Ce6) was assembled on the surface of MoS2 NSs to form MHC NSs. Without the HAase secreted by methicillin-resistant Staphylococcus aureus (MRSA), the fluorescence of Ce6 is quenched by MoS2 NSs, while in the presence of MRSA, HAase can degrade the HA and release Ce6, which restores the fluorescence and photodynamic activity of Ce6. The experimental results show that MHC NSs can fluorescently image the MRSA both in vitro and in vivo by HAase activation. Meanwhile, MHC NSs can serve as PTT/PDT dual-mode antibacterial agents for MRSA. In vitro antibacterial results show that MHC NSs can kill 99.97% MRSA under 635 nm and 785 nm laser irradiation. In vivo study further shows that MHC NSs can kill 99.9% of the bacteria in MRSA infected tissues in mice and prompt wound healing by combined PTT/PDT. This work provides novel HAase-responsive phototheranostic nanoagents for effective detection and treatment of bacterial infections.

Silver-incorporating peptide and protein supramolecular nanomaterials for biomedical applications

The natural biomolecules of peptides and proteins are able to form elegant metal incorporating supramolecular nanomaterials through multiple weak non-covalent interactions. The use of toxic chemical reagents to fabricate silver nanoparticles poses a danger to apply them in various biomedical applications. Peptide and protein biomolecules have the potential to overcome this barrier by the supramolecular chemistry approach. In this review, we focus on the self-assembly of peptides and proteins to synthesize silver incorporating supramolecular nanoarchitectures, which in turn enhance the biological properties of these silver nanomaterials being used in nanomedicine. This review aims to illustrate the recent developments in amphiphilic peptides, oligopeptides, collagen, bovine serum albumin (BSA), and human serum albumin (HSA) as capping, stabilizing, and reducing agents to form silver incorporating supramolecular nanostructures. Finally, we provide some biomedical applications of silver-incorporating supramolecular nanomaterials along with future perspectives.

Novel carbazole-oxadiazoles as potential Staphylococcus aureus germicides

Staphylococcus aureus resistance poses nonnegligible threats to the livestock industry. In light of this, carbazole-oxadiazoles were designed and synthesized for treating S. aureus infection. Bioassay discovered that 3,6-dibromocarbazole derivative 13a had effective inhibitory activities to several Gram-positive bacteria, in particular to S. aureus, S. aureus ATCC 29213, MRSA and S. aureus ATCC 25923 (MICs = 0.6-4.6 nmol/mL), which was more active than norfloxacin (MICs = 6-40 nmol/mL). Subsequent studies showed that 3,6-dibromocarbazole derivative 13a acted rapidly on S. aureus ATCC 29213 and possessed no obvious tendency to induce bacterial resistance. Further evaluations indicated that 3,6-dibromocarbazole derivative 13a showed strong abilities to disrupt bacterial biofilm and interfere with DNA, which might be the power sources of antibacterial performances. Moreover, 3,6-dibromocarbazole derivative 13a also exhibited slight cell lethality toward Hek 293 T and LO2 cells and low hemolytic toxicity to red blood cells. The above results implied that the active molecule 13a could be studied in the future development of agricultural available antibiotics.

The Influence of Permeability through Bacterial Porins in Whole-Cell Compound Accumulation

The lack of new drugs for Gram-negative pathogens is a global threat to modern medicine. The complexity of their cell envelope, with an additional outer membrane, hinders internal accumulation and thus, the access of molecules to their targets. Our limited understanding of the molecular basis for compound influx and efflux from these pathogens is a major bottleneck for the discovery of effective antibacterial compounds. Here we analyse the correlation between the whole-cell compound accumulation of ~200 molecules and their predicted porin permeability coefficient (influx), using a recently developed scoring function. We found a strong linear relationship (74%) between the two, confirming porins key in compound uptake in Gram-negative bacteria. The analysis of this unique dataset aids to better understand the molecular descriptors behind whole-cell accumulation and molecular uptake in Gram-negative bacteria.

Bacillus sp. Bacteriocins: Natural Weapons against Bacterial Enemies

BACKGROUND

Currently, antibiotic-resistant pathogenic bacteria are emerging as an important health problem worldwide. The search for new compounds with antibiotic characteristics is the most promising alternative. Bacteriocins are natural compounds that are inhibitory against pathogens, and Bacillus species are the major producers of these compounds, which have shown antimicrobial activity against clinically important bacteria. These peptides not only have potential in the pharmaceutical industry but also in food and agricultural sectors.

OBJECTIVE

We provide an overview of the recent bacteriocins isolated from different species of Bacillus including their applications and the older bacteriocins.

RESULTS

In this review, we have revised some works about the improvements carried out in the production of bacteriocins.

CONCLUSION

These applications make bacteriocins very promising compounds that need to study for industrial production.

The effect of glutathione as adjuvant therapy on levels of TNF-α and IL-10 in wistar rat peritonitis model

Background

Peritonitis is the second most common cause of severe sepsis that associated with a significant mortality rate. Due to a large gap of newer antibiotics innovation and antibiotic resistance emergence, the use of antioxidant has a possible alternative as adjuvant therapy in peritonitis management. It has been studied that glutathione as an alternative in the development of new anti-inflammatory effect. Thus, the aim of this study was to evaluate the levels of TNF-α and IL-10 after glutathione administration as adjuvant therapy in rat peritonitis model.

Materials and methods

Male wistar rats were divided into four groups (n = 6 per group), Group 1: control group (C), Group 2: peritonitis group (P), Group 3: peritonitis + Ceftriaxone group (P + Cef), Group 4: peritonitis + Ceftriaxone + Glutathione group (P + Cef + Glu). Twenty-four hours after peritonitis induction, the blood samples were taken to evaluate TNF-α and IL-10 levels.

Results

There was a significantly increase of mean TNF-α level in group 2 (P) 473,86 ± 388,99 pg/ml (p value 0,00) and significantly decrease of mean TNF-α level after glutathione injection in group 4 (P + Cef + Glu) (p value 0,02). No significant changes in IL-10 levels in rats peritonitis model.

Conclusions

Glutathione supplementation is significantly decrease the mean level of TNF-α in rats induced peritonitis, however there is no difference compare to antibiotic only. Moreover, there no significant changes level of IL-10 in rats induced peritonitis after glutathione injection.

Brief Overview of Approaches and Challenges in New Antibiotic Development: A Focus On Drug Repurposing

Drug repurposing, or identifying new uses for existing drugs, has emerged as an alternative to traditional drug discovery processes involving de novo synthesis. Drugs that are currently approved or under development for non-antibiotic indications may possess antibiotic properties, and therefore may have repurposing potential, either alone or in combination with an antibiotic. They might also serve as "antibiotic adjuvants" to enhance the activity of certain antibiotics.

Myrindole A, an Antimicrobial Bis-indole from a Marine Sponge Myrmekioderma sp

Myrindole A, a bis-indole alkaloid, was isolated from the deep-sea sponge Myrmekioderma sp. The high degree of unsaturation of the molecule complicated the assignment of its structure by standard 2D-NMR experiments but was ultimately achieved by a combination of ¹H-¹⁵N-HMBC and 1,n-ADEQUATE experiments as well as the comparison of measured and calculated CD spectra. Myrindole A showed antimicrobial activity against Gram-positive and Gram-negative bacteria.

Mastering the Gram-negative bacterial barrier - Chemical approaches to increase bacterial bioavailability of antibiotics

To win the battle against resistant, pathogenic bacteria, novel classes of anti-infectives and targets are urgently needed. Bacterial uptake, distribution, metabolic and efflux pathways of antibiotics in Gram-negative bacteria determine what we here refer to as bacterial bioavailability. Understanding these mechanisms from a chemical perspective is essential for anti-infective activity and hence, drug discovery as well as drug delivery. A systematic and critical discussion of in bacterio, in vitro and in silico assays reveals that a sufficiently accurate holistic approach is still missing. We expect new findings based on Gram-negative bacterial bioavailability to guide future anti-infective research.

Promising role of defensins peptides as therapeutics to combat against viral infection

Antimicrobial peptides (AMPs) are ubiquitously present small peptides, which play a critical function in the innate immune system. The defensin class of AMPs represented an evolutionarily ancient family containing cationic cysteine residue and frequently expressed in epithelial or neutrophils cells. It plays myriad functions in host innate immune responses against various infection. Defensin has a broad spectrum of antimicrobial activities, including anti-bacteria, anti-viruses (AVPs), anti-fungi, anti-cancers, and also overcoming bacterial drug resistance. In this review, we compiled the progress on defensin, particularly incorporating the mechanism of action, their application as an antiviral agent, prospects in different areas, and limitations to be solved as an antiviral peptide. Defensins were explored, in particular, their capacity to stimulate innate and adaptive immunity by trigging as anti-coronavirus (COVID-19) peptides. The present review summarised its immunomodulatory and immunoenhancing properties and predominantly focused on its promising therapeutic adjuvant choices for combat against viral infection.

Synthetic biology-inspired strategies and tools for engineering of microbial natural product biosynthetic pathways

Microbial-derived natural products (NPs) and their derivative products are of great importance and used widely in many fields, especially in pharmaceutical industries. However, there is an immediate need to establish innovative approaches, strategies, and techniques to discover new NPs with novel or enhanced biological properties, due to the less productivity and higher cost on traditional drug discovery pipelines from natural bioresources. Revealing of untapped microbial cryptic biosynthetic gene clusters (BGCs) using DNA sequencing technology and bioinformatics tools makes genome mining possible for NP discovery from microorganisms. Meanwhile, new approaches and strategies in the area of synthetic biology offer great potentials for generation of new NPs by engineering or creating synthetic systems with improved and desired functions. Development of approaches, strategies and tools in synthetic biology can facilitate not only exploration and enhancement in supply, and also in the structural diversification of NPs. Here, we discussed recent advances in synthetic biology-inspired strategies, including bioinformatics and genetic engineering tools and approaches for identification, cloning, editing/refactoring of candidate biosynthetic pathways, construction of heterologous expression hosts, fitness optimization between target pathways and hosts and detection of NP production.

Prevalence of antibiotic resistance genes and bacterial pathogens along the soil-mangrove root continuum

Plants roots are colonised by soil bacteria that are known to be the reservoir of antibiotic resistance genes (ARGs). ARGs can transfer between these microorganisms and pathogens, but to what extent these ARGs and pathogens disseminate from soil into plant is poorly understood. Here, we examined a high-resolution resistome profile along the soil-root continuum of mangrove saplings using amplicon and metagenomic sequencing. Data revealed that 91.4% of total ARGs were shared across four root-associated compartments (endosphere, episphere, rhizosphere and unplanted soil). Rather than compartment-selective dynamics of microbiota, the resistome was disseminated in a continuous fashion along the soil-root continuum. Such dissemination was independent of underlying root-associated bacterial and fungal microbiota, but might be facilitated by a multiplicity of mobile genetic elements. As the multiple-drug resistant pathogens, Vibrio vulnificus, pathogenic Escherichia coli and Klebsiella pneumoniae consistently predominated across four compartments, indicating the potential dissemination of antibiotic pathogens along the soil-root continuum. Through deciphering the profile and dynamics of the root-associated resistome and pathogens, our study identified the soil-root continuum as an interconnected sink through which certain ARGs and pathogens can flow from soil into the plant.

Theranostic platforms for specific discrimination and selective killing of bacteria

Bacterial infections are serious threats to public health due to lack of advanced techniques to rapidly and accurately diagnose these infections in clinics. Although bacterial infections can be treated with broad-spectrum antibiotics based on empirical judgment, the emergence of antimicrobial resistance has attracted global attention due to long-term misuse and abuse of antibiotics by humans in recent decades. Therefore, it is imperative to selectively discriminate and precisely eliminate pathogenic bacteria. Herein, in addition to the conventional methods for bacterial identification, we comprehensively reviewed the recently developed theranostic platforms for specific discrimination and selective killing of bacteria according to their different interactions with the target bacteria, such as electrostatic and hydrophobic interactions, molecular recognition, microenvironment response, metabolic labeling, bacteriophage targeting, and others. These theranostic agents not only benefit from improved therapeutic efficiency but also present limited susceptibility to induce bacterial resistance. The strategies summarized in this review will open up new avenues in developing effective antimicrobial materials to accurately diagnose and treat bacterial infections in the post-antibiotic era. STATEMENT OF SIGNIFICANCE: Bacterial infections are difficult to be rapidly and accurately diagnosed, and are generally treated with broad-spectrum antibiotics, which leads to the development of drug resistance. By integrating imaging modalities and therapeutic methods in a single treatment, various theranostic agents have been developed to address the abovementioned issues. Therefore, the emerging theranostic platforms for selective identification and elimination of bacteria based on the distinct interactions of the theranostic agents with the target bacteria are summarized in this review. We believe that the information provided in this review will guide researchers in designing advanced antibacterial theranostics for practical applications in the post-antibiotic era.

Tetralone Derivatives From a Deep-Sea-Derived Fungus Cladosporium Sp. HDN17-58

One new tetralone derivative, named aladothalen (1), and one known biogenetically related compound, (3 S,4 S)−3,4,8-trihydroxy-3,4-dihydronaphthalen-1(2 hours)-one (2), were isolated from a deep-sea-derived-fungal Cladosporium sp. HDN17-58. Their structures, including absolute configurations, were elucidated by extensive NMR, MS, and ECD analyses. Compound 1 exhibited potent bacteriostatic activity against Bacillus cereus, Mycobacterium phlei and methicillin-resistant coagulase-negative Staphylococci, with a MIC value of 25 µM.

Antimicrobial Potential of Naturally Occurring Bioactive Secondary Metabolites

The use of traditional medicines of natural origin has been prevalent since ancient times globally as the plants produce a great diversity in their secondary metabolites. The naturally occurring bioactive constituents in food and other plant materials have shown widespread attention for their use as alternative medicine to prevent and cure microbial growth with the least toxic manifestations. The inclusion of these contents revealed their crucial role to improve the therapeutic efficacy of the classical drugs against various pathogenic microorganisms. Furthermore, several metabolites have also been explored in combination with antimicrobial agents to overcome the problems associated with drug resistance. This current review discusses the antimicrobial activities of secondary metabolites as well as their role in drug sensitivity against multiple-drug resistant pathogenic microbes.

Tetrahydropiperic acid (THPA) conjugated cationic hybrid dipeptides as antimicrobial agents

The present work describes the synthesis of hybrid dipeptides H-Lys-Gpn-PEA, C1; H-Lys-β^3,3A_C6C-PEA, C2, and THPA conjugated dipeptides, THPA-Lys-Gpn-PEA, C3, and THPA-Lys-β^3,3A_C6C-PEA, C4. All the peptides were evaluated against both Gram-negative and Gram-positive bacterial strains. Among all, peptide C4 exhibited the most potent activity with MIC 1.56 μM against P. aeruginosa (MTCC 424) and S. aureus (MTCC 737). Further, time-kill kinetics, fluorescence assays, and scanning electron microscopy (SEM) studies were performed in order to understand the mechanism of action and efficacy of peptide C4, The fluorescence assays and SEM images demonstrated the bacterial killing through membrane disruption. The peptide C4 exhibited very low hemolytic activity with negligible cytotoxicity against normal human breast cell line FR2.

Synergistic Quinolone Sensitization by Targeting the recA SOS Response Gene and Oxidative Stress

Suppression of the recA SOS response gene and reactive oxygen species (ROS) overproduction have been shown, separately, to enhance fluoroquinolone activity and lethality. Their putative synergistic impact as a strategy to potentiate the efficacy of bactericidal antimicrobial agents such as fluoroquinolones is unknown. We generated Escherichia coli mutants that exhibited a suppressed ΔrecA gene in combination with inactivated ROS detoxification system genes (ΔsodA, ΔsodB, ΔkatG, ΔkatE, and ΔahpC) or inactivated oxidative stress regulator genes (ΔoxyR and ΔrpoS) to evaluate the interplay of both DNA repair and detoxification systems in drug response. Synergistic sensitization effects, ranging from 7.5- to 30-fold relative to the wild type, were observed with ciprofloxacin in double knockouts of recA and inactivated detoxification system genes. Compared to recA knockout, inactivation of an additional detoxification system gene reduced MIC values up to 8-fold. In growth curves, no growth was evident in mutants doubly deficient for recA gene and oxidative detoxification systems at subinhibitory concentrations of ciprofloxacin, in contrast to the recA-deficient strain. There was a marked reduction of viable bacteria in a short period of time when the recA gene and other detoxification system genes (katG, sodA, or ahpC) were inactivated (using absolute ciprofloxacin concentrations). At 4 h, a bactericidal effect of ciprofloxacin was observed for ΔkatG ΔrecA and ΔahpC ΔrecA double mutants compared to the single ΔrecA mutant (Δ3.4 log₁₀ CFU/ml). Synergistic quinolone sensitization, by targeting the recA gene and oxidative detoxification stress systems, reinforces the role of both DNA repair systems and ROS in antibiotic-induced bacterial cell death, opening up a new pathway for antimicrobial sensitization.

A Cell-Free Screen for Bacterial Membrane Disruptors Identifies Mefloquine as a Novel Antibiotic Adjuvant

Antibacterial discovery efforts have lagged far behind the need for new antibiotics. An approach that has gained popularity recently is targeting bacterial phospholipid membranes. We leveraged the differences between bacterial and mammalian phospholipid compositions to develop a high-throughput screen that identifies agents that selectively disrupt bacterial membranes while leaving mammalian membranes intact. This approach was used to screen 4480 compounds representing a subset of the Maybridge HitFinderTM V.11 Collection and the Prestwick Chemical Drug Library®. The screen identified 35 "positives" (0.8% hit rate) that preferentially damage bacterial model membranes. Among these, an antimalarial compound, mefloquine, and an aminoglycoside, neomycin, were identified. Further investigation of mefloquine's activity against Staphylococcus aureus showed that it has little antibiotic activity on its own but can alter membrane fluidity, thereby potentiating a β-lactam antibiotic, oxacillin, against both methicillin-susceptible and methicillin-resistant S. aureus. This study indicates that our cell-free screening approach is a promising platform for discovering bacterial membrane disruptors as antibacterials antibiotic adjuvants.