Protective effect of neglected plant Diplocyclos palmatus on quorum sensing mediated infection of Serratia marcescens and UV-A induced photoaging in model Caenorhabditis elegans

Geranium essential oil downregulates virulence genes and mitigates MRSA wound infections through a multifunctional hydrogel

This study presents the development of a multifunctional hydrogel system that incorporates a natural therapeutic agent to promote wound healing and combat bacterial infections. A geranium essential oil (GEO)-loaded carboxymethyl chitosan-pullulan (CMCS-PLN-GEO) hydrogel was formulated for the treatment of MRSA-infected wounds. GEO exhibited potent antibiofilm and antivirulence properties by significantly downregulating key virulence-associated genes such as sarA, agrA, icaA, icaD, and clfA, indicating its potential as an effective therapeutic agent against MRSA. Integration of GEO into the CMCS-PLN hydrogel matrix enhanced its mechanical strength, reduced pore size, and enabled sustained GEO release. In a zebrafish wound model, the CMCS-PLN-GEO hydrogel markedly accelerated wound closure and suppressed MRSA colonization. Furthermore, it demonstrated strong anti-inflammatory activity through the downregulation of interleukin-1β (IL-1β), while promoting tissue regeneration via upregulation of transforming growth factor-β (TGF-β) and inhibition of matrix metalloproteinases MMP-9 and MMP-13. The synergistic integration of GEO with the CMCS-PLN polymer matrix offers dual antibacterial and anti-inflammatory effects, presenting a holistic therapeutic approach for the effective management of MRSA-infected wounds. The present study suggests that GEO-loaded hydrogel is a promising biomaterial for treating MRSA-infected wounds, potentially advancing toward clinical applications.

Caenorhabditis elegans as a Model to Study Aging and Photoaging

Caenorhabditis elegans (C. elegans) has emerged as an outstanding model organism for investigating the aging process due to its shortened lifespan, well-defined genome, and accessibility of potent genetic tools. This review presents the current findings on chronological aging and photoaging in C. elegans, exploring the elaborate molecular pathways that control these processes. The progression of chronological aging is characterized by a gradual deterioration of physiological functions and is influenced by an interaction of genetic and environmental factors, including the insulin/insulin-like signaling (IIS) pathway. In contrast, photoaging is characterized by increased oxidative stress, DNA damage, and activation of stress response pathways induced by UV exposure. Although the genetic mechanisms of chronological aging in C. elegans have been characterized by extensive research, the pathways regulating photoaging are comparatively less well-studied. Here, we provide an overview of the current understanding of aging research, including the crucial genes and genetic pathways involved in the aging and photoaging processes of C. elegans. Understanding the complex interactions between these factors will provide invaluable insights into the molecular mechanisms underlying chronological aging and photoaging and may lead to novel therapeutic approaches and further studies for promoting healthy aging in humans.

Applications of genetic code expansion technology in eukaryotes

Unnatural amino acids (UAAs) have gained significant attention in protein engineering and drug development owing to their ability to introduce new chemical functionalities to proteins. In eukaryotes, genetic code expansion (GCE) enables the incorporation of UAAs and facilitates posttranscriptional modification (PTM), which is not feasible in prokaryotic systems. GCE is also a powerful tool for cell or animal imaging, the monitoring of protein interactions in target cells, drug development, and switch regulation. Therefore, there is keen interest in utilizing GCE in eukaryotic systems. This review provides an overview of the application of GCE in eukaryotic systems and discusses current challenges that need to be addressed.

Light exposure and its applications in human health

Light exposure has been proven to have a significant impact on human health. As a result, researchers are increasingly exploring its potential benefits and drawbacks. With advancements in understanding light and the manufacturing of light sources, modern health lighting has become widely utilized in daily life and plays a critical role in the prevention and treatment of various illnesses. The use of light in healthcare is a global trend, with many countries actively promoting the development and application of relevant scientific research and medical technology. This field has gained worldwide attention and support from scientists and doctors alike. In this review, we examine the application of lighting in human health and recent breakthroughs in light exposure related to pathology, therapeutic strategies, molecular changes, and more. Finally, we also discuss potential future developments and areas of application.

Pyrogallol loaded chitosan-based polymeric hydrogel for controlling Acinetobacter baumannii wound infections: Synthesis, characterization, and topical application

Antibacterial hydrogels have emerged as a promising approach for wound healing, owing to their ability to integrate antibacterial agents into the hydrogel matrix. Benefiting from its remarkable antibacterial and wound-healing attributes, pyrogallol has been introduced into chitosan-gelatin for the inaugural development of an innovative antibacterial polymeric hydrogel tailored for applications in wound healing. Hence, we observed the effectiveness of pyrogallol in inhibiting the growth of A. baumannii, disrupting mature biofilms, and showcasing robust antioxidant activity both in vitro and in vivo. In addition, pyrogallol promoted the migration of human epidermal keratinocytes and exhibited wound healing activity in zebrafish. These findings suggest that pyrogallol holds promise as a therapeutic agent for wound healing. Interestingly, the pyrogallol-loaded chitosan-gelatin (Pyro-CG) hydrogel exhibited enhanced mechanical strength, stability, controlled drug release, biodegradability, antibacterial activity, and biocompatibility. In vivo results established that Pyro-CG hydrogel promotes wound closure and re-epithelialization in A. baumannii-induced wounds in molly fish. Therefore, the prepared Pyro-CG polymeric hydrogel stands poised as a potent and promising agent for wound healing with antibacterial properties. This holds considerable promise for the development of effective therapeutic interventions to address the increasing menace of A. baumannii-induced wound infections.

Bacterial biofilm inhibitors: An overview

Bacteria that cause infectious diseases adopt biofilms as one of their most prevalent lifestyles. Biofilms enable bacteria to tolerate environmental stress and evade antibacterial agents. This bacterial defense mechanism has rendered the use of antibiotics ineffective for the treatment of infectious diseases. However, many highly drug-resistant microbes have rapidly emerged owing to such treatments. Different signaling mechanisms regulate bacterial biofilm formation, including cyclic dinucleotide (c-di-GMP), small non-coding RNAs, and quorum sensing (QS). A cell density-dependent phenomenon, QS is associated with c-di-GMP (a global messenger), which regulates gene expression related to adhesion, extracellular matrix production, the transition from the planktonic to biofilm stage, stability, pathogenicity, virulence, and acquisition of nutrients. The article aims to provide information on inhibiting biofilm formation and disintegrating mature/preformed biofilms. This treatment enables antimicrobials to target the free-living/exposed bacterial cells at lower concentrations than those needed to treat bacteria within the biofilm. Therefore, a complementary action of antibiofilm and antimicrobial agents can be a robust strategic approach to dealing with infectious diseases. Taken together, these molecules have broad implications for human health.

Caenorhabditis elegans as an In Vivo Model for the Discovery and Development of Natural Plant-Based Antimicrobial Compounds

Antimicrobial resistance (AMR) due to the prevalence of multidrug-resistant (MDR) pathogens is rapidly increasing worldwide, and the identification of new antimicrobial agents with innovative mechanisms of action is urgently required. Medicinal plants that have been utilised for centuries with minor side effects may hold great promise as sources of effective antimicrobial products. The free-living nematode Caenorhabditis elegans (C. elegans) is an excellent live infection model for the discovery and development of new antimicrobial compounds. However, while C. elegans has widely been utilised to explore the effectiveness and toxicity of synthetic antibiotics, it has not been used to a comparable extent for the analysis of natural products. By screening the PubMed database, we identified articles reporting the use of the C. elegans model for the identification of natural products endowed with antibacterial and antifungal potential, and we critically analysed their results. The studies discussed here provide important information regarding "in vivo" antimicrobial effectiveness and toxicity of natural products, as evaluated prior to testing in conventional vertebrate models, thereby supporting the relevance of C. elegans as a highly proficient model for their identification and functional assessment. However, their critical evaluation also underlines that the characterisation of active phytochemicals and of their chemical structure, and the unravelling of their mechanisms of action represent decisive challenges for future research in this area.

Ethnomedicines for the treatment of scorpion stings: A perspective study

ETHNOPHARMACOLOGICAL RELEVANCE

Scorpion sting is a public health concern with limited clinical symptomatic treatment. The clinical treatment uses anti-scorpion antivenom and prazosin (α-adrenergic inhibitor), often in combination with insulin, to reduce scorpion venom-induced hyperglycemia and other complications. However, these therapies also possess some limitations, necessitating urgent exploration of ethnomedicines, mainly traditional medicinal plants, to treat scorpion stings. Unfortunately, several conventional treatments are not scientifically validated, thus raising questions about their quality and utility. Therefore, pharmacological re-assessment of such medicinal plants to alleviate scorpion stings' complications is essential.

AIM OF THE STUDY

The principal objectives of this study are to provide a brief overview of medically important scorpions of the world, outline the extant traditional practices, and comprehensively review plants used in conventional ethnic medicines to treat scorpion stings over time. Modern technological advances in identifying and characterizing plant bioactive molecules are also mentioned in this review.

MATERIALS AND METHODS

The traditionally used medicinal plants against scorpion stings were reviewed from the available literature in the database. The Plant List (http://www.theplantlist.org/) was used to validate the scientific names of the plants mentioned in this study. The search targeted literature on conventional treatments and crude plant extracts or their bioactive components with proven neutralization capacity against scorpion stings. Search words used were 'scorpion sting,' 'treatment for a scorpion sting,' 'antivenom and scorpion sting,' 'traditional treatment for scorpion stings, and 'natural compounds against scorpion stings'.

RESULTS

A list of more than 200 medicinal plants traditionally used in several countries for treating scorpion stings is presented in this review. Though some myth-based remedies are practiced to treat scorpion stings, no empirical evidence exists to validate this aspect of traditional knowledge. Only 38 traditional medicinal plant extracts have been tested under in-vivo and in-vitro conditions to determine their neutralization potency of scorpion envenomation. Although a few bioactive plant constituents showing scorpion venom neutralization potency have been characterized, they are not yet commercially available for clinical application.

CONCLUSIONS

There is tremendous potential locked in medicinal plants' traditional knowledge for scorpion envenomation treatment. Translating this knowledge into the clinical application will require pharmacological reassessment, in tandem with isolation and characterization of active compounds to prove their prophylactic prowess. Almost equally important would be the formulation of stringent strategies to conserve such medicinal plants from overexploitation.

Hesperidin methylchalcone (HMC) hinders amyloid-β induced Alzheimer's disease by attenuating cholinesterase activity, macromolecular damages, oxidative stress and apoptosis via regulating NF-κB and Nrf2/HO-1 pathways

Phytocompounds therapy has recently emerged as an effective strategy to treat Alzheimer's disease. Herein, the protective effect of hesperidin methylchalcone (HMC) was evaluated through Alzheimer's disease models of Neuro-2a cells and Wistar rats. The in vitro results showed that HMC possesses significant ability to inhibit the acetylcholinesterase enzyme and exhibiting anti-aggregation and disaggregation properties. Furthermore, HMC could protect the Neuro-2a cells against Aβ-induced neurotoxicity. Simultaneously, HMC treatment significantly improved the cognitive deficits caused by Aβ-peptide on spatial memory in Wistar rats. HMC significantly enhanced the cholinergic effects by inhibiting AChE, BuChE, β-secretase activity, caspase-3 activity, and attenuating macromolecular damages and apoptosis. Notably, HMC reduced the Aβ-induced oxidative stress by activating the antioxidative defence enzymes. In addition, the HMC treatment suppressed the expression of immunocytokines such as p-NF-κB p65, p-IκBα, induced by Aβ; whereas upregulating Nrf2, HO-1 in brain homogenate. These results suggest that HMC could attenuate Aβ-induced neuroinflammation in brain via suppressing NF-κB signalling pathway and activating the Nrf2/HO-1 pathway, thereby improving memory and cognitive impairments in Wistar rats. Overall, the present study reports that HMC can act as a potent candidate with multi-faceted neuroprotective potential against Aβ-induced memory dysfunction in Wistar rats for the treatment of Alzheimer's disease.

Effects of Vegetal Extracts and Metabolites against Oxidative Stress and Associated Diseases: Studies in Caenorhabditis elegans

Oxidative stress is a natural physiological process where the levels of oxidants, such as reactive oxygen species (ROS) and nitrogen (RNS), exceed the strategy of antioxidant defenses, culminating in the interruption of redox signaling and control. Oxidative stress is associated with multiple pathologies, including premature aging, neurodegenerative diseases, obesity, diabetes, atherosclerosis, and arthritis. It is not yet clear whether oxidative stress is the cause or consequence of these diseases; however, it has been shown that using compounds with antioxidant properties, particularly compounds of natural origin, could prevent or slow down the progress of different pathologies. Within this context, the Caenorhabditis elegans (C. elegans) model has served to study the effect of different metabolites and natural compounds, which has helped to decipher molecular targets and the effect of these compounds on premature aging and some diseases such as neurodegenerative diseases and dyslipidemia. This article lists the studies carried out on C. elegans in which metabolites and natural extracts have been tested against oxidative stress and the pathologies associated with providing an overview of the discoveries in the redox area made with this nematode.

Hesperidin methyl chalcone, a citrus flavonoid, inhibits Aeromonas hydrophila infection mediated by quorum sensing

Plant-derived phytocompounds are effective in treating a variety of ailments and disorders, the most common of which are bacterial infections in humans, which are a major public health concern. Flavonoids, one of the groups of phytocompounds, are known to have significant antimicrobial and anti-infective properties. Hence, the current study investigates the efficacy of the citrus flavonoid hesperidin methylchalcone (HMC) in addressing this major issue. The results of this study indicate that the anti-quorum sensing (anti-QS) action against Aeromonas hydrophila infections is exhibited with a decrease in biofilm development and virulence factors production through in vitro and in silico analyses. In addition, the qPCR findings indicate that HMC has antivirulence action on A. hydrophila by reducing the expression of QS-related virulence genes, including ahyR, ahyB, ahh1, aerA, and lip. Interestingly, HMC significantly rescued the A. hydrophila-infected zebrafish by reducing the internal colonization, demonstrating the in vivo anti-infective potential of HMC against A. hydrophila infection. Based on these results, this study recommends that HMC could be employed as a possible therapeutic agent to treat A. hydrophila-related infections in humans.

Tocopherol-assisted magnetic Ag-Fe3O4-TiO2 nanocomposite for photocatalytic bacterial-inactivation with elucidation of mechanism and its hazardous level assessment with zebrafish model

In recent years, many endeavours have been prompted with photocatalytic nanomaterials by the need to eradicate pathogenic microorganisms from water bodies. Herein, a tocopherol-assisted Ag-Fe₃O₄-TiO₂ nanocomposite (TAFTN) was synthesized for photocatalytic bacterial inactivation. The prepared TAFTN became active under sunlight due to its narrowed bandgap, inactivating the bacterial contaminants via photo-induced ROS stress. The ROS radicals destroy bacteria by creating oxidative stress, which damages the cell membrane and cellular components such as nucleic acids and proteins. For the first time, the nano-LC-MS/MS-based quantitative proteomics reveals that the disrupted proteins are involved in a variety of cellular functions; the most of these are involved in the metabolic pathway, eventually leading to bacterial death during TAFTN-photocatalysis under sunlight. Furthermore, the toxicity analysis confirmed that the inactivated bacteria seemed to have no detrimental impact on zebrafish model, showing that the disinfected water via TAFTN-photocatalysis is enormously safe. Furthermore, the TAFTN-photocatalysis successfully killed the bacterial cells in natural seawater, indicating the consistent photocatalytic efficacy when recycled repeatedly. The results of this work demonstrate that the produced nanocomposite might be a powerful recyclable and sunlight-active photocatalyst for environmental water treatment.

Prevalence and Characterization of Serratia marcescens Isolated from Clinical Bovine Mastitis Cases in Ningxia Hui Autonomous Region of China

Purpose

This study aimed to investigate the prevalence and genetic characterization of Serratia marcescens isolates from clinical bovine mastitis in Ningxia Hui Autonomous Region of China.

Methods

S. marcescens was identified by the polymerase-chain reaction of 16S rRNA gene and sequencing. Antimicrobial susceptibility was tested by the disk diffusion method. Genes of resistance and virulence were determined by the PCR.

Results

Overall, S. marcescens were confirmed from 32 of 2897 (1.1%) mastitis milk samples. These isolates showed high resistance to cefazolin (30/32, 93.8%) and chloramphenicol (28/32, 87.5%). A 12.5% (4/32) of the isolates displayed multidrug resistance (MDR). The most prevalent resistant genes found in S. marcescens were TEM (32/32, 100%) and CTX-M (24/32, 75.0%; CTX-M-15, 14/32, 43.8%; CTX-M-14, 8/32, 25.0%; CTX-M-65, 2/32, 6.3%) for extended-spectrum beta-lactamase, cmlA (28/32, 87.5%) and floR (16/32, 50.0%) for chloramphenicol resistance, SIM-1 (2/32, 6.3%) for carbapenemases, and sdeB (28/32, 87.5%), sdeY (26/32, 81.3%), sdeR (26/32, 81.3%) and sdeD (20/32, 62.5%) for efflux pumps. Moreover, all isolates carried virulence genes flhD, entB, and kpn, and most of them contained mrkD (30/32, 93.8%), ycfM (26/32, 81.3%), bsmB (26/32, 81.3%), pigP (26/32, 81.3%), kfu (24/32, 75.0%) and shlB (24/32, 75.0%).

Conclusion

To our knowledge, this is the first report of genetic determinants for antimicrobial resistance and virulence in S. marcescens isolated from bovine mastitis cases in China. These findings are useful for developing strategies for prevention and treatment of bovine mastitis caused by S. marcescens in China.

RNA-dependent RNA polymerase could extend the lasting validity period of exogenous dsRNA

BACKGROUND

Previous studies have found that pesticide double-stranded (ds)RNA usually has a long-lasting validity period in plants. However, it is uncertain if any factors in plants could extend dsRNA duration. It has been reported that RNA-dependent RNA polymerases (RdRP) in plants and some other eukaryotes could catalyze RNA amplification and be involved in RNAi (interference). Thus, this study evaluated the effect of RdRP on the tissue content, activity, and duration of exogenous dsRNA.

RESULTS

We found that RdRP knockdown in Arabidopsis thaliana had no significant effect on tissue contents of reporter dsRNA parent molecules (8.91% reduction), but it caused significant decrease in the tissue contents of derived short fragments of 200, 120 and 59 bp tested (51.22%, 52.83% and 59.35%, respectively). Aphid inoculation tests showed that the same dose of insecticidal dsAgZFP exhibited a significantly lower lethal effect (mortality 58.8%) in the plants with RdRP knockdown than in the control plants with normal RdRP (86.0%). For Caenorhabditis elegans, the worms treated simultaneously with dsRdRP and reporter dsRNA had similar body contents to reporter dsRNA parent molecules and its long-fragment derivative (200 bp) as the control (1.28- and 1.07-fold greater, respectively). However, 120- and 59-bp short-fragment derivatives were significantly reduced by 28.78% and 59.84%, respectively, which also diminished faster in the descendants.

CONCLUSIONS

We conclude that RdRP could significantly enhance the tissue content of dsRNA derivatives by catalyzing amplification, thus improving dsRNA activity and extending its lasting validity period. Otherwise, RNAi by exogenous dsRNA was proven to be noninheritable in A. thaliana. This work confirmed the merit of dsRNA as a plant protectant. © 2022 Society of Chemical Industry.

Repurposing of Doxycycline to Hinder the Viral Replication of SARS-CoV-2: From in silico to in vitro Validation

Since the rapid spread of coronavirus disease (COVID-19) became a global pandemic, healthcare ministries around the world have recommended specific control methods such as quarantining infected peoples, identifying infections, wearing mask, and practicing hand hygiene. Since no effective treatment for COVID-19 has yet been discovered, a variety of drugs approved by Food and Drug Administration (FDA) have been suggested for repurposing strategy. In the current study, we predicted that doxycycline could interact with the nucleotide triphosphate (NTP) entry channel, and is therefore expected to hinder the viral replication of SARS-CoV-2 RNA-dependent RNA-polymerase (RdRp) through docking analysis. Further, the molecular dynamics results revealed that the RdRp-Doxycycline complex was structurally relatively stable during the dynamic period (100 ns), and its complex maintained close contact with their active catalytic domains of SARS-CoV-2 RdRp. The molecular mechanics Poisson–Boltzmann surface area (MM-PBSA) calculation of binding free energy also showed that the doxycycline has worthy affinities with SARS-CoV-2 RdRp. As expected, doxycycline effectively inhibited the viral replication of IHU strains of SARS-CoV-2 (IHUMI-3 and IHUMI-6), identified from the hospitalized patients in IHU Méditerranée Infection (IHUMI), Marseille, France. Moreover, doxycycline inhibited the viral load in vitro at both on-entry and after viral entry of IHU variants of SARS-CoV-2. The results suggest that doxycycline exhibits strains-dependant antiviral activity against COVID-19. As a result, the current study concludes that doxycycline may be more effective in combination with other drugs for better COVID-19 treatment efficacy.

Evaluation of antibiofilm potential of four-domain α-amylase from Streptomyces griseus against exopolysaccharides (EPS) of bacterial pathogens using Danio rerio

Biofilm formation is a major issue in healthcare settings as 75% of nosocomial infection arises due to biofilm residing bacteria. Exopolysaccharides (EPS), a key component of the biofilm matrix, contribute to the persistence of cells in a complex milieu and defends greatly from exogenous stress and demolition. It has been shown to be vital for biofilm scaffold and pathogenic features. The present study was aimed to investigate the effectiveness of four domain-containing α-amylase from Streptomyces griseus (SGAmy) in disrupting the EPS of multidrug-resistant bacteria, especially methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. In vitro analysis of preformed biofilm unveiled the antibiofilm efficacy of SGAmy against MRSA (85%, p < 0.05) and P. aeruginosa (82%, p < 0.05). The total carbohydrate content in the EPS matrix of MRSA and P. aeruginosa was significantly reduced to 71.75% (p < 0.01) and 74.09% (p < 0.01), respectively. The findings inferred from in vitro analysis were further corroborated through in vivo studies using an experimental model organism, Danio rerio. Remarkably, the survival rate was extended to 88.8% (p < 0.05) and 74.2% (p < 0.05) in MRSA and P. aeruginosa infected fishes, respectively. An examination of gills, kidneys, and intestines of D. rerio organs depicted the reduced level of microbial colonization in SGAmy-treated cohorts and these findings were congruent with bacterial enumeration results.

Growth-phase specific regulation of cviI/R based quorum sensing associated virulence factors in Chromobacterium violaceum by linalool, a monoterpenoid

Quorum sensing (QS)-dependent gene regulation in bacteria performs a vital role in synchronization of cell-density-dependent functions. In Chromobacterium violaceum QS-dependent cviI/R regulatory genes are activated during the mid- or late-exponential phase of growth. However, sufficient evidence is lacking on the role of QS inhibitors on gene regulation at different phases of growth. Hence, we report the role of linalool, a natural monoterpenoid on QS mediated gene regulation at different stages of growth in C. violaceum by performing biosensor, growth kinetic and gene expression studies. In vitro and in vivo studies were performed for establishing role of linalool in reducing the virulence and infection by using HEK-293 T cell lines and Caenorhabditis elegans models respectively. C. violaceum CV026 with C₆-HSL was used as control. The results showed linalool to be a QS inhibitor with an estimated IC₅₀ of 63 µg/mL for violacein inhibition. At this concentration the cell density difference (delta OD₆₀₀) of 0.14 from the compound was observed indicating the quorum concentration. The expression of cviI/R was initiated at mid-log phase (~ 18 h) and reached the maximum at 36 h in control whereas in treatment it remained significantly downregulated at all time points. The expression of violacein biosynthetic genes vioA, vioC, vioD and vioE was also downregulated by linalool. Infection studies with linalool showed higher survival rates in HEK-293T cell lines and C. elegans compared to the infection control. Taken together, this study proves linalool to be a QS inhibitor capable of attenuation of QS by controlling the cell density through cviI/R downregulation at the early phase of growth and hence offering scope for its application for controlling infections.

Marine Bacterial Secondary Metabolites: A Treasure House for Structurally Unique and Effective Antimicrobial Compounds

The prevalence of antimicrobial resistance reduces the effectiveness of antimicrobial drugs in preventing and treating infectious diseases caused by pathogenic organisms, such as bacteria, fungi, and viruses. Because of the burgeoning growth of microbes with antimicrobial-resistant traits, there is a dire need to identify and develop novel and effective antimicrobial agents to treat infections from antimicrobial-resistant strains. The marine environment is rich in ecological biodiversity and can be regarded as an untapped resource for prospecting novel bioactive compounds. Therefore, exploring the marine environment for antimicrobial agents plays a significant role in drug development and biomedical research. Several earlier scientific investigations have proven that bacterial diversity in the marine environment represents an emerging source of structurally unique and novel antimicrobial agents. There are several reports on marine bacterial secondary metabolites, and many are pharmacologically significant and have enormous promise for developing effective antimicrobial drugs to combat microbial infections in drug-resistant pathogens. In this review, we attempt to summarize published articles from the last twenty-five years (1996–2020) on antimicrobial secondary metabolites from marine bacteria evolved in marine environments, such as marine sediment, water, fauna, and flora.

Bacterial Biofilm Inhibition: A Focused Review on Recent Therapeutic Strategies for Combating the Biofilm Mediated Infections

Biofilm formation is a major concern in various sectors and cause severe problems to public health, medicine, and industry. Bacterial biofilm formation is a major persistent threat, as it increases morbidity and mortality, thereby imposing heavy economic pressure on the healthcare sector. Bacterial biofilms also strengthen biofouling, affecting shipping functions, and the offshore industries in their natural environment. Besides, they accomplish harsh roles in the corrosion of pipelines in industries. At biofilm state, bacterial pathogens are significantly resistant to external attack like antibiotics, chemicals, disinfectants, etc. Within a cell, they are insensitive to drugs and host immune responses. The development of intact biofilms is very critical for the spreading and persistence of bacterial infections in the host. Further, bacteria form biofilms on every probable substratum, and their infections have been found in plants, livestock, and humans. The advent of novel strategies for treating and preventing biofilm formation has gained a great deal of attention. To prevent the development of resistant mutants, a feasible technique that may target adhesive properties without affecting the bacterial vitality is needed. This stimulated research is a rapidly growing field for applicable control measures to prevent biofilm formation. Therefore, this review discusses the current understanding of antibiotic resistance mechanisms in bacterial biofilm and intensely emphasized the novel therapeutic strategies for combating biofilm mediated infections. The forthcoming experimental studies will focus on these recent therapeutic strategies that may lead to the development of effective biofilm inhibitors than conventional treatments.

An innovative role for luteolin as a natural quorum sensing inhibitor in Pseudomonas aeruginosa

AIMS

The emergence of antibiotic tolerance was a tricky problem in the treatment of chronic Pseudomonas aeruginosa-infected cystic fibrosis and burn victims. The quorum sensing (QS) inhibitor may serve as a new tactic for the bacterial resistance by inhibiting the biofilm formation and the production of virulence factors. This study explored the potential of luteolin as a QS inhibitor against P. aeruginosa and the molecular mechanism involved.

MAIN METHODS

Crystal violet staining, CLSM observation, and SEM analysis were carried out to assess the effect of luteolin on biofilm formation. The motility assays and the production of virulence factors were determined to evaluate the QS-inhibitory activity of luteolin. Acyl-homoserine lactone, RT-PCR, and molecular docking assays were conducted to explain its anti-QS mechanisms.

KEY FINDINGS

The biofilm formation, the production of virulence factors, and the motility of P. aeruginosa could be efficiently inhibited by luteolin. Luteolin could also attenuate the accumulation of the QS-signaling molecules N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL) and N-butanoyl-L-homoserine lactone (BHL) (P < 0.01) and downregulate the transcription levels of QS genes (lasR, lasI, rhlR, and rhlI) (P < 0.01). Molecular docking analysis indicated that luteolin had a greater docking affinity with LasR regulator protein compared with OdDHL.

SIGNIFICANCE

This study is important as it reports the molecular mechanisms involved in the anti-biofilm formation activity of luteolin against P. aeruginosa. This study also indicated that luteolin could be helpful when used for the treatment of clinical drug-resistant infections of P. aeruginosa.

Differential susceptibility of airway and ocular surface cell lines to FlhDC-mediated virulence factors PhlA and ShlA from Serratia marcescens

Introduction. Serratia marcescens is a bacterial pathogen that causes ventilator-associated pneumonia and ocular infections. The FlhD and FlhC proteins complex to form a heteromeric transcription factor whose regulon, in S. marcescens, regulates genes for the production of flagellum, phospholipase A and the cytolysin ShlA. The previously identified mutation, scrp-31, resulted in highly elevated expression of the flhDC operon. The scrp-31 mutant was observed to be more cytotoxic to human airway and ocular surface epithelial cells than the wild-type bacteria and the present study sought to identify the mechanism underlying the increased cytotoxicity phenotype.Hypothesis/Gap Statement. Although FlhC and FlhD have been implicated as virulence determinants, the mechanisms by which these proteins regulate bacterial cytotoxicity to different cell types remains unclear.Aim. This study aimed to evaluate the mechanisms of FlhDC-mediated cytotoxicity to human epithelial cells by S. marcescens.Methodology. Wild-type and mutant bacteria and bacterial secretomes were used to challenge airway and ocular surface cell lines as evaluated by resazurin and calcein AM staining. Pathogenesis was further tested using a Galleria mellonella infection model.Results. The increased cytotoxicity of scrp-31 bacteria and secretomes to both cell lines was eliminated by mutation of flhD and shlA. Mutation of the flagellin gene had no impact on cytotoxicity under any tested condition. Elimination of the phospholipase gene, phlA, had no effect on bacteria-induced cytotoxicity to either cell line, but reduced cytotoxicity caused by secretomes to airway epithelial cells. Mutation of flhD and shlA, but not phlA, reduced bacterial killing of G. mellonella larvae.Conclusion. This study indicates that the S. marcescens FlhDC-regulated secreted proteins PhlA and ShlA, but not flagellin, are cytotoxic to airway and ocular surface cells and demonstrates differences in human epithelial cell susceptibility to PhlA.

Proteomic analysis deciphers the multi-targeting antivirulence activity of tannic acid in modulating the expression of MrpA, FlhD, UreR, HpmA and Nrp system in Proteus mirabilis

In the present study, the multi-targeting antivirulence activity of tannic acid (TA) was explored against Proteus mirabilis through MS-based proteomic approach. The in vitro biofilm biomass quantification assay and microscopic analysis demonstrated the antibiofilm activity of TA against P. mirabilis in which, minimum biofilm inhibitory concentration (MBIC) of TA was found to be 200 μg/mL concentration. Moreover, the nanoscale liquid chromatography coupled to tandem mass spectrometry (nano LC-MS/MS) analysis revealed that TA (at MBIC) differentially regulated the proteins involved in fimbrial adhesion, flagellar motility, iron acquisition, Fe-S cluster assembly, heat shock response, virulence enzymes, and toxin secretion. Further, the transcriptomic analysis validated the outcomes of proteomic analysis in which, the expression level of virulence genes responsible for MR/P fimbrial adhesion (mrpA), flagellar transcriptional activation (flhD), biosynthesis of urease (ureR), hemolysin (hpmA), non-ribosomal peptide siderophore system (Nrp), oxidative stress responsible enzymes and fitness factors proteins were down-regulated in TA exposed P. mirabilis. These observations were also in correspondence with the in vitro bioassays. Thus, this study reports the feasibility of TA to act as a promising therapeutic agent against multifactorial P. mirabilis infections.

Anti-quorum Sensing and Protective Efficacies of Naringin Against Aeromonas hydrophila Infection in Danio rerio

It is now well known that the quorum sensing (QS) mechanism coordinates the production of several virulence factors and biofilm formation in most pathogenic microorganisms. Aeromonas hydrophila is a prime pathogen responsible for frequent outbreaks in aquaculture settings. Recent studies have also continuously reported that A. hydrophila regulates virulence factor production and biofilm formation through the QS system. In addition to the presence of antibiotic resistance genes, biofilm-mediated antibiotic resistance increases the severity of A. hydrophila infections. To control the bacterial pathogenesis and subsequent infections, targeting the QS mechanism has become one of the best alternative methods. Though very few compounds were identified as QS inhibitors against A. hydrophila, to date, the screening and identification of new and effective natural QS inhibitors is a dire necessity to control the infectious A. hydrophila. The present study endorses naringin (NA) as an anti-QS and anti-infective agent against A. hydrophila. Initially, the NA showed a concentration-dependent biofilm reduction against A. hydrophila. Furthermore, the results of microscopic analyses and quantitative virulence assays displayed the promise of NA as a potential anti-QS agent. Subsequently, the downregulation of ahh1, aerA, lip and ahyB validate the interference of NA in virulence gene expression. Furthermore, the in vivo assays were carried out in zebrafish model system to evaluate the anti-infective potential of NA. The outcome of the immersion challenge assay showed that the recovery rate of the zebrafish has substantially increased upon treatment with NA. Furthermore, the quantification of the bacterial load upon NA treatment showed a decreased level of bacterial counts in zebrafish when compared to the untreated control. Moreover, the NA treatment averts the pathogen-induced histoarchitecture damages in vital organs of zebrafish, compared to their respective controls. The current study has thus analyzed the anti-QS and anti-infective capabilities of NA and could be employed to formulate effective treatment measures against A. hydrophila infections.

Inhibitory Effect of Morin Against Candida albicans Pathogenicity and Virulence Factor Production: An in vitro and in vivo Approaches

Candida albicans is considered an exclusive etiologic agent of candidiasis, a very common fungal infection in human. The expression of virulence factors contributes highly to the pathogenicity of C. albicans. These factors include biofilm formation, yeast-to-hyphal transition, adhesins, aspartyl proteases, and phospholipases secretion. Moreover, resistance development is a critical issue for the therapeutic failure of antifungal agents against systemic candidiasis. To circumvent resistance development, the present study investigated the virulence targeted therapeutic activity of the phyto-bioactive compound morin against C. albicans. Morin is a natural compound commonly found in medicinal plants and widely used in the pharmaceutical and cosmetic products/industries. The present study explicated the significant inhibitory potential of morin against biofilm formation and other virulence factors' production, such as yeast-hyphal formation, phospholipase, and exopolymeric substances, in C. albicans. Further, qPCR analysis confirmed the downregulation of biofilm and virlence-related genes in C. albicans upon morin treatment, which is in correspondence with the in vitro bioassays. Further, the docking analysis revealed that morin shows strong affinity with Hwp-1 protein, which regulates the expression of biofilm and hyphal formation in C. albicans and, thereby, abolishes fungal pathogenicity. Moreover, the anti-infective potential of morin against C. albicans-associated systemic candidiasis is confirmed through an in vivo approach using biomedical model organism zebrafish (Danio rerio). The outcomes of the in vivo study demonstrate that the morin treatment effectively rescues animals from C. albicans infections and extends their survival rate by inhibiting the internal colonization of C. albicans. Histopathology analysis revealed extensive candidiasis-related pathognomonic changes in the gills, intestine, and kidney of animals infected with C. albicans, while no extensive abnormalities were observed in morin-treated animals. The results evidenced that morin has the ability to protect against the pathognomonic effect and histopathological lesions caused by C. albicans infection in zebrafish. Thus, the present study suggests that the utilization of morin could act as a potent therapeutic medication for C. albicans instigated candidiasis.

Metal sensing-carbon dots loaded TiO2-nanocomposite for photocatalytic bacterial deactivation and application in aquaculture

Nowadays, bioactive nanomaterials have been attracted the researcher's enthusiasm in various fields. Herein, Diplocyclos palmatus leaf extract-derived green-fluorescence carbon dots (DP-CDs) were prepared using the hydrothermal method. Due to the strong fluorescence stability, the prepared DP-CDs were coated on filter-paper to make a fluorometric sensor-strip for Fe3+ detection. After, a bandgap-narrowed DP-CDs/TiO2 nanocomposite (DCTN) was prepared using the methanolic extract of D. palmatus. The prepared DCTN exhibited improved photocatalytic bacterial deactivation under sunlight irradiation. The DCTN-photocatalysis slaughtered V. harveyi cells by the production of reactive oxygen species, which prompting oxidative stress, damaging the cell membrane and cellular constituents. These results suggest the plausible mode of bactericidal action of DCTN-photocatalysis under sunlight. Further, the DCTN has shown potent anti-biofilm activity against V. harveyi, and thereby, DCTN extended the survival of V. harveyi-infected shrimps during the in vivo trial with Litopenaeus vannamei. Notably, this is the first report for the disinfection of V. harveyi-mediated acute-hepatopancreatic necrosis disease (AHPND) using nanocomposite. The reduced internal-colonization of V. harveyi on the hepatopancreas as well as the rescue action of the pathognomonic effect in the experimental animals demonstrated the anti-infection potential of DCTN against V. harveyi-mediated AHPND in aquaculture.

Quinolines-Based SARS-CoV-2 3CLpro and RdRp Inhibitors and Spike-RBD-ACE2 Inhibitor for Drug-Repurposing Against COVID-19: An in silico Analysis

The novel coronavirus SARS-CoV-2 disease “COVID-19” emerged in China and rapidly spread to other countries; due to its rapid worldwide spread, the WHO has declared this as a global emergency. As there is no specific treatment prescribed to treat COVID-19, the seeking of suitable therapeutics among existing drugs seems valuable. The structure availability of coronavirus macromolecules has encouraged the finding of conceivable anti-SARS-CoV-2 therapeutics through in silico analysis. The results reveal that quinoline,1,2,3,4-tetrahydro-1-[(2-phenylcyclopropyl)sulfonyl]-trans-(8CI) and saquinavir strongly interact with the active site (Cys-His catalytic dyad), thereby are predicted to hinder the activity of SARS-CoV-2 3CLpro. Out of 113 quinoline-drugs, elvitegravir and oxolinic acid are able to interact with the NTP entry-channel and thus interfere with the RNA-directed 5′-3′ polymerase activity of SARS-CoV-2 RdRp. The bioactivity-prediction results also validate the outcome of the docking study. Moreover, as SARS-CoV-2 Spike-glycoprotein uses human ACE2-receptor for viral entry, targeting the Spike-RBD-ACE2 has been viewed as a promising strategy to control the infection. The result shows rilapladib is the only quinoline that can interrupt the Spike-RBD-ACE2 complex. In conclusion, owing to their ability to target functional macromolecules of SARS-CoV-2, along with positive ADMET properties, quinoline,1,2,3,4-tetrahydro-1-[(2-phenylcyclopropyl)sulfonyl]-trans-(8CI), saquinavir, elvitegravir, oxolinic acid, and rilapladib are suggested for the treatment of COVID-19.

Attenuation of Proteus mirabilis colonization and swarming motility on indwelling urinary catheter by antibiofilm impregnation: An in vitro study

Proteus mirabilis is one of the important etiologic agents of urinary tract infections (UTI), which complicates the long-term urinary catheterization process in clinical settings. Owing to its crystalline biofilm forming ability and flagellar motility, elimination of P. mirabilis from urinary system becomes very difficult. Thus, the present study is focused to prepare antibiofilm-impregnated Silicone Foley Catheter (SFC) to prevent P. mirabilis instigated UTIs. Through solvent swelling method, the antibiofilm compounds such as linalool (LIN) and 2-hydroxy-4-methoxy benzaldehyde (HMB) were successfully infused into SFCs. Surface topography was studied using AFM analysis, which unveiled the unmodified surface roughness of normal and antibiofilm-impregnated SFCs. In addition, UV-spectrometric and FT-IR analyses revealed good impregnation efficacy and prolonged stability of antibiofilm compounds. Further, in vitro biofilm biomass quantification assay exhibited a maximum of 87 % and 84 % crystalline biofilm inhibition in LIN (350 μg/cm³) and HMB (120 μg/cm³) impregnated SFCs, respectively against P. mirabilis in artificial urine medium. Also, the LIN & HMB-impregnated SFCs demonstrated long-term crystalline biofilm inhibitory activity for more than 30 days, which is ascribed to the sustained release of the compounds. Furthermore, the results of swarming motility analysis revealed the efficacy of antibiofilm-impregnated catheters to mitigate the migration of pathogens over them. Thus, antibiofilm-impregnated catheter is proposed to act as a suitable strategy for reducing P. mirabilis infections and associated complications in long-term urinary catheter users.

Explication of the Potential of 2-Hydroxy-4-Methoxybenzaldehyde in Hampering Uropathogenic Proteus mirabilis Crystalline Biofilm and Virulence

Proteus mirabilis is an important etiological agent of catheter-associated urinary tract infections (CAUTIs) owing to its efficient crystalline biofilm formation and virulence enzyme production. Hence, the present study explicated the antibiofilm and antivirulence efficacies of 2-hydroxy-4-methoxybenzaldehyde (HMB) against P. mirabilis in a non-bactericidal manner. HMB showed concentration-dependent biofilm inhibition, which was also evinced in light, confocal, and scanning electron microscopic (SEM) analyses. The other virulence factors such as urease, hemolysin, siderophores, and extracellular polymeric substances production as well as swimming and swarming motility were also inhibited by HMB treatment. Further, HMB treatment effectively reduced the struvite/apatite production as well as crystalline biofilm formation by P. mirabilis. Furthermore, the results of gene expression analysis unveiled the ability of HMB to impair the expression level of virulence genes such as flhB, flhD, rsbA, speA, ureR, hpmA, and hpmB, which was found to be in correlation with the results of in vitro bioassays. Additionally, the cytotoxicity analysis divulged the innocuous characteristic of HMB against human embryonic kidney cells. Thus, the present study reports the potency of HMB to act as a promising therapeutic remedy for P. mirabilis-instigated CAUTIs.