Raffinose, a plant galactoside, inhibits Pseudomonas aeruginosa biofilm formation via binding to LecA and decreasing cellular cyclic diguanylate levels

Benefits of fungal-to-bacterial quorum quenching as anti-biofouling strategy in membrane bioreactors for wastewater treatment and water reuse

This study addresses membrane biofouling in membrane bioreactors (MBRs) by exploring fungal-to-bacterial quorum quenching (QQ) strategies. While most research has been focused on bacterial-to-bacterial QQ tactics, this study identified fungal strain Vanrija sp. MS1, which is capable of degrading N-acyl-homoserine lactones (signaling molecules of Gram-negative bacteria). To determine the benefits of fungal over bacterial strains, after immobilization on fluidizing spherical beads in an MBR, MS1 significantly reduced the fouling rate by 1.8-fold compared to control MBR, decreased extracellular polymeric substance levels in the biofilm during MBR operation, and favorably changed microbial community and bacterial network, resulting in biofouling mitigation. It is noteworthy that, unlike Rhodococcus sp. BH4, MS1 enhanced QQ activity when switching from neutral to acidic conditions. These results suggest that MS1 has the potential for the effective treatment of acidic industrial wastewater sources such as semiconductor and secondary battery wastewater using MBRs.

Nucleotides as Bacterial Second Messengers

In addition to comprising monomers of nucleic acids, nucleotides have signaling functions and act as second messengers in both prokaryotic and eukaryotic cells. The most common example is cyclic AMP (cAMP). Nucleotide signaling is a focus of great interest in bacteria. Cyclic di-AMP (c-di-AMP), cAMP, and cyclic di-GMP (c-di-GMP) participate in biological events such as bacterial growth, biofilm formation, sporulation, cell differentiation, motility, and virulence. Moreover, the cyclic-di-nucleotides (c-di-nucleotides) produced in pathogenic intracellular bacteria can affect eukaryotic host cells to allow for infection. On the other hand, non-cyclic nucleotide molecules pppGpp and ppGpp are alarmones involved in regulating the bacterial response to nutritional stress; they are also considered second messengers. These second messengers can potentially be used as therapeutic agents because of their immunological functions on eukaryotic cells. In this review, the role of c-di-nucleotides and cAMP as second messengers in different bacterial processes is addressed.

Reduced glutathione and raffinose lengthens postharvest storage of cassava root tubers by improving antioxidant capacity and antibiosis

Cassava is an ideal food security crop in marginal and drought environment. However, the post-harvest storage of cassava is urgent problem to be resolved. In this study, the storage tolerant and non-tolerant cassava were screened by measuring the change of Peroxidase (POD), Superoxide dismutase (SOD), Catalase (CAT) and Malondialdehyde (MDA) in seven cultivars of cassava. Compared with other cultivars, the cultivar of SC14 showed the highest level of SOD, MDA and POD respectively at 0 day, 12 day and 9 day postharvest while exhibited lowest level of CAT at 0 day postharvest, indicating the strongest antioxidant capability and storage tolerance. In contrast, GR15231, termed as storage non-tolerance cultivars, showed lowest SOD and POD at 12 day and kept a relative high level of CAT at 12 day post-harvest. In addition, SC14 has higher level of starch and dry substance than GR15231. Mass spectrum was performed for SC14 and GR15231 to explore the key metabolites regulating the storage tolerance of cassava. The results showed that the expression of glutathione (reduced) and raffinose was significantly decreased at 12 day post-harvest both in tolerant SC14 and non-tolerant GR15231. Compared with GR15231, SC14 showed higher level of raffinose both at 0 and 12 day post-harvest, indicating that raffinose may be the potential metabolites protecting SC14 cultivar from deterioration post-harvest. Additionally, raffinose ratio of SC14a/SC14b was five times less than that of GR15231a/GR15231b, reflecting the slower degradation of raffinose in SC14 cultivar compared with GR15231 cultivar. In conclusion, the antioxidant microenvironment induced by reduced glutathione and higher level of raffinose in SC14 cultivar might be the promising metabolites to improve its antioxidant capacity and antibiosis and thus maintained the quality of Cassava root tubers.

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.

Identification and Alternative Splicing Profile of the Raffinose synthase Gene in Grass Species

Raffinose synthase (Rafs) is an important enzyme in the synthesis pathway of raffinose from sucrose and galactinol in higher plants and is involved in the regulation of seed development and plant responses to abiotic stresses. In this study, we analyzed the Rafs families and profiled their alternative splicing patterns at the genome-wide scale from 10 grass species representing crops and grasses. A total of 73 Rafs genes were identified from grass species such as rice, maize, foxtail millet, and switchgrass. These Rafs genes were assigned to six groups based the phylogenetic analysis. We compared the gene structures, protein domains, and expression patterns of Rafs genes, and also unraveled the alternative transcripts of them. In addition, different conserved sequences were observed at these putative splice sites among grass species. The subcellular localization of PvRafs5 suggested that the Rafs gene was expressed in the cytoplasm or cell membrane. Our findings provide comprehensive knowledge of the Rafs families in terms of genes and proteins, which will facilitate further functional characterization in grass species in response to abiotic stress.

Novel Dietary Approach with Probiotics, Prebiotics, and Synbiotics to Mitigate Antimicrobial Resistance and Subsequent Out Marketplace of Antimicrobial Agents: A Review

Antimicrobial resistance (AMR) is a significant public health concern worldwide. The continuous use and misuse of antimicrobial agents have led to the emergence and spread of resistant strains of bacteria, which can cause severe infections that are difficult to treat. One of the reasons for the constant development of new antimicrobial agents is the need to overcome the resistance that has developed against existing drugs. However, this approach is not sustainable in the long term, as bacteria can quickly develop resistance to new drugs as well. Additionally, the development of new drugs is costly and time-consuming, and there is no guarantee that new drugs will be effective or safe. An alternative approach to combat AMR is to focus on improving the body's natural defenses against infections by using probiotics, prebiotics, and synbiotics, which are helpful to restore and maintain a healthy balance of bacteria in the body. Probiotics are live microorganisms that can be consumed as food or supplements to promote gut health and improve the body's natural defenses against infections. Prebiotics are non-digestible fibers that stimulate the growth of beneficial bacteria in the gut, while synbiotics are a combination of probiotics and prebiotics that work together to improve gut health. By promoting a healthy balance of bacteria in the body, these can help to reduce the risk of infections and the need for antimicrobial agents. Additionally, these approaches are generally safe and well tolerated, and they do not contribute to the development of AMR. In conclusion, the continuous development of new antimicrobial agents is not a sustainable approach to combat AMR. Instead, alternative approaches such as probiotics, prebiotics, and synbiotics should be considered as they can help to promote a healthy balance of bacteria in the body and reduce the need for antibiotics.

Biocompatibility and Antibacterial Effect of Ginger Fraction Loaded PLGA Microspheres Fabricated by Coaxial Electrospray

Various poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with the ginger fraction were fabricated by controlling the electrospray parameters and their biocompatibility and antibacterial activity were identified in this study. The morphology of the microspheres was observed using scanning electron microscopy. The core-shell structures of the microparticles and the presence of ginger fraction in the microspheres were confirmed by fluorescence analysis using a confocal laser scanning microscopy system. In addition, the biocompatibility and antibacterial activity of PLGA microspheres loaded with ginger fraction were evaluated through a cytotoxicity test using osteoblast MC3T3-E1 cells and an antibacterial test using Streptococcus mutans and Streptococcus sanguinis, respectively. The optimum PLGA microspheres loaded with ginger fraction were fabricated under electrospray operational conditions with 3% PLGA concentration in solution, an applied voltage of 15.5 kV, a flow rate of 15 µL/min in the shell nozzle, and 3 µL/min in the core nozzle. The effectual antibacterial effect and enhanced biocompatibility were identified when a 3% ginger fraction in PLGA microspheres was loaded.

Identification, Characterization and Expression Profiling of the RS Gene Family during the Withering Process of White Tea in the Tea Plant (Camellia sinensis) Reveal the Transcriptional Regulation of CsRS8

Raffinose synthetase (RS) is a key enzyme in the process of raffinose (Raf) synthesis and is involved in plant development and stress responses through regulating Raf content. As a sweetener, Raf makes an important contribution to the sweet taste of white tea. However, studies on the identification, analysis and transcriptional regulation of CsRSs (Camellia sinensis RS genes) are still lacking. In this study, nine CsRSs were identified from the tea plant (Camellia sinensis) genome database. The CsRSs were classified into five groups in the phylogenetic tree. Expression level analysis showed that the CsRSs varied in different parts of the tea plant. Transcriptome data showed that CsRSs could respond to persistent drought and cold acclimation. Except for CsRS5 and CsRS9, the expression pattern of all CsRSs increased at 12 h and decreased at 30 h during the withering process of white tea, consistent with the change trend of the Raf content. Furthermore, combining yeast one-hybrid assays with expression analysis, we found that CsDBB could potentially regulate the expression of CsRS8. Our results provide a new perspective for further research into the characterization of CsRS genes and the formation of the white tea flavour.

Recent advances on the regulation of bacterial biofilm formation by herbal medicines

Biofilm formation is a fundamental part of life cycles of bacteria which affects various aspects of bacterial-host interactions including the development of drug resistance and chronic infections. In clinical settings, biofilm-related infections are becoming increasingly difficult to treat due to tolerance to antibiotics. Bacterial biofilm formation is regulated by different external and internal factors, among which quorum sensing (QS) signals and nucleotide-based second messengers play important roles. In recent years, different kinds of anti-biofilm agents have been discovered, among which are the Chinese herbal medicines (CHMs). CHMs or traditional Chinese medicines have long been utilized to combat various diseases around the world and many of them have the ability to inhibit, impair or decrease bacterial biofilm formation either through regulation of bacterial QS system or nucleotide-based second messengers. In this review, we describe the research progresses of different chemical classes of CHMs on the regulation of bacterial biofilm formation. Though the molecular mechanisms on the regulation of bacterial biofilm formation by CHMs have not been fully understood and there are still a lot of work that need to be performed, these studies contribute to the development of effective biofilm inhibitors and will provide a novel treatment strategy to control biofilm-related infections.

Small Carbohydrate Derivatives as Potent Antibiofilm Agents

Biofilm formation by most pathogenic bacteria is considered as one of the key mechanisms associated with virulence and antibiotic resistance. Biofilm-forming bacteria adhere to the surfaces of biological or implant medical devices and create communities within their self-produced extracellular matrix that are difficult to treat by existing antibiotics. There is an urgent need to synthesize and screen structurally diverse molecules for their antibiofilm activity that can remove or minimize the bacterial biofilm. The development of carbohydrate-based small molecules as antibiofilm agents holds a great promise in addressing the problem of the eradication of biofilm-related infections. Owing to their structural diversity and specificity, the sugar scaffolds are valuable entities for developing antibiofilm agents. In this perspective, we discuss the literature pertaining to carbohydrate-based natural antibiofilm agents and provide an overview of the design, activity, and mode of action of potent synthetic carbohydrate-based molecules.

Raffinose Inhibits Streptococcus mutans Biofilm Formation by Targeting Glucosyltransferase

Streptococcus mutans is a representative biofilm-forming bacterium that causes dental caries through glucosyltransferase (GTF) activity. Glucans are synthesized from sucrose by GTFs and provide binding sites for S. mutans to adhere tightly to the tooth enamel. Therefore, if a novel compound that interferes with GTF function is developed, biofilm formation control in S. mutans would be possible. We discovered that raffinose, an oligosaccharide from natural products, strongly inhibited biofilm formation, GTF-related gene expression, and glucan production. Furthermore, biofilm inhibition on saliva-coated hydroxyapatite discs through the reduction of bacterial adhesion indicated the applicability of raffinose in oral health. These effects of raffinose appear to be due to its ability to modulate GTF activity in S. mutans. Hence, raffinose may be considered an antibiofilm agent for use as a substance for oral supplies and dental materials to prevent dental caries. IMPORTANCE Dental caries is the most prevalent infectious disease and is expensive to manage. Dental biofilms can be eliminated via mechanical treatment or inhibited using antibiotics. However, bacteria that are not entirely removed or are resistant to antibiotics can still form biofilms. In this study, we found that raffinose inhibited biofilm formation by S. mutans, a causative agent of dental caries, possibly through binding to GtfC. Our findings support the notion that biofilm inhibition by raffinose can be exerted by interference with GTF function, compensating for the shortcomings of existing commercialized antibiofilm methods. Furthermore, raffinose is an ingredient derived from natural products and can be safely utilized in humans; it has no smell and tastes sweet. Therefore, raffinose, which can control S. mutans biofilm formation, has been suggested as a substance for oral supplies and dental materials to prevent dental caries.

Chimeric Ligands of Pili and Lectin A Inhibit Tolerance, Persistence, and Virulence Factors of Pseudomonas aeruginosa over a Wide Range of Phenotypes

Bacteria readily form resilient phenotypes to counter environmental and antibiotic stresses. Here, we demonstrate a class of small molecules that inhibit a wide range of Pseudomonas aeruginosa phenotypes and enable antibiotics to kill previously tolerant bacteria, preventing the transition of tolerant bacteria into a persistent population. We identified two proteins, type IV pili and lectin LecA, as receptors for our molecules by methods including a new label-free assay based on bacterial motility sensing the chemicals in the environment, the chemical inhibition of bacteriophage adsorption on pili appendages of bacteria, and fluorescence polarization. Structure–activity relationship studies reveal a molecule that inhibits only pili appendage and a class of chimeric ligands that inhibit both LecA and pili. Important structural elements of the ligand are identified for each protein. This selective ligand binding identifies the phenotypes each protein receptor controls. Inhibiting LecA results in reducing biofilm formation, eliminating small colony variants, and is correlated with killing previously tolerant bacteria. Inhibiting pili appendages impedes swarming and twitching motilities and pyocyanin and elastase production. Because these phenotypes are controlled by a broad range of signaling pathways, this approach simultaneously controls the multiple signaling mechanisms preventing bacteria to elude antibiotic treatments.

Role of Antimicrobial Drug in the Development of Potential Therapeutics

Population of the world run into several health-related emergencies among mankind and humans as it creates a challenge for the evolution of novel drug discoveries. One such can be the emergence of multidrug-resistant (MDR) strains in both hospital and community settings, which have been due to an inappropriate use and inadequate control of antibiotics that has led to the foremost human health concerns with a high impact on the global economy. So far, there has been application of two strategies for the development of anti-infective agents either by classical antibiotics that have been derived for their synthetic analogs with increased efficacy or screening natural compounds along with the synthetic compound libraries for the antimicrobial activities. However, need for newer treatment options for infectious diseases has led research to develop new generation of antimicrobial activity to further lessen the spread of antibiotic resistance. Currently, the principles aim to find novel mode of actions or products to target the specific sites and virulence factors in pathogens by a series of better understanding of physiology and molecular aspects of the microbial resistance, mechanism of infection process, and gene-pathogenicity relationship. The design various novel strategies tends to provide us a path for the development of various antimicrobial therapies that intends to have a broader and wider antimicrobial spectrum that helps to combat MDR strains worldwide. The development of antimicrobial peptides, metabolites derived from plants, microbes, phage-based antimicrobial agents, use of metal nanoparticles, and role of CRISPR have led to an exceptional strategies in designing and developing the next-generation antimicrobials. These novel strategies might help to combat the seriousness of the infection rates and control the health crisis system.

Raffinose Family Oligosaccharides: Friend or Foe for Human and Plant Health?

Raffinose family oligosaccharides (RFOs) are widespread across the plant kingdom, and their concentrations are related to the environment, genotype, and harvest time. RFOs are known to carry out many functions in plants and humans. In this paper, we provide a comprehensive review of RFOs, including their beneficial and anti-nutritional properties. RFOs are considered anti-nutritional factors since they cause flatulence in humans and animals. Flatulence is the single most important factor that deters consumption and utilization of legumes in human and animal diets. In plants, RFOs have been reported to impart tolerance to heat, drought, cold, salinity, and disease resistance besides regulating seed germination, vigor, and longevity. In humans, RFOs have beneficial effects in the large intestine and have shown prebiotic potential by promoting the growth of beneficial bacteria reducing pathogens and putrefactive bacteria present in the colon. In addition to their prebiotic potential, RFOs have many other biological functions in humans and animals, such as anti-allergic, anti-obesity, anti-diabetic, prevention of non-alcoholic fatty liver disease, and cryoprotection. The wide-ranging applications of RFOs make them useful in food, feed, cosmetics, health, pharmaceuticals, and plant stress tolerance; therefore, we review the composition and diversity of RFOs, describe the metabolism and genetics of RFOs, evaluate their role in plant and human health, with a primary focus in grain legumes.

Enhanced Antibacterial Potential of Amoxicillin against Helicobacter pylori Mediated by Lactobionic Acid Coated Zn-MOFs

H. pylori (Helicobacter pylori) causes a common chronic infectious disease and infects around 4.4 billion people worldwide. H. pylori was classified as a member of the primary class of stomach cancer (stomach adenocarcinoma). Hence, this study was conducted to design a novel lactobionic acid (LBA)-coated Zn-MOFs to enhance bactericidal activity of Amoxicillin (AMX) against H. pylori. The synthesized Zn-MOFs were characterized by various techniques which included Dynamic Light Scattering (DLS), Fourier Transform Infrared (FT-IR) Spectroscopy, Powder X-ray diffraction, scanning electron microscope, and atomic force microscope. They were capable of encapsulating an increased amount of AMX and investigated for their efficacy to enhance the antibacterial potential of their loaded drug candidate. Interestingly, it was found that LBA-coated Zn-MOFs significantly reduced the IC₅₀, MIC, and MBIC values of AMX against H. pylori. Morphological investigation of treated bacterial cells further authenticated the above results as LBA-coated Zn-MOFs-treated cells underwent complete distortion compared with non-coated AMX loaded Zn-MOFs. Based on the results of the study, it can be suggested that LBA-coated Zn-MOFs may be an effective alternate candidate to provide new perspective for the treatment of H. pylori infections.

Carrier-Free Immobilization of α-Galactosidase as Nano-Biocatalysts for Synthesizing Prebiotic α-Galacto-Oligosaccharides

α-Galacto-oligosaccharides (α-GOSs) have great functions as prebiotics and therapeutics. This work established the method of batch synthesis of α-GOSs by immobilized α-galactosidase for the first time, laying a foundation for industrial applications in the future. The α-galactosidase from Aspergillus niger L63 was immobilized as cross-linked enzyme aggregates (CLEAs) nano-biocatalyst through enzyme precipitating and cross-linking steps without using carriers. Among the tested agents, the ammonium sulfate showed high precipitation efficacy and induced regular structures of α-galactosidase CLEAs (Aga-CLEAs) that had been analyzed by scanning electron microscopy and Fourier-transform infrared spectroscopy. Through optimization by response surface methodology, the ammonium sulfate-induced Aga-CLEAs achieved a high activity recovery of around 90% at 0.55 U/mL of enzymes and 36.43 mM glutaraldehyde with cross-linking for 1.71 h. Aga-CLEAs showed increased thermal stability and organic solvent tolerance. The storage ability was also improved since it maintained 74.5% activity after storing at 4 °C for three months, significantly higher than that of the free enzyme (21.6%). Moreover, Aga-CLEAs exhibited excellent reusability in the α-GOSs synthesis from galactose, retaining above 66% of enzyme activity after 10 batch reactions, with product yields all above 30%.

Effect of broad-spectrum biofilm inhibitor raffinose, a plant galactoside, on the inhibition of co-culture biofilm on the microfiltration membrane

A membrane bioreactor (MBR) integrates process such as membrane filtration and biological treatment of activated sludge. However, organic, inorganic and biological matters cause membrane fouling, which seriously affects membrane performance. The goal of this study was to evaluate the biofouling inhibition capacity of raffinose during the MBR process. The results showed that 0-1,000 μM raffinose significantly reduced the formation of the P. aeruginosa and S. aureus co-culture biofilm by about 25-52 % in a concentration-dependent manner. In addition, the effect of raffinose on the microfiltration membrane biofilm was tested in a flow reactor and lab-scale MBR unit. The results showed that the co-culture biofilm and transmembrane pressure were decreased by raffinose treatment compared to those by furanone C-30 treatment. These results clearly demonstrated that raffinose, broad-spectrum biofilm inhibitor, inhibits biofilm formation in mixed cultures and could be used to mitigate biofouling in MBR processes.

Linoleic acid inhibits Pseudomonas aeruginosa biofilm formation by activating diffusible signal factor-mediated quorum sensing

Bacterial biofilm formation causes serious problems in various fields of medical, clinical, and industrial settings. Antibiotics and biocide treatments are typical methods used to remove bacterial biofilms, but biofilms are difficult to remove effectively from surfaces due to their increased resistance. An alternative approach to treatment with antimicrobial agents is using biofilm inhibitors that regulate biofilm development without inhibiting bacterial growth. In the present study, we found that linoleic acid (LA), a plant unsaturated fatty acid, inhibits biofilm formation under static and continuous conditions without inhibiting the growth of Pseudomonas aeruginosa. LA also influenced the bacterial motility, extracellular polymeric substance production, and biofilm dispersion by decreasing the intracellular cyclic diguanylate concentration through increased phosphodiesterase activity. Furthermore, quantitative gene expression analysis demonstrated that LA induced the expression of genes associated with diffusible signaling factor-mediated quorum sensing that can inhibit or induce the dispersion of P. aeruginosa biofilms. These results suggest that LA is functionally and structurally similar to a P. aeruginosa diffusible signaling factor (cis-2-decenoic acid) and, in turn, act as an agonist molecule in biofilm dispersion.

Inactivation of Pseudomonas aeruginosa Biofilms by 405-Nanometer-Light-Emitting Diode Illumination

Biofilm formation by Pseudomonas aeruginosa contributes to its survival on surfaces and represents a major clinical threat because of the increased tolerance of biofilms to disinfecting agents. This study aimed to investigate the efficacy of 405-nm light-emitting diode (LED) illumination in eliminating P. aeruginosa biofilms formed on stainless steel coupons under different temperatures. Time-dependent killing assays using planktonic and biofilm cells were used to determine the antimicrobial and antibiofilm activities of LED illumination. We also evaluated the effects of LED illumination on the disinfectant susceptibility, biofilm structure, extracellular polymeric substance (EPS) structure and composition, and biofilm-related gene expression of P. aeruginosa biofilm cells. Results showed that the abundance of planktonic P. aeruginosa cells was reduced by 0.88, 0.53, and 0.85 log CFU/ml following LED treatment for 2 h compared with untreated controls at 4, 10, and 25°C, respectively. For cells in biofilms, significant reductions (1.73, 1.59, and 1.68 log CFU/cm2) were observed following LED illumination for 2 h at 4, 10, and 25°C, respectively. Moreover, illuminated P. aeruginosa biofilm cells were more sensitive to benzalkonium chloride or chlorhexidine than untreated cells. Scanning electron microscopy and confocal laser scanning microscopic observation indicated that both the biofilm structure and EPS structure were disrupted by LED illumination. Further, reverse transcription-quantitative PCR revealed that LED illumination downregulated the transcription of several genes associated with biofilm formation. These findings suggest that LED illumination has the potential to be developed as an alternative method for prevention and control of P. aeruginosa biofilm contamination.IMPORTANCEPseudomonas aeruginosa can form biofilms on medical implants, industrial equipment, and domestic surfaces, contributing to high morbidity and mortality rates. This study examined the antibiofilm activity of 405-nm light-emitting diode (LED) illumination against mature biofilms formed on stainless steel coupons. We found that the disinfectant susceptibility, biofilm structure, and extracellular polymeric substance structure and composition were disrupted by LED illumination. We then investigated the transcription of several critical P. aeruginosa biofilm-related genes and analyzed the effect of illumination temperature on the above characteristics. Our results confirmed that LED illumination could be developed into an effective and safe method to counter P. aeruginosa biofilm contamination. Further research will be focused on the efficacy and application of LED illumination for elimination of complicated biofilms in the environment.

Design, synthesis, and evaluation of compounds capable of reducing Pseudomonas aeruginosa virulence

Anti-virulence approaches in the treatment of Pseudomonas aeruginosa (PA)-induced infections have shown clinical potential in multiple in vitro and in vivo studies. However, development of these compounds is limited by several factors, including the lack of molecules capable of penetrating the membrane of gram-negative organisms. Here, we report the identification of novel structurally diverse compounds that inhibit PqsR and LasR-based signaling and diminish virulence factor production and biofilm growth in two clinically relevant strains of P. aeruginosa. It is the first report where potential anti-virulent agents were evaluated for inhibition of several virulence factors of PA. Finally, co-treatment with these inhibitors significantly reduced the production of virulence factors induced by the presence of sub-inhibitory levels of ciprofloxacin. Further, we have analyzed the drug-likeness profile of designed compounds using quantitative estimates of drug-likeness (QED) and confirmed their potential as hit molecules for further development.

In vitro fermentation of raffinose by the human gut bacteria

Raffinose has become a major focus of research interest and recent studies have shown that besides beneficial bifidobacteria and lactobacilli, Escherichia coli, Enterococcus faecium and Streptococcus pneumoniae can also utilize raffinose and raffinose might lead to flatulence in some hosts. Therefore, it is required to find out the raffinose-metabolizing bacteria in the gut and the bacteria responsible for the flatulence. The BLASTP search results showed that the homologous proteins of glycosidases related to raffinose utilization are widely distributed in 196 of the 528 gut bacterial strains. Fifty-nine bacterial strains belonging to nine species of five genera were isolated from human feces and were found to be capable of utilizing raffinose; of these species, Enterococcus avium and Streptococcus salivarius were reported for the first time. High-performance liquid chromatography (HPLC) analysis of the supernatants of the nine species revealed that the bacteria could utilize raffinose in different manners. Glucose and melibiose were detected in the supernatants of Enterococcus avium E5 and Streptococcus salivarius B5, respectively. However, no resulting saccharides of raffinose degradation were detected in the supernatants of other seven strains, indicating that they had different raffinose utilization types from Enterococcus avium E5 and Streptococcus salivarius B5. Gas was produced with raffinose utilization by Escherichia coli, Enterococcus faecium, Streptococcus macedonicus, Streptococcus pasteurianus and Enterococcus avium. Thus, more attention should be paid to the raffinose-utilizing bacteria besides bifidobacteria and further studies are required to reveal the mechanisms of raffinose utilization to clarify the relationship between raffinose and gut bacteria.

The Quest for Novel Antimicrobial Compounds: Emerging Trends in Research, Development, and Technologies

Pathogenic antibiotic resistant bacteria pose one of the most important health challenges of the 21st century. The overuse and abuse of antibiotics coupled with the natural evolutionary processes of bacteria has led to this crisis. Only incremental advances in antibiotic development have occurred over the last 30 years. Novel classes of molecules, such as engineered antibodies, antibiotic enhancers, siderophore conjugates, engineered phages, photo-switchable antibiotics, and genome editing facilitated by the CRISPR/Cas system, are providing new avenues to facilitate the development of antimicrobial therapies. The informatics revolution is transforming research and development efforts to discover novel antibiotics. The explosion of nanotechnology and micro-engineering is driving the invention of antimicrobial materials, enabling the cultivation of "uncultivable" microbes and creating specific and rapid diagnostic technologies. Finally, a revival in the ecological aspects of microbial disease management, the growth of prebiotics, and integrated management based on the "One Health" model, provide additional avenues to manage this health crisis. These, and future scientific and technological developments, must be coupled and aligned with sound policy and public awareness to address the risks posed by rising antibiotic resistance.

Antibiofilm and Antivirulence Activities of 6-Gingerol and 6-Shogaol Against Candida albicans Due to Hyphal Inhibition

Candida albicans is an opportunistic pathogen and responsible for candidiasis. C. albicans readily forms biofilms on various biotic and abiotic surfaces, and these biofilms can cause local and systemic infections. C. albicans biofilms are more resistant than its free yeast to antifungal agents and less affected by host immune responses. Transition of yeast cells to hyphal cells is required for biofilm formation and is believed to be a crucial virulence factor. In this study, six components of ginger were investigated for antibiofilm and antivirulence activities against a fluconazole-resistant C. albicans strain. It was found 6-gingerol, 8-gingerol, and 6-shogaol effectively inhibited biofilm formation. In particular, 6-shogaol at 10 μg/ml significantly reduced C. albicans biofilm formation but had no effect on planktonic cell growth. Also, 6-gingerol and 6-shogaol inhibited hyphal growth in embedded colonies and free-living planktonic cells, and prevented cell aggregation. Furthermore, 6-gingerol and 6-shogaol reduced C. albicans virulence in a nematode infection model without causing toxicity at the tested concentrations. Transcriptomic analysis using RNA-seq and qRT-PCR showed 6-gingerol and 6-shogaol induced several transporters (CDR1, CDR2, and RTA3), but repressed the expressions of several hypha/biofilm related genes (ECE1 and HWP1), which supported observed phenotypic changes. These results highlight the antibiofilm and antivirulence activities of the ginger components, 6-gingerol and 6-shogaol, against a drug resistant C. albicans strain.

Measuring Cyclic Diguanylate (c-di-GMP)-Specific Phosphodiesterase Activity Using the MANT-c-di-GMP Assay

The second messenger, cyclic diguanylate (c-di-GMP), regulates a variety of bacterial cellular and social behaviors. A key determinant of c-di-GMP levels in cells is its degradation by c-di-GMP-specific phosphodiesterases (PDEs). Here, we describe an assay to determine c-di-GMP degradation rates in vitro using 2'-O-(N'-methylanthraniloyl)-cyclic diguanylate (MANT-c-di-GMP). Additionally, a protocol for the production and purification of recombinant Pseudomonas aeruginosa RocR, a c-di-GMP-specific PDE that may serve as a control in MANT-c-di-GMP assays, is provided. The use of the fluorescent MANT-c-di-GMP analogue can deliver fundamental information about PDE function, and is suitable for identifying and investigating c-di-GMP-specific PDE activators and inhibitors.

Recent perspectives on the molecular basis of biofilm formation by Pseudomonas aeruginosa and approaches for treatment and biofilm dispersal

Pseudomonas aeruginosa, a Gram-negative, rod-shaped bacterium causes widespread diseases in humans. This bacterium is frequently related to nosocomial infections such as pneumonia, urinary tract infections (UTIs) and bacteriaemia especially in immunocompromised patients. The current review focuses on the recent perspectives on biofilms formation by these bacteria. Biofilms are communities of microorganisms in which cells stick to each other and often adhere to a surface. These adherent cells are usually embedded within a self-produced matrix of extracellular polymeric substance (EPS). Pel, psl and alg operons present in P. aeruginosa are responsible for the biosynthesis of extracellular polysaccharide which plays an important role in cell surface interactions during biofilm formation. Recent studies suggested that cAMP signalling pathway, quorum-sensing pathway, Gac/Rsm pathway and c-di-GMP signalling pathway are the main mechanism that leads to the biofilm formation. Understanding the bacterial virulence depends on a number of cell-associated and extracellular factors and is very essential for the development of potential drug targets. Thus, the review focuses on the major genes involved in the biofilm formation, the state of art update on the biofilm treatment and the dispersal approaches such as targeting adhesion and maturation, targeting virulence factors and other strategies such as small molecule-based inhibitors, phytochemicals, bacteriophage therapy, photodynamic therapy, antimicrobial peptides and natural therapies and vaccines to curtail the biofilm formation by P. aeruginosa.

Regulation of Seed Vigor by Manipulation of Raffinose Family Oligosaccharides in Maize and Arabidopsis thaliana

Raffinose family oligosaccharides (RFOs) accumulate in seeds during maturation desiccation in many plant species. However, it remains unclear whether RFOs have a role in establishing seed vigor. GALACTINOL SYNTHASE (GOLS), RAFFINOSE SYNTHASE (RS), and STACHYOSE SYNTHASE (STS) are the enzymes responsible for RFO biosynthesis in plants. Interestingly, only raffinose is detected in maize seeds, and a unique maize RS gene (ZmRS) was identified. In this study, we found that two independent mutator (Mu)-interrupted zmrs lines, containing no raffinose but hyperaccumulating galactinol, have significantly reduced seed vigor, compared with null segregant controls. Unlike maize, Arabidopsis thaliana seeds contain several RFOs (raffinose, stachyose, and verbascose). Manipulation of A. thaliana RFO content by overexpressing ZmGOLS2, ZmRS, or AtSTS demonstrated that co-overexpression of ZmGOLS2 and ZmRS, or overexpression of ZmGOLS2 alone, significantly increased the total content of RFOs and enhanced Arabidopsis seed vigor. Surprisingly, while overexpression of ZmRS increased seed raffinose content, its overexpression dramatically decreased seed vigor and reduced the seed amounts of galactinol, stachyose, and verbascose. In contrast, the atrs5 mutant seeds are similar to those of the wild type with regard to seed vigor and RFO content, except for stachyose, which accumulated in atrs5 seeds. Total RFOs, RFO/sucrose ratio, but not absolute individual RFO amounts, positively correlated with A. thaliana seed vigor, to which stachyose and verbascose contribute more than raffinose. Taken together, these results provide new insights into regulatory mechanisms of seed vigor and reveal distinct requirement for RFOs in modulating seed vigor in a monocot and a dicot.

Complementary feeding with cowpea reduces growth faltering in rural Malawian infants: a blind, randomized controlled clinical trial

Background: Growth faltering is common in rural African children and is attributed to inadequate dietary intake and environmental enteric dysfunction (EED).Objective: We tested the hypothesis that complementary feeding with cowpea or common bean flour would reduce growth faltering and EED in 6-mo-old rural Malawians compared with the control group receiving a corn-soy blend.Design: A prospective, double-blind, randomized controlled clinical trial was conducted in which children received daily feeding for 6 mo (200 kcal/d when 6-9 mo old and 300 kcal/d when 10-12 mo old). The primary outcomes were change in length-for-age z score (LAZ) and improvements in EED, as measured by percentage of lactulose excretion (%L). %L <0.2% was considered normal. Anthropometric measurements and %L through urine were compared between each legume group and the control group with Student's t test.Results: Of the 355 infants enrolled, 291 infants completed the trial, and 288 were breastfed throughout the duration of the study. Cowpea and common bean added 4.6-5.2 g protein/d and 4-5 g indigestible carbohydrate/d to the diet. LAZ and weight-for-height z score were reduced in all 3 groups from 6 to 12 mo of age. The changes in LAZ [mean (95% CI)] for the cowpea, common bean, and control groups from 6 to 9 mo were -0.14 (-0.24, -0.04), -0.27 (-0.38, -0.16), and -0.27 (-0.35, -0.19), respectively. LAZ was reduced less in infants receiving cowpea than in those receiving control food from 6 to 9 mo (P = 0.048). The absolute value of %L did not differ between the dietary groups at 9 mo of age (mean ± SD: 0.30 ± 0.43, 0.23 ± 0.21, and 0.26 ± 0.31 for cowpea, common bean, and control, respectively), nor did the change in %L from 6 to 9 mo.Conclusion: Addition of cowpea to complementary feeding in Malawian infants resulted in less linear growth faltering. This trial was registered at clinicaltrials.gov as NCT02472262.

Photorhabdus luminescens lectin A (PllA): A new probe for detecting α-galactoside-terminating glycoconjugates

Lectins play important roles in infections by pathogenic bacteria, for example, in host colonization, persistence, and biofilm formation. The Gram-negative entomopathogenic bacterium Photorhabdus luminescens symbiotically lives in insect-infecting Heterorhabditis nematodes and kills the insect host upon invasion by the nematode. The P. luminescens genome harbors the gene plu2096, coding for a novel lectin that we named PllA. We analyzed the binding properties of purified PllA with a glycan array and a binding assay in solution. Both assays revealed a strict specificity of PllA for α-galactoside-terminating glycoconjugates. The crystal structures of apo PllA and complexes with three different ligands revealed the molecular basis for the strict specificity of this lectin. Furthermore, we found that a 90° twist in subunit orientation leads to a peculiar quaternary structure compared with that of its ortholog LecA from Pseudomonas aeruginosa We also investigated the utility of PllA as a probe for detecting α-galactosides. The α-Gal epitope is present on wild-type pig cells and is the main reason for hyperacute organ rejection in pig to primate xenotransplantation. We noted that PllA specifically recognizes this epitope on the glycan array and demonstrated that PllA can be used as a fluorescent probe to detect this epitope on primary porcine cells in vitro In summary, our biochemical and structural analyses of the P. luminescens lectin PllA have disclosed the structural basis for PllA's high specificity for α-galactoside-containing ligands, and we show that PllA can be used to visualize the α-Gal epitope on porcine tissues.

Raffinose Induces Biofilm Formation by Streptococcus mutans in Low Concentrations of Sucrose by Increasing Production of Extracellular DNA and Fructan

Streptococcus mutans is the primary etiological agent of dental caries and causes tooth decay by forming a firmly attached biofilm on tooth surfaces. Biofilm formation is induced by the presence of sucrose, which is a substrate for the synthesis of extracellular polysaccharides but not in the presence of oligosaccharides. Nonetheless, in this study, we found that raffinose, which is an oligosaccharide with an intestinal regulatory function and antiallergic effect, induced biofilm formation by S. mutans in a mixed culture with sucrose, which was at concentrations less than those required to induce biofilm formation directly. We analyzed the possible mechanism behind the small requirement for sucrose for biofilm formation in the presence of raffinose. Our results suggested that sucrose contributed to an increase in bacterial cell surface hydrophobicity and biofilm formation. Next, we examined how the effects of raffinose interacted with the effects of sucrose for biofilm formation. We showed that the presence of raffinose induced fructan synthesis by fructosyltransferase and aggregated extracellular DNA (eDNA, which is probably genomic DNA released from dead cells) into the biofilm. eDNA seemed to be important for biofilm formation, because the degradation of DNA by DNase I resulted in a significant reduction in biofilm formation. When assessing the role of fructan in biofilm formation, we found that fructan enhanced eDNA-dependent cell aggregation. Therefore, our results show that raffinose and sucrose have cooperative effects and that this induction of biofilm formation depends on supportive elements that mainly consist of eDNA and fructan.IMPORTANCE The sucrose-dependent mechanism of biofilm formation in Streptococcus mutans has been studied extensively. Nonetheless, the effects of carbohydrates other than sucrose are inadequately understood. Our findings concerning raffinose advance the understanding of the mechanism underlying the joint effects of sucrose and other carbohydrates on biofilm formation. Since raffinose has been reported to have positive effects on enterobacterial flora, research on the effects of raffinose on the oral flora are required prior to its use as a beneficial sugar for human health. Here, we showed that raffinose induced biofilm formation by S. mutans in low concentrations of sucrose. The induction of biofilm formation generally generates negative effects on the oral flora. Therefore, we believe that this finding will aid in the development of more effective oral care techniques to maintain oral flora health.

Lauroyl Arginate Ethyl Blocks the Iron Signals Necessary for Pseudomonas aeruginosa Biofilm Development

Pseudomonas aeruginosa is a ubiquitous gram-negative bacterium capable of forming a biofilm on living and non-living surfaces, which frequently leads to undesirable consequences. We found that lauroyl arginate ethyl (LAE), a synthetic non-oxidizing biocide, inhibited biofilm formation by P. aeruginosa at a sub-growth inhibitory concentration under both static and flow conditions. A global transcriptome analysis was conducted using a gene chip microarray to identify the genes targeted by LAE. In response to LAE treatment, P. aeruginosa cells up-regulated iron acquisition and signaling genes and down-regulated iron storage genes. LAE demonstrated the capacity to chelate iron in an experiment in which free LAE molecules were measured by increasing the ratio of iron to LAE. Furthermore, compared to untreated cells, P. aeruginosa cells treated with LAE exhibited enhanced twitching motility, a phenotype that is usually evident when the cells are starved for iron. Taken together, these results imply that LAE generated iron-limiting conditions, and in turn, blocked iron signals necessary for P. aeruginosa biofilm development. As destroying or blocking signals leading to biofilm development would be an efficient way to mitigate problematic biofilms, our findings suggest that LAE can aid in reducing P. aeruginosa biofilms for therapeutic and industrial purposes.

Identification of berberine as a direct thrombin inhibitor from traditional Chinese medicine through structural, functional and binding studies

Thrombin acts as a key enzyme in the blood coagulation cascade and represents a potential drug target for the treatment of several cardiovascular diseases. The aim of this study was to identify small-molecule direct thrombin inhibitors from herbs used in traditional Chinese medicine (TCM). A pharmacophore model and molecular docking were utilized to virtually screen a library of chemicals contained in compositions of traditional Chinese herbs, and these analyses were followed by in vitro bioassay validation and binding studies. Berberine (BBR) was first confirmed as a thrombin inhibitor using an enzymatic assay. The BBR IC₅₀ value for thrombin inhibition was 2.92 μM. Direct binding studies using surface plasmon resonance demonstrated that BBR directly interacted with thrombin with a K_D value of 16.39 μM. Competitive binding assay indicated that BBR could bind to the same argartroban/thrombin interaction site. A platelet aggregation assay demonstrated that BBR had the ability to inhibit thrombin-induced platelet aggregation in washed platelets samples. This study proved that BBR is a direct thrombin inhibitor that has activity in inhibiting thrombin-induced platelet aggregation. BBR may be a potential candidate for the development of safe and effective thrombin-inhibiting drugs.

Searching for a potential antibacterial lead structure against bacterial biofilms among new naphthoquinone compounds

AIMS

The aims of this study were to design, synthesize and to evaluate 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones against Gram-negative and Gram-positive bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA) and its biofilm, to probe for potential lead structures.

METHODS AND RESULTS

Thirty-six new analogues were prepared with good yields using a simple, fast, operational three-procedure reaction and a thiol addition to an ο-quinone methide using microwave irradiation. All compounds were tested against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Proteus mirabilis ATCC 15290, Serratia marcescens ATCC 14756, Klebsiella pneumoniae ATCC 4352, Enterobacter cloacae ATCC 23355, Enterococcus faecalis ATCC 29212, S. aureus ATCC 25923, Staphylococcus simulans ATCC 27851, Staphylococcus epidermidis ATCC 12228 and a hospital strain of MRSA. Their antibacterial activity was determined using the disc diffusion method, revealing the activity of 19 compounds, mainly against Gram-positive strains. Interestingly, the minimal inhibitory concentration ranges detected for the hit molecules (32-128 μg ml^-1 ) were within Clinical and Laboratory Standards Institute levels. Promisingly, compound 15 affected the MRSA strain, with a reduction of up to 50% in biofilm formation, which is better than vancomycin as biofilm forms a barrier against the antibiotic that avoids its action.

CONCLUSIONS

After probing 36 naphthoquinones for a potential antibacterial lead structure against the bacterial biofilm, we found that compound 15 should be explored further and also should be structurally modified in the near future to test against Gram-negative strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

Since vancomycin is one of the last treatment options currently available, and it is unable to inhibit biofilm, the research of new antimicrobials is urgent. In this context, 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones proved to be a promising lead structure against MRSA and bacterial biofilm.