Gallic Acid an Agricultural Byproduct Modulates the Biofilm Matrix Exopolysaccharides of the Phytopathogen Ralstonia solanacearum

Evaluation of antibacterial, antifungal and antibiofilm activities of A. baumannii-derived tannase and gallic acid against uropathogenic microorganisms

One of the most prevalent infectious diseases and a key driver of antibiotic prescriptions in pediatrics is urinary tract infection (UTI). Due to the emergence of more resistant uropathogenic bacterial and fungal strains, current treatments are no longer effective, necessitating the urgent development of novel antibacterial and antifungal drugs. In this study, the antifungal, antibacterial, and anti-biofilm capabilities of compounds, such as tannase (TN) and gallic acid (GA), which were produced from a novel natural source, Acinetobacter baumannii (AB11) bacteria, were assessed for the inactivation of uropathogenic microorganisms (UMs). Ammonium sulphate precipitation, ion exchange, high-performance liquid chromatography, and gel filtration were used to purify TN and GA that were isolated from A. baumannii. A 43.08 % pure TN with 1221.2 U/mg specific activity and 10.51 mg/mL GA was obtained. The antibacterial, antifungal and anti-biofilm activities of TN and GA were evaluated against UMs and compared to those of commercially available antibiotics including sulfamethoxazole (SXT), levofloxacin (LEV), ciprofloxacin (CIP), amikacin (Ak), and nitrofurantoin (F). The results showed that TN and GA were superior to commercial antibiotics in their ability to inactivate UMs and considerably reduced biofilms formation. Additionally, the GA emerges as the top substitute for currently available medications, demonstrating superior antibacterial and antibiofilm properties against all UMs evaluated in this study. The results of this investigation showed that A. baumannii-derived TN and GA could be utilized as an alternative medication to treat UTIs.

Evolving biofilm inhibition and eradication in clinical settings through plant-based antibiofilm agents

BACKGROUND

After almost 100 years since evidence of biofilm mode of growth and decades of intensive investigation about their formation, regulatory pathways and mechanisms of antimicrobial tolerance, nowadays there are still no therapeutic solutions to eradicate bacterial biofilms and their biomedical related issues.

PURPOSE

This review intends to provide a comprehensive summary of the recent and most relevant published studies on plant-based products, or their isolated compounds with antibiofilm activity mechanisms of action or identified molecular targets against bacterial biofilms. The objective is to offer a new perspective of most recent data for clinical researchers aiming to prevent or eliminate biofilm-associated infections caused by bacterial pathogens.

METHODS

The search was performed considering original research articles published on PubMed, Web of Science and Scopus from 2015 to April 2023, using keywords such as "antibiofilm", "antivirulence", "phytochemicals" and "plant extracts".

RESULTS

Over 180 articles were considered for this review with a focus on the priority human pathogens listed by World Health Organization, including Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae and Escherichia coli. Inhibition and detachment or dismantling of biofilms formed by these pathogens were found using plant-based extract/products or derivative compounds. Although combination of plant-based products and antibiotics were recorded and discussed, this topic is currently poorly explored and only for a reduced number of bacterial species.

CONCLUSIONS

This review clearly demonstrates that plant-based products or derivative compounds may be a promising therapeutic strategy to eliminate bacterial biofilms and their associated infections. After thoroughly reviewing the vast amount of research carried out over years, it was concluded that plant-based products are mostly able to prevent biofilm formation through inhibition of quorum sensing signals, but also to disrupt mature biofilms developed by multidrug resistant bacteria targeting the biofilm extracellular polymeric substance. Flavonoids and phenolic compounds seemed the most effective against bacterial biofilms.

Biofilm-Forming Ability of Phytopathogenic Bacteria: A Review of its Involvement in Plant Stress

Phytopathogenic bacteria not only affect crop yield and quality but also the environment. Understanding the mechanisms involved in their survival is essential to develop new strategies to control plant disease. One such mechanism is the formation of biofilms; i.e., microbial communities within a three-dimensional structure that offers adaptive advantages, such as protection against unfavorable environmental conditions. Biofilm-producing phytopathogenic bacteria are difficult to manage. They colonize the intercellular spaces and the vascular system of the host plants and cause a wide range of symptoms such as necrosis, wilting, leaf spots, blight, soft rot, and hyperplasia. This review summarizes up-to-date information about saline and drought stress in plants (abiotic stress) and then goes on to focus on the biotic stress produced by biofilm-forming phytopathogenic bacteria, which are responsible for serious disease in many crops. Their characteristics, pathogenesis, virulence factors, systems of cellular communication, and the molecules implicated in the regulation of these processes are all covered.

Alkyl Gallates as Potential Antibiofilm Agents: A Review

Biofilms, which consist of microorganisms embedded in a polymer-rich matrix, contribute to a variety of infections and increase antimicrobial resistance. Thus, there is a constant need to develop new chemotherapeutic agents to combat biofilms. This review article focuses on the use of alkyl gallates, gallic acid and its esters (methyl, ethyl, propyl, butyl, hexyl, octyl, and dodecyl gallate), most of which are found in plants, to inhibit biofilm formation. The studies under review reveal that alkyl gallates have the capacity to prevent biofilm development and eradicate mature biofilms through mechanisms that suppress the synthesis of the extracellular polymeric matrix, inhibit quorum-sensing signaling, and alter the microbial cell membrane. The effects are stronger the greater the length of the alkyl chain. Moreover, the alkyl gallates' preventive activity against biofilm formation occurs at doses below the minimum inhibitory concentration. More importantly, combining alkyl gallates with antimicrobials or blue-light irradiation produces a synergistic effect on the inhibition of biofilm formation that can be used to treat infections and overcome microbial resistance.

Biocontrol Streptomyces Induces Resistance to Bacterial Wilt by Increasing Defense-Related Enzyme Activity in Solanum melongena L

Streptomyces strains were isolated from rhizosphere soil and evaluated for in vitro plant growth and antagonistic potential against Ralstonia solanacearum. Based on their in vitro screening, seven Streptomyces were evaluated for plant growth promotion (PGP) and biocontrol efficacy by in-planta and pot culture study. In the in-planta study, Streptomyces-treated eggplant seeds showed better germination percentage, plant growth, and disease occurrence against R. solanacearum than the control treatment. Hence, all seven Streptomyces cultures were developed as a bioformulation by farmyard manure and used for pot culture study. The highest plant growth, weight, and total chlorophyll content were observed in UP1A-1-treated eggplant followed by UP1A-4, UT4A-49, and UT6A-57. Similarly, the maximum biocontrol efficacy was observed in UP1A-1-treated eggplants against bacterial wilt. The biocontrol potential of Streptomyces is also confirmed through metabolic responses by assessing the activities of the defense-related enzymes peroxidase (POX), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) and as well as the levels of total phenol. Treatment with UP1A-1/ UT4A-49 and challenge with R. solanacearum led to maximum changes in the activities of POX, PPO, and PAL and the levels of total phenol in the eggplants at different time intervals. Alterations in enzymes of UP1A-1 treatment were related to early defense responses in eggplant. Therefore, the treatment with UP1A-1 significantly delayed the establishment of bacterial wilt in eggplant. Altogether, the present study suggested that the treatment of Streptomyces maritimus UP1A-1 fortified farmyard manure has improved the plant growth and stronger disease control against R. solanacearum on eggplant.

Heteroleptic pincer palladium(II) complex coated orthopedic implants impede the AbaI/AbaR quorum sensing system and biofilm development by Acinetobacter baumannii

Implant-associated infections mediated by Acinetobacter baumannii biofilms have become a major concern in the healthcare sector. As biofilm formation by this important pathogen is mediated by quorum sensing, quorum sensing inhibitors (QSI) have gained much attention. The present study confirms that novel thiazolinyl-picolinamide based palladium(II) complexes had good biofilm disruptive and QSI properties against A. baumannii. Key QS-mediated virulence factors like pili mediated surface motility and polysaccharide production were inhibited by the best Pd(II) complex (E). This also showed potent inhibitory activity against both the standard and clinical strains of A. baumannii. Molecular docking analysis also proved the potent binding affinity of Pd(II)-E with the virulence targets. The Pd(II) complex also disrupted preformed biofilms and down-regulated the expression of QS mediated virulence genes in the biofilms established on implant material (titanium plates). As a whole, the present study showed that the novel thiazolinyl-picolinamide based Pd(II) complexes offer a promising anti-infective strategy to combat biofilm-mediated implant infections.

Gallic Acid Induces Neural Stem Cell Differentiation into Neurons and Proliferation through the MAPK/ERK Pathway

Neural stem cell (NSC) differentiation and proliferation are important biological processes in the cerebral neural network. However, these two abilities of NSCs are limited. Thus, the induction of differentiation and/or proliferation through the administration of plant-derived small-molecule compounds could be used to repair damaged neural networks. The present study reported that gallic acid (GA), an important phenolic acid found in tea, selectively caused NSCs to differentiate into immature neurons and promoted NSC proliferation by activating the mitogen-activated protein kinase/extracellular-regulated kinase (MAPK/ERK) pathway. In addition, it was found that 3,4-dihydroxybenzoic acid was the main active structure exhibiting neurotrophic activity. The substitution of the carboxyl group on the benzene ring with the ester group may promote differentiation based on the structure of 3,4-dihydroxybenzoic acid. Furthermore, the introduction of the 5-hydroxyl group may promote proliferation. The present study identified that GA can promote the differentiation and proliferation of NSCs in vitro and exert pharmacological activity on NSCs.

Regulatory mechanisms of sub-inhibitory levels antibiotics agent in bacterial virulence

Antibiotics play a key role in the prevention and treatment of bacterial diseases for human and animals. The widespread use of antibiotics results in bacterial exposure to the concentrations that are lower than the MIC (that is, sub-inhibitory concentration (sub-MIC)) in the environment, humans, and livestock, which can lead to antibiotic resistance. In this review, we focus on the impact of sub-MIC antibiotics in bacterial virulence. This paper summarized the known relationships between sub-MIC antibiotics in the environment and bacterial virulence. Together, considering the impact of sub-MIC antibiotics and their alternative products in the virulence of bacteria, it is helpful to the rational use of antibiotics and the development of antibiotic alternative products to provide new insights.Key points• Sub-MIC level antibiotics exist in the environment, humans, and livestock.• The review includes mechanisms of sub-MIC antibiotics in bacterial virulence.• New antibacterial strategies and agents are being a new way to weaken virulence. Graphical Abstract.

Computational characterizations of GDP-mannose 4,6-dehydratase (NoeL) Rhizobial proteins

A growing body of evidence suggests that Nod Factors molecules are the critical structural components in nitrogen fixation. These molecules have been implicated in plant-microbe signaling. Many enzymes involved in Nod factors biosynthesis; however, the enzymes that decorate (modify) nod factor main structure play a vital role. Here, the computational analysis of GDP-mannose 4,6-dehydratase (NoeL) proteins with great impact in modification of nod factor structure in four genomes of agriculturally important rhizobia (Bradyrhizobium, Mesorhizobium, Rhizobium, Sinorhizobium) presented. The NoeL number of amino acids was in the range of 147 (M5AMF5) to 372 (A0A023XWX0, Q89TZ1). The molecular weights were around 41 KDa. The results showed that the strain-specific purification strategy should apply as the pI of the sequences varied significantly (in the range of 5.59 to 9.12). The enzyme sequences and eight 3-dimensional structures predicted with homology modeling and machine learning representing the phylogenetic tree revealed the stability of enzymes in different conditions (Instability and Aliphatic index); however, this stability is also strain-specific. Disulphide bonds were observed in some species; however, the pattern was not detected in all members of the same species. Alpha helix was the dominant secondary structure predicted in all cytoplasmic NoeL. All models were homo-tetramer with acceptable sequence identity, GMEAN and coverage (60, - 1.80, 88, respectively). Additionally, Ramachandran maps showed that more than 94% of residues are in favored regions. We also highlight several key characterizations of NoeL from four rhizobia genomes annotation. These findings provide novel insights into the complexity and diversity of NoeL enzymes among important rhizobia and suggest considering a broader framework of biofilm for future research.