Antibiofilm potential of synthetic 2-amino-5-chlorobenzophenone Schiff bases and its confirmation through fluorescence microscopy

Chemical composition, cytotoxicity, antimicrobial, antibiofilm, and anti-quorum sensing potential of Mentha Piperita essential oil against the oral pathogen Streptococcus mutans

Dental caries is a highly prevalent oral disease affecting billions of individuals globally. The disease occurs chemically as a result of breakdown of the tooth surface attributed to metabolic activity in colonizing biofilm. Biofilms, composed of exopolysaccharides and proteins, protect bacteria like Streptococcus mutans, which is notable for its role in tooth decay due to its acid-producing abilities. While various antimicrobial agents may prevent biofilm formation, these drugs often produce side effects including enamel erosion and taste disturbances. This study aimed to examine utilization of the Mentha piperita essential oil as a potential antibiofilm activity agent against S. mutans. M. piperita oil significantly (1) reduced bacterial biofilm, (2) exhibited a synergistic effect when combined with chlorhexidine, and (3) did not induce cell toxicity. Chemical analysis identified the essential oil with 99.99% certainty, revealing menthol and menthone as the primary components, constituting approximately 42% and 26%, respectively. Further, M. piperita oil eradicated preformed biofilms and inhibited biofilm formation at sub-inhibitory concentrations. M. piperita oil also interfered with bacterial quorum sensing communication and did not produce any apparent cell toxicity in immortalized human keratinocytes (HaCaT). M. piperita represented an alternative substance for combating S. mutans and biofilm formation and a potential combination option with chlorhexidine to minimize side effects. An in-situ performance assessment requires further studies.

Decoding antimicrobial resistance: unraveling molecular mechanisms and targeted strategies

Antimicrobial resistance poses a significant global health threat, necessitating innovative approaches for combatting it. This review explores various mechanisms of antimicrobial resistance observed in various strains of bacteria. We examine various strategies, including antimicrobial peptides (AMPs), novel antimicrobial materials, drug delivery systems, vaccines, antibody therapies, and non-traditional antibiotic treatments. Through a comprehensive literature review, the efficacy and challenges of these strategies are evaluated. Findings reveal the potential of AMPs in combating resistance due to their unique mechanisms and lower propensity for resistance development. Additionally, novel drug delivery systems, such as nanoparticles, show promise in enhancing antibiotic efficacy and overcoming resistance mechanisms. Vaccines and antibody therapies offer preventive measures, although challenges exist in their development. Non-traditional antibiotic treatments, including CRISPR-Cas systems, present alternative approaches to combat resistance. Overall, this review underscores the importance of multifaceted strategies and coordinated global efforts to address antimicrobial resistance effectively.

Combating Cariogenic Streptococcus mutans Biofilm Formation and Disruption with Coumaric Acid on Dentin Surface

Streptococcus mutans, the primary cause of dental caries, relies on its ability to create and sustain a biofilm (dental plaque) for survival and pathogenicity in the oral cavity. This study was focused on the antimicrobial biofilm formation control and biofilm dispersal potential of Coumaric acid (CA) against Streptococcus mutans on the dentin surface. The biofilm was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) viability assay, microtiter plate assay, production of extracellular polymeric substances (EPSs), florescence microscopy (surface coverage and biomass μm2) and three-dimensional (3D) surface plots. It was observed that CA at 0.01 mg/mL reduced bacterial growth by 5.51%, whereases at 1 mg/mL, a significant (p < 0.05) reduction (98.37%) was observed. However, at 1 mg/mL of CA, a 95.48% biofilm formation reduction was achieved, while a 73.45% biofilm dispersal (after 24 h. treatment) was achieved against the preformed biofilm. The MTT assay showed that at 1 mg/mL of CA, the viability of bacteria in the biofilm was markedly (p < 0.05) reduced to 73.44%. Moreover, polysaccharide (EPS) was reduced to 24.80 μg/mL and protein (EPS) to 41.47 μg/mL. ImageJ software (version 1.54 g) was used to process florescence images, and it was observed that the biofilm mass was reduced to 213 (μm2); the surface coverage was reduced to 0.079%. Furthermore, the 3D surface plots showed that the untreated biofilm was highly dense, with more fibril-like projections. Additionally, molecular docking predicted a possible interaction pattern of CA (ligand) with the receptor Competence Stimulating Peptide (UA159sp, PDB ID: 2I2J). Our findings suggest that CA has antibacterial and biofilm control efficacy against S. mutans associated with dental plaque under tested conditions.

Small Schiff Base Molecules-A Possible Strategy to Combat Biofilm-Related Infections

Microorganisms participating in the development of biofilms exhibit heightened resistance to antibiotic treatment, therefore infections involving biofilms have become a problem in recent years as they are more difficult to treat. Consequently, research efforts are directed towards identifying novel molecules that not only possess antimicrobial properties but also demonstrate efficacy against biofilms. While numerous investigations have focused on antimicrobial capabilities of Schiff bases, their potential as antibiofilm agents remains largely unexplored. Thus, the objective of this article is to present a comprehensive overview of the existing scientific literature pertaining to small molecules categorized as Schiff bases with antibiofilm properties. The survey involved querying four databases (Web of Science, ScienceDirect, Scopus and Reaxys). Relevant articles published in the last 10 years were selected and categorized based on the molecular structure into two groups: classical Schiff bases and oximes and hydrazones. Despite the majority of studies indicating a moderate antibiofilm potential of Schiff bases, certain compounds exhibited a noteworthy effect, underscoring the significance of considering this type of molecular modeling when seeking to develop new molecules with antibiofilm effects.

Effect of chemical modifications of tannins on their antimicrobial and antibiofilm effect against Gram-negative and Gram-positive bacteria

Background

Tannins have demonstrated antibacterial and antibiofilm activity, but there are still unknown aspects on how the chemical properties of tannins affect their biological properties. We are interested in understanding how to modulate the antibiofilm activity of tannins and in delineating the relationship between chemical determinants and antibiofilm activity.

Materials and methods

The effect of five different naturally acquired tannins and their chemical derivatives on biofilm formation and planktonic growth of Salmonella Typhimurium, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus was determined in the Calgary biofilm device.

Results

Most of the unmodified tannins exhibited specific antibiofilm activity against the assayed bacteria. The chemical modifications were found to alter the antibiofilm activity level and spectrum of the tannins. A positive charge introduced by derivatization with higher amounts of ammonium groups shifted the anti-biofilm spectrum toward Gram-negative bacteria, and derivatization with lower amounts of ammonium groups and acidifying derivatization shifted the spectrum toward Gram-positive bacteria. Furthermore, the quantity of phenolic OH-groups per molecule was found to have a weak impact on the anti-biofilm activity of the tannins.

Conclusion

We were able to modulate the antibiofilm activity of several tannins by specific chemical modifications, providing a first approach for fine tuning of their activity and antibacterial spectrum.

Enoxacin-based derivatives: antimicrobial and antibiofilm agent: a biology-oriented drug synthesis (BIODS) approach

Background: To find alternative molecules against Klebsiella pneumonia, Proteus mirabilis and methicillin-resistant Staphylococcus aureus, new enoxacin derivatives were synthesized and screened. Methods: All derivatives exhibited promising antibacterial activities as compared to standard enoxacin (2 μg/ml) and standard cefixime (82 μg/ml). Compounds 2, 3 and 5 significantly downregulated the gene expression of biofilm-forming genes. Conclusion: Based on our results, these molecules may serve as potential drug candidates to cure several bacterial infections in the future.

Virtual Screening, Synthesis and Biological Evaluation of Streptococcus mutans Mediated Biofilm Inhibitors

Dental caries, a global oral health concern, is a biofilm-mediated disease. Streptococcus mutans, the most prevalent oral microbiota, produces extracellular enzymes, including glycosyltransferases responsible for sucrose polymerization. In bacterial communities, the biofilm matrix confers resistance to host immune responses and antibiotics. Thus, in cases of chronic dental caries, inhibiting bacterial biofilm assembly should prevent demineralization of tooth enamel, thereby preventing tooth decay. A high throughput screening was performed in the present study to identify small molecule inhibitors of S. mutans glycosyltransferases. Multiple pharmacophore models were developed, validated with multiple datasets, and used for virtual screening against large chemical databases. Over 3000 drug-like hits were obtained that were analyzed to explore their binding mode. Finally, six compounds that showed good binding affinities were further analyzed for ADME (absorption, distribution, metabolism, and excretion) properties. The obtained in silico hits were evaluated for in vitro biofilm formation. The compounds displayed excellent antibiofilm activities with minimum inhibitory concentration (MIC) values of 15.26–250 µg/mL.

Serum Stable and Low Hemolytic Temporin-SHa Peptide Analogs Disrupt Cell Membrane of Methicillin-Resistant Staphylococcus aureus (MRSA)

Anti-microbial peptides (AMPs) have attracted major attention due to their potential bio-activities against some multidrug resistant pathogens. The present study evaluated the mechanism of actions of highly potent AMP temporin-SHa analogs, i.e., [G4a]-SHa, [G7a]-SHa, and [G10a]-SHa, against methicillin-resistant Staphylococcus aureus (MRSA) NCTC (13277) with minimum inhibitory concentrations (MICs) of 14.35, 7.16, and 3.58 µM, respectively. These analogs exhibited significant anti-MRSA activity at physiological salt concentration, 30% fetal bovine serum, and 30% human serum. [G4a]-SHa and [G7a]-SHa were non-hemolytic and non-cytotoxic to normal mouse fibroblast 3T3 cell and human Caco-2 cell line. Atomic force microscopy revealed that these analogs have profound effect on the morphological changes in MRSA surface with significant leakage of cell cytoplasmic content. Propidium iodide uptake kinetic assay and (bis-(1,3-dibutylbarbituric acid) trimethine oxonol) DiBAC₄(3) membrane depolarization assay demonstrated that these analogs display a membrane disrupting property, characterized by elevation of plasma membrane permeability and rapid transmembrane potential depolarization. [G10a]-SHa showed a significant anti-biofilm activity against biofilm forming S. aureus (ATCC 6538). Acute in vivo toxicity studies revealed that [G10a]-SHa possesses some toxic effect at 100-mg/kg dose. While [G4a]-SHa at 100 mg/kg, i.p. has no toxic effect even after 48 h, [G7a]-SHa also did not show any toxic effect at the dose of 100 mg/kg, i.p. during 24-h observation of animals. In conclusion, [G4a]-SHa, [G7a]-SHa, and [G10a]-SHa show improved activity against MRSA and stability compared to SHa peptide. Although highly potent, [G10a]-SHa, due to its hemolytic activity, might be more suitable for topical application, whereas [G4a]-SHa and [G7a]-SHa have potential to be used for systemic application.

Combating Biofilm by Targeting Its Formation and Dispersal Using Gallic Acid against Single and Multispecies Bacteria Causing Dental Plaque

Exploring biological agents to control biofilm is a vital alternative in combating pathogenic bacteria that cause dental plaque. This study was focused on antimicrobial, biofilm formation and biofilm dispersal efficacy of Gallic acid (GA) against bacteria, including Proteus spp., Escherichia coli, Pseudomonas spp., Salmonella spp., Streptococcus mutans, and Staphylococcus aureus and multispecies bacteria. Biofilm was qualitatively and quantitatively assessed by crystal violet assay, florescence microscopy (bacterial biomass (µm²), surface coverage (%)) and extracellular polymeric substances (EPS). It was exhibited that GA (1-200 mg/L) can reduce bacterial growth. However, higher concentrations (100-200 mg/L) markedly reduced (86%) bacterial growth and biofilm formation (85.5%), while GA did not exhibit any substantial dispersal effects on pre-formed biofilm. Further, GA (20-200 mg/L) exhibited 93.43% biomass reduction and 88.6% (p < 0.05) EPS (polysaccharide) reduction. Microscopic images were processed with BioImageL software. It was revealed that biomass surface coverage was reduced to 2% at 200 mg/L of GA and that 13,612 (µm²) biomass was present for control, while it was reduced to 894 (µm²) at 200 mg/L of GA. Thus, this data suggest that GA have antimicrobial and biofilm control potential against single and multispecies bacteria causing dental plaque.

Bacterial virulence factors: a target for heterocyclic compounds to combat bacterial resistance

Antibiotic resistance is one of the most important challenges of the 21st century. However, the growing understanding of bacterial pathogenesis and cell-to-cell communication has revealed many potential strategies for the discovery of drugs that can be used for the treatment of bacterial infections. Interfering with bacterial virulence and/or quorum sensing could be a particularly interesting approach, because it is believed to exert less selective pressure on the bacterial resistance than with traditional strategies, geared toward killing bacteria or preventing their growth. Here, we discuss the mechanism of bacterial virulence, presenting promising strategies and recently synthesized heterocyclic compounds to combat future bacterial infections.

Synthesis of new chrysin derivatives with substantial antibiofilm activity

Multidrug resistance mechanism of microorganisms towards conventional antimicrobials nowadays faces a common health problem. So, searching and development of new antibacterials are in the frontier areas of biochemistry. Functionalizations of various natural products or synthesis of compounds through molecular modeling followed by virtual screening are the ways to obtain potential leads. Chrysin is one of the plant secondary metabolites and is ubiquitously present in majority of plants. It has multi-dimensional potentiality however, with a very low bioavailability causing a very low efficacy. Very few chrysin derivatives possessing antimicrobial activity with a low anti-biofilm efficacy have been found in the literature. Thus, it has been attempted to synthesize a series of new chrysin derivatives (CDs). In this study, twenty-two new derivatives have been synthesized via its 7-OH modulation and antibiofilm activity was evaluated against a model bacterium viz. Escherichia coli MTCC 40 (Gram negative). Eleven CDs coded as 2a, 2b, 2c, 2e, 2f, 2g, 2h, 2i, 3j, 3k and 3l have been found more potent compared to chrysin (precursor of CDs) against planktonic form of E. coli. Biofilm inhibition studies indicated a noteworthy results for 2a (93.57%), 2b (92.14%), 2f (92.14%) and 3l (93.57%) compared to chrysin (33.57%). E. coli motility was also highly restricted by 2a, 2b, 2f and 3l than chrysin at their sub-inhibitory concentrations. Solubility studies indicated an extended-release of 2a, 2b, 2f and 3l in physiological systems. Relatively higher bioavailability of 2a, 2b, 2f and 3l than chrysin was revealed from the dissolution experiments and was further validated through in silico ADME-based SAR analysis. Hence, this study is more interesting in regard to antibacterial potentiality of chrysin derivatives against Escherichia coli MTCC 40 (Gram negative). Thus, this article might be useful for further design and development of new leads in the context of biofilm-associated bacterial infections.

CPF-C1 analog with effective antimicrobial and antibiofilm activities against Staphylococcus aureus including MRSA

The evolution of Staphylococcus aureus (S. aureus) with the ability to acquire and develop resistance to antibiotics has been described as a distinct strain emergence event. Methicillin-resistant S. aureus (MRSA) is responsible for most global S. aureus bacteremia cases. Bacterial biofilms are one of the primary reasons for drug resistance. Biofilms formed by S. aureus are the most common cause of biofilm-associated infections, which increase the difficulty of treatment. Antimicrobial peptides (AMPs) represent promising candidates for the future treatment of antibiotic-resistant bacterial and biofilm-associated infections. In this study, we designed and synthesized a series of analogs to increase the druggability of the natural antimicrobial peptide CPF-C1. Among the analogs, CPF-2 showed high antimicrobial activity against MRSA and multidrug-resistant S. aureus isolated from clinics. In the serum and physiological salt environment, CPF-2 also exhibited effective antimicrobial activity. Importantly, CPF-2 did not determine resistance and showed no hemolytic activity at the active concentration. Concerning the mechanism of action, CPF-2 produced a rapid bactericidal effect by interrupting the bacterial membranes. Even more surprisingly, CPF-2 showed an excellent ability to prevent and eradicate biofilms caused by S. aureus and MRSA not only in vitro but also in vivo. Our results suggested that CPF-2 has potential as a lead compound to treat infections caused by S. aureus and MRSA, including the associated biofilms.

N-Benzylanilines as Fatty Acid Synthesis Inhibitors against Biofilm-related Methicillin-resistant Staphylococcus aureus

Bacterial fatty acid synthase system is a well validated target for the development of novel antimicrobial agents. This study reports the synthesis of Schiff bases and their reductive N-benzylanilines. Most N-benzylanilines were active against Gram-positive bacteria, among which compound 4k performed best against both S. aureus and MRSA with the MIC value at 0.5 mg/L. Moreover, we identified the strong antibacterial activity for compound 4k against 19 clinical MRSA strains isolated from different specimen, which indicated its potential in clinical application. In vitro biofilm inhibition and microscopy assay revealed compound 4k inhibits biofilm formation and eradicates preformed biofilm effectively. The size-exclusion chromatography and docking study indicated that compound 4k mimics the binding mode of triclosan with saFabI. The efficiency of the protein-inhibitor interaction was evaluated by measuring NADPH reduction using trans-2-octenoyl-CoA as substrate. Overall, our data demonstrate that N-benzylaniline is a promising scaffold for anti-staphylococcal drug development.

Mentha piperita essential oils loaded in a chitosan nanogel with inhibitory effect on biofilm formation against S. mutans on the dental surface

Mentha piperita essential oils (MPEO) were loaded into chitosan nanogel to use as antibiofilm agent against Streptococcus mutans and to protect its dental plaque. Chitosan nanoparticles (CsNPs) were prepared by sol-gel method using linking bridge of tripolyphosphate (TPP). Physiological properties of MPEO-CNs were assessed by FTIR, SEM/EDX, DLS and zeta potential. Release kinetics, MIC and MBC were determined for MPEO-CNs. Expression of biofilm-associated genes including 8 genes: grfB, C and D, brpA, spaP, gbpB, relA and vicR was investigated at the presence of sub-MIC of MPEO-CNs. Most abundant bioactive compounds of MPEO were l-menthol (45.05%) and l-menthal (17.53%). SEM/EDX exhibited successful entrapment of MPEO into CsNPs followed by the changes in abundance of elemental peaks. A signal at 1737 cm^-1 on chitosan spectrum was attributed to the carboxylic (CO) groups overlapped by MPEO incorporation. A new signal at 2361 cm^-1 was assigned to electrostatic interactions of amine groups in chitosan with phosphoric units of TPP within the MPEO-chitosan. MPEO incorporation into porous nanogel decreased monodispersity of the nanoparticles and then raises z-average. Maximum release of MPEO was about 50% during 360 h in a hydroalcoholic solvent at ambient temperature. The adherence of bacterial cells showed high sensitivity to the nanoformulation of MPEO compared with unloaded chitosan-nanogel. Antibiofilm inhibition of S. mutans occurred in 50 and 400 μg/mL for MPEO-CNs and unloaded-nanogel, respectively. Among biofilm synthesis genes, gtfB, gtfC, gtfD were slightly affected by MPEO-CNs treatment, while gbpB, spaP, brpA, relA, and vicR genes underwent significant down-regulation in the presence of both unloaded-nanogel and MPEO-loaded-nanogel. This study demonstrated that the MPEO-CNs promised an efficient nanoformulation with the greatest inhibitory action against some glycosyltransferase genes (gtfB, C and D) as important enzymes involved in extracellular polymers. Finally, the results concluded that MPEO-CNs have a potential use as antibiofilm agent in toothpaste or mouth washing formulations.

Schiff bases of tryptamine as potent inhibitors of nucleoside triphosphate diphosphohydrolases (NTPDases): Structure-activity relationship

Overexpression of NTPDases leads to a number of pathological situations such as thrombosis, and cancer. Thus, effective inhibitors are required to combat these pathological situations. Different classes of NTPDase inhibitors are reported so far including nucleotides and their derivatives, sulfonated dyes such as reactive blue 2, suramin and its derivatives, and polyoxomatalates (POMs). Suramin is a well-known and potent NTPDase inhibitor, nonetheless, a range of side effects are also associated with it. Reactive blue 2 also had non-specific side effects that become apparent at high concentrations. In addition, most of the NTPDase inhibitors are high molecular weight compounds, always required tedious chemical steps to synthesize. Hence, there is still need to explore novel, low molecular weight, easy to synthesize, and potent NTPDase inhibitors. Keeping in mind the known NTPDase inhibitors with imine functionality and nitrogen heterocycles, Schiff bases of tryptamine, 1-26, were synthesized and characterized by spectroscopic techniques such as EI-MS, HREI-MS, ¹H-, and ¹³C NMR. All the synthetic compounds were evaluated for the inhibitory avidity against activities of three major isoforms of NTPDases: NTPDase-1, NTPDase-3, and NTPDase-8. Cumulatively, eighteen compounds were found to show potent inhibition (Ki = 0.0200-0.350 μM) of NTPDase-1, twelve (Ki = 0.071-1.060 μM) of NTPDase-3, and fifteen compounds inhibited (Ki = 0.0700-4.03 μM) NTPDase-8 activity. As a comparison, the Kis of the standard inhibitor suramin were 1.260 ± 0.007, 6.39 ± 0.89 and 1.180 ± 0.002 μM, respectively. Kinetic studies were performed on lead compounds (6, 5, and 21) with human (h-) NTPDase-1, -3, and -8, and Lineweaver-Burk plot analysis showed that they were all competitive inhibitors. In silico study was conducted on compound 6 that showed the highest level of inhibition of NTPDase-1 to understand the binding mode in the active site of the enzyme.