Combinatorial approaches with selected phytochemicals to increase antibiotic efficacy against Staphylococcus aureus biofilms

Antibiotic adjuvants against multidrug-resistant Gram-negative bacteria: important component of future antimicrobial therapy

The swift emergence and propagation of multidrug-resistant (MDR) bacterial pathogens constitute a tremendous global health crisis. Among these pathogens, the challenge of antibiotic resistance in Gram-negative bacteria is particularly pressing due to their distinctive structure, such as highly impermeable outer membrane, overexpressed efflux pumps, and mutations. Several strategies have been documented to combat MDR Gram-negative bacteria, including the structural modification of existing antibiotics, the development of antimicrobial adjuvants, and research on novel targets that MDR bacteria are sensitive to. Drugs functioning as adjuvants to mitigate resistance to existing antibiotics may play a pivotal role in future antibacterial therapy strategies. In this review, we provide a brief overview of potential antibacterial adjuvants against Gram-negative bacteria and their mechanisms of action, and discuss the application prospects and potential for bacterial resistance to these adjuvants, along with strategies to reduce this risk.

Staphylococcus aureus and biofilms: transmission, threats, and promising strategies in animal husbandry

Staphylococcus aureus (S. aureus) is a common pathogenic bacterium in animal husbandry that can cause diseases such as mastitis, skin infections, arthritis, and other ailments. The formation of biofilms threatens and exacerbates S. aureus infection by allowing the bacteria to adhere to pathological areas and livestock product surfaces, thus triggering animal health crises and safety issues with livestock products. To solve this problem, in this review, we provide a brief overview of the harm caused by S. aureus and its biofilms on livestock and animal byproducts (meat and dairy products). We also describe the ways in which S. aureus spreads in animals and the threats it poses to the livestock industry. The processes and molecular mechanisms involved in biofilm formation are then explained. Finally, we discuss strategies for the removal and eradication of S. aureus and biofilms in animal husbandry, including the use of antimicrobial peptides, plant extracts, nanoparticles, phages, and antibodies. These strategies to reduce the spread of S. aureus in animal husbandry help maintain livestock health and improve productivity to ensure the ecologically sustainable development of animal husbandry and the safety of livestock products.

Hydrocinnamic acid and perillyl alcohol are effective against Escherichia coli biofilms when used alone and combined with antibiotics

AIMS

The use of phytochemicals to improve the effectiveness of antibiotics is a promising strategy for the development of novel antimicrobials. In this study, the antibiofilm activity of perillyl alcohol and hydrocinnamic acid, both phytochemicals present in several plants, and two antibiotics from different classes (amoxicillin and chloramphenicol) was tested, alone and in combination, against Escherichia coli.

METHODS AND RESULTS

Each molecule was tested at the minimum inhibitory concentration (MIC), 5 × MIC, and 10 × MIC, and characterized concerning biomass removal, metabolic inactivation, and cellular culturability. The highest percentages of metabolic inactivation (88.5% for 10 × MIC) and biomass reduction (61.7% for 10 × MIC) were obtained with amoxicillin. Interestingly, for 5 × MIC and 10 × MIC, phytochemicals provided a total reduction of colony-forming units (CFUs). Dual and triple combinations of phytochemicals and antibiotics (at MIC and 5 × MIC) demonstrated high efficacy in metabolic inactivation, moderate efficacy in terms of biomass reduction, and total reduction of cellular culturability for 5 × MIC.

CONCLUSIONS

The results demonstrated the antibiofilm potential of phytochemicals, highlighting the advantage of phytochemical/antibiotic combinations for biofilm control.

The combinatorial applications of 1,4-naphthoquinone and tryptophan inhibit the biofilm formation of Staphylococcus aureus

Microorganisms embedded within an extracellular polymeric matrix are known as biofilm. The extensive use of antibiotics to overcome the biofilm-linked challenges has led to the emergence of multidrug-resistant strains. Staphylococcus aureus is one such nosocomial pathogen that is known to cause biofilm-linked infections. Thus, novel strategies have been adopted in this study to inhibit the biofilm formation of S. aureus. Two natural compounds, namely, 1,4-naphthoquinone (a quinone derivative) and tryptophan (aromatic amino acid), have been chosen as they could independently show efficient antibiofilm activity. To enhance the antibiofilm potential, the two compounds were combined and tested against the same organism. Several experiments like crystal violet (CV) assay, protein estimation, extracellular polymeric substance (EPS) extraction, and estimation of metabolic activity confirmed that the combination of the two compounds could significantly inhibit the biofilm formation of S. aureus. To comprehend the underlying mechanism, efforts were further directed to understand whether the two compounds could inhibit biofilm formation by compromising the cell surface hydrophobicity of the bacteria. The results revealed that the cell surface hydrophobicity got reduced by ~ 49% when the compounds were applied together. Thus, the combinations could show enhanced antibiofilm activity by attenuating cell surface hydrophobicity. Further studies revealed that the selected concentrations of the compounds could disintegrate (~ 70%) the pre-existing biofilm of the test bacteria without showing any antimicrobial activity. Hence, the combined application of tryptophan and 1,4-naphthoquinone could be used to inhibit the biofilm threats of S. aureus.

Design of Cinnamaldehyde- and Gentamicin-Loaded Double-Layer Corneal Nanofiber Patches with Antibiofilm and Antimicrobial Effects

In this study, two-layer poly(vinyl alcohol)/gelatin (PVA/GEL) nanofiber patches containing cinnamaldehyde (CA) in the first layer and gentamicin (GEN) in the second layer were produced by the electrospinning method. The morphology, chemical structures, and thermal temperatures of the produced pure (PVA/GEL), CA-loaded (PVA/GEL/CA), GEN-loaded (PVA/GEL/GEN), and combined drug-loaded (PVA/GEL/CA/GEN) nanofiber patches were determined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and differential scanning calorimetry, respectively. Their mechanical properties, swelling and degradation behavior, and drug release kinetics were investigated. SEM images showed that both drug-free and drug-loaded nanofiber patches possess smooth and monodisperse structures, and nanofiber size increase occurred as the amount of drug increased. The tensile test results showed that the mechanical strength decreased as the drug was loaded. According to the drug release results, CA release ended at the 96th hour, while GEN release continued until the 264th hour. The antibacterial and antibiofilm activities of PVA/GEL, PVA/GEL/CA, PVA/GEL/GEN, and PVA/GEL/CA/GEN nanofiber patches against Pseudomonas aeruginosa and Staphylococcus aureus were evaluated. Results showed that PVA/GEL/GEN and PVA/GEL/CA/GEN nanofiber patches have excellent antibacterial and antibiofilm activities. Moreover, all materials were biocompatible, with no cytotoxic effects in the mammalian cell model for 8 days. PVA/GEL/GEN nanofiber patches were the most promising material for a high cell survival ratio, which was confirmed by SEM images. This research aims to develop an alternative method to stop and treat the rapid progression of bacterial keratitis.

Inhibition of Erythromycin and Erythromycin-Induced Resistance among Staphylococcus aureus Clinical Isolates

The increasing incidence of erythromycin and erythromycin-induced resistance to clindamycin among Staphylococcus aureus (S. aureus) is a serious problem. Patients infected with inducible resistance phenotypes may fail to respond to clindamycin. This study aimed to identify the prevalence of erythromycin and erythromycin-induced resistance and assess for potential inhibitors. A total of 99 isolates were purified from various clinical sources. Phenotypic detection of macrolide-lincosamide-streptogramin B (MLSB)-resistance phenotypes was performed by D-test. MLSB-resistance genes were identified using PCR. Different compounds were tested for their effects on erythromycin and inducible clindamycin resistance by broth microdilution and checkerboard microdilution methods. The obtained data were evaluated using docking analysis. Ninety-one isolates were S. aureus. The prevalence of constitutive MLSB, inducible MLSB, and macrolide-streptogramin (MS) phenotypes was 39.6%, 14.3%, and 2.2%, respectively. Genes including ermC, ermA, ermB, msrA, msrB, lnuA, and mphC were found in 82.6%, 5.8%, 7.7%, 3.8%, 3.8%, 13.5%, and 3.8% of isolates, respectively. Erythromycin resistance was significantly reduced by doxorubicin, neomycin, and omeprazole. Quinine, ketoprofen, and fosfomycin combated and reversed erythromycin/clindamycin-induced resistance. This study highlighted the significance of managing antibiotic resistance and overcoming clindamycin treatment failure. Doxorubicin, neomycin, omeprazole, quinine, ketoprofen, and fosfomycin could be potential inhibitors of erythromycin and inducible clindamycin resistance.

Insights into antibiofilm mechanisms of phytochemicals: Prospects in the food industry

The recalcitrance of microbial aggregation or biofilm in the food industry underpins the emerging antimicrobial resistance among foodborne pathogens, exacerbating the phenomena of food spoilage, processing and safety management failure, and the prevalence of foodborne illnesses. The challenges of growing tolerance to current chemical and disinfectant-based antibiofilm strategies have driven the urgency in finding a less vulnerable to bacterial resistance, effective alternative antibiofilm agent. To address these issues, various novel strategies are suggested in current days to combat bacterial biofilm. Among the innovative approaches, phytochemicals have already demonstrated their excellent performance in preventing biofilm formation and bactericidal actions against resident bacteria within biofilms. However, the diverse group of phytochemicals and their different modes of action become a barrier to applying them against specific pathogenic biofilm-formers. This phenomenon mandates the need to elucidate the multi-mechanistic actions of phytochemicals to design an effective novel antibiofilm strategy. Therefore, this review critically illustrates the structure - activity relationship, functional sites of actions, and target molecules of diverse phytochemicals regarding multiple major antibiofilm mechanisms and reversal mechanisms of antimicrobial resistance. The implementation of the in-depth knowledge will hopefully aid future studies for developing phytochemical-based next-generation antimicrobials.

Effects of Traditional Chinese Medicine and its Active Ingredients on Drug-Resistant Bacteria

The increasing and widespread application of antibacterial drugs makes antibiotic resistance a prominent and growing concern in clinical practice. The emergence of multidrug-resistant bacteria presents a global threat. However, the development and use of novel antibacterial agents involves time-consuming and costly challenges that may lead to yet further drug resistance. More recently, researchers have turned to traditional Chinese medicine to stem the rise of antibiotic resistance in pathogens. Many studies have shown traditional Chinese medicines to have significant bacteriostatic and bactericidal effects, with the advantage of low drug resistance. Some of which when combined with antibiotics, have also demonstrated antibacterial activity by synergistic effect. Traditional Chinese medicine has a variety of active components, including flavonoids, alkaloids, phenols, and quinones, which can inhibit the growth of drug-resistant bacteria and be used in combination with a variety of antibiotics to treat various drug-resistant bacterial infections. We reviewed the interaction between the active ingredients of traditional Chinese medicines and antibiotic-resistant bacteria. At present, flavonoids and alkaloids are the active ingredients that have been most widely studied, with significant synergistic activity demonstrated when used in combination with antibiotics against drug-resistant bacteria. The reviewed studies show that traditional Chinese medicine and its active ingredients have antimicrobial activity on antibiotic-resistant bacteria, which may enhance the susceptibility of antibiotic-resistant bacteria, potentially reduce the required dosage of antibacterial agents and the rate of drug resistance. Our results provide direction for finding and developing alternative methods to counteract drug-resistant bacteria, offering a new therapeutic strategy for tackling antibiotic resistance.

Chemical Components of Aqueous Extracts of Melia azedarach Fruits and Their Effects on The Transcriptome of Staphylococcus aureus

Staphylococcus aureus is the causative agent of numerous and varied clinical infections. Crude aqueous extracts of Melia azedarach fruits inhibit the planktonic growth and initial biofilm formation of S. aureus in a dose-dependent manner. Moreover, the biofilm topologies became sparse and decreased as the concentration of the aqueous extracts increased. RNA-Seq analyses revealed 532 differentially expressed genes (DEGs) after S. aureus exposure to 0.25 g/ml extracts; 319 of them were upregulated, and 213 were downregulated. The majority of DEGs were categorized into abundant sub-groups in the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Finally, untargeted UHPLC-MS/MS analyses of the aqueous extracts of M. azedarach fruits demonstrated a highly complex profile in positive and negative electrospray ionization modes. The extracts primarily consisted of lipids and lipid-like molecules, organic acids and their derivatives, phenylpropanoids, polyketides, organoheterocyclic compounds, and benzenoids annotated by abundant lipid maps and KEGG pathways. Overall, this study provides evidences that the aqueous extracts of M. azedarach fruits can control S. aureus infections and sought to understand the mode of action of these extracts on S. aureus.

Increasing Antibiotic Susceptibility: The Use of Cationic Gold Nanoparticles in Gram-Negative Bacterial Membrane Models

Antibiotic resistance will be one of the most prominent challenges to health-care systems in the coming decades, with the OECD predicting that up to 2.4 million deaths will be caused between 2015 and 2050 by drug-resistant bacterial infections in first-world countries alone, with infections costing health-care systems billions of dollars each year. Developing new methods to increase bacterial susceptibility toward drugs is an important step in treating resistant infections. Here, the synergistic effects of gold nanoparticles and the antibiotic drug colistin sulfate have been examined. A tethered lipid bilayer membrane was used to mimic a Gram-negative bacterial cell membrane. Exposing the membrane to gold nanoparticles prior to adding the antibiotic significantly increased the effect of the antibiotic on the membrane. Cationic gold nanoparticles could thus be used to enhance bacterial susceptibility to antibiotics, leading to a more potent treatment.

Biofilm Formation of Multidrug-Resistant MRSA Strains Isolated from Different Types of Human Infections

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main pathogens causing chronic infections, mainly due to its capacity to form biofilms. However, the mechanisms underlying the biofilm formation of MRSA strains from different types of human infections are not fully understood. MRSA strains isolated from distinct human infections were characterized aiming to determine their biofilm-forming capacity, the biofilm resistance to conventional antibiotics and the prevalence of biofilm-related genes, including, icaA, icaB, icaC, icaD, fnbA, fnbB, clfA, clfB, cna, eno, ebpS, fib and bbp. Eighty-three clinical MRSA strains recovered from bacteremia episodes, osteomyelitis and diabetic foot ulcers were used. The biofilm-forming capacity was evaluated by the microtiter biofilm assay and the biofilm structure was analyzed via confocal scanning laser microscopy. The antimicrobial susceptibility of 24-h-old biofilms was assessed against three antibiotics and the biomass reduction was measured. The metabolic activity of biofilms was evaluated by the XTT assay. The presence of biofilm-related genes was investigated by whole-genome sequencing and by PCR. Despite different intensities, all strains showed the capacity to form biofilms. Most strains had also a large number of biofilm-related genes. However, strains isolated from osteomyelitis showed a lower capacity to form biofilms and also a lower prevalence of biofilm-associated genes. There was a significant reduction in the biofilm biomass of some strains tested against antibiotics. Our results provide important information on the biofilm-forming capacity of clinical MRSA strains, which may be essential to understand the influence of different types of infections on biofilm production and chronic infections.

Inhibition of biofilm formation and quorum sensing mediated virulence in Pseudomonas aeruginosa by marine sponge symbiont Brevibacterium casei strain Alu 1

The alternative antimicrobial strategies that mitigate the threat of antibiotic resistance is the quorum-sensing inhibition (QSI) mechanism, which targets autoinducer dependent virulence gene expression in bacterial pathogens. N-acyl homoserine lactone (AHL) acts as a key regulator in the production of virulence factors and biofilm formation in Pseudomonas aeruginosa PAO1 and violacein pigment production in Chromobacterium violaceum ATCC 12472. In the present study, the marine sponge Haliclona fibulata symbiont Brevibacterium casei strain Alu 1 showed potential QSI activity in a concentration-dependent manner (0.5-2% v/v) against the N-acyl homoserine lactone (AHL)-mediated violacein production in C. violaceum (75-95%), and biofilm formation (53-96%), protease (27-82%), pyocyanin (82-95%) and pyoverdin (29-38%) productions in P. aeruginosa. Further, the microscopic analyses validated the antibiofilm activity of the cell-free culture supernatant (CFCS) of B. casei against P. aeruginosa. Subsequently, the biofilm and pyoverdin inhibitory efficacy of the ethyl acetate extract of B. casei CFCS was assessed against P. aeruginosa. Further, the gas chromatography-mass spectrometry (GC-MS) analysis revealed the presence of variety of components in which diethyl phthalate was found to be a major active component. This phthalate ester, known as diethyl ester of phthalic acid, could act as a potential therapeutic agent for preventing bacterial biofilm and virulence associated infectious diseases.

Current Trends in Experimental and Computational Approaches to Combat Antimicrobial Resistance

A multitude of factors, such as drug misuse, lack of strong regulatory measures, improper sewage disposal, and low-quality medicine and medications, have been attributed to the emergence of drug resistant microbes. The emergence and outbreaks of multidrug resistance to last-line antibiotics has become quite common. This is further fueled by the slow rate of drug development and the lack of effective resistome surveillance systems. In this review, we provide insights into the recent advances made in computational approaches for the surveillance of antibiotic resistomes, as well as experimental formulation of combinatorial drugs. We explore the multiple roles of antibiotics in nature and the current status of combinatorial and adjuvant-based antibiotic treatments with nanoparticles, phytochemical, and other non-antibiotics based on synergetic effects. Furthermore, advancements in machine learning algorithms could also be applied to combat the spread of antibiotic resistance. Development of resistance to new antibiotics is quite rapid. Hence, we review the recent literature on discoveries of novel antibiotic resistant genes though shotgun and expression-based metagenomics. To decelerate the spread of antibiotic resistant genes, surveillance of the resistome is of utmost importance. Therefore, we discuss integrative applications of whole-genome sequencing and metagenomics together with machine learning models as a means for state-of-the-art surveillance of the antibiotic resistome. We further explore the interactions and negative effects between antibiotics and microbiomes upon drug administration.

Demonstration of bactericidal and synergistic activity of quercetin with meropenem among pathogenic carbapenem resistant Escherichia coli and Klebsiella pneumoniae

Rapid dissemination of carbapenem resistant Enterobacteriaceae (CRE) is considered to be a global issue. Quercetin is a well known antimicrobial agent. Hence, it would be important to investigate bactericidal and synergistic interaction of quercetin with meropenem and elucidate effects of quercetin alone and quercetin-meropenem combination on bla_NDM, bla_VIM,acrB, ompC, ompF, ompk35 and ompk36 expressions, cellular morphology and cell-wall/membrane integrity. MIC, Time-kill and Baclight assays were performed to determine antibacterial/bactericidal activity of quercetin. Synergism with meropenem was evaluated by checkerboard assay followed by dose-response, isobologram analysis and FIC index, combination index calculation. Effects of meropenem, quercetin and their combinations on bla_NDM, bla_VIM,acrB, ompC, ompF, ompk35 and ompk36 expressions were evaluated by qRT-PCR. SEM was performed to evaluate effects of aforesaid combinations on cellular morphology. Quercetin alone exhibited at least four-fold reduced MIC value (16-256 μg/mL) than that of meropenem against CRE. It exhibited synergism with meropenem against 89.25% CRE. Again, only 128 μg/mL quercetin killed upto 99.95% bacteria within 4-6 h of dosing, which increased further to 99.99% in MIC combination of meropenem-quercetin. Thus, effective bactericidal activity of quercetin-meropenem combination might have been achieved through alteration of bla_VIM, ompC expression and cellular morphology of bacteria. Quercetin exhibited bactericidal and synergistic activity with meropenem.

Biocide Potentiation Using Cinnamic Phytochemicals and Derivatives

Surface disinfection is of utmost importance in the prevention of bacterial infections. This study aims to assess the ability of ten phytochemicals and related derivatives as potentiators of two commonly used biocides-cetyltrimethylammonium bromide (CTAB) and lactic acid (LA). LA in combination with cinnamic, hydrocinnamic, α-methylcinnamic, and α-fluorocinnamic acids had a factional inhibitory concentration index (FICI) ≤ 1 for Escherichia coli and Staphylococcus aureus. Several phytochemicals/derivatives in combination with biocides improved the biocidal efficacy against early sessile bacteria. The most effective combination was LA with allyl cinnamate (2.98 ± 0.76 log CFU.cm^-2 reduction) against E. coli. The combination with CTAB was successful for most phytochemicals/derivatives with a maximum bactericidal efficacy against sessile E. coli when combined with allyl cinnamate (2.20 ± 0.07 log CFU.cm^-2 reduction) and for S. aureus when combined with α-methylcinnamic acid (1.68 ± 0.30 log CFU.cm^-2 reduction). This study highlights the potential of phytochemicals and their derivatives to be used in biocide formulations.

Reserpine attenuates biofilm formation and virulence of Staphylococcus aureus

This study investigated the effects of reserpine, the main bioactive compound of Rauwolfia serpentina, on biofilm formation and biofilm-associated virulence factors production in a Gram-positive pathogen, Staphylococcus aureus. Crystal violet assay, MTT assay, Congo red binding, CLSM studies were performed to assess the antibiofilm activity. Molecular docking was performed to explain the possible mode of action, catheter model was used to evaluate its application potential and the combinatorial study was performed in search of an improved therapeutic formulation. Reserpine affected biofilm formation, EPS production, biofilm cell viability and virulence factor production. It could eradicate 72.7% biofilm at ½ × MIC dose and could also stop the metabolic activity of 50.6% bacterial cells in a biofilm. Staphylococcus aureus biofilm- and virulence-regulatory proteins like AgrA, AtlE, Bap, IcaA, SarA and SasG were found to interact with reserpine which might lead to the attenuation of its pathogenicity. Reserpine along with other commercial antibiotics could generate a hightened antibiofilm response, and also eradicated a good percentage of bacterial biofilm from a urinary catheter model. These findings suggested reserpine as a good alternative entity to generate new improved therapeutic formulations.

Antimicrobial Activity of Cinnamaldehyde on Streptococcus mutans Biofilms

Streptococcus mutans is considered the most relevant bacteria in the transition of non-pathogenic commensal oral microbiota to biofilms which contribute to the dental caries process. The present study aimed to evaluate the antimicrobial activity of a natural plant product, cinnamaldehyde against S. mutans biofilms. Minimum inhibitory concentrations (MIC), minimal bactericidal concentration (MBC), and growth curves were determined to assess its antimicrobial effect against planktonic S. mutans. The biofilm biomass and metabolism with different concentrations of cinnamaldehyde and different incubation time points were assessed using the crystal violet and MTT assays. The biofilms were visualized using confocal laser scanning microscopy (CLSM). Bacterial cell surface hydrophobicity, aggregation, acid production, and acid tolerance were evaluated after cinnamaldehyde treatment. The gene expression of virulence-related factors (gtfB, gtfC, gtfD, gbpB, comDE, vicR, ciaH, ldh and relA) was investigated by real-time PCR. The MIC and MBC of cinnamaldehyde against planktonic S. mutans were 1000 and 2000 μg/mL, respectively. The results showed that cinnamaldehyde can decrease biofilm biomass and metabolism at sub-MIC concentrations. CLSM images revealed that the biofilm-covered surface areas decreased with increasing concentrations of cinnamaldehyde. Cinnamaldehyde increased cell surface hydrophobicity, reduced S. mutans aggregation, inhibited acid production, and acid tolerance. Genes expressions in the biofilms were down-regulated in the presence of cinnamaldehyde. Therefore, our data demonstrated that cinnamaldehyde at sub-MIC level suppressed the microbial activity on S. mutans biofilm by modulating hydrophobicity, aggregation, acid production, acid tolerance, and virulence gene expression.

Mechanisms of Bacterial Tolerance and Persistence in the Gastrointestinal and Respiratory Environments

Pathogens that infect the gastrointestinal and respiratory tracts are subjected to intense pressure due to the environmental conditions of the surroundings. This pressure has led to the development of mechanisms of bacterial tolerance or persistence which enable microorganisms to survive in these locations. In this review, we analyze the general stress response (RpoS mediated), reactive oxygen species (ROS) tolerance, energy metabolism, drug efflux pumps, SOS response, quorum sensing (QS) bacterial communication, (p)ppGpp signaling, and toxin-antitoxin (TA) systems of pathogens, such as Escherichia coli, Salmonella spp., Vibrio spp., Helicobacter spp., Campylobacter jejuni, Enterococcus spp., Shigella spp., Yersinia spp., and Clostridium difficile, all of which inhabit the gastrointestinal tract. The following respiratory tract pathogens are also considered: Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Burkholderia cenocepacia, and Mycobacterium tuberculosis Knowledge of the molecular mechanisms regulating the bacterial tolerance and persistence phenotypes is essential in the fight against multiresistant pathogens, as it will enable the identification of new targets for developing innovative anti-infective treatments.

Cytotoxicity and antimicrobial action of selected phytochemicals against planktonic and sessile Streptococcus mutans

Background

Dental caries remains the most prevalent and costly oral infectious disease worldwide, encouraging the search for new and more effective antimicrobials. Therefore, the aim of this work was to study the antimicrobial action of selected phytochemicals (eugenol, citronellol, sabinene hydrate, trans-cinnamaldehyde, terpineol and cinnamic acid) against Streptococcus mutans in planktonic and biofilm states as well as the cytotoxicity of these compounds.

Methods

The antibacterial activity of the selected compounds was evaluated by the determination of the minimal bactericidal concentration. The resazurin assay was used to assess the metabolic activity of sessile S. mutans. The cytotoxicity was determined using a fibroblast cell line.

Results

Among the tested phytochemicals, citronellol, cinnamic acid and trans-cinnamaldehyde were the most effective against both planktonic and sessile S. mutans, an effect apparently related to their hydrophobic character. Additionally, these three compounds did not compromise fibroblasts cell viability.

Discussion

Citronellol, cinnamic acid and trans-cinnamaldehyde demonstrated significant antimicrobial activity and low cytotoxicity proposing their potential as a novel group of therapeutic compounds to control oral infectious diseases. Moreover, their effects are particularly relevant when benchmarked against eugenol, a phytochemical commonly used for prosthodontic applications in dentistry.

Effect of reserpine on Pseudomonas aeruginosa quorum sensing mediated virulence factors and biofilm formation

This study aimed to evaluate the effect of reserpine, a plant-derived indole-alkaloid, against Pseudomonas aeruginosa PAO1 biofilms. The anti-biofilm activity of reserpine was evaluated by crystal violet staining, MTT assay, confocal laser scanning microscopy and scanning electron microscopy. Reserpine effects were also assessed by qRT-PCR of quorum sensing (QS)-regulated genes and biochemical quantification of the QS-mediated virulence factors pyocyanin, rhamnolipids, proteases and elastases. Reserpine reduced biofilm formation, cell motility, virulence factor production, and QS-controlled gene expression. Additionally, molecular docking analysis for AHL synthase LasI and QS transcriptional regulators LasR/MvfR revealed a plausible molecular mechanisms of reserpine QS inhibition. These findings provide insights into the underlying mode of action of reserpine, which may be useful in the development of new drugs against biofilm-related infections.