Antibiofilm and anti-quorum sensing activities of eugenol and linalool from Ocimum tenuiflorum against Pseudomonas aeruginosa biofilm

Critical review on plant-derived quorum sensing signaling inhibitors in pseudomonas aeruginosa

Pseudomonas aeruginosa, a biofilm-forming organism with complex quorum mechanisms (Las, Rhl, PQS, and IQS), poses an imminent danger to the healthcare sector and renders current treatment options for chemotherapy ineffectual. The pathogen's diverse pathogenicity, antibiotic resistance, and biofilms make it difficult to eradicate it effectively. Quorum sensing, a complex system reliant on cell density, controls P. aeruginosa's pathogenesis. Quorum-sensing genes are key components of P. aeruginosa's pathogenic arsenal, and their expression determines how severe the spread of infection becomes. Over the past ten years, there has been a noticeable increase in the quest for and development of new antimicrobial medications. Quorum sensing may be an effective treatment for infections triggered by bacteria. Introducing quorum-sensing inhibitors as an anti-virulent strategy might be an intriguing therapeutic method that can be effectively employed along with current medications. Amongst the several speculated processes, a unique anti-virulence strategy using anti-quorum sensing and antibiofilm medications for targeting pseudomonal infestations seems to be at the forefront. Due to their noteworthy quorum quenching capabilities, biologically active phytochemicals have become more well-known in the realm of science in this context. Recent research showed how different phytochemical quorum quenching actions affect P. aeruginosa's QS-dependent pathogenicity. This review focuses on the most current data supporting the implementation of plant bio-actives to treat P.aeruginosa-associated diseases, as well as the benefits and future recommendationsof employing them in anti-virulence therapies as a supplementary drug development approach towards conventional antibiotic approaches.

Anti-biofilm mechanisms of action of essential oils by targeting genes involved in quorum sensing, motility, adhesion, and virulence: A review

Biofilms are a critical factor for food safety, causing important economic losses. Among the novel strategies for controlling biofilms, essential oils (EOs) can represent an environmentally friendly approach, able to act both on early and mature stages of biofilm formation. This review reports the anti-biofilm mechanisms of action of EOs against five pathogenic bacterial species known for their biofilm-forming ability. These mechanisms include disturbing the expression of genes related to quorum sensing (QS), motility, adhesion, and virulence. Biofilms and QS are interconnected processes, and EOs interfere with the communication system (e.g. regulating the expression of agrBDCA, luxR, luxS, and pqsA genes), thus influencing biofilm formation. In addition, QS is an important mechanism that regulates gene expression related to bacterial survival, virulence, and pathogenicity. Similarly, EOs also influence the expression of many virulence genes. Moreover, EOs exert their effects modulating the genes associated with bacterial adhesion and motility, for example those involved in curli (csg), fimbriae (fim, lpf), and flagella (fla, fli, flh, and mot) production, as well as the ica genes responsible for synthetizing polysaccharide intercellular adhesin. This review provides a comprehensive framework on the topic for a better understanding of EOs biofilm mechanisms of action.

Impact of eugenol on biofilm development in Shigella flexneri 1457: a plant terpenoid based-approach to inhibit food-borne pathogen

Shigella flexneri is a gram-negative bacterium responsible for shigellosis and bacterial dysentery. Despite using various synthetic antimicrobial agents and antibiotics, their efficacy is limited, prompting concerns over antibiotic resistance and associated health risks. This study investigated eugenol, a polyphenol with inherent antioxidant and antibacterial properties, as a potential alternative treatment. We aimed to evaluate eugenol's antibacterial effects and mechanisms of action against S. flexneri and its impact on biofilm formation. We observed significant growth suppression of S. flexneri with eugenol concentrations of 8-10 mM (98.29%). Quantitative analysis using the Crystal Violet assay demonstrated a marked reduction in biofilm formation at 10 mM (97.01 %). Assessment of Cell Viability and morphology via Fluorescence-Activated Cell Sorting and Scanning Electron Microscopy confirmed these findings. Additionally, qPCR analysis revealed the downregulation of key genes responsible for adhesion (yebL), quorum sensing (rcsC, sdiA), and EPS production (s0482) associated with bacterial growth and biofilm formation. The present study suggests eugenol could offer a promising alternative to conventional antibiotics for treating shigellosis caused by S. flexneri.

The anti-quorum sensing and biofilm inhibitory potential of Piper betle L. leaf extract and prediction of the roles of the potent phytocompounds

The leaves of Piper betle L., known as betel leaf, have immense medicinal properties. It possesses potent antimicrobial efficacies and can be a valuable tool to combat drug-resistant microorganisms. Quorum sensing (QS) inhibition is one of the best strategies to combat drug resistance. The present study investigates the anti-quorum sensing and biofilm inhibitory potential of Piper betle L. leaf extract against two bacterial strains, Chromobacterium violaceum and Pseudomonas aeruginosa. The extract produced substantial QS-inhibition zones in a biosensor strain of C. violaceum (CV026), indicating interference with quorum-sensing signals. The Results demonstrated significant inhibition in biofilm formation and different QS-regulated virulence factors (violacein, exopolysaccharides, pyocyanin, pyoverdine, elastase) in both C. violaceum and P. aeruginosa at sub-MIC concentrations of the extract and tetracycline, an antibiotic with known anti-QS activity. The quantitative real-time PCR (qRT-PCR) revealed decreased gene expression in different QS-related genes in C. violaceum (cviI, cviR, and vioA) and P. aeruginosa (lasI, lasR, lasB, rhlI, rhlR, and rhlA) strains after treatment. Gas Chromatography-Mass Spectrometry (GC-MS) analysis identified the significant phytocompounds, mainly derivatives of chavicol and eugenol, in the extract. Of these compounds, chavicol acetate (affinity: -7.00 kcal/mol) and acetoxy chavicol acetate (affinity: -7.87 kcal/mol) showed the highest potential to bind with the CviR and LasR protein, respectively, as evident from the in-silico molecular docking experiment. The findings of this endeavour highlight the promising role of Piper betle L. as a source of natural compounds with anti-quorum sensing properties against pathogenic bacteria, opening avenues for developing novel therapeutic agents to combat bacterial infections.

Computational and experimental strategies for combating MBL P. aeruginosa (MBLPA) biofilms using phytochemicals: Targeting the quorum sensing network

Pseudomonas aeruginosa is a Gram-negative opportunistic bacterium, ubiquitously found in nature and causative agent in many infections. Due to increased antibiotic resistance, there is a need to develop more robust antibacterial agents from natural sources. In this study, we worked on two metallo-β-lactamase (MBL) producing Pseudomonas aeruginosa strains and targeted the Quorum Sensing mechanism (QS) of these bacteria to combat antibiotic resistance. Our study aimed at using phytochemicals which have been used since centuries in herbal medicine. We used fifteen commercially available phytochemicals and check their effects on biofilm formation, quorum sensing and inter-related mechanisms. Sub-inhibitory concentration of isoliquiritin inhibited biofilm formation 55 % in P8 at day 6 and 48 % in P6 at day 6; quorum sensing 83 % in P6 and 61 % in P8 whereas sub-inhibitory concentration of 6-gingerol suppressed biofilm formation by 48 % in P8 at day 6 and 44 % in P6 at day 6; quorum sensing 69 % in P6 and 48 % in P8, respectively. The results indicated isoliquiritin, epigallocatechin gallate, eugenol, luteolin and chrysin to be the potential candidates in inhibiting QS and related mechanisms. Isoliquiritin which was never been used before against biofilm and QS related studies, showed remarkable results and found to be more efficient in inhibiting QS than 6-gingerol -a known QS inhibitor. For examining the molecular interaction between phytochemicals and QS, In-silico molecular docking was performed between phytoligands and four QS proteins (Las I, Las R, RhlI and Rhl R). In-silico docking analysis revealed that isoliquiritin showed strong bond with amino acids (Trp34, Asp35, Asp35, Tyr105, Arg104, Val138, Thr140) present at the active site of RhlI with binding energy value of -8.4 kcal/mol as compared to that of 6-gingerol with Rhl1 (-7.3 kcal/mol). In conclusion, our study may help in controlling nosocomial infections caused by carbapenem-resistant metallo beta-lactamase P. aeruginosa (MBL-PA) by utilizing these phytochemicals in biofilms disruption and quorum sensing inhibition. Moreover their synergism with antibiotics may help in lowering the MIC of carbapenem antibiotics against such Multi-drug resistant strains.

Linalool Reduces Virulence and Tolerance to Adverse Conditions of Listeria monocytogenes

Listeria monocytogenes, a foodborne pathogen causing listeriosis, poses substantial societal, economic, and public health challenges due to its resistance, persistence, and biofilm formation in the food industry. Exploring subinhibitory concentrations of compounds to target virulence inhibition and increase susceptibility to adverse conditions presents a promising strategy to mitigate its impact of L. monocytogenes and unveils new potential applications. Thus, this study aims to explore the effect of linalool on virulence factors of L. monocytogenes and potential use in the reduction in its tolerance to stressful conditions. This action was analysed considering the use of two sub-inhibitory concentrations of linalool, 0.312 and 0.625 mg/mL. We found that even with the lowest tested concentrations, a 65% inhibition of violacein production by Chromobacterium violaceum, 55% inhibition in biofilm formation by L. monocytogenes and 62% reduction on haemolysis caused by this bacterium were observed. In addition to its impact on virulence factors, linalool diminished the tolerance to osmotic stress (up to 4.3 log reduction after 24 h with 12% NaCl), as well as to high (up to 3.8 log reduction after 15 min at 55 °C) and low temperatures (up to 4.6 log reduction after 84 days with 12% NaCl at 4 °C). Thus, this study paves the way to further investigation into the potential utilization of linalool to mitigate the threat posed by L. monocytogenes in the field of food safety and public health.

Inhibitory effect of natural compounds on quorum sensing system in Pseudomonas aeruginosa: a helpful promise for managing biofilm community

Pseudomonas aeruginosa biofilm is a community of bacteria that adhere to live or non-living surfaces and are encapsulated by an extracellular polymeric substance. Unlike individual planktonic cells, biofilms possess a notable inherent resistance to sanitizers and antibiotics. Overcoming this resistance is a substantial barrier in the medical and food industries. Hence, while antibiotics are ineffective in eradicating P. aeruginosa biofilm, scientists have explored alternate strategies, including the utilization of natural compounds as a novel treatment option. To this end, curcumin, carvacrol, thymol, eugenol, cinnamaldehyde, coumarin, catechin, terpinene-4-ol, linalool, pinene, linoleic acid, saponin, and geraniol are the major natural compounds extensively utilized for the management of the P. aeruginosa biofilm community. Noteworthy, the exact interaction of natural compounds and the biofilm of this bacterium is not elucidated yet; however, the interference with the quorum sensing system and the inhibition of autoinducer production in P. aeruginosa are the main possible mechanisms. Noteworthy, the use of different drug platforms can overcome some drawbacks of natural compounds, such as insolubility in water, limited oral bioavailability, fast metabolism, and degradation. Additionally, drug platforms can deliver different antibiofilm agents simultaneously, which enhances the antibiofilm potential of natural compounds. This article explores many facets of utilizing natural compounds to inhibit and eradicate P. aeruginosa biofilms. It also examines the techniques and protocols employed to enhance the effectiveness of these compounds.

Attenuation of Las/Rhl quorum sensing regulated virulence and biofilm formation in Pseudomonas aeruginosa PAO1 by Artocarpesin

The emergence of multidrug resistance and increased pathogenicity in microorganisms is conferred by the presence of highly synchronized cell density dependent signalling pathway known as quorum sensing (QS). The QS hierarchy is accountable for the secretion of virulence phenotypes, biofilm formation and drug resistance. Hence, targeting the QS phenomenon could be a promising strategy to counteract the bacterial virulence and drug resistance. In the present study, artocarpesin (ACN), a 6-prenylated flavone was investigated for its capability to quench the synthesis of QS regulated virulence factors. From the results, ACN showed significant inhibition of secreted virulence phenotypes such as pyocyanin (80%), rhamnolipid (79%), protease (69%), elastase (84%), alginate (88%) and biofilm formation (88%) in opportunistic pathogen, Pseudomonas aeruginosa PAO1. Further, microscopic observation of biofilm confirmed a significant reduction in biofilm matrix when P. aeruginosa PAO1 was supplemented with ACN at its sub-MIC concentration. Quantitative gene expression studies showed the promising aspects of ACN in down regulation of several QS regulatory genes associated with production of virulence phenotypes. Upon treatment with sub-MIC of ACN, the bacterial colonization in the gut of Caenorhabditis elegans was potentially reduced and the survival rate was greatly improved. The promising QS inhibition activities were further validated through in silico studies, which put an insight into the mechanism of QS inhibition. Thus, ACN could be considered as possible drug candidate targeting chronic microbial infections.

A review on antimicrobial strategies in mitigating biofilm-associated infections on medical implants

Biomedical implants are crucial in providing support and functionality to patients with missing or defective body parts. However, implants carry an inherent risk of bacterial infections that are biofilm-associated and lead to significant complications. These infections often result in implant failure, requiring replacement by surgical restoration. Given these complications, it is crucial to study the biofilm formation mechanism on various biomedical implants that will help prevent implant failures. Therefore, this comprehensive review explores various types of implants (e.g., dental implant, orthopedic implant, tracheal stent, breast implant, central venous catheter, cochlear implant, urinary catheter, intraocular lens, and heart valve) and medical devices (hemodialyzer and pacemaker) in use. In addition, the mechanism of biofilm formation on those implants, and their pathogenesis were discussed. Furthermore, this article critically reviews various approaches in combating implant-associated infections, with a special emphasis on novel non-antibiotic alternatives to mitigate biofilm infections.

Cymbopogon citratus L. essential oil as a potential anti-biofilm agent active against antibiotic-resistant bacteria isolated from chronic rhinosinusitis patients

Chronic rhinosinusitis (CRS) is long-term inflammation of the sinuses that can be caused by infection due to antibiotic-resistant bacteria. Biofilm developed by microbes is postulated to cause antibiotic treatment failure. Thus, the anti-biofilm activities of seven Thai herbal essential oils (EOs) against antibiotic-resistant bacteria isolated from CRS patients was investigated. Lemongrass (Cymbopogon citratus L.) EO showed the most effective antibiofilm activity against Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus epidermidis grown as biofilm. GC-MS analysis found that myrcene was the major bioactive compound. Pretreatment with lemongrass EO significantly inhibited biofilm formation of all bacterial strains in more than 50% of cases. Furthermore, confocal microscopy analysis revealed the biofilm-disrupting activity of lemongrass EO against the biofilm matrix of all these bacterial species and also increased P. aeruginosa swarming motility with no toxicity to human cells. These results suggest that lemongrass EO has promising clinical applications as an anti-biofilm agent for CRS patients.

Chemical Composition and Quorum Sensing Inhibitory Effect of Nepeta curviflora Methanolic Extract against ESBL Pseudomonas aeruginosa

Objectives

Bacterial biofilm is regarded as a significant threat to the production of safe food and the arise of antibiotic-resistant bacteria. The objective of this investigation is to evaluate the quorum sensing inhibitory effect of Nepeta curviflora methanolic extract.

Methods

The effectiveness of the leaves at sub-inhibitory concentrations of 2.5, 1.25, and 0.6 mg/mL on the virulence factors and biofilm formation of P. aeruginosa was evaluated. The effect of N. curviflora methanolic extract on the virulence factors of P. aeruginosa, including pyocyanin, rhamnolipid, protease, and chitinase, was evaluated. Other tests including the crystal violet assay, scanning electron microscopy (SEM), swarming motility, aggregation ability, hydrophobicity and exopolysaccharide production were conducted to assess the effect of the extract on the formation of biofilm. Insight into the mode of anti-quorum sensing action was evaluated by examining the effect of the extract on the activity of N-Acyl homoserine lactone (AHL) and the expression of pslA and pelA genes.

Results

The results showed a significant attenuation in the production of pyocyanin and rhamnolipid and in the activities of protease and chitinase enzymes at 2.5 and 1.25 mg/mL. In addition, N. curviflora methanolic extract significantly inhibited the formation of P. aeruginosa biofilm by decreasing aggregation, hydrophobicity, and swarming motility as well as the production of exopolysaccharide (EPS). A significant reduction in AHL secretion and pslA gene expression was observed, indicating that the extract inhibited quorum sensing by disrupting the quorum-sensing systems. The quorum-sensing inhibitory effect of N. curviflora extract appears to be attributed to the presence of kaempferol, quercetin, salicylic acid, rutin, and rosmarinic acid, as indicated by LCMS analysis.

Conclusion

The results of the present study provide insight into the potential of developing anti-quorum sensing agents using the extract and the identified compounds to treat infections resulting from quorum sensing-mediated bacterial pathogenesis.

Antibiofilm Effect of Curcumin Against Staphylococcus aureus Surface Wound Biofilm-Associated Infection: In Vitro and In Silico

Biofilm is the consortia of the sessile group of microbial species that are adhered to the biotic and abiotic surfaces with the help of extracellular polymeric substances (EPS) and glycocalyx. A wound is a lesion on the epidermal surface that exposes the underlying tissues to the external environment and thus forms a region of proliferation for several species of Staphylococcus aureus. S. aureus is the most commonly observed nosocomial biofilm-forming organism that is responsible for the development of wound-associated infections. The biofilm prevents the penetration of the drug molecules thereby resulting in the development of antibiotic and multi-drug resistance among the organism. Thus, the use of alternative therapeutics has paved the path in the treatment of biofilm-associated infections. Curcumin has been used for the purpose of treating various illnesses from time immemorial. In this study, we observed that curcumin was able to bring about a reduction in the biofilm formed by S. aureus in the wound infection among the patients. The in silico studies revealed that curcumin possessed the ability to bring about interaction with the biofilm-forming proteins of S. aureus effectively.

Antibacterial and Antibiofilm Effects of Different Samples of Five Commercially Available Essential Oils

Essential oils (EOs) have gained economic importance due to their biological activities, and increasing amounts are demanded everywhere. However, substantial differences between the same essential oil samples from different suppliers are reported-concerning their chemical composition and bioactivities-due to numerous companies involved in EOs production and the continuous development of online sales. The present study investigates the antibacterial and antibiofilm activities of two to four samples of five commercially available essential oils (Oregano, Eucalyptus, Rosemary, Clove, and Peppermint oils) produced by autochthonous companies. The manufacturers provided all EOs' chemical compositions determined through GC-MS. The EOs' bioactivities were investigated in vitro against Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The antibacterial and antibiofilm effects (ABE% and, respectively, ABfE%) were evaluated spectrophotometrically at 562 and 570 nm using microplate cultivation techniques. The essential oils' calculated parameters were compared with those of three standard broad-spectrum antibiotics: Amoxicillin/Clavulanic acid, Gentamycin, and Streptomycin. The results showed that at the first dilution (D1 = 25 mg/mL), all EOs exhibited antibacterial and antibiofilm activity against all Gram-positive and Gram-negative bacteria tested, and MIC value > 25 mg/mL. Generally, both effects progressively decreased from D1 to D3. Only EOs with a considerable content of highly active metabolites revealed insignificant differences. E. coli showed the lowest susceptibility to all commercially available essential oils-15 EO samples had undetected antibacterial and antibiofilm effects at D2 and D3. Peppermint and Clove oils recorded the most significant differences regarding chemical composition and antibacterial/antibiofilm activities. All registered differences could be due to different places for harvesting the raw plant material, various technological processes through which these essential oils were obtained, the preservation conditions, and complex interactions between constituents.

Antibiofilm Activity and Mechanism of Linalool against Food Spoilage Bacillus amyloliquefaciens

Pellicle biofilm-forming bacteria Bacillus amyloliquefaciens are the major spoilage microorganisms of soy products. Due to their inherent resistance to antibiotics and disinfectants, pellicle biofilms formed are difficult to eliminate and represent a threat to food safety. Here, we assessed linalool's ability to prevent the pellicle of two spoilage B. amyloliquefaciens strains. The minimum biofilm inhibitory concentration (MBIC) of linalool against B. amyloliquefaciens DY1a and DY1b was 4 μL/mL and 8 μL/mL, respectively. The MBIC of linalool had a considerable eradication rate of 77.15% and 83.21% on the biofilm of the two strains, respectively. Scanning electron microscopy observations revealed that less wrinkly and thinner pellicle biofilms formed on a medium supplemented with 1/2 MBIC and 1/4 MBIC linalool. Also, linalool inhibited cell motility and the production of extracellular polysaccharides and proteins of the biofilm matrix. Furthermore, linalool exposure reduced the cell surface hydrophobicity, zeta potential, and cell auto-aggregation of B. amyloliquefaciens. Molecular docking analysis demonstrated that linalool interacted strongly with quorum-sensing ComP receptor and biofilm matrix assembly TasA through intermolecular hydrogen bonds, hydrophobic contacts, and van der Waals forces interacting with site residues. Overall, our findings suggest that linalool may be employed as a potential antibiofilm agent to control food spoilage B. amyloliquefaciens.

Chemical Composition, Antioxidant, and Antimicrobial Activities of the Leaf and Fruit Essential Oils of the West African Plum, Vitex doniana

Vitex doniana (West African plum or black plum) is a plant with varying phytoconstituents and biological activities across different countries. In this study, essential oils extracted from the leaves and fruits of Vitex doniana cultivated in Ghana were investigated for their antimicrobial and antioxidant activities. The antioxidant actions of the essential oils were determined using hydrogen peroxide (H2O2), phosphomolybdenum, thiobarbituric acid reactive substances (TBARS), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays. For both essential oils, the total antioxidant capacities ranged from 44 to 68 µg/g AAE, the IC50 values for H2O2 scavenging activity were between 87 and 242 µg/mL, whereas that for DPPH assay were between 322 and 599 µg/mL. The IC50 for the TBARS assay for both essential oils also ranged from 247 to 414 µg/mL. The antimicrobial activities of the essential oils were investigated using the broth dilution assay. The minimum inhibition concentration for the essential oils ranged from 12.5 to 50 mg/mL. Biofilm inhibitory activity was also evaluated for both essential oils, and the fruit essential oil showed a half-maximal inhibition of biofilm formation (BIC50) at 44.40 ± 0.6 mg/mL, whereas the BIC50 value of the leaf essential oil was 109.1 ± 0.9 mg/mL. The fruit essential oil was superior to the leaf essential oil in inhibiting the secretion of pyoverdine. Molecular docking analyses suggested that methyl cinnamate, ethyl cinnamate, p-menth-4-en-3-one, trans-α-ionone, benzyl benzoate, isobutyl cinnamate, and folic acid likely interacted with LasR and algC proteins, and hence, contributed to the inhibition of biofilm formation and pyoverdine secretion. Essential oils from Vitex doniana could, therefore, be exploited as a natural source of radical scavenging and antimicrobial agents and could be useful in the pharmaceutical, food, and cosmetic industries.

Plasma-activated liquids for mitigating biofilms on food and food contact surfaces

Plasma-activated liquids (PALs) are emerging and promising alternatives to traditional decontamination technologies and have evolved as a new technology for applications in food, agriculture, and medicine. Contamination caused by foodborne pathogens and their biofilms has posed challenges and concerns to the food industry in terms of safety and quality. The nature of the food and the food processing environment are major factors that contribute to the growth of various microorganisms, followed by the biofilm characteristics that ensure their survival in severe environmental conditions and against traditional chemical disinfectants. PALs show an efficient impact against microorganisms and their biofilms, with various reactive species (short- and long-lived ones), physiochemical properties, and plasma processing factors playing a crucial role in mitigating biofilms. Moreover, there is potential to improve and optimize disinfection strategies using a combination of PALs with other technologies for the inactivation of biofilms. The overarching aim of this study is to build a better understanding of the parameters that govern the liquid chemistry generated in a liquid exposed to plasma and how these translate into biological effects on biofilms. This review provides a current understanding of PALs-mediated mechanisms of action on biofilms; however, the precise inactivation mechanism is still not clear and is an important part of the research. Implementation of PALs in the food industry could help overcome the disinfection hurdles and can enhance biofilm inactivation efficacy. Future perspectives in this field to expand existing state of the art to seek breakthroughs for scale-up and implementation of PALs technology in the food industry are also discussed.

Hybrid Bio-Based Silicone Coatings with Anti-adhesive Properties

Hybrid polysiloxanes and polysilsesquioxanes grafted with naturally occurring bioactive phytochemicals: eugenol and linalool, were synthesized and investigated with regard to their structure and properties. The two series of materials, differing in the type of inorganic structure and the content of active groups, were coated onto the surface of glass plates, and their antibiofilm activities against bacteria Aeromonas hydrophila were assessed by luminometry and fluorescence microscopy. Bioactivity was correlated with specific properties of the hybrid coatings (chemical structure, surface free energy and adhesiveness). The functionalized polysilsesquioxanes exhibited the most favorable anti-adhesive effects. Cell adhesion after 6 days of incubation, expressed as RLU/cm², was significantly reduced (44 and 67 for, respectively, Z-E-100 and Z-L-100, compared to 517 for the control glass carrier). The surface stickiness of polysiloxane films deteriorated their anti-adhesion properties, despite the presence of a large amount of bioactive species.

Levofloxacin loaded clove oil nanoscale emulgel promotes wound healing in Pseudomonas aeruginosa biofilm infected burn wound in mice

Owing to their tolerance to antibiotics, bacterial biofilms continue to pose a threat to mankind and are leading cause for non-healing of burn wounds. Within the biofilm matrix, antibiotics become functionally inactive due to restricted penetration and enzymatic degradation leading to rise of antimicrobial resistance. The objective of present investigation was to develop and characterize levofloxacin (LFX) loaded clove oil nanoscale emulgel (LFX-NE gel) and evaluate its in vivo therapeutic efficacy in Pseudomonas aeruginosa biofilm infected burn wound in mice. The optimized emulgel was found to possess good texture profile and showed shear thinning behavior. In vitro release study demonstrated complete drug release in 8 h and emulgel was found to be stable for 3 months at 25 °C and 40 °C. In vivo study revealed biofilm dispersal, complete wound closure, re-epithelialization and collagen deposition by LFX-NE gel in comparison to various control groups. LFX-NE gel was able to clear the infection within 7 days of treatment and promote wound healing as well. Therefore, administration of LFX-incorporated NE gel could be a beneficial treatment strategy for P. aeruginosa biofilm-infected burn wounds.

Citrus sinensis Essential Oils an Innovative Antioxidant and Antipathogenic Dual Strategy in Food Preservation against Spoliage Bacteria

The present study evaluates the chemical compositions and antioxidant and antipathogenic properties of commercial orange (Citrus sinensis (L.) Osbeck) essential oils obtained using the cold-press method (EOP) and the cold-press method followed by steam distillation (EOPD). The chemical compositions of the volatilizable fractions, determined by gas chromatography-mass spectrometry, were similar in both samples. A relatively large amount of γ-terpinene was found in the EOPD (1.75%) as compared to the EOP (0.84%). Monoterpene hydrocarbons with limonene (90.4-89.8%) followed by myrcene (3.2-3.1%) as the main compounds comprised the principal phytochemical group. The non-volatile phenolics were eight times higher in the EOP than in the EOPD. Several assays with different specificity levels were used to study the antioxidant activity. Although both essential oils presented similar reducing capacities, the radical elimination ability was higher for the EOP. Regarding the antipathogenic properties, the EOs inhibited the biomass and cell viability of Staphylococcus aureus and Pseudomonas aeruginosa biofilms. Furthermore, both EOs similarly attenuated the production of elastase, pyocyanin, and quorum-sensing autoinducers as assessed using Gram-negative bacteria. The EOP and EOPD showed important antioxidant and antipathogenic properties, so they could represent natural alternatives to extend the shelf life of food products by preventing oxidation and contamination caused by microbial spoilage.

Marine bioactive compounds as antibiofilm agent: a metabolomic approach

The ocean is a treasure trove of both living and nonliving creatures, harboring incredibly diverse group of organisms. A plethora of marine sourced bioactive compounds are discovered over the past few decades, many of which are found to show antibiofilm activity. These are of immense clinical significance since the formation of microbial biofilm is associated with the development of high antibiotic resistance. Biofilms are also responsible to bring about problems associated with industries. In fact, the toilets and wash-basins also show degradation due to development of biofilm on their surfaces. Antimicrobial resistance exhibited by the biofilm can be a potent threat not only for the health care unit along with industries and daily utilities. Various recent studies have shown that the marine members of various kingdom are capable of producing antibiofilm compounds. Many such compounds are with unique structural features and metabolomics approaches are essential to study such large sets of metabolites. Associating holobiome metabolomics with analysis of their chemical attribute may bring new insights on their antibiofilm effect and their applicability as a substitute for conventional antibiotics. The application of computer-aided drug design/discovery (CADD) techniques including neural network approaches and structured-based virtual screening, ligand-based virtual screening in combination with experimental validation techniques may help in the identification of these molecules and evaluation of their drug like properties.

Chemical Characterization, Antioxidant, Antimicrobial, and Antibiofilm Activities of Essential Oils of Plumeria alba (Forget-Me-Not)

Essential oils are known to possess many biological properties such as antimicrobial and antioxidant activities. Plumeria alba flowers are used in traditional remedies for diarrhea, cough, fever, and asthma treatment. This work evaluated the chemical composition and the biological activities of essential oils obtained from the flowers and leaves of Plumeria alba. The essential oils were extracted using the Clevenger-type apparatus and characterized using GC-MS. In the flower essential oil, a total of 17 compounds were identified, with linalool (23.91%), α-terpineol (10.97%), geraniol (10.47%), and phenyl ethyl alcohol (8.65%) being abundant. In the leaf essential oil, a total of 24 compounds were identified, with benzofuran, 2,3-di, hydro-(3.24%), and muurolol (1.40%) being present. Antioxidant activities were assessed using hydrogen peroxide scavenging, phosphomolybdenum, and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging assays. Antimicrobial activities were assessed through a microdilution assay. The essential oil showed antimicrobial activity against test microorganisms with minimum inhibitory concentrations ranging from 25.0 to 50.0 mg/mL. Biofilm inhibition ranged from 27.14 ± 1.0 to 58.99 ± 0.6 mg/mL. The essential oil exhibited total antioxidant capacities which ranged from 17.5 μg/g AAE to 83 μg/g AAE in the phosphomolybdenum assay. The IC₅₀ values in the DPPH and hydrogen peroxide radical scavenging assays for both flowers and leaves ranged from 18.66 μg/mL to 38.28 μg/mL. Both essential oils also displayed good antibiofilm activities, with the concentration required for half-maximal inhibition of biofilm formation being ∼60 mg/mL for both oils. This study shows that essential oils of Plumeria alba possess good antioxidant and antimicrobial activities and could be used as a source of natural antioxidants and antimicrobial agents.

Periodontitis: An Oral Disease with Severe Consequences

Periodontitis, being a multifactorial disorder is found to be the most common oral disease denoted by the inflammation of gingiva and resorption of tooth supporting alveolar bone. The disease being closely linked with fast life style and determined by unhygienic behavioural factors, the internal milieu of oral cavity and formation of plaque biofilm on the dental and gingival surfaces. Porphyromonas gingivalis, being the major keystone pathogen of the periodontal biofilm evokes host immune responses that causes damage of gingival tissues and resorption of bones. The biofilm associated microbial community progressively aggravates the condition resulting in chronic inflammation and finally tooth loss. The disease often maintains bidirectional relationship with different systemic, genetic, autoimmune, immunodeficiency diseases and even psychological disorders. The disease can be diagnosed and predicted by various genetic, radiographic and computer-aided design (CAD) & computer-aided engineering (CAE) and artificial neural network (ANN). The elucidation of genetic background explains the inheritance of the disease. The therapeutic approaches commonly followed include mechanical removal of dental plaque with the use of systemic antibiotics. Awareness generation amongst local people, adoption of good practice of timely tooth brushing preferably with fluoride paste or with nanoconjugate pastes will reduce the chance of periodontal plaque formation. Modern tissue engineering technology like 3D bioprinting of periodontal tissue may help in patient specific flawless regeneration of tooth structures and associated bones.

Anti-quorum sensing evaluation of methyleugenol, the principal bioactive component, from the Melaleuca bracteata leaf oil

Quorum sensing (QS) is a cell-to-cell communication in bacteria that couples gene expression through the accumulation of signaling molecules, which finally induce the production of several virulence factors and modulate bacterial behaviors. Plants have evolved an array of quorum sensing inhibitors (QSIs) to inhibit the pathogens, of which aromatic compounds are widely recognized. The essential oil of Melaleuca bracteata was found to exhibit anti-quorum sensing activity, and its principal bioactive component, methyleugenol (ME), had been isolated in our previous study. Here, ME interfered effectively with the QS-regulated processes of toxin secretion in Chomobacterium violaceum ATCC31532, resulting in strong inhibition of QS genes, cviR, cviI, vioA-E, hmsHNR, lasA-B, pilE1-3, and hcnABC, leading to impaired virulence, including violacein production, biofilm biomass, and swarming motility. The accumulation of the signal molecule (N-hexanoyl-DL-homoserine lactone, C6-HSL) in C. violaceum declined upon treatment with ME, suggesting an inhibition effect on the C6-HSL production, and the ME was also capable of degrading the C6-HSL in vitro assay. Molecular docking technique and the consumption change of exogenous C6-HSL in C. violaceum CV026 revealed the anti-QS mechanism of ME consisted of inhibition of C6-HSL production, potentially via interaction with CviR and/or CviI protein. Collectively, the isolated ME, the principal active components of M. bracteata EO, exhibited a wide range of inhibition processes targeting C. violaceum QS system, which supports the potential anti-pathogenic use of M. bracteata EO and ME for treatment of pathogen contamination caused by bacterial pathogens.

Citrus Essential Oils: a Treasure Trove of Antibiofilm Agent

Biofilms are groups of adherent cell communities that cohere to the biotic and abiotic surfaces with the help of extracellular polymeric substances (EPS). EPS allow bacteria to form a biofilm that facilitates their binding to biotic and abiotic surfaces and provides resistance to the host immune responses and to antibiotics. There are efforts that have led to the development of natural compounds that can overcome this biofilm-mediated resistance. Essential oils (EOs) are a unique mixture of compounds that plays a key role in preventing the development of biofilm. The present overview focusses on the role of various types of citrus essential oils in acting against the biofilm, and the antibiofilm properties of natural compounds that may show an avenue to treat the multidrug-resistant bacteria.

Essential Oils Biofilm Modulation Activity and Machine Learning Analysis on Pseudomonas aeruginosa Isolates from Cystic Fibrosis Patients

The opportunistic pathogen Pseudomonas aeruginosa is often involved in airway infections of cystic fibrosis (CF) patients. It persists in the hostile CF lung environment, inducing chronic infections due to the production of several virulence factors. In this regard, the ability to form a biofilm plays a pivotal role in CF airway colonization by P. aeruginosa. Bacterial virulence mitigation and bacterial cell adhesion hampering and/or biofilm reduced formation could represent a major target for the development of new therapeutic treatments for infection control. Essential oils (EOs) are being considered as a potential alternative in clinical settings for the prevention, treatment, and control of infections sustained by microbial biofilms. EOs are complex mixtures of different classes of organic compounds, usually used for the treatment of upper respiratory tract infections in traditional medicine. Recently, a wide series of EOs were investigated for their ability to modulate biofilm production by different pathogens comprising S. aureus, S. epidermidis, and P. aeruginosa strains. Machine learning (ML) algorithms were applied to develop classification models in order to suggest a possible antibiofilm action for each chemical component of the studied EOs. In the present study, we assessed the biofilm growth modulation exerted by 61 commercial EOs on a selected number of P. aeruginosa strains isolated from CF patients. Furthermore, ML has been used to shed light on the EO chemical components likely responsible for the positive or negative modulation of bacterial biofilm formation.

A Fresh Look at Mouthwashes-What Is Inside and What Is It For?

Mouthwashes are a very popular additional oral hygiene element and there are plenty of individual products, whose compositions are in a state of flux. The aim of our study was to investigate the compositions of mouthwashes and their functions, as well as to discuss their effectiveness in preventing and curing oral diseases and side effects. We searched for mouthwashes available on the market in Poland. We identified 241 individual mouthwash products. The extraction of compositions was performed and functions of the ingredients were assessed. Then, analysis was performed. The evaluation revealed that there are plenty of ingredients, but a typical mouthwash is a water-glycerine mixture and consists of additional sweetener, surfactant, preservative, and some colourant and flavouring agent, as well as usually having two oral health substances, anticaries sodium fluoride and antimicrobial essential oils. The effectiveness or side effects of several substances of mouthwashes were thoroughly discussed. We recommend not multiplying individual mouthwash products and their ingredients beyond medical or pharmaceutical necessity, especially without scientific proof.

Targeting Microbial Bio-film: an Update on MDR Gram-Negative Bio-film Producers Causing Catheter-Associated Urinary Tract Infections

In every age group, urinary tract infection (UTI) is found as a major recurrence infectious disorder. Bio-films produced by bacteria perform a vital role in causing infection in the tract of the urinary system, leading to recurrences and relapses. The purpose of this review is to present the role and mechanism of bio-film producing MDR Gram-negative bacteria causing UTI, their significance, additionally the challenges for remedy and prevention of catheter-associated UTI. This work appreciates a new understanding of bio-film producers which are having multi-drug resistance capability and focuses on the effect and control of bio-film producing uropathogenic bacteria related to catheterization. We have tried to analyze approaches to target bio-film and reported phytochemicals with anti-bio-film activity also updated on anti-bio-film therapy.

Eugenol-Mediated Inhibition of Biofilm Formed by S. aureus: a Potent Organism for Pediatric Digestive System Diseases

Ocimum tenuiflorum (KT) is a common ethnobotanical plant of Southeast Asia. The ethnic communities of these regions use the various parts of the plants, especially the leaves, for the treatment of various ailments like cold and flu, chronic infections, and surface ailments. The leaves of these plants are consumed to act as immune boosters in the body. With this ethnical background, we performed the antimicrobial and antibiofilm potential of the methanolic extract of Ocimum tenuiflorum against biofilm formed by S. aureus biofilm. The biofilm formed by S. aureus is a potent cause for the development of gastrointestinal (GI)-associated chronic infection. The extract from the KT leaf was analyzed using UV spectroscopy and HPLC to confirm the presence of the active ingredients present within the extract. The HPLC and GC-MS studies revealed the presence of eugenol and linalool in a greater proportion having the maximum drug-like properties. It was observed that KT showed maximum inhibition of biofilms, proteins, and carbohydrates being present with the extracellular polymeric substance (EPS). Interestingly, the maximum inhibition to the quorum sensing (QS) and the genomic DNA, RNA content was reduced by eugenol and linalool in comparison to the plant extract. The studies were supported by in silico interaction between eugenol and linalool with the QS proteins of S. aureus. The studies were further confirmed with microscopic studies SEM and FCM. The IR studies also confirmed much reduction in biofilm when treated with eugenol, linalool, and KT with respect to the untreated sample.

Antibacterial mechanism of linalool emulsion against Pseudomonas aeruginosa and its application to cold fresh beef

Pseudomonas aeruginosa (P. aeruginosa) is the dominant spoilage bacterium in cold fresh beef. The current strategy is undertaken to overcome the low water solubility of linalool by encapsulating linalool into emulsions. The results of field emission scanning electron microscopy and particle size distribution revealed that the appearance of the bacterial cells was severely disrupted after exposure to linalool emulsion (LE) with an minimum inhibitory concentration (MIC) of 1.5 mL/L. Probes combined with fluorescence spectroscopy were performed to detect cell membrane permeability, while intracellular components (protein and ion leakage) and crystal violet staining were further measured to characterize cell membrane integrity and biofilm formation ability. The results confirmed that LE could destroy the structure of the cell membrane, thereby leading to the leakage of intracellular material and effective removal of biofilms. Molecular docking confirmed that LE can interact with the flagellar cap protein (FliD) and DNA of P. aeruginosa, inhibiting biofilm formation and causing genetic damage. Furthermore, the results of respiratory metabolism and reactive oxygen species (ROS) accumulation revealed that LE could significantly inhibit the metabolic activity of P. aeruginosa and induce oxidative stress. In particular, the inhibition rate of LE on P. aeruginosa was 23.03% and inhibited mainly the tricarboxylic acid cycle (TCA). Finally, LE was applied to preserve cold fresh beef, and the results showed that LE could effectively inhibit the activity of P. aeruginosa and delay the quality change of cold fresh beef during the storage period. These results are of great significance to developing natural preservatives and extending the shelf life of cold fresh beef.

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

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

Phytocompound Mediated Blockage of Quorum Sensing Cascade in ESKAPE Pathogens

Increased resistance of Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter sp. (ESKAPE) pathogens against various drugs has enhanced the urge for the development of alternate therapeutics. Quorum sensing (QS) is a density dependent cell-to-cell communication mechanism responsible for controlling pathogenicity with the regulation of gene expression. Thus, QS is considered a potential target for the development of newer anti-biofilm agents that do not depend on the utilization of antibiotics. Compounds with anti-QS effects are known as QS inhibitors (QSIs), and they can inhibit the QS mechanism that forms the major form in the development of bacterial pathogenesis. A diverse array of natural compounds provides a plethora of anti-QS effects. Over recent years, these natural compounds have gained importance as new strategies for combating the ESKAPE pathogens and inhibiting the genes involved in QS. Different pharmacognostical and pharmacological studies have been carried out so far for identification of novel drugs or for the discovery of their unique structures that may help in developing more effective anti-biofilm therapies. The main objective of this review is to discuss the various natural compounds, so far identified and their employed mechanisms in hindering the genes responsible for QS leading to bacterial pathogenesis.

Simultaneous Hydrodistillation-Steam Distillation of Rosmarinus officinalis, Lavandula angustifolia and Citrus aurantium from Morocco, Major Terpenes: Impact on Biological Activities

Interest in the use of essential oils (EOs) in the biomedical and food industries have seen growing over the last decades due to their richness in bioactive compounds. The challenges in developing an EO extraction process that assure an efficient levels of monoterpenes with impact on biological activities have driven the present study, in which the EO extraction process of rosemary, lavender and citrus was performed by simultaneous hydrodistillation-steam distillation, and the influence of EO composition on biological activities, namely antioxidant, anti-inflammatory, antidiabetic, anti-acetylcholinesterase, anti-tyrosinase, antibacterial, and antibiofilm activity, were evaluated. The EO yields of combinations were generally higher than the individual plants (R. officinalis (Ro), L. angustifolia (La), and C. aurantium (Ca)) extracted by the conventional hydrodistillation. The EOs obtained by this process generally had a better capacity for scavenging the free radicals, inhibiting α-glucosidase, and acetylcholinesterase activities than the individual EOs. The combination of EOs did not improve the ability for scavenging peroxide hydrogen or the capacity for inhibiting lipoxygenase activity. The antioxidant activity or the enzyme inhibition activity could not only be attributed to their major compounds because they presented lower activities than the EOs. The chemical composition of the combination Ro:La:Ca, at the ratio 1/6:1/6:2/3, was enriched in 1,8-cineole, linalool, and linalyl acetate and resulted in lower MIC values for all tested strains in comparison with the ratio 1/6:2/3:1/6 that was deprived on those components. The biofilm formation of Gram positive and Gram negative bacteria was impaired by the combination Ro:La:Ca at a sub-inhibitory concentration.