Study on Antibacterial and Quorum-Sensing Inhibition Activities of Cinnamomum camphora Leaf Essential Oil

In Vitro Methods for Assessing the Antibacterial and Antibiofilm Properties of Essential Oils as Potential Root Canal Irrigants-A Simplified Description of the Technical Steps

BACKGROUND

Essential oils have gained in significance due to their various biological activities, and there is a growing demand for them in many industries. The present article focuses on the technical steps for an in vitro evaluation of the antibacterial and antibiofilm activities of essential oils for potential use as root canal irrigant in dentistry.

METHODS

The bioactivities of the essential oil were investigated through in vitro assays. The gram-positive bacterium Enterococcus faecalis was used as a micro-organism model. The antibacterial activity of the essential oil was assessed using the microdilution method, and resazurin staining to determine the minimal inhibition concentrations (MICs) and the minimal bactericidal concentrations (MBCs). The antibiofilm effect was evaluated spectrophotometrically at 570 nm using the microplate cultivation technique and crystal violet staining.

CONCLUSIONS

This article features a detailed in vitro protocol to facilitate the preparation of the essential oil samples, the bacterial suspension, and the methods used for assessment of the antibiofilm and antibacterial activities of the essential oil. The advantages of these approaches are presented in relation to the limits linked to the choice of the bacteria and the essential oil.

Green-synthesized zinc oxide nanoparticles by Enterobacter sp.: unveiling characterization, antimicrobial potency, and alleviation of copper stress in Vicia faba (L.) plants

BACKGROUND

The biosynthesis of zinc oxide nanoparticles (ZnO NPs) using Enterobacter sp. and the evaluation of their antimicrobial and copper stress (Cu+ 2)-reducing capabilities in Vicia faba (L.) plants. The green-synthesized ZnO NPs were validated using X-ray powder diffraction (XRD); Fourier transformed infrared (FTIR), Ultraviolet-Visible spectroscopy (UV-Vis), Transmission electron microscope (TEM) and scanning electron microscopy (SEM) techniques. ZnO NPs could serve as an improved bactericidal agent for various biological applications. as well as these nanoparticles used in alleviating the hazardous effects of copper stress on the morphological and physiological traits of 21-day-old Vicia faba (L.) plants.

RESULTS

The results revealed that different concentrations of ZnO NPs (250, 500, or 1000 mg L-1) significantly alleviated the toxic effects of copper stress (100 mM CuSO4) and increased the growth parameters, photosynthetic efficiency (Fv/Fm), and pigments (Chlorophyll a and b) contents in Cu-stressed Vicia faba (L.) seedlings. Furthermore, applying high concentration of ZnO NPs (1000 mg L-1) was the best dose in maintaining the levels of antioxidant enzymes (CAT, SOD, and POX), total soluble carbohydrates, total soluble proteins, phenolic and flavonoid in all Cu-stressed Vicia faba (L.) seedlings. Additionally, contents of Malondialdehyde (MDA) and hydrogen peroxide (H2O2) were significantly suppressed in response to high concentrations of ZnO NPs (1000 mg L-1) in all Cu-stressed Vicia faba (L.) seedlings. Also, it demonstrates strong antibacterial action (0.9 mg/ml) against various pathogenic microorganisms.

CONCLUSIONS

The ZnO NPs produced in this study demonstrated the potential to enhance plant detoxification and tolerance mechanisms, enabling plants to better cope with environmental stress. Furthermore, these nanoparticles could serve as an improved bactericidal agent for various biological applications.

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.

Magnetic separation, sunlight-driven photocatalytic activity, and antibacterial studies of Sm-doped Co0.33Mg0.33Ni0.33Fe2O4 nanoparticles

Magnetic nanoparticles have emerged as a promising tool for wastewater treatment due to their unique properties. In this regard, Co0.33Mg0.33Ni0.33SmxFe2-xO4 (0.00 ≤ x ≤ 0.08) nanoparticles were prepared to examine their magnetic separation efficiency (MSE), photocatalytic, antibacterial, and antibiofilm performances. Pure nanoparticles, having the highest saturation magnetization (Ms = 31.87 emu/g), exhibit the highest MSE, where 95.6% of nanoparticles were separated after 20 min of applying a magnetic field of 150 mT. The catalytic performance of the prepared samples is examined by the photodegradation of rhodamine B (RhB) dye exposed to direct sunlight radiation. Improved photocatalytic activity is exhibited by Co0.33Mg0.33Ni0.33Sm0.04Fe1.96O4 nanoparticles, labeled as Sm0.04, where the rate of the degradation reaction is enhanced by 4.1 times compared to pure nanoparticles. Rising the pH and reaction temperature improves the rate of the photodegradation reaction of RhB. The incorporation of 15 wt% reduced graphene oxide (rGO) with Sm0.04 enhanced the rate of the reaction by 1.7 and 2.4 times compared with pure Sm0.04 sample and rGO, respectively. The antibacterial and antibiofilm activities against Escherichia coli, Leclercia adecarboxylata, Staphylococcus aureus, and Enterococcus faecium are assessed by the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) broth microdilution, the agar well diffusion, the time-kill assays, the biofilm formation, and destruction assays. The bacteria used in these assessments are isolated from wastewater. The nanoparticles exhibit a bacteriostatic activity, with a better effect against the Gram-positive isolates. Co0.33Mg0.33Ni0.33SmxFe2O4 (x = 0.00) nanoparticles have the best effect. The effect is exerted after 2-3 h of incubation. Gram-positive biofilms are more sensitive to nanoparticles.

Oxidative Stress-Mediated Repression of Virulence Gene Transcription and Biofilm Formation as Antibacterial Action of Cinnamomum burmannii Essential Oil on Staphylococcus aureus

This work aimed to identify the chemical compounds of Cinnamomum burmannii leaf essential oil (CBLEO) and to unravel the antibacterial mechanism of CBLEO at the molecular level for developing antimicrobials. CBLEO had 37 volatile compounds with abundant borneol (28.40%) and showed good potential to control foodborne pathogens, of which Staphylococcus aureus had the greatest inhibition zone diameter (28.72 mm) with the lowest values of minimum inhibitory concentration (1.0 μg/mL) and bactericidal concentration (2.0 μg/mL). To unravel the antibacterial action of CBLEO on S. aureus, a dynamic exploration of antibacterial growth, material leakage, ROS formation, protein oxidation, cell morphology, and interaction with genome DNA was conducted on S. aureus exposed to CBLEO at different doses (1/2-2×MIC) and times (0-24 h), indicating that CBLEO acts as an inducer for ROS production and the oxidative stress of S. aureus. To highlight the antibacterial action of CBLEO on S. aureus at the molecular level, we performed a comparative association of ROS accumulation with some key virulence-related gene (sigB/agrA/sarA/icaA/cidA/rsbU) transcription, protease production, and biofilm formation in S. aureus subjected to CBLEO at different levels and times, revealing that CBLEO-induced oxidative stress caused transcript suppression of virulence regulators (RsbU and SigB) and its targeted genes, causing a protease level increase destined for the biofilm formation and growth inhibition of S. aureus, which may be a key bactericidal action. Our findings provide valuable information for studying the antibacterial mechanism of essential oil against pathogens.

Current status, technology, regulation and future perspectives of essential oils usage in the food and drink industry

Nowadays, essential oils (EOs) have a wide use in many applications such as in food, cosmetics, pharmaceutical and animal feed products. Consumers' preferences concerning healthier and safer foodstuffs lead to an increased demand for natural products, in replacement of synthetic substances, used as preservatives, flavourings etc. EOs, besides being safe, are promising alternatives as natural food additives, and much research has been carried out on their antioxidant and antimicrobial activity. The initial purpose of this review is to discuss conventional and 'green' extraction techniques along with their basic mechanism for the isolation of EOs from aromatic plants. This review aims to provide a broad overview of the current knowledge about the chemical constitution of EOs while considering the existence of different chemotypes, since bioactivity is attributed to the chemical composition - qualitative and quantitative - of EOs. Although the food industry primarily uses EOs as flavourings, an overview on recent applications of EOs in food systems and active packaging is provided. EOs exhibit poor solubility in water, oxidation susceptibility, negative organoleptic effect and volatility, restricting their use. Encapsulation techniques have been proven to be one of the best approaches to preserve the biological activities of EOs and minimize their effects on food sensory qualities. Herein, different encapsulation techniques and their basic mechanism for loading EOs are discussed. EOs are highly accepted by consumers, who are often under the misconception that 'natural' means safe. This is, however, an oversimplification, and the possible toxicity of EOs should be taken into consideration. Thus, in the final section of the current review, the focus is on current EU legislation, safety assessment and sensory evaluation of EOs. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Minimal Inhibitory Concentrations of Thymol and Carvacrol: Toward a Unified Statistical Approach to Find Common Trends

Thymol and carvacrol are some of the most important and used components of Essential oils (EOs); they are widely studied, and there are much data available in the literature. Their Minimal Inhibitory Concentration (MIC) values found in the literature from 2005 to present were used to assess the bioactivity toward yeasts, molds, Gram-positive bacteria, and Gram-negative bacteria, as well as on some bacterial species/serotypes (Salmonella sp., Escherichia coli, E. coli O157:H7, lactic acid bacteria, Listeria monocytogenes, Staphylococcus aureus, S. epidermidis, etc.) to find possible common trends or differences between the two compounds and among the tested species. The results were quite interesting and pointed out that there is a common range for the MIC of thymol and carvacrol for some bacterial species (150-400 mg/L), with some exceptions to this generalized statement. In addition, the statistics pointed out that bacteria could experience homogeneous (S. epidermidis, E. coli O157:H7) or heterogeneous trends (for example, Salmonella sp.) depending on the existence of possible sub-species or different experimental set-ups. Moreover, this paper suggests that there are some drawbacks and issues that should be solved for the effective use of EOs, which are the strong variability among the microorganisms and the lack of standard protocols and reference strains.

Influence of Lanthanum Doping on the Photocatalytic and Antibacterial Capacities of Mg0.33Ni0.33Co0.33Fe2O4 Nanoparticles

The increase in environmental pollution, especially water pollution, has intensified the requirement for new strategies for the treatment of water sources. Furthermore, the improved properties of nano-ferrites permit their usage in wastewater treatment. In this regard, novel Mg0.33Ni0.33Co0.33LaxFe2−xO4 nanoparticles (NPs), where 0.00≤x≤0.08, were synthesized to test their photocatalytic, antibacterial and antibiofilm activities. The structural and optical properties of the prepared NPs were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-Vis spectroscopy and photoluminescence (PL) analysis. As La content increases, the bandgap energy increases, whereas the particle size decreases. The photocatalytic activity of the prepared NPs is evaluated by the degradation of methylene blue (MB) dye under sunlight irradiation. Superior activity is exhibited by Mg0.33Ni0.33Co0.33La0.01Fe1.99O4 NPs. The influence of catalyst dosage, pH, temperature and addition of graphene (Gr) on the photodegradation reaction was studied. Increasing the pH and temperature improved the rate of the photodegradation reaction. The antibacterial and antibiofilm activities of the NPs were assessed against Escherichia coli, Leclercia adecarboxylata, Staphylococcus aureus and Enterococcus faecium. Mg0.33Ni0.33Co0.33Fe2O4 NPs inhibited bacterial growth. They had bacteriostatic activity on all isolates, with a greater effect on Gram-positive bacteria. All tested nano-ferrites had significant antibiofilm activities against some biofilms.

Biofilm control strategies in the light of biofilm-forming microorganisms

Biofilm is a complex consortium of microorganisms attached to biotic or abiotic surfaces and live in self-produced or acquired extracellular polymeric substances (EPSs). EPSs are mainly formed by lipids, polysaccharides, proteins, and extracellular DNAs. The adherence to the surface of microbial communities is seen in food, medical, dental, industrial, and environmental fields. Biofilm development in food processing areas challenges food hygiene, and human health. In addition, bacterial attachment and biofilm formation on medical implants inside human tissue can cause multiple critical chronic infections. More than 30 years of international research on the mechanisms of biofilm formation have been underway to address concerns about bacterial biofilm infections. Antibiofilm strategies contain cold atmospheric plasma, nanotechnological, phage-based, antimicrobial peptides, and quorum sensing inhibition. In the last years, the studies on environmentally-friendly techniques such as essential oils and bacteriophages have been intensified to reduce microbial growth. However, the mechanisms of the biofilm matrix formation are still unclear. This review aims to discuss the latest antibiofilm therapeutic strategies against biofilm-forming bacteria.

Antimicrobial Resistance and Recent Alternatives to Antibiotics for the Control of Bacterial Pathogens with an Emphasis on Foodborne Pathogens

Antimicrobial resistance (AMR) is one of the most important global public health problems. The imprudent use of antibiotics in humans and animals has resulted in the emergence of antibiotic-resistant bacteria. The dissemination of these strains and their resistant determinants could endanger antibiotic efficacy. Therefore, there is an urgent need to identify and develop novel strategies to combat antibiotic resistance. This review provides insights into the evolution and the mechanisms of AMR. Additionally, it discusses alternative approaches that might be used to control AMR, including probiotics, prebiotics, antimicrobial peptides, small molecules, organic acids, essential oils, bacteriophage, fecal transplants, and nanoparticles.

Inhibitory effects of hexanal on acylated homoserine lactones (AHLs) production to disrupt biofilm formation and enzymes activity in Erwinia carotovora and Pseudomonas fluorescens

Erwinia carotovora and Pseudomonas fluorescens were two bacteria commonly caused the spoilage of vegetables through biofilm formation and secretion of extracellular enzymes. In this study, N-(3-oxohexanoyl)-L-homoserine lactone (3-oxo-C6-HSL) and N-Octanoyl-L-homoserine lactone (C8-HSL) were confirmed as acylated homoserine lactones (AHLs) signal molecule produced by E. carotovora and P. fluorescens, respectively. In addition, quorum sensing inhibitory (QSI) effects of hexanal on AHLs production were evaluated. Hexanal at 1/2 minimum inhibitory concentration (MIC) was achieved 76.27% inhibitory rate of 3-oxo-C6-HSL production in E. carotovora and a inhibitory rate of C8-HSL (60.78%) in P. fluorescens. The amount of biofilm formation and activity of extracellular enzymes treated with 1/2 MIC of hexanal were restored with different concentrations (10 ng/mL, 50 ng/mL, 100 ng/mL) of exogenous AHLs (P < 0.05), which verified QSI effect of hexanal on biofilm and extracellular enzymes were due to its inhibition on AHLs production. Molecular docking analysis showed that hexanal could interact with EcbI and PcoI protein to disrupt AHLs production. Furthermore, results showed that sub-MICs of hexanal could suppress expressions of ecbI and pcoI genes in AHL-mediated QS system of E. carotovora and P. fluorescens. This study provides theoretical support for the application of essential oils as QS inhibitors in the preservation of vegetables.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05624-9.

Inhibitory Effect of Monoterpenoid Glycosides Extracts from Peony Seed Meal on Streptococcus suis LuxS/AI-2 Quorum Sensing System and Biofilm

Streptococcus suis LuxS/AI-2 quorum sensing system regulates biofilm formation, resulting in increased pathogenicity and drug resistance, and diminished efficacy of antibiotic treatment. The remaining peony seed cake after oil extraction is rich in monoterpenoid glycosides, which can inhibit the formation of bacterial biofilm. In this study, we investigated the effect of seven major monocomponents (suffruticosol A, suffruticosol B, suffruticosol C, paeonifloin, albiflorin, trans-ε-viniferin, gnetin H) of peony seed meal on minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of S. suis. The results showed that the MICs of the seven single components were all greater than 200 μg/mL, with no significant bacteriostatic and bactericidal advantages. Crystal violet staining and scanning electron microscope observation showed that the seven single components had a certain inhibitory effect on the biofilm formation ability of S. suis at sub-MIC concentration. Among them, the ability of paeoniflorin to inhibit biofilm was significantly higher than that of the other six single components. AI-2 signaling molecules were detected by bioreporter strain Vibrio harvey BB170. The detection results of AI-2 signal molecules found that at 1/2 MIC concentration, paeoniflorin significantly inhibited the production of S. suis AI-2 signal, and the inhibitory effect was better than that of the other six single components. In addition, molecular docking analysis revealed that paeoniflorin had a significant binding activity with LuxS protein compared with the other six single components. The present study provides evidence that paeoniflorin plays a key role in the regulation of the inhibition of S. suis LuxS/AI-2 system and biofilm formation in peony seed meal.

Potential of Aromatic Plant-Derived Essential Oils for the Control of Foodborne Bacteria and Antibiotic Resistance in Animal Production: A Review

Antibiotic resistance has become a severe public threat to human health worldwide. Supplementing antibiotic growth promoters (AGPs) at subtherapeutic levels has been a commonly applied method to improve the production performance of livestock and poultry, but the misuse of antibiotics in animal production plays a major role in the antibiotic resistance crisis and foodborne disease outbreaks. The addition of AGPs to improve production performance in livestock and poultry has been prohibited in some countries, including Europe, the United States and China. Moreover, cross-resistance could result in the development of multidrug resistant bacteria and limit therapeutic options for human and animal health. Therefore, finding alternatives to antibiotics to maintain the efficiency of livestock production and reduce the risk of foodborne disease outbreaks is beneficial to human health and the sustainable development of animal husbandry. Essential oils (EOs) and their individual compounds derived from aromatic plants are becoming increasingly popular as potential antibiotic alternatives for animal production based on their antibacterial properties. This paper reviews recent studies in the application of EOs in animal production for the control of foodborne pathogens, summarizes their molecular modes of action to increase the susceptibility of antibiotic-resistant bacteria, and provides a promising role for the application of nanoencapsulated EOs in animal production to control bacteria and overcome antibiotic resistance.

Synthesis and evaluation of inhibitory potentials of microbial biofilms and quorum-sensing by 3-(1,3-dithian-2-ylidene) pentane-2,4-dione and ethyl-2-cyano-2-(1,3-dithian-2-ylidene) acetate

The virulence and resistance of pathogenic microorganisms are promoted by quorum-sensing (QS) mediated traits and biofilms. The development of antimicrobial agents which can reduce the incidence of microbial resistance by disrupting the establishment of biofilms and QS, constitute a suitable strategy to reduce the emergence of pathogenic strains that are resistant to antibiotics. In this study, 3-(1,3-dithian-2-ylidene) pentane-2,4-dione (1) and ethyl-2-cyano-2-(1,3-dithian-2-ylidene) acetate (2) were successfully synthesized and characterized using EIMS, 1H NMR and 13C NMR techniques. On S. aureus, both compounds had MIC (minimal inhibitory concentrations) of 0.625 mg/mL while on E. coli and C. albicans, compound 2 showed higher activity than compound 1. All compounds inhibited formation of biofilms by C. albicans and S. aureus at sub-MIC with compound 1 being more active than compound 2. On E. coli, only compound 1 inhibited biofilm formation. Violacein production of violacein in C. violaceum CV12472 and quorum sensing in C. violaceum CV026 were inhibited indicating that the compounds could block signal production and reception. Anti-quorum sensing at sub-MIC concentrations revealed by inhibition zones were 13.0±0.5 mm and 8.0±0.5 mm at MIC and MIC/2 respectively for compound 1 and for compound 2, they were 11.5±0.4 mm and 7.5±0.0 mm at MIC and MIC/2 respectively. Concentration-dependent swarming motility was exhibited by both compounds with compound 1 slightly more active than compound 2. The results indicate that the organosulphur compounds could be suitable candidates for modern antibiotics.

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.

The Derived Components of Gnaphalium hypoleucum DC. Reduce Quorum Sensing of Chromobacterium violaceum

Gnaphalium hypoleucum DC. was first recorded in the Chinese National Pharmacopoeia “Yi Plant Medicine”. There is no detailed report on its main components’ activity in suppressing the quorum sensing activity (QS) of bacteria. Our study aimed to screen the main components in extracts of G. hypoleucum DC. in order to measure their effects on bacterial QS activity and to explore specific quorum sensing mechanisms that are affected by G. hypoleucum DC. extracts. Crude extracts of G. hypoleucum DC. contained significant amounts of two compounds shown to inhibit bacterial QS activity, namely apigenin and luteolin. Apigenin and luteolin in crude extracts of G. hypoleucum DC. showed substantial inhibition of pigment formation, biofilm production, and motility in Chromobacterium violaceum ATCC 12472 compared to the effects of other phytochemicals from G. hypoleucum DC. Apigenin and luteolin exhibited a strong QS inhibitory effect on C. violaceum, interfering with the violacein pigment biosynthesis by downregulating the vioB, vioC, and vioD genes. In the presence of signal molecules, the QS effect is prevented, and the selected compounds can still inhibit the production of the characteristic purple pigment in C. violaceum. Based on qualitative and quantitative research using genomics and bioinformatics, we concluded that apigenin and luteolin in crude extracts of G. hypoleucum DC can interfere with the generation of QS in C. violaceum by downregulating the vioB, vioC, and vioD genes. Indeed, G. hypoleucum DC. is used for the treatment of bacterial infections, and this research provides new ideas and potential alternative uses for medicinal plants.

Cinnamomum: The New Therapeutic Agents for Inhibition of Bacterial and Fungal Biofilm-Associated Infection

Due to the potent antibacterial properties of Cinnamomum and its derivatives, particularly cinnamaldehyde, recent studies have used these compounds to inhibit the growth of the most prevalent bacterial and fungal biofilms. By inhibiting flagella protein synthesis and swarming motility, Cinnamomum could suppress bacterial attachment, colonization, and biofilm formation in an early stage. Furthermore, by downregulation of Cyclic di‐guanosine monophosphate (c‐di‐GMP), biofilm-related genes, and quorum sensing, this compound suppresses intercellular adherence and accumulation of bacterial cells in biofilm and inhibits important bacterial virulence factors. In addition, Cinnamomum could lead to preformed biofilm elimination by enhancing membrane permeability and the disruption of membrane integrity. Moreover, this substance suppresses the Candida species adherence to the oral epithelial cells, leading to the cell wall deformities, damage, and leakages of intracellular material that may contribute to the established Candida’s biofilm elimination. Therefore, by inhibiting biofilm maturation and destroying the external structure of biofilm, Cinnamomum could boost antibiotic treatment success in combination therapy. However, Cinnamomum has several disadvantages, such as poor solubility in aqueous solution, instability, and volatility; thus, the use of different drug-delivery systems may resolve these limitations and should be further considered in future investigations. Overall, Cinnamomum could be a promising agent for inhibiting microbial biofilm-associated infection and could be used as a catheter and other medical materials surface coatings to suppress biofilm formation. Nonetheless, further in vitro toxicology analysis and animal experiments are required to confirm the reported molecular antibiofilm effect of Cinnamomum and its derivative components against microbial biofilm.

Advances in Biosynthesis and Pharmacological Effects of Cinnamomum camphora (L.) Presl Essential Oil

Cinnamomum camphora (L.) Presl essential oil (CCEO) is a volatile oil with aroma and is extracted from various tissues of Cinnamomum camphora. It is traditionally used as a spice, preservative, as an anti-inflammatory and for sterilization. Terpenoids are the main active components in CCEO. Based on currently available research, considerable effort is still needed to study the biosynthesis and regulation of terpenoids in CCEO. In this review, the research progress related to terpenoid biosynthesis and bioactivity in CCEO in recent years is summarized, with the data compiled and presented mainly from online resources such as PubMed, Scopus and CNKI in China up to May 2022. The research advances related to key enzymes in the terpenoid biosynthesis pathway are mainly discussed. Previous studies have isolated some genes encoding key enzymes involved in terpenoid biosynthesis; however, among these genes, only a few TPS genes have been verified to catalyze the production of terpenoid synthases at the protein level. Most genes encoding key enzymes have been cloned and isolated, but no transgenic experiments have been carried out to verify gene function. In-depth study of the biosynthesis of terpenoids in CCEO may contribute to a better understanding of the differential accumulation of terpenoids in different types of C. camphora and provide reference for improving terpenoid content in CCEO.

Unani medicinal herbs as potential air disinfectants: an evidence-based review

OBJECTIVES

Indoor air quality has a significant impact on our health and quality of life, as people spends 80-90% of their time indoors. Fumigation of several medicinal herbs has been recommended by Unani scholars to improve air quality, but their efficacy in air purification is still unknown. Hence, this article aims to discuss the applicability of proposed medicinal herbs in the light of current researches.

METHODS

A manual literature survey of classical Unani texts was conducted to collect information about the herbs recommended for air purification. In addition, research databases such as PubMed, Google Scholar, and ScienceDirect were extensively searched for evidence on the efficacy and mechanism of action of the suggested herbs in air purification.

RESULTS

In classical Unani texts, authors have found descriptions of 26 herbs that have been recommended for improving air quality. In-vitro studies have confirmed the antimicrobial activity of 19 of these herbs. Moreover, the efficacy of Styrax benzoin, Commiphora myrrha and Acorus calamus fumigation on aerial microbes have also been validated by studies.

CONCLUSIONS

The findings of the literature review clearly demonstrated that the herbs recommended by Unani scholars for air purification have broad-spectrum antimicrobial activity, indicating that these herbs could be a potential candidate for air disinfectant. Therefore, authors recommend the further researches on proposed herbs to validate their efficiency against airborne pathogens in the vapour phase.

Quorum sensing inhibitory potential of vaccenic acid against Chromobacterium violaceum and methicillin-resistant Staphylococcus aureus

Quorum sensing (QS) is a potential target for inhibiting bacterial antibiotic resistance and associated pathogenicity. The present study aimed to investigate vaccenic acid anti-QS and antibiofilm potential against Chromobacterium violaceum and methicillin-resistant Staphylococcus aureus (MRSA). In the broth microdilution method, we determined the minimum inhibitory concentration (MIC) of vaccenic acid against C. violaceum and MRSA. Then, we determined the vaccenic acid anti-QS potential against C. violaceum via a violacein inhibition assay. Vaccenic acid at a sub-MIC concentration significantly inhibited violacein pigment production. Vaccenic acid also inhibits C. violaceum and MRSA biofilm formation at sub-MIC concentrations. The effect of vaccenic acid antivirulence potential was evaluated by phenotypic virulence assays. The results showed that vaccenic acid at a sub-MIC concentration significantly inhibited the virulence production of C. violaceum (chitinase and motility) and MRSA (hemolysin and staphyloxanthin production). Quantitative PCR analysis revealed the downregulation of QS associated genes upon vaccenic acid treatment. This resulted in the downregulation of genes involved in QS mechanisms such as cviI, cviR, and SarA and pigment production such as vioB and crtM. The results of the present study suggest that vaccenic acid is a promising agent to combat C. violaceum and MRSA.

Mechanisms of Inhibition of Quorum Sensing as an Alternative for the Control of E. coli and Salmonella

Quorum sensing (QS) is a process of cell–cell communication for bacteria such as E. coli and Salmonella that cause foodborne diseases, with the production, release, and detection of autoinducer (AI) molecules that participate in the regulation of virulence genes. All of these proteins are useful in coordinating collective behavior, the expression of virulence factors, and the pathogenicity of Gram-negative bacteria. In this work, we review the natural or synthetic inhibitor molecules of QS that inactivate the autoinducer and block QS regulatory proteins in E. coli and Salmonella. Furthermore, we describe mechanisms of QS inhibitors (QSIs) that act as competitive inhibitors, being a useful tool for preventing virulence gene expression through the downregulation of AI-2 production pathways and the disruption of signal uptake. In addition, we showed that QSIs have negative regulatory activity of genes related to bacterial biofilm formation on clinical artifacts, which confirms the therapeutic potential of QSIs in the control of infectious pathogens. Finally, we discuss resistance to QSIs, the design of next-generation QSIs, and how these molecules can be leveraged to provide a new antivirulence therapy to combat diseases caused by E. coli or Salmonella.

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.

Influence of Essential Oils on the Microbiological Quality of Fish Meat during Storage

Simple Summary

Fish meat is highly perishable due to its composition and the naturally present microbiota. The food industry aims to provide healthy, safe, and high-quality products to the market. Several strategies, including the use of natural preservatives, may be used to enhance food shelf life, and they can also be combined with others, such as vacuum packaging. This being the case, essential oils are natural plant components that, due to their composition, possess high antimicrobial and antioxidant effects, and are therefore good candidates to be tested as fish preservatives together with vacuum packaging. In the present study, essential oils from Citrus lemon and Cinnamomum camphora were added to rainbow trout meat for evaluating the microbiological quality (counts of bacteria and identification of present microbiota) of the fish when vacuum packed and stored for 7 days at 4 °C. Our results show that lemon (0.5% and 1%) as well as C. camphora essential oils (0.5% and 1%) had a positive effect on the microbiological quality of fish meat, keeping a high microbial quality of the fish fillets during 7 days of cold storage. The use of these essential oils in combination with vacuum packaging is beneficial in extending the shelf life of rainbow trout meat. All isolated species under the tested conditions are identified in the present study; such information will be useful for the future development of preservation methodologies that target isolated microorganisms, which will enable the food industry to enhance the shelf life and safety of fish.

Abstract

The aim of the present study was to evaluate the microbiological quality of rainbow trout meat treated with essential oils (EOs from Citrus limon and Cinnamomum camphora) at concentrations of 0.5% and 1.0% in combination with vacuum packaging during storage. The composition of the EOs were analyzed by gas chromatography coupled with mass spectrometry, and total viable counts (TVCs), coliform bacteria (CB), and lactic acid bacteria (LAB) were determined on the zeroth, first, third, fifth, and seventh days of storage at 4 °C. Individual species of isolated microorganisms were identified using a MALDI-TOF MS Biotyper. The results show that the major components of the EOs were linalool (98.1%) in C. camphora and α-limonene in C. limon. The highest number of TVCs and CB were 4.49 log CFU/g and 2.65 log CFU/g in aerobically packed samples at the seventh day. The lowest TVCs were those of samples treated with 1% C. camphora EO. For CB the most effective treatment was 1% lemon EO. LAB were only detected in a few samples, and were never present in aerobically packed samples; the highest number of LAB was 1.39 log CFU/g in samples treated with 1% lemon EO at day seven. The most commonly isolated coliform bacteria were Hafnia alvei, Serratia fonticola, Serratia proteamaculans, Pantoea agglomerans, and Yersinia ruckeri. Lactobacillus sakei, Staphylococcus hominis, and Carnobacterium maltaromaticum were the most frequently isolated bacteria from lactic acid bacteria. In conclusion, C. camphora EO at a concentration of 1% showed the highest antimicrobial activity.

Camphor wood, a potentially harmful museum storage material: an analytical study using instrumental methods

Camphor wood is welcomed by museums due to its insect-repelling effect but the smell indicates a potential risk to the collections. In order to judge the suitability of camphor wood as a museum storage material, typical camphor wood (Cinnamomum camphora) samples aged for different years were evaluated by conducting the Oddy test. Gas chromatography-mass spectrometry (GC-MS), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and time of flight-secondary ion mass spectrometry (ToF-SIMS) were applied to identifying the volatile organic compounds (VOCs) emitted by the materials and the corrosion products, respectively. The results showed that the camphor wood samples led to visible corrosion on copper and lead coupons. GC-MS indicated that the major VOCs emitted were terpenes and their derivatives, while XRD, EDS, and ToF-SIMS provided various clues to the corrosion mechanisms. Pb₁₀(CO₃)₆(OH)₆O and CuO were regarded as the major corrosion products of lead and copper coupons, respectively. The study provides the museum curators and the conservators with abundant information to reassess the application of camphor wood to museums as well as a different way to understand the mechanism of metallic corrosion caused by camphor wood.

Quorum sensing inhibitory effect of bergamot oil and aspidosperma extract against Chromobacterium violaceum and Pseudomonas aeruginosa

Quorum sensing (QS) represents a major target for reducing bacterial pathogenicity and antibiotic resistance. This study identifies bergamot and aspidosperma as new potential sources of anti-QS agents. We investigated the anti-QS activity of plant materials on both Chromobacterium violaceum and Pseudomonas aeruginosa. Initially, we determined the minimum inhibitory concentrations (MICs) of plant materials using a broth microdilution method. Subsequently, we tested the effect of sub-MIC concentrations on QS-regulated traits and virulence factors production in test bacteria. Results revealed that bergamot and aspidosperma inhibited the ability of C. violaceum to produce violacein. Other QS-controlled phenotypes of C. violaceum, namely chitinolytic activity, motility, and biofilm formation, were also reduced by both plant materials. Moreover, QS-linked traits of P. aeruginosa were also reduced. Bergamot inhibited swarming but not swimming motility, while aspidosperma diminished both motility types in P. aeruginosa. Both plant materials also demonstrated antibiofilm activity and inhibited the production of protease and pyocyanin in P. aeruginosa. Furthermore, we tested the anti-QS effect of plant materials on the transcriptional level using RT-qPCR. Bergamot dramatically downregulated the C. violaceum autoinducer synthase gene cviI and the vioB gene involved in violacein biosynthesis, confirming the phenotypic observation on its anti-QS activity. Aspidosperma also reduced the expression of cviI and vioB but less drastically than bergamot. In P. aeruginosa, downregulation in the transcripts of the QS genes lasI, lasR, rhlI, and rhlR was also achieved by bergamot and aspidosperma. Therefore, data in the present study suggest the usefulness of bergamot and aspidosperma as sources of antivirulence agents.

Sub-Tissue Localization of Phytochemicals in Cinnamomum camphora (L.) J. Presl. Growing in Northern Italy

In the present paper, we focused our attention on Cinnamomum camphora (L.) J. Presl. (Lauraceae), studied at three levels: (i) micromorphological, with the analysis of the secretory structures and a novel in-depth histochemical characterization of the secreted compounds; (ii) phytochemical, with the characterization of the essential oils from young stems, fruits, and leaves, subjected to different conservation procedures (fresh, dried, stored at −20 °C, stored at −80 °C) and collected in two different years; (iii) bioactive, consisting of a study of the potential antibacterial activity of the essential oils. The micromorphological investigation proved the presence of secretory cells characterized by a multi-layered wall in the young stems and leaves. They resulted in two different types: mucilage cells producing muco-polysaccharides and oil cells with an exclusive terpene production. The phytochemical investigations showed a predominance of monoterpenes over sesquiterpene derivatives; among them, the main components retrieved in all samples were 1,8-cineole followed by α-terpineol and sabinene. Conservation procedures seem to only influence the amounts of specific components, i.e., 1,8-cineole and α-terpineol, while analyses on each plant part revealed the presence of some peculiar secondary constituents for each of them. Finally, the evaluation of the antibacterial activity of the essential oil showed a promising activity against various microorganisms, as Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis and Pseudomonas aeruginosa. In conclusion, we combined a micromorphological and phytochemical approach of the study on different plant parts of C. camphora, linking the occurrence of secretory cells to the production of essential oils. We compared, for the first time, the composition of essential oils derived from different plant matrices conserved with different procedures, allowing us to highlight a relation between the conservation technique and the main components of the profiles. Moreover, the preliminary antibacterial studies evidenced the potential activity of the essential oils against various microorganisms potentially dangerous for plants and humans.

A Preliminary Study of Chemical Profiles of Honey, Cerumen, and Propolis of the African Stingless Bee Meliponula ferruginea

Recently, the honey and propolis of stingless bees have been attracting growing attention because of their health-promoting properties. However, studies on these products of African Meliponini are still very scarce. In this preliminary study, we analyzed the chemical composition of honey, two cerumen, and two resin deposits (propolis) samples of Meliponula ferruginea from Tanzania. The honey of M. ferruginea was profiled by NMR and indicated different long-term stability from Apis mellifera European (Bulgarian) honey. It differed significantly in sugar and organic acids content and had a very high amount of the disaccharide trehalulose, known for its bioactivities. We suggested trehalulose to be a potential marker for African stingless bee honey analogously to the recent proposal for Meliponini honey from Asia, South America, and Australia and demonstrated its easy discrimination by ¹³C NMR. Propolis and cerumen were studied by GC-MS (gas chromatography-mass spectometry). The samples contained mainly terpenoids (di-and triterpenes) but demonstrated qualitative and quantitative differences. This fact was an indication that possibly M. ferruginea has no strict preferences for resins used to construct and protect their nests. The antimicrobial and anti-quorum sensing properties of the two materials were also tested. These first results demonstrated that the honey, cerumen, and propolis of African stingless bees were rich in biologically active substances and deserved further research.

Molecular cloning and functional identification of a high-efficiency (+)-borneol dehydrogenase from Cinnamomum camphora (L.) Presl

Cinnamomum camphora (L.) Presl, rich in terpenoids, is an important commercial plant. The monoterpenes borneol and camphor are highly desired compounds that have been widely and diversely used in medicine and spices since ancient times. However, the key enzymes in the biosynthetic pathway of borneol and camphor in C. camphora remains unknown, which limits access to these natural products. Here, the chirality of borneol and camphor were identified in C. camphora leaves. Besides the main (+)-borneol and (+)-camphor, C. camphora also contains small amounts of (-)-borneol and (-)-camphor. Then, CcBDH3 - an efficient (+)-borneol dehydrogenase (BDH) - was identified that catalyzed (+)-borneol into (+)-camphor in the presence of NAD⁺. The K_m value was 25.1 μM with a k_cat value of 5.4 × 10^-3 s^-1 at pH 8.5 and 30 °C. CcBDH3, which also yields (-)-camphor from (-)-borneol as a substrate, had a K_m value of 36.9 μM with a k_cat of 2.1 × 10^-3 s^-1, and pH of 8.0 and temperature of 32 °C. We further compared the conformational specificity of two other reported BDHs, ZSD1 and ADH2, and found that ZSD1 had the highest conversion rate with (-)-borneol. These findings provide a new way for the production of camphor with various optical activities by metabolic engineering, and the identified camphor biosynthesis pathway provides the foundation for using genetic engineering to improve the production and purity of (+)-borneol in planta.

Anti-quorum Sensing and Anti-biofilm Activity of Zinc Oxide Nanospikes

This study evaluates the impact of two separate incubation periods (4 and 6 weeks) on the morphology of sol-gel-fabricated ZnO nanospikes (ZNs), that is, ZN1 and ZN2, respectively. We further analyzed the inhibitory effects of ZN1 and ZN2 on quorum sensing (QS) and biofilm formation in Pseudomonas aeruginosa (PAO1) and Chromobacterium violaceum (strains 12472 and CVO26). The size of the synthesized ZNs was in the range of 40-130 nm, and finer nanoparticles were synthesized after an incubation period of 6 weeks. Treatment with ZNs decreased the production of violacein in the pathogen without affecting the bacterial growth, which indicated that ZNs inhibited the QS signaling regulated by N-acyl homoserine lactone. ZN2 had a higher inhibitory action on the virulence factor productivity than ZN1. Furthermore, ZN2-treated cells displayed a substantial decrease in azocasein-degrading protease activity (80%), elastase activity (83%), and pyocyanin production (85%) relative to untreated P. aeruginosa PAO1 cells. Treatment with ZN2 decreased swarming motility and exopolysaccharide production by 89 and 85%, respectively. ZN2 was effective against both the las & pqs systems of P. aeruginosa and exhibited broad-spectrum activity. Additionally, ZN2 was more efficient in inhibiting the biofilm formation at the attachment stage than ZN1. These findings revealed that in P. aeruginosa, ZN2 demonstrated inhibitory effects on QS as well as on the development of biofilms. Thus, ZN2 can be potentially used to treat drug-resistant P. aeruginosa infections.

Effect of kitasamycin and nitrofurantoin at subinhibitory concentrations on quorum sensing regulated traits of Chromobacterium violaceum

Quorum sensing (QS) is a mechanism of intercellular communication in bacteria that received substantial attention as alternate strategy for combating bacterial resistance and the development of new anti-infective agents. The present investigation reports on the assessment of using subinhibitory concentrations of antibiotics for the inhibition of QS-regulated phenotypes in Chromobacterium violaceum. Primarily, the minimum inhibitory concentrations of a series of antibiotics were determined by a microdilution method. Subsequently, the inhibitory effects of selected antibiotics on QS-regulated traits, namely violacein and chitinase production, biofilm formation and motility were evaluated using C. violaceum CV026 and C. violaceum ATCC 12472. Results revealed that kitasamycin and nitrofurantoin exhibited the highest quorum sensing inhibitory (QSI) activity. The amount of violacein produced by C. violaceum was significantly reduced in the presence of either kitasamycin or nitrofurantoin. Moreover, the chitinolytic activity, biofilm formation, and motility were also impaired in kitasamycin or nitrofurantoin-treated cultures. We further confirmed QSI effects at the molecular level using molecular docking and real-time quantitative polymerase chain reaction (RT-qPCR). Results of molecular docking suggested that both antibiotics can interact with CviR transcriptional regulator of C. violaceum. Furthermore, RT-qPCR revealed the suppressive effect of kitasamycin and nitrofurantoin on five genes under the control of the CviI/CviR system: cviI, cviR, vioB, vioC, and vioD. Giving that kitasamycin and nitrofurantoin are being safely used for decades, this study emphasizes their potential application as antivirulence agents to disarm resistant bacterial strains, making their removal an easier task for the immune system or for another antibacterial agent.

Phenotypic detection of quorum sensing inhibition in Pseudomonas aeruginosa pyoverdine and swarming by volatile organic products

Aim: To determine phenotypically the anti quorum-sensing (QS) activity of 30 volatile organic products (VOPs) through the inhibition of swarming motility and pyoverdine production in Pseudomonas aeruginosa. Materials & methods: Twenty-four essential oils and six small volatile organic compounds randomly selected were screened for their anti-QS activity by violacein inhibition on Chromobacterium violaceum. The VOPs with positive results were subsequently evaluated for swarming motility and pyoverdine production on P. aeruginosa determining the colony diameter and fluorescence under UV light, respectively. Results: Fifty percent of VOPs tested showed strong violacein inhibition, 40% presented anti-swarming activity and 33% inhibited pyoverdine production. Conclusion: Our data demonstrate that VOPs have a great potential to inhibit virulence factors mediated by QS in P. aeruginosa

Optimization and Characterization of Microwave-Assisted Hydro-Distillation Extraction of Essential Oils from Cinnamomum camphora Leaf and Recovery of Polyphenols from Extract Fluid

In this study, the efficiency of microwave-assisted hydro-distillation (MAHD) to extract essential oil from Cinnamomum camphora leaf, and the recovery of polyphenols from extract fluid were investigated. The effects of microwave power, liquid-to-material ratio, and extraction time on the extraction efficiency were studied by a single factor test as well as the response surface methodology (RSM) based on the central composite design method. The optimal extraction conditions were a microwave power of 786.27 W, liquid-to-material ratio of 7.47:1 mL/g, and extraction time of 35.57 min. The yield of essential oil was 3.26 ± 0.05% (w/w), and the recovery of polyphenols was 4.97 ± 0.02 mg gallic acid equivalent/g dry weight under the optimal conditions. Furthermore, the comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) was used to characterize the essential oils of fresh and fallen leaves, and 159 individual compounds were tentatively identified, accounting for more than 89.68 and 87.88% of the total contents, respectively. The main ingredients include sabinene, l-β-pinene, β-myrcene, α-terpineol, 3-heptanone, and β-thujene, as well as δ-terpineol and 3-heptanone, which were first identified in C. camphora essential oil. In conclusion, the MAHD method could extract essential oil from C. camphora with high efficiency, and the polyphenols could be obtained from the extract fluid at the same time, improving the utilization of C. camphora leaf.