Thymol as a critical component of Thymus vulgaris L. essential oil combats Pseudomonas aeruginosa by intercalating DNA and inactivating biofilm

A phytotherapeutic approach to hinder the resistance against clindamycin by MRSA: in vitro and in silico studies

AIMS

This study investigates the potential effects of essential oils (EOs) in enhancing the efficacy of clindamycin against Methicillin-resistant Staphylococcus aureus (MRSA) using in vitro and computer simulations. The research seeks to identify essential oils that exhibit synergistic activity with clindamycin and determine their potential key active components.

MATERIALS AND METHODS

Essential oils commonly used in traditional medicine were tested for their antimicrobial activity against MRSA. The minimum inhibitory concentration (MIC) was determined using in vitro microdilution assays. A synergistic test with clindamycin was performed, and molecular docking studies evaluated the interaction between a key compound (trans-cinnamaldehyde) and MRSA protein.

RESULTS

EOs from Cinnamomum verum, Rosmarinus officinalis, Salvia officinalis, and Thymus vulgaris demonstrated significant inhibitory and synergistic activities against MRSA, standard strain, and human clinical isolates. Gas Chromatography/Mass Spectroscopy identified trans-cinnamaldehyde, eucalyptol, and thymol as prominent antibacterial compounds. Molecular docking studies confirmed trans-cinnamaldehyde's strong binding to MRSA's AgrA protein, elucidating its enhanced efficacy.

CONCLUSION

The study underscores the potential of plant-based therapies to augment the effectiveness of conventional antibiotics like clindamycin in combating MRSA and addressing antibiotic resistance by integrating traditional plant remedies with modern medical approaches.

Flavourzyme Suppresses Pseudomonas aeruginosa Biofilms by Targeting Motility, Quorum Sensing, and Virulence Genes

The biofilm-mediated persistence of Pseudomonas aeruginosa in the food and biomedical sectors is currently a global concern. In light of this challenge, this study investigated a preventive approach against P. aeruginosa biofilm formation using Flavourzyme, a food-grade peptidase, considering its antibiofilm potential. The results revealed that a co-culture comprising 300 µL/mL (1 × minimum inhibitory concentration [MIC]) of Flavourzyme could kill P. aeruginosa. On the MBEC™ biofilm-forming device, 0.125 × MIC of Flavourzyme inhibited > 4.5 log CFU/peg of biofilm. Cell motilities and the biosynthesis of quorum sensing (QS) molecules such as N-acyl-homoserine lactones (AHLs), including C4-HSL, decreased significantly at 0.06 × MIC of Flavourzyme and became undetectable at 0.125 × MIC. Interestingly, while 0.03 × MIC of Flavourzyme elicited diverse expressions of QS and virulence-regulating genes, ≥ 0.06 × MIC of Flavourzyme remarkably suppressed the relative genomic expressions. This study proposes Flavourzyme as a potent antibiofilm agent against P. aeruginosa biofilms, recommending specific concentrations for effective use in food preservation.

Antibacterial Activity of Selected Essential Oil Components and Their Derivatives: A Review

Essential oils (EOs) are gaining ground and have been intensively studied due to their widespread use in the pharmaceutical, food, and cosmetics industries. The essential components of EOs have been recognized for diverse therapeutic activities and have gained significant attention for their potential antibacterial activities. Despite the popularity of EOs and potent biological properties, their bioactive components and their derivatives are still not comprehensively characterized. This review explores the antibacterial efficacy of selected EO components and their derivatives, focusing on monoterpenes chosen (i.e., carvacrol, menthol, and thymol) and phenylpropanoids (i.e., cinnamaldehyde and eugenol). Furthermore, this review highlights recent advancements in developing derivatives of these EO components, which have shown improved antibacterial activity with reduced toxicity. By summarizing recent studies, this review reveals the potential of these natural compounds and their derivatives as promising candidates for pharmaceuticals, food preservation, and as alternatives to synthetic antibiotics in combating bacterial resistance.

Evaluation of Antibacterial Activity in Some Algerian Essential Oils and Selection of Thymus vulgaris as a Potential Biofilm and Quorum Sensing Inhibitor Against Pseudomonas aeruginosa

Biofilm formation and virulence factor production by Pseudomonas aeruginosa are identified as the main mechanisms of its antibiotic resistance and pathogenicity. In this context, the study of the chemical composition of three Algerian essential oils (EOs) and the screening of their antibacterial, antibiofilm, and virulence factor inhibitory activities enabled us to select the thyme EO as the best oil to control the P. aeruginosa strain isolated from hospital environments. This EO, composed essentially of thymol (55.82%) associated with carvacrol, had an anti-adhesive activity of 69.8% at a concentration of 5 µL/mL and a biofilm eradication activity of 74.86% at a concentration of 2.5 µL/mL. In addition, this EO was able to inhibit P. aeruginosa twitching motility by 100% at a concentration of 2.5 µL/mL. Pyocyanin was inhibited by 99.33% at a thyme EO concentration of 1.25 µL/mL. Rhamnolipids were significantly inhibited by 63.33% in the presence of thyme EO at a concentration of 1.25 µL/mL after 24 h of incubation. Molecular docking showed that carvacrol and thymol can bind to the three quorum sensing receptors in P. aeruginosa, RhlR, LasR, and PqsR, with good affinities, which can inhibit or modulate biofilm formation and the production of certain virulence factors.

Methods for Determination of Antimicrobial Activity of Essential Oils In Vitro-A Review

Essential oils (EOs) have been gaining popularity in the past decades among researchers due to their potential to replace conventional chemicals used in the fight against pests, pathogenic and spoilage microbes, and oxidation processes. EOs are complex mixtures with many chemical components, the content of which depends on many factors-not just the plant genus, species, or subspecies, but also chemotype, locality, climatic conditions, phase of vegetation, method of extraction, and others. Due to this fact, there is still much to study, with antimicrobial effect being one of the key properties of EOs. There are many methods that have been frequently used by researchers for in vitro evaluation; however, although the research has been going on for decades, an internationally accepted standard is still missing. Most of methods are based on time-proven standards used for the testing of antibiotics. Due to the specific properties of EOs and their components, such as volatility and hydrophobicity, many modifications of these standard procedures have been adopted. The aim of this review is to describe the most common methods and their modifications for the testing of antimicrobial properties of EOs and to point out the most controversial variables which can potentially affect results of the assays.

Investigation of genes involved in scent and color production in Rosa damascena Mill

Rosa damascena Mill., commonly known as the King Flower, is a fragrant and important species of the Rosaceae family. It is widely used in the perfumery and pharmaceutical industries. The scent and color of the flowers are significant characteristics of this ornamental plant. This study aimed to investigate the relative expression of MYB1, CCD1, FLS, PAL, CER1, GT1, ANS and PAR genes under two growth stages (S1 and S2) in two morphs. The CCD1 gene pathway is highly correlated with the biosynthesis of volatile compounds. The results showed that the overexpression of MYB1, one of the important transcription factors in the production of fragrance and color, in the Hot pink morph of sample S2 increased the expression of PAR, PAL, FLS, RhGT1, CCD1, ANS, CER1, and GGPPS. The methyl jasmonate (MeJA) stimulant had a positive and cumulative effect on gene expression in most genes, such as FLS in ACC.26 of the S2 sample, RhGT1, MYB1, CCD1, PAR, ANS, CER1, and PAL in ACC.1. To further study, a comprehensive analysis was performed to evaluate the relationship between the principal volatile compounds and colors. Our data suggest that the rose with pink flowers had a higher accumulation content of flavonoids and anthocyanin. To separate essential oil compounds, GC/MS analysis identified 26 compounds in four samples. The highest amount of geraniol, one of the main components of damask rose, was found in the Hot pink flower, 23.54%, under the influence of the MeJA hormone.

Microencapsulation to Harness the Antimicrobial Potential of Essential Oils and Their Applicability in Dairy Products: A Comprehensive Review of the Literature

This literature review explores cutting-edge microencapsulation techniques designed to enhance the antimicrobial efficacy of essential oils in dairy products. As consumer demand for natural preservatives rises, understanding the latest advancements in microencapsulation becomes crucial for improving the shelf life and safety of these products. The bibliometric analysis utilized in this review highlighted a large number of documents published on this topic in relation to the following keywords: essential oils, AND antimicrobials, AND dairy products, OR microencapsulation. The documents published in the last 11 years, between 2013 and 2023, showed a diversity of authors and countries researching this topic and the keywords commonly used. However, in the literature consulted, no study was identified that was based on bibliometric analysis and that critically evaluated the microencapsulation of essential oils and their antimicrobial potential in dairy products. This review synthesizes findings from diverse studies, shedding light on the various encapsulation methods employed and their impact on preserving the quality of dairy goods. Additionally, it discusses the potential applications and challenges associated with implementation in the dairy industry. This comprehensive analysis aims to provide valuable insights for researchers, food scientists, and industry professionals seeking to optimize the use of essential oils with antimicrobial properties in dairy formulations.

Insights into the antibacterial effectiveness of linalool against Shigella flexneri on pork surface: Changes in bacterial growth and pork quality

Shigella flexneri has the ability to contaminate pork and cause foodborne diseases. This study aimed to examine the effectiveness of linalool (a natural preservative) against S. flexneri and explore its potential application in contaminated pork. The results showed that linalool was capable of damaging the cell membrane and binding to the DNA of S. flexneri, and inhibiting biofilm formation and disrupting mature biofilms. The antibacterial effectiveness of linalool on the surface of pork was further demonstrated by analyzing the physicochemical properties of the pork (i.e., weight loss rate, pH value, color index, and TVB-N value) and its protein profiles. Linalool did not completely kill S. flexneri in pork at minimum bactericidal concentration (MBC) concentration and its antibacterial effect of linalool was stronger during the initial stage of storage. During storage, linalool influenced the abundance of specific proteins in the pork, particularly those involved in pathways related to fat metabolism. These findings offer novel insights into the antibacterial efficacy of linalool and its underlying mechanism in pork.

Gelatin/agar pH-indicator film based on cranberry extract loaded with linalool nanoparticle: Survey on physical, antimicrobial, and antioxidant properties

In this study, linalool-nanoparticles (L-NPs) were prepared (encapsulation efficiency was 68.54 %) and introduced pH-indicator film based on cranberry-extract (CEF) to develop multifunctional smart films. XRD analysis and FTIR spectroscopy indicated that cranberry-extract (CE) and L-NPs were uniformly distributed in the gelatin/agar matrix and could change the intermolecular structure of the film. Color change of smart films showed that CE endowed the film with pH-sensitive property. As CE and L-NPs were added to the film, the water contact angle (WCA) was increased from 57.03° to 117.73°, the elongation at break (EAB) was increased from 12.30 % to 34.60 %. Additionally, the introduction of L-NPs enhanced the antioxidant activity (DPPH free radical scavenging rate increased from 26.80 % to 36.35 %) and antibacterial activity (against S. aureus and E. coli) of the smart film, which were verified by its retarding effect on pork spoilage.

Eco-Friendly Sanitization of Indoor Environments: Effectiveness of Thyme Essential Oil in Controlling Bioaerosol Levels and Disinfecting Surfaces

Bioaerosols and pathogens in indoor workplaces and residential environments are the primary culprits of several infections. Techniques for sanitizing air and surfaces typically involve the use of UV rays or chemical sanitizers, which may release chemical residues harmful to human health. Essential oils, natural substances derived from plants, which exhibit broad antimicrobial properties, could be a viable alternative for air and surface sanitation. The objective of this study has been to investigate the efficacy of thyme essential oil (TEO) in environmental sanitation processes. In Vitro assays through agar well diffusion, disk volatilization and tube dilution methods revealed significant antimicrobial activity of TEO 100% against foodborne and environmental isolates, with both bacteriostatic/fungistatic and bactericidal/fungicidal effects. Therefore, aqueous solutions of TEO 2.5% and 5% were formulated for air sanitation through nebulization and surface disinfection via direct contact. Bioaerosol samples and surface swabs were analyzed before and after sanitation, demonstrating the efficacy of aqueous solutions of TEO in reducing mesophilic and psychrophilic bacteria and environmental fungi levels in both air and on surfaces. The obtained results prove the antimicrobial potential of aqueous solutions of TEO in improving indoor air quality and surface cleanliness, suggesting thyme essential oil as an effective and safe natural sanitizer with minimal environmental impact compared to dangerous chemical disinfectants.

Combined in vitro/in silico approaches, molecular dynamics simulations and safety assessment of the multifunctional properties of thymol and carvacrol: A comparative insight

Bioactive compounds derived from medicinal plants have acquired immense attentiveness in drug discovery and development. The present study investigated in vitro and predicted in silico the antibacterial, antifungal, and antiviral properties of thymol and carvacrol, and assessed their safety. The performed microbiological assays against Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica Typhimurium revealed that the minimal inhibitory concentration values ranged from (0.078 to 0.312 mg/mL) and the minimal fungicidal concentration against Candida albicans was 0.625 mg/mL. Molecular docking simulations, stipulated that these compounds could inhibit bacterial replication and transcription functions by targeting DNA and RNA polymerases receptors with docking scores varying between (-5.1 to -6.9 kcal/mol). Studied hydroxylated monoterpenes could hinder C. albicans growth by impeding lanosterol 14α-demethylase enzyme and showed a (ΔG=-6.2 and -6.3 kcal/mol). Computational studies revealed that thymol and carvacrol could target the SARS-Cov-2 spike protein of the Omicron variant RBD domain. Molecular dynamics simulations disclosed that these compounds have a stable dynamic behavior over 100 ns as compared to remdesivir. Chemo-computational toxicity prediction using Protox II webserver indicated that thymol and carvacrol could be safely and effectively used as drug candidates to tackle bacterial, fungal, and viral infections as compared to chemical medication.

Synergistic Effect of Thymol-Ciprofloxacin Combination on Planktonic Cells and Biofilm of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic bacteria causing severe and life-threatening infections in individuals with weakened immune systems. P. aeruginosa forms antibiotic-resistant biofilms, rendering it challenging to treat; hence, alternate therapies are required to eliminate it. Treatment of infections using a combination of drugs is gaining momentum to combat drug-resistant pathogens, including P. aeruginosa. This study explores the synergistic effects of Thymol in combination with Ciprofloxacin, Amikacin and Colistin against planktonic cells and biofilm of P. aeruginosa. Thymol in combination with Ciprofloxacin yields the fractional inhibitory concentration index values 0.156 and 0.375 in P. aeruginosa strains, GC14 and ATCC 9027, respectively, highlighting a robust synergistic effect on both the planktonic and biofilm of P. aeruginosa. The results showed that Thymol (512 μg/mL) and Ciprofloxacin (0.125 μg/mL) were the most effective combination with 95 and 93.5% total biofilm inhibition in GC14 and PA27, respectively, compared to the Thymol (512 μg/mL) and Ciprofloxacin (0.125 μg/mL) alone. Our findings suggest that the combinations of Thymol and Ciprofloxacin may be a potential therapeutic strategy to address the issue of infections caused by P. aeruginosa biofilms.

Comparison of Antibacterial Activity of Phytochemicals against Common Foodborne Pathogens and Potential for Selection of Resistance

Antimicrobial resistance is now commonly observed in bacterial isolates from multiple settings, compromising the efficacy of current antimicrobial agents. Therefore, there is an urgent requirement for efficacious novel antimicrobials to be used as therapeutics, prophylactically or as preservatives. One promising source of novel antimicrobial chemicals is phytochemicals, which are secondary metabolites produced by plants for numerous purposes, including antimicrobial defence. In this report, we compare the bioactivity of a range of phytochemical compounds, testing their ability to directly inhibit growth or to potentiate other antimicrobials against Salmonella enterica Typhimurium, Pseudomonas aeruginosa, Listeria monocytogenes, and Staphylococcus aureus. We found that nine compounds displayed consistent bioactivity either as direct antimicrobials or as potentiators. Thymol at 0.5 mg/mL showed the greatest antimicrobial effect and significantly reduced the growth of all species, reducing viable cell populations by 66.8%, 43.2%, 29.5%, and 70.2% against S. enterica Typhimurium, S. aureus, P. aeruginosa, and L. monocytogenes, respectively. Selection of mutants with decreased susceptibility to thymol was possible for three of the pathogens, at a calculated rate of 3.77 × 10-8, and characterisation of S. enterica Typhimurium mutants showed a low-level MDR phenotype due to over-expression of the major efflux system AcrAB-TolC. These data show that phytochemicals can have strong antimicrobial activity, but emergence of resistance should be evaluated in any further development.

Comparison of the efficacy of physical and chemical strategies for the inactivation of biofilm cells of foodborne pathogens

Biofilm formation is a strategy in which microorganisms generate a matrix of extracellular polymeric substances to increase survival under harsh conditions. The efficacy of sanitization processes is lowered when biofilms form, in particular on industrial devices. While various traditional and emerging technologies have been explored for the eradication of biofilms, cell resistance under a range of environmental conditions renders evaluation of the efficacy of control challenging. This review aimed to: (1) classify biofilm control measures into chemical, physical, and combination methods, (2) discuss mechanisms underlying inactivation by each method, and (3) summarize the reduction of biofilm cells after each treatment. The review is expected to be useful for future experimental studies and help to guide the establishment of biofilm control strategies in the food industry.

Antimicrobial Effect of Ocimum gratissimum L. Essential Oil on Shewanella putrefaciens: Insights Based on the Cell Membrane and External Structure

The main objective of this study was to assess the in vitro antibacterial effectiveness of Ocimum gratissimum L. essential oil (OGEO) against Shewanella putrefaciens. The minimum inhibitory concentration and minimum bactericidal concentration of OGEO acting on S. putrefaciens were both 0.1% and OGEO could inhibit the growth of S. putrefaciens in a dose-dependent manner. The restraint of the biofilm growth of S. putrefaciens was found in the crystal violet attachment assay and confocal laser scanning microscopy. The disruption of cell membranes and exudation of contents in S. putrefaciens with OGEO treatment were observed by scanning electron microscopy, hemolysis and ATPase activity. The results demonstrated that OGEO had a positive inhibitory effect on the growth of S. putrefaciens, which primarily developed its antibacterial function against S. putrefaciens by disrupting the formation of biofilms and cell membranes. This study could provide a new method of inhibiting the spoilage of food in which the dominant spoilage bacteria are S. putrefaciens.

Antimicrobial properties of the essential oil of Schinus areira (Aguaribay) against planktonic cells and biofilms of S. aureus

The essential oil (EO) of Schinus areira L. (Anacardiaceae) leaves has shown antibacterial activity against Staphylococcus aureus. In this study we aimed to unravel the mechanisms of its antibacterial action by using bacterial cells and model membranes. First, the integrity of S. aureus membrane was evaluated by fluorescence microscopy. It was observed an increase in the permeability of cells that was dependent on the EO concentration as well as the incubation time. For a deep evaluation of the action of the EO on the lipids, its effect on the membrane fluidity was evaluated on DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine): DMPG (1,2-dimyristoyl-sn-glycero-3-phospho-1'-rac-glycerol) (5:1) liposomes by dynamic scattering light and by using Laurdan doped liposomes. The results indicate that EO produces changes in lipid membrane packing, increasing the fluidity, reducing the cooperative cohesive interaction between phospholipids and increasing access of water or the insertion of some components of the EO to the interior of the membrane. In addition, the potential effect of EO on intracellular targets, as the increase of cytosolic reactive oxygen species (ROS) and DNA damage, were evaluated. The EO was capable of increasing the production of ROS as well as inducing a partial degradation of DNA. Finally, the effect of EO on S. aureus biofilm was tested. These assays showed that EO was able to inhibit the biofilm formation, and also eradicate preformed biofilms. The results show, that the EO seems to have several bacterial targets involved in the antibacterial activity, from the bacterial membrane to DNA. Furthermore, the antibacterial action affects not only planktonic cells but also biofilms; reinforcing the potential application for this EO.

Essential oils and essential oil compounds in animal production as antimicrobials and anthelmintics: an updated review

Several countries have shown an increased prevalence of drug resistance in animal production due to the indiscriminate use of antibiotics and antiparasitics in human and veterinary medicine. This article aims to review existing methods using naturally occurring essential oils (EOs) and their isolated compounds (EOCs) as alternatives to antimicrobials and antiparasitic compounds in animal production and, consequently, to avoid resistance. The most-reported mechanism of action of EOs and EOCs was cell membrane damage, which leads to the leakage of cytoplasmic content, increased membrane permeability, inhibition of metabolic and genetic pathways, morphologic changes, antibiofilm effects, and damage to the genetic material of infections. In parasites, anticoccidial effects, reduced motility, growth inhibition, and morphologic changes have been reported. Although these compounds regularly show a similar effect to those promoted by traditional drugs, the elucidation of their mechanisms of action is still scarce. The use of EOs and EOCs can also positively influence crucial parameters in animal production, such as body weight gain, feed conversion rate, and cholesterol reduction, which also positively impact meat quality. The application of EOs and EOCs is enhanced by their association with other natural compounds or even by the association with synthetic chemicals, which has been found to cause synergism in their antimicrobial effect. By reducing the effective therapeutical/prophylactic dose, the chances of off-flavors – the most common issue in EO and EOC application – is greatly mitigated. However, there is very little work on the combination of EOs and EOCs in large in vivo studies. In addition, research must apply the correct methodology to properly understand the observed effects; for example, the use of only high concentrations may mask potential results obtained at lower dosages. Such corrections will also allow the elucidation of finer mechanisms and promote better biotechnologic use of EOs and EOCs. This manuscript presents several information gaps to be filled before the use of EOs and EOCs are fully applicable in animal production.

Thymus vulgaris Essential Oil in Beta-Cyclodextrin for Solid-State Pharmaceutical Applications

Antimicrobial resistance related to the misuse of antibiotics is a well-known current topic. Their excessive use in several fields has led to enormous selective pressure on pathogenic and commensal bacteria, driving the evolution of antimicrobial resistance genes with severe impacts on human health. Among all the possible strategies, a viable one could be the development of medical features that employ essential oils (EOs), complex natural mixtures extracted from different plant organs, rich in organic compounds showing, among others, antiseptic properties. In this work, green extracted essential oil of Thymus vulgaris was included in cyclic oligosaccharides cyclodextrins (CD) and prepared in the form of tablets. This essential oil has been shown to have a strong transversal efficacy both as an antifungal and as an antibacterial agent. Its inclusion allows its effective use because an extension of the exposure time to the active compounds is obtained and, therefore, a more marked efficacy, especially against biofilm-producing microorganisms such as P. aeruginosa and S. aureus, was registered. The efficacy of the tablet against candidiasis opens their possible use as a chewable tablet against oral candidiasis and as a vaginal tablet against vaginal candidiasis. Moreover, the registered wide efficacy is even more positive since the proposed approach can be defined as effective, safe, and green. In fact, the natural mixture of the essential oil is produced by the steam current method; therefore, the manufacturer employs substances that are not harmful, with very low production and management costs.

In-Depth Study of Thymus vulgaris Essential Oil: Towards Understanding the Antibacterial Target Mechanism and Toxicological and Pharmacological Aspects

Questions have been raised apropos the emerging problem of microbial resistance, which may pose a great hazard to the human health. Among biosafe compounds are essential oils which captured consumer draw due to their multifunctional properties compared to chemical medication drugs. Here, we examined the chemical profile and the mechanism(s) of action of the Thymus vulgaris essential oil (TVEO) against a Gram-negative bacterium Salmonella enterica Typhimurium ATTCC 10028 (S. enterica Typhimurium ATTCC 10028) and two Gram-positive bacteria Staphyloccocus aureus ATCC 6538 (S. aureus ATCC 6538) and Listeria monocytogenes ATCC 19117 (L. monocytogenes ATCC 19117). Findings showed that TVEO was principally composed of thymol, o-cymene, and γ-terpinene with 47.44, 16.55, and 7.80%, respectively. Molecular docking simulations stipulated that thymol and β-sesquiphellandrene (a minor compound at 1.37%) could target multiple bacterial pathways including topoisomerase II and DNA and RNA polymerases of the three tested bacteria. This result pointed plausible impairments of the pathogenic bacteria cell replication and transcription processes. Through computational approach, the VEGA quantitative structure–activity relationship (QSAR) model, we revealed that among twenty-six TVEO compounds, sixteen had no toxic effects and could be safe for human consumption as compared to the Food and Drug Administration (FDA) approved drugs (ciprofloxacin and rifamycin SV). Assessed by the SwissADME server, the pharmacokinetic profile of all identified TVEO compounds define their absorption, distribution, metabolism, and excretion (ADME) properties and were assessed. In order to predict their biological activity spectrum based on their chemical structure, all TVEO compounds were subjected to PASS (Prediction of Activity Spectra for Substances) online tool. Results indicated that the tested compounds could have multiple biological activities and various enzymatic targets. Findings of our study support that identified compounds of TVEO can be a safe and effective alternative to synthetic drugs and can easily combats hazardous multidrug-resistant bacteria.

The Antibacterial Activity of Thymol Against Drug-Resistant Streptococcus iniae and Its Protective Effect on Channel Catfish (Ictalurus punctatus)

Streptococcus iniae is a zoonotic pathogen, which seriously threatens aquaculture and human health worldwide. Antibiotics are the preferred way to treat S. iniae infection. However, the unreasonable use of antibiotics leads to the enhancement of bacterial resistance, which is not conducive to the prevention and treatment of this disease. Therefore, it is urgent to find new efficient and environmentally friendly antibacterial agents to replace traditional antibiotics. In this study, the antibacterial activity and potential mechanism of thymol against S. iniae were evaluated by electron microscopy, lactate dehydrogenase, DNA and protein leakage and transcriptomic analysis. Thymol exhibited potent antibacterial activity against S. iniae in vitro, and the MIC and MBC were 128 and 256μg/mL, respectively. SEM and TEM images showed that the cell membrane and cell wall were damaged, and the cells were abnormally enlarged and divided. 2MIC thymol disrupted the integrity of cell walls and membranes, resulting in the release of intracellular macromolecules including nucleotides, proteins and inorganic ions. The results of transcriptomic analysis indicated that thymol interfered with energy metabolism and membrane transport, affected DNA replication, repair and transcription in S. iniae. In vivo studies showed that thymol had a protective effect on experimental S. iniae infection in channel catfish. It could reduce the cumulative mortality of channel catfish and the number of S. iniae colonization in tissues, and increase the activities of non-specific immune enzymes in serum, including catalase, superoxide dismutase, lysozyme and acid phosphatase. Taken together, these findings suggested that thymol may be a candidate plant agent to replace traditional antibiotics for the prevention and treatment of S. iniae infection.

Protective Impact of Chitosan Film Loaded Oregano and Thyme Essential Oil on the Microbial Profile and Quality Attributes of Beef Meat

Edible films and essential oil (EO) systems have the potency to enhance the microbial quality and shelf life of food. This investigation aimed to evaluate the efficacy of chitosan films including essential oils against spoilage bacteria and foodborne pathogens associated with meat. Antimicrobial activity (in vitro and in vivo) of chitosan films (CH) incorporated with oregano oil (OO) and thyme oil (TO) at 0.5 and 1% was done against spoilage bacteria and foodborne pathogens, compared to the control sample and CH alone. Preliminary experiments (in vitro) showed that the 1% OO and TO were more active against Staphylococcus aureus compared to Escherichia coli O157:H7 and Salmonella Typhimurium. In in vivo studies, CH containing OO and TO effectively inhibited the three foodborne pathogens and spoilage bacteria linked with packed beef meat which was kept at 4 °C/30 days compared to the control. The total phenolic content of the EOs was 201.52 mg GAE L-1 in thyme and 187.64 mg GAE L-1 in oregano. The antioxidant activity of thyme oil was higher than oregano oil. The results demonstrated that the shelf life of meat including CH with EOs was prolonged ~10 days compared to CH alone. Additionally, CH-OO and CH-TO have improved the sensory acceptability until 25 days, compared to the control. Results revealed that edible films made of chitosan and containing EOs improved the quality parameters and safety attributes of refrigerated or fresh meat.

Pseudomonas aeruginosa: A typical biofilm forming pathogen and an emerging but underestimated pathogen in food processing

Pseudomonas aeruginosa (P. aeruginosa) is a notorious gram-negative pathogenic microorganism, because of several virulence factors, biofilm forming capability, as well as antimicrobial resistance. In addition, the appearance of antibiotic-resistant strains resulting from the misuse and overuse of antibiotics increases morbidity and mortality in immunocompromised patients. However, it has been underestimated as a foodborne pathogen in various food groups for instance water, milk, meat, fruits, and vegetables. Chemical preservatives that are commonly used to suppress the growth of food source microorganisms can cause problems with food safety. For these reasons, finding effective, healthy safer, and natural alternative antimicrobial agents used in food processing is extremely important. In this review, our ultimate goal is to cover recent advances in food safety related to P. aeruginosa including antimicrobial resistance, major virulence factors, and prevention measures. It is worth noting that food spoilage caused by P. aeruginosa should arouse wide concerns of consumers and food supervision department.

Effect of Juglone against Pseudomonas syringae pv Actinidiae Planktonic Growth and Biofilm Formation

Pseudomonas syringaepv Actinidiae (P. syringae) is a common pathogen causing plant diseases. Limoli proved that its strong pathogenicity is closely related to biofilm state. As a natural bacteriostatic agent with broad-spectrum bactericidal properties, juglone can be used as a substitute for synthetic bacteriostatic agents. To explore the antibacterial mechanism, this study was carried out to examine the inhibitory effect of juglone on cell membrane destruction, abnormal oxidative stress, DNA insertion and biofilm prevention of P. syringae. Results showed that juglone at 20 μg/mL can act against planktogenic P. syringae (10⁷ CFU/mL). Specially, the application of juglone significantly damaged the permeability and integrity of the cell membrane of P. syringae. Additionally, juglone caused abnormal intracellular oxidative stress, and also embedded in genomic DNA, which affected the normal function of the DNA of P. syringae. In addition, environmental scanning electron microscope (ESEM) and other methods showed that juglone effectively restricted the production of extracellular polymers, and then affected the formation of the cell membrane. This study provided a possibility for the development and utilization of natural juglone in plants, especially P. syringae.

Juglone Inactivates Pseudomonas aeruginosa through Cell Membrane Damage, Biofilm Blockage, and Inhibition of Gene Expression

Due to the strong drug resistance of Pseudomonas aeruginosa (P. aeruginosa), the inhibition effects of conventional disinfectants and antibiotics are not obvious. Juglone extracted from discarded walnut husk, as a kind of plant-derived antimicrobial agent, has the advantages of naturalness, high efficiency, and low residue, with a potential role in the inhibition of P. aeruginosa. This study elucidated the inhibitory effect of juglone on the growth of plankton and the formation of P. aeruginosa biofilm. The results showed that juglone (35 μg/mL) had an irreversible inhibitory effect on P. aeruginosa colony formation (about 10⁷ CFU/mL). The integrity and permeability of the cell membrane were effectively destroyed, accompanied by disorder of the membrane permeability, mass leakage of the cytoplasm, and ATP consumption. Further studies manifested that juglone could induce the abnormal accumulation of ROS in cells and block the formation of the cell membrane. In addition, RT-qPCR showed that juglone could effectively block the expression of five virulence genes and two genes involved in the production of extracellular polymers, thereby reducing the toxicity and infection of P. aeruginosa and preventing the production of extracellular polymers. This study can provide support for the innovation of antibacterial technology toward P. aeruginosa in food.

Chemical composition, extraction sources and action mechanisms of essential oils: Natural preservative and limitations of use in meat products

The antimicrobial activity of essential oils (EO) is associated with the presence of secondary metabolites synthesized by plants. Its mechanism of action involves the interaction of its hydrophobic components with the lipids present in the cell membrane of microorganism, resulting in metabolic damages and cell death. Spoilage and pathogenic microorganisms are contaminants in meat and meat products with considerable impacts on food quality and safety. Research shows the potential of applying essential oils in the preservation of meat food systems as compounds of low toxicity, extracted from a natural source, and as an alternative to consumer demand for healthy foods with a more natural appeal. In addition, there is a great diversity of plants from which essential oils can be extracted, whose antimicrobial activity in vitro and in meat and meat products has been proven.