Essential Oils of Aromatic Plants with Antibacterial, Anti-Biofilm and Anti-Quorum Sensing Activities against Pathogenic Bacteria

A versatile two-light mode triggered system for highly localized sequential release of reactive oxygen species and conjugated drugs from mesoporous organosilica particles

The increasing prevalence of antimicrobial resistance and adverse effects of systemic treatments calls for urgent reevaluation of current methods that rely on excessive, uncontrolled drug administration. In recent years triggerable systems have emerged as promising alternatives, enabling time-controlled and localized drug release, which are only activated if necessary. Light is an obvious candidate as an external trigger, since it allows for localized activation, is non-invasive and its wavelength and intensity can be tailored to fit the demands of the drug release system. Such localized and triggered systems minimize off-target effects and undesired exposure, making it a promising tool for combating health threats such as antimicrobial resistance. However, the limited tissue penetration of visible light significantly limits the applicability of this concept in vivo. Here, we introduce an innovative triggerable drug release system, based on mono-, bi-, and tri-functionalized mesoporous organosilica particles (MOPs). The limited tissue penetration is addressed by an advanced trigger system featuring two-photon absorption. Two-photon absorption enables utilization of near-infrared (NIR) light as a trigger, which is known to exhibit an enhanced penetration depth. The particles are designed to release reactive oxygen species (ROS) upon NIR irradiation and undergo Förster resonance energy transfer (FRET) to a ROS producing dye. Moreover, by oxidative cleavage, an additional therapeutic agent is released in a cascade reaction, enhancing the system's effectiveness. The ROS release is microscopically demonstrated in situ and, for the first time, release of a fluorescent compound (therapeutic agent) in a cascade reaction is observed in real-time, providing valuable insights into the behavior and performance of our particles. This novel sequential dual-release platform for light-triggered therapeutic delivery has great potential for advanced therapeutic applications in both superficial and deep tissue treatments.

Hidden Places for Foodborne Bacterial Pathogens and Novel Approaches to Control Biofilms in the Meat Industry

Biofilms are of great concern for the meat industry because, despite the implementation of control plans, they remain important hotspots of contamination by foodborne pathogens, highlighting the need to better understand the ecology of these microecosystems. The objective of this paper was to critically survey the recent scientific literature on microbial biofilms of importance for meat safety and quality, also pointing out the most promising methods to combat them. For this, the databases PubMed, Scopus, Science Direct, Web of Science, and Google Scholar were surveyed in a 10-year time frame (but preferably papers less than 5 years old) using selected keywords relevant for the microbiology of meats, especially considering bacteria that are tolerant to cleaning and sanitization processes. The literature findings showed that massive DNA sequencing has deeply impacted the knowledge on the species that co-habit biofilms with important foodborne pathogens (Listeria monocytogenes, Salmonella, pathogenic Escherichia coli, and Staphylococcus aureus). It is likely that recalcitrant commensal and/or spoilage microbiota somehow protect the more fastidious organisms from harsh conditions, in addition to harboring antimicrobial resistance genes. Among the members of background microbiota, Pseudomonas, Acinetobacter, and Enterobacteriales have been commonly found on food contact and non-food contact surfaces in meat processing plants, in addition to less common genera, such as Psychrobacter, Enhydrobacter, Brevundimonas, and Rothia, among others. It has been hypothesized that these rare taxa may represent a primary layer in microbial biofilms, offering better conditions for the adhesion of otherwise poor biofilm formers, especially considering their tolerance to cold conditions and sanitizers. Taking into consideration these findings, it is not only important to target the foodborne pathogens per se in cleaning and disinfection plans but the use of multiple hurdles is also recommended to dismantle the recalcitrant structures of biofilms. In this sense, the last part of this manuscript presents an updated overview of the antibiofilm methods available, with an emphasis on eco-friendly approaches.

Natural Solutions to Antimicrobial Resistance: The Role of Essential Oils in Poultry Meat Preservation with Focus on Gram-Negative Bacteria

The increase in antimicrobial resistance (AMR) is a major global health problem with implications on human and veterinary medicine, as well as food production. In the poultry industry, the overuse and misuse of antimicrobials has led to the development of resistant or multi-drug resistant (MDR) strains of bacteria such as Salmonella spp., Escherichia coli and Campylobacter spp., which pose a serious risk to meat safety and public health. The genetic transfer of resistance elements between poultry MDR bacteria and human pathogens further exacerbates the AMR crisis and highlights the urgent need for action. Traditional methods of preserving poultry meat, often based on synthetic chemicals, are increasingly being questioned due to their potential impact on human health and the environment. This situation has led to a shift towards natural, sustainable alternatives, such as plant-derived compounds, for meat preservation. Essential oils (EOs) have emerged as promising natural preservatives in the poultry meat industry offering a potential solution to the growing AMR problem by possessing inherent antimicrobial properties making them effective against a broad spectrum of pathogens. Their use in the preservation of poultry meat not only extends shelf life, but also reduces reliance on synthetic preservatives and antibiotics, which contribute significantly to AMR. The unique chemical composition of EOs, that contains a large number of different active compounds, minimizes the risk of bacteria developing resistance. Recent advances in nano-encapsulation technology have further improved the stability, bioavailability and efficacy of EOs, making them more suitable for commercial use. Hence, in this manuscript, the recent literature on the mechanisms of AMR in the most important Gram-negative poultry pathogens and antimicrobial properties of EOs on these meat isolates was reviewed. Additionally, chemical composition, extraction methods of EOs were discussed, as well as future directions of EOs as natural food preservatives. In conclusion, by integrating EOs into poultry meat preservation strategies, the industry can adopt more sustainable and health-conscious practices and ultimately contribute to global efforts to combat AMR.

Anti-quorum sensing activity of essential oils against multidrug-resistant Klebsiella pneumoniae: a novel approach to control bacterial virulence

The increasing resistance of microbes to conventional drugs is a serious problem worldwide that has increased the need for alternative antimicrobial compounds. Naturally occurring essential oils (EOs) are considered an important component of traditional pharmacopeia because of their antimicrobial and antioxidant properties. This has attracted researchers to identify novel therapeutic anti-pathogenic agents that could act as non-toxic quorum sensing inhibitors, thus controlling infections without encouraging the development of bacterial resistance. This prompted to undertake the current investigation to unravel the efficacy of EOs as QS modulators in reducing the virulence of multidrug resistant (MDR) strains of Klebsiella pneumoniae. The study highlighted the anti-QS activity of fifteen EOs in modulating the QS-related traits by a reduction in capsular polysaccharide, exopolysaccharide and siderophore production in addition to inhibition of biofilm formation. The overall results suggest using EOs to develop alternate intervention strategies to mitigate infections caused by MDR strains of K. pneumoniae.

Antibacterial and Antibiofilm Activity of Essential Oils Against Aeromonas spp. Isolated from Rainbow Trout

Aeromonas spp. is a major pathogen in aquaculture with a great negative economic impact. Essential oils (EOs) are compounds of the secondary metabolism of plants known for their antibacterial and antibiofilm activities. In this study, in vitro antibacterial activity of eight EOs: tea tree (extracted from Melaleuca alternifolia), eucalyptus (extracted from Eucalyptus globulus LABILL.), knee timber (extracted from Pini mungo L.), peppermint (extracted from Mentha piperita L.), oregano (extracted from Origanum vulgare L.), rosemary (extracted from Rosmarinus officinalis L.), thyme (extracted from Thymus vulgaris L.) and pine EO (extracted from Pinus silvestris L.), obtained from Calendula a.s., was evaluated. Their antibacterial activity was demonstrated against Aeromonas spp. isolates. Oregano and thyme EOs showed the strongest activity against all tested isolates at low concentrations, followed by tea tree and peppermint EOs. The MIC value ranged from 0.06 µL/mL to 1.0 µL/mL. The tested EOs showed a significant antibiofilm activity against biofilm-forming isolates with MBIC50 ranging from 0.015 µL/mL to 0.25 µL/mL. All tested isolates were obtained from rainbow trout free of clinical signs of infection. Twelve isolates of Aeromonas salmonicida subsp. masoucida, four Aeromonas hydrophila, and four isolates of Aeromonas veronii were identified. The results of the in vitro study showed a significant effect of EOs against Aeromonas spp., which confirmed their potential for use in aquaculture as a prevention against bacterial diseases and a way of reducing the use of antibiotics.

Bactericidal and Synergistic Effects of Lippia origanoides Essential Oil and Its Main Constituents against Multidrug-Resistant Strains of Acinetobacter baumannii

Bacterial resistance in Acinetobacter baumannii is a significant public health challenge, as these bacteria can evade multiple antibiotics, leading to difficult-to-treat infections with high mortality rates. As part of the search for alternatives, essential oils from medicinal plants have shown promising antibacterial potential due to their diverse chemical constituents. This study evaluated the antibacterial, antibiofilm, and synergistic activities of the essential oil of Lippia origanoides (EOLo) and its main constituents against multidrug-resistant clinical isolates of A. baumannii. Additionally, the antibacterial and antibiofilm potential of a nanoemulsion containing carvacrol (NE-CAR) was assessed. EOLo was extracted through hydrodistillation, and its components were identified via gas chromatography coupled with mass spectrometry. The A. baumannii isolates (n = 9) were identified and tested for antimicrobial susceptibility using standard disk diffusion methods. Antibacterial activity was determined by broth microdilution, while antibiofilm activity was measured using colorimetric methods with crystal violet and scanning electron microscopy. Synergism tests with antibiotics (meropenem, ciprofloxacin, gentamicin, and ampicillin+sulbactam) were performed using the checkerboard method. The primary constituents of EOLo included carvacrol (48.44%), p-cymene (14.58%), and thymol (10.16%). EOLo, carvacrol, and thymol demonstrated significant antibacterial activity, with carvacrol showing the strongest effect. They were also effective in reducing biofilm formation, as was NE-CAR. The combinations with antibiotics revealed significant synergistic effects, lowering the minimum inhibitory concentration of the tested antibiotics. Therefore, this study confirms the notable antibacterial activity of the essential oil of L. origanoides and its constituents, especially carvacrol, suggesting its potential as a therapeutic alternative for A. baumannii infections.

The Potential of Thymus serpyllum Essential Oil as an Antibacterial Agent against Pseudomonas aeruginosa in the Preservation of Sous Vide Red Deer Meat

Foodborne infections caused by microbes are a serious health risk. Regarding this, customer preferences for "ready-to-eat" or minimally processed (MP) deer meat are one of the main risk factors. Given the health dangers associated with food, essential oil (EO) is a practical substitute used to decrease pathogenic germs and extend the shelf-life of MP meals. Nonetheless, further data regarding EO use in MP meals are required. In order to evaluate new, safer alternatives to chemicals for disease control and food preservation, this research was carried out in the following areas to assess the antibacterial and antibiofilm characteristics of Thymus serpyllum (TSEO) essential oil, which is extracted from dried flowering stalks. Furthermore, this study applied an essential oil of wild thyme and inoculated the sous vide deer meat with Pseudomonas aeruginosa for seven days at 4 °C in an effort to prolong its shelf-life. Against P. aeruginosa, the essential oil exhibited potent antibacterial action. The findings of the minimal biofilm inhibition concentration (MBIC) crystal violet test demonstrated the substantial antibiofilm activity of the TSEO. The TSEO modified the protein profiles of bacteria on glass and plastic surfaces, according to data from MALDI-TOF MS analysis. Moreover, it was discovered that P. aeruginosa was positively affected by the antibacterial properties of TSEO. The anti-Pseudomonas activity of the TSEO was marginally higher in vacuum-packed sous vide red deer meat samples than in control samples. The most frequently isolated species from sous vide deer meat, if we do not consider the applied bacteria Pseudomonas aeruginosa, were P. fragi, P. lundensis, and P. taetrolens. These results highlight the antibacterial and antibiofilm qualities of TSEO, demonstrating its potential for food preservation and extending the shelf-life of deer meat.

Unveiling the impact of selected essential oils on MRSA strain ATCC 33591: antibacterial efficiency, biofilm disruption, and staphyloxanthin inhibition

This work aimed to evaluate the effects of 4 selected essential oils on planktonic cells and microbial biofilms of the Staphylococcus aureus strain (MRSA ATCC 33591). The antibacterial activities of the four essential oils Geranium (Pelargonium graveolens), PgEO, Tea Tree (Melaleuca alternifolia) MaEO, Lemon peel (Citrus limon) ClEO and Peppermint (Mentha piperita) MpEO had MICs ranging from 1.56 to 12.5 µl/ml. The evaluation of the antibiofilm activities of the 4 EOs revealed that they had antiadhesive activities against S. aureus MRSA biofilms; the activity reached 60% (the EO of MpEO peppermint at a concentration of 3.12 µl/ml), and the eradication activity was 80% (the EO of PgEO and MpEO at 3.12 µl/ml). The antibiofilm activity of S. aureus has been explained by the binding of several essential oil bioactive molecules to the SarA protein, the main target protein involved in biofilm formation. The synthesis of the virulence factor staphyloxanthin by S. aureus MRSA ATCC 33591 was significantly inhibited in the presence of PgEO at a concentration of MIC/2. This inhibition was explained by the binding of the main PgEO molecules (β-citronellol and geraniol) to the CrTM protein involved in the staphyloxanthin synthesis pathway. There is evidence that these essential oils could be used as potential anti-virulents to control Staphylococcus biofilm formation.

Chemical Composition and Phytotoxic and Antibiofilm Activity of the Essential Oils of Two Moroccan Retama Species

This study reports chemical composition, phytotoxic and antibiofilm activities of essential oils (EOs) of R. dasycarpa and R. sphaerocarpa from Morocco. EOs were analyzed by GC/MS and their phytotoxicities were evaluated against germination and seedling growth of Lolium multiflorum, Sinapis alba and Raphanus sativus. The antimicrobial and anti-biofilm activities were studied against Gram-negative (Pseudomonas aeruginosa, Escherichia coli and Acinetobacter baumannii) and Gram-positive bacteria (Staphylococcus aureus and Listeria monocytogenes). Both EOs were abundant in oxygenated monoterpenes (40.01% and 23.57 %, respectively). Carvacrol is the predominant component in R. dasycarpa EO (17.80 %), and it also represents an appreciable amount in R. sphaerocarpa (8.96 %). R. sphaerocarpa showed total inhibition at high doses against all seeds. S. alba seeds were the most sensitive to all EOs. Minimum inhibitory concentration (MIC) values indicated significant inhibition for R. sphaerocarpa, between 24 and 30 μg/mL, with a remarkable antibacterial potential and biofilm formation inhibition. R. sphaerocarpa EO showed significant biofilm inhibition with variable efficacy depending on the strain and concentration, except for S. aureus. R. dasycarpa exhibited activity against all bacterial strains and effect on metabolism with activity also on mature biofilms. Results suggest that Retama EOs could have potential applications in the fields of food and health.

Assessment of Antimicrobial and Cytotoxic Activities of Liposomes Loaded with Curcumin and Lippia origanoides Essential Oil

(1) Introduction: Curcumin and Lippia origanoides essential oils have a broad spectrum of biological activities; however, their physicochemical instability, low solubility, and high volatility limit their therapeutic use. Encapsulation in liposomes has been reported as a feasible approach to increase the physicochemical stability of active substances, protect them from interactions with the environment, modulate their release, reduce their volatility, improve their bioactivity, and reduce their toxicity. To date, there are no reports on the co-encapsulation of curcumin and Lippia origanoides essential oils in liposomes. Therefore, the objective of this work is to prepare and physiochemical characterize liposomes loaded with the mixture of these compounds and to evaluate different in vitro biological activities. (2) Methods: Liposomes were produced using the thin-layer method and physiochemical characteristics were calculated. The antimicrobial and cytotoxic activities of both encapsulated and non-encapsulated compounds were evaluated. (3) Results: Empty and loaded nanometric-sized liposomes were obtained that are monodisperse and have a negative zeta potential. They inhibited the growth of Staphylococcus aureus and did not exhibit cytotoxic activity against mammalian cells. (4) Conclusions: Encapsulation in liposomes was demonstrated to be a promising strategy for natural compounds possessing antimicrobial activity.

Overexpression of AcWRKY31 Increases Sensitivity to Salt and Drought and Improves Tolerance to Mealybugs in Pineapple

Pineapple is a globally significant tropical fruit, but its cultivation faces numerous challenges due to abiotic and biotic stresses, affecting its quality and quantity. WRKY transcription factors are known regulators of stress responses, however, their specific functions in pineapple are not fully understood. This study investigates the role of AcWRKY31 by overexpressing it in pineapple and Arabidopsis. Transgenic pineapple lines were obtained using Agrobacterium-mediated transformation methods and abiotic and biotic stress treatments. Transgenic AcWRKY31-OE pineapple plants showed an increased sensitivity to salt and drought stress and an increased resistance to biotic stress from pineapple mealybugs compared to that of WT plants. Similar experiments in AcWRKY31-OE, AtWRKY53-OE, and the Arabidopsis Atwrky53 mutant were performed and consistently confirmed these findings. A comparative transcriptomic analysis revealed 5357 upregulated genes in AcWRKY31-OE pineapple, with 30 genes related to disease and pathogen response. Notably, 18 of these genes contained a W-box sequence in their promoter region. A KEGG analysis of RNA-Seq data showed that upregulated DEG genes are mostly involved in translation, protein kinases, peptidases and inhibitors, membrane trafficking, folding, sorting, and degradation, while the downregulated genes are involved in metabolism, protein families, signaling, and cellular processes. RT-qPCR assays of selected genes confirmed the transcriptomic results. In summary, the AcWRKY31 gene is promising for the improvement of stress responses in pineapple, and it could be a valuable tool for plant breeders to develop stress-tolerant crops in the future.

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.

Potential Anti-Infectious Activity of Essential Oil Chemotypes of Lippia origanoides Kunth on Antibiotic-Resistant Staphylococcus aureus Strains

Staphylococcus aureus infections are prevalent in healthcare and community environments. Methicillin-resistant S. aureus is catalogued as a superbug of high priority among the pathogens. This Gram-positive coccus can form biofilms and produce toxins, leading to persistent infection and antibiotic resistance. Limited effective antibiotics have encouraged the development of innovative strategies, with a particular emphasis on resistance mechanisms and/or virulence factors. Medicinal aromatic plants have emerged as promising alternative sources. This study investigated the antimicrobial, antibiofilm, and antihemolysis properties of three different chemotypes of Lippia origanoides essential oil (EO) against susceptible and drug-resistant S. aureus strains. The chemical composition of the EO was analyzed using GC-MS, revealing high monoterpene concentrations, with carvacrol and thymol as the major components in two of the chemotypes. The third chemotype consisted mainly of the sesquiterpene β-caryophyllene. The MIC values for the two monoterpene chemotypes ranged from 62.5 to 500 µg/mL for all strains, whereas the sesquiterpene chemotype showed activity against seven strains at concentrations of 125-500 µg/mL, which is the first report of its anti-S. aureus activity. The phenolic chemotypes inhibited biofilm formation in seven S. aureus strains, whereas the sesquiterpene chemotype only inhibited biofilm formation in four strains. In addition, phenolic chemotypes displayed antihemolysis activity, with IC50 values ranging from 58.9 ± 3.8 to 128.3 ± 9.2 µg/mL. Our study highlights the importance of L. origanoides EO from the Yucatan Peninsula, which has the potential for the development of anti-S. aureus agents.

Emerging Approaches for Mitigating Biofilm-Formation-Associated Infections in Farm, Wild, and Companion Animals

The importance of addressing the problem of biofilms in farm, wild, and companion animals lies in their pervasive impact on animal health and welfare. Biofilms, as resilient communities of microorganisms, pose a persistent challenge in causing infections and complicating treatment strategies. Recognizing and understanding the importance of mitigating biofilm formation is critical to ensuring the welfare of animals in a variety of settings, from farms to the wild and companion animals. Effectively addressing this issue not only improves the overall health of individual animals, but also contributes to the broader goals of sustainable agriculture, wildlife conservation, and responsible pet ownership. This review examines the current understanding of biofilm formation in animal diseases and elucidates the complex processes involved. Recognizing the limitations of traditional antibiotic treatments, mechanisms of resistance associated with biofilms are explored. The focus is on alternative therapeutic strategies to control biofilm, with illuminating case studies providing valuable context and practical insights. In conclusion, the review highlights the importance of exploring emerging approaches to mitigate biofilm formation in animals. It consolidates existing knowledge, highlights gaps in understanding, and encourages further research to address this critical facet of animal health. The comprehensive perspective provided by this review serves as a foundation for future investigations and interventions to improve the management of biofilm-associated infections in diverse animal populations.

Potential role of Citrus bergamia flower essential oil against oral pathogens

BACKGROUND

Oral bacterial infections are difficult to treat due to emergence of resistance against antibiotic therapy. Essential oils are considered emerging alternate therapy against bacterial infections and biofilms. We investigated Citrus bergemia flower essential oil against oral pathogens.

METHODS

The essential oil was analsyed using Gas Chromatography(GC-MS), in silico investigations, antioxidant, antimicrobial, antibiofilm and antiquorum sensing assays.

RESULTS

Gas Chromatography analysis confirmed presence of 17 compounds including 1,6-Octadien-3-ol,3,7-dimethyl, 48.17%), l-limonene (22.03%) and p-menth-1-ol, 8-ol (7.31%) as major components. In silico analysis showed compliance of all tested major components with Lipinski's rule, Bioavailability and antimicrobial activity using PASS (prediction of activity spectrum of substances). Molecular docking with transcriptional regulators 3QP5, 5OE3, 4B2O and 3Q3D revealed strong interaction of all tested compounds except 1,6-Octadien-3-ol,3,7-dimethyl. All tested compounds presented significant inhibition of DPPH (2,2-diphenyl-1-picrylhydrazyl) (IC50 0.65 mg/mL), H2O2 (hydrogen peroxide) (63.5%) and high FRAP (ferrous reducing antioxidant power) value (239.01 µg). In antimicrobial screening a significant activity (MIC 0.125 mg/mL) against Bacillus paramycoides and Bacillus chungangensis was observed. Likewise a strong antibiofilm (52.1 - 69.5%) and anti-QS (quorum sensing) (4-16 mm) activity was recorded in a dose dependent manner.

CONCLUSION

It was therefore concluded that C. bergemia essential oil posess strong antioxidant, antimicrobial and antibiofilm activities against tested oral pathogens.

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

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

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

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

Essential oils of Pinus sylvestris, Citrus limon and Origanum vulgare exhibit high bactericidal and anti-biofilm activities against Neisseria gonorrhoeae and Streptococcus suis

Antimicrobial resistance is a worldwide problem that urges novel alternatives to treat infections. In attempts to find novel molecules, we assess the antimicrobial potential of seven essential oils (EO) of different plants (Pinus sylvestris, Citrus limon, Origanum vulgare, Cymbopogon martini, Cinnamomum cassia, Melaleuca alternifolia and Eucalyptus globulus) against two multidrug-resistant bacteria species, i.e. Neisseria gonorrhoeae and Streptococcus suis. EOs of P. sylvestris and C. limon revealed higher bactericidal activity (MIC ≤ 0.5 mg/mL) and capacity to rapidly disperse biofilms of several N. gonorrhoeae clinical isolates than other EOs. Examination of biofilms exposed to both EO by electron microscopy revealed a reduction of bacterial aggregates, high production of extracellular vesicles, and alteration of cell integrity. This activity was dose-dependent and was enhanced in DNase I-treated biofilms. Antibiotic susceptibility studies confirmed that both EOs affected the outer membrane permeability, and analysis of EO- susceptibility of an LPS-deficient mutant suggested that both EO target the LPS bilayer. Further analysis revealed that α- and β-pinene and d-limonene, components of both EO, contribute to such activity. EO of C. martini, C. cassia, and O. vulgare exhibited promising antimicrobial activity (MIC ≤ 0.5 mg/mL) against S. suis, but only EO of O. vulgare exhibited a high biofilm dispersal activity, which was also confirmed by electron microscopy studies. To conclude, the EO of P. sylvestris, C. limon and O. vulgare studied in this work exhibit bactericidal and anti-biofilm activities against gonococcus and streptococcus, respectively.

Sloanea chocoana and S. pittieriana (Elaeocarpaceae): Chemical and Biological Studies of Ethanolic Extracts and Skincare Properties

The Colombian Chocó is known for its rich biodiversity and to harbor plant species that are under-explored, including the genus Sloanea. This study aimed to analyze the chemical composition of derivatized ethanolic extracts from S. chocoana and S. pittieriana using BSTFA and TMCS through GC-MS, and to assess cell viability of immortalized human non-tumorigenic keratinocytes (HaCaT) and periodontal ligament fibroblast cells using crude extracts through MTS assay. Antioxidant and photoprotective properties were determined using DPPH assay and spectrophotometry. Antifungal activity of extracts against Candida species was developed following the CLSI standard M27, 4th ed. The sun protective factor (SPF) and UVA/UVB ratio values were calculated using the Mansur equation and the Boots star rating system. The critical wavelength (λc) was determined by calculating the integrated optical density curve's area. The transmission of erythema and pigmentation was calculated through equations that use constants to calculate the flux of erythema and pigmentation. The GC-MS analysis identified 37 compounds for S. chocoana and 38 for S. pittieriana, including alkaloids, triterpenoids, and polyphenolics, among others. Both extracts exhibited proliferative effects on periodontal ligament fibroblasts, did not affect the viability of HaCaT cells, and showed excellent antioxidant activities (46.1% and 43.7%). Relevant antifungal activity was observed with S. pittieriana extract against Candida albicans (GM-MIC: 4 µg/mL), followed by C. auris and C. glabrata (GM-MIC: 32 µg/mL), while S. chocoana extract was active against C. albicans and C. glabrata (GM-MIC: 16 and 32 µg/mL, respectively). High SPF values (31.0 and 30.0), λc (393.98 and 337.81 nm), UVA/UVB ratio (1.5 and 1.2), and low percentage of transmission of erythema and pigmentation were determined for S. chocoana and S. pittieriana, respectively. Results showed that species of Sloanea constitute a promising alternative as ingredients for developing skincare products, and exhaustive studies are required for their sustainable uses.

The Antibacterial Effect of Selected Essential Oils and Their Bioactive Constituents on Pseudomonas savastanoi pv. savastanoi: Phytotoxic Properties and Potential for Future Olive Disease Control

Plant pathogenic bacteria pose a significant threat to olive cultivation, leading to substantial economic losses and reduced yield. The efficacy of antimicrobial agents against these pathogens is of great interest for sustainable disease management strategies. As such, the management of olive knot disease is one of the major challenges in olive protection. In the presented study, through a series of in vitro assays, we investigated the antimicrobial effect of six essential oils (EOs) and their most concentrated constituents against causative agent of olive knot disease-Pseudomonas savastanoi pv. savastanoi, highlighting the high potential of Origanum compactum EO and its constituent carvacrol. Carvacrol exhibited the highest potential for practical application, demonstrating membrane disruption as its mechanism of action even at the lowest concentration. The bactericidal effect of antimicrobials was confirmed in a time-kill assay, where concentrations of MIC, 2× MIC, and 4× MIC were evaluated. Some of the applied treatments resulted in inhibition equal or higher than copper-based treatment. Additionally, we assessed the phytotoxicity of carvacrol by foliar application on olive cv. Leccino. The appearance of phytotoxic injuries majorly occurred on the young leaves of olive plants, with the highest proportion of damaged canopy observed when the 2× MIC concentration was applied. Due to its great efficiency against P. savastanoi pv. savastanoi in vitro, these findings highlight the potential of carvacrol as a molecule of interest for the development of environmentally friendly biopesticides. This study also contributes to the advancement of disease management practices in olive cultivation, leading to enhanced crop protection.

Selected antimicrobial essential oils to eradicate multi-drug resistant bacterial biofilms involved in human nosocomial infections

Biofilms are the primary source of contamination linked to nosocomial infections by promoting bacterial resistance to antimicrobial agents, including disinfectants. Using essential oils, this study aims to inhibit and eradicate the biofilm of enterobacteria and staphylococci responsible for nosocomial infections at Guelma Hospital, northeastern Algeria. Thymbra capitata, Thymus pallescens and Artemesia herba-alba essential oils were evaluated against clinical strains of Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus. The antimicrobial activity of the essential oils under consideration was assessed using an agar disc diffusion assay and the determination of minimum inhibitory concentrations (MICs). In addition, the crystal violet method and scanning electron microscopy (SEM) evaluated biofilm inhibition and eradication by those antimicrobial agents. The results indicate that T. pallescens essential oil was the most effective antimicrobial agent against pathogenic bacteria, with large zones of inhibition (up to 50 mm against S. aureus), low MICs (0.16 to 0.63 mg/mL), and powerful biofilm eradication up to 0.16 mg/mL in both 24 h and 60-min exposure times. Thus, Algerian thyme and oregano could be used in various ways to combat the biofilm that causes nosocomial infection in local hospitals.

Flowering phenophases influence the antibacterial and anti-biofilm effects of Thymus vulgaris L. essential oil

BACKGROUND

Essential oils are becoming increasingly popular in medicinal applications because of their antimicrobial effect. Thymus vulgaris L. (Lamiaceae) is a well-known and widely cultivated medicinal plant, which is used as a remedy for cold, cough and gastrointestinal symptoms. Essential oil content of thyme is responsible for its antimicrobial activity, however, it has been reported that the chemical composition of essential oils influences its biological activity. In order to explore flowering phenophases influence on the chemical composition of thyme essential oil and its antibacterial and anti-biofilm activity, plant materials were collected at the beginning of flowering, in full bloom and at the end of flowering periods in 2019.

METHODS

Essential oils from fresh and dried plant materials were distilled and analyzed with gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID). The antibacterial activity was performed by broth microdilution and thin layer chromatography-direct bioautography (TLC-DB) assays and the anti-biofilm effect by crystal violet assay, respectively. Scanning electron microscopy was applied to illustrate the cellular changes of bacterial cells after essential oil treatment.

RESULTS

Thymol (52.33-62.46%) was the main component in the thyme essential oils. Thyme oil distilled from fresh plant material and collected at the beginning of flowering period exerted the highest antibacterial and anti-biofilm activity against Haemophilus influenzae, H. parainfluenzae and Pseudomonas aeruginosa.

CONCLUSION

The different flowering periods of Thymus vulgaris influence the antibacterial and anti-biofilm activity of its essential oils, therefore, the collection time has to be taken into consideration and not only the full bloom, but the beginning of flowering period may provide biological active thyme essential oil.

Effect of Essential Oil from Lippia origanoides on the Transcriptional Expression of Genes Related to Quorum Sensing, Biofilm Formation, and Virulence of Escherichia coli and Staphylococcus aureus

Microbial infections resistant to conventional antibiotics constitute one of the most important causes of mortality in the world. In some bacterial species, such as Escherichia coli and Staphylococcus aureus pathogens, biofilm formation can favor their antimicrobial resistance. These biofilm-forming bacteria produce a compact and protective matrix, allowing their adherence and colonization to different surfaces, and contributing to resistance, recurrence, and chronicity of the infections. Therefore, different therapeutic alternatives have been investigated to interrupt both cellular communication routes and biofilm formation. Among these, essential oils (EO) from Lippia origanoides thymol-carvacrol II chemotype (LOTC II) plants have demonstrated biological activity against different biofilm-forming pathogenic bacteria. In this work, we determined the effect of LOTC II EO on the expression of genes associated with quorum sensing (QS) communication, biofilm formation, and virulence of E. coli ATCC 25922 and S. aureus ATCC 29213. This EO was found to have high efficacy against biofilm formation, decreasing-by negative regulation-the expression of genes involved in motility (fimH), adherence and cellular aggregation (csgD), and exopolysaccharide production (pgaC) in E. coli. In addition, this effect was also determined in S. aureus where the L. origanoides EO diminished the expression of genes involved in QS communication (agrA), production of exopolysaccharides by PIA/PNG (icaA), synthesis of alpha hemolysin (hla), transcriptional regulators of the production of extracellular toxins (RNA III), QS and biofilm formation transcriptional regulators (sarA) and global regulators of biofilm formation (rbf and aur). Positive regulation was observed on the expression of genes encoding inhibitors of biofilm formation (e.g., sdiA and ariR). These findings suggest that LOTCII EO can affect biological pathways associated with QS communication, biofilm formation, and virulence of E. coli and S. aureus at subinhibitory concentrations and could be a promising candidate as a natural antibacterial alternative to conventional antibiotics.

Metabolomic Analysis of the Effect of Lippia origanoides Essential Oil on the Inhibition of Quorum Sensing in Chromobacterium violaceum

Bacteria can communicate through quorum sensing, allowing them to develop different survival or virulence traits that lead to increased bacterial resistance against conventional antibiotic therapy. Here, fifteen essential oils (EOs) were investigated for their antimicrobial and anti-quorum-sensing activities using Chromobacterium violaceum CV026 as a model. All EOs were isolated from plant material via hydrodistillation and analyzed using GC/MS. In vitro antimicrobial activity was determined using the microdilution technique. Subinhibitory concentrations were used to determine anti-quorum-sensing activity by inhibition of violacein production. Finally, a possible mechanism of action for most bioactive EOs was determined using a metabolomic approach. Among the EOs evaluated, the EO from Lippia origanoides exhibited antimicrobial and anti-quorum activities at 0.37 and 0.15 mg/mL, respectively. Based on the experimental results, the antibiofilm activity of EO can be attributed to the blockage of tryptophan metabolism in the metabolic pathway of violacein synthesis. The metabolomic analyses made it possible to see effects mainly at the levels of tryptophan metabolism, nucleotide biosynthesis, arginine metabolism and vitamin biosynthesis. This allows us to highlight the EO of L. origanoides as a promising candidate for further studies in the design of antimicrobial compounds against bacterial resistance.

Antifungal and Antibiofilm Activity of Colombian Essential Oils against Different Candida Strains

Most Candida species are opportunistic pathogens with the ability to form biofilms, which increases their resistance to antifungal drug therapies and the host immune response. Essential oils (EOs) are an alternative for developing new antimicrobial drugs, due to their broad effect on cellular viability, cell communication, and metabolism. In this work, we evaluated the antifungal and antibiofilm potential of fifty EOs on C. albicans ATCC 10231, C. parapsilosis ATCC 22019, and Candida auris CDC B11903. The EOs’ antifungal activity was measured by means of a broth microdilution technique to determine the minimum inhibitory and fungicidal concentrations (MICs/MFCs) against the different Candida spp. strains. The effects on biofilm formation were determined by a crystal violet assay using 96-well round-bottom microplates incubated for 48 h at 35 °C. The EOs from Lippia alba (Verbenaceae family) carvone-limonene chemotype and L. origanoides exhibited the highest antifungal activity against C. auris. The L. origanoides EOs also presented antifungal and antibiofilm activity against all three Candida spp., thus representing a promising alternative for developing new antifungal products focused on yeast infections, especially those related to biofilm formation, virulence factors, and antimicrobial resistance.

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.

Antibacterial activity and synergic effects of the essential oils of Amomum verum Blackw and Zanthoxylum limonella (Dennst.) Alston

The antibacterial activity of Amomum verum Blackw, Zanthoxylum limonella (Dennst.) Alston, Zanthoxylum bungeanum, and Zingiber montanum (J. Koenig) Link ex A. Dietr essential oils were investigated against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa. The essential oils of A. verum Blackw, Z. limonella (Dennst.) Alston, Z. bungeanum, and Z. montanum (J. Koenig) Link ex A. Dietr displayed strong antibacterial activity with a minimum inhibitory concentration and minimumbactericidal concentration ranging from 0.31 to 1.25 µg/mL and 0.62-5.00 µg/mL, respectively. The chemical composition of A. verum Blackw, Z. limonella (Dennst.) Alston, Z. bungeanum, and Z. montanum (J. Koenig) Link ex A. Dietr essential oils were analysed using gas chromatography-mass spectrometry. 1,8-Cineole and limonene were detected in high amounts in the A. verum Blackw and Z. limonella (Dennst.) Alston essential oils, respectively. The major compound in Z. bungeanum and Z. montanum (J. Koenig) Link ex A. Dietr essential oil was 2,4-dimethylether-phloroacetophenone and terpinene-4-ol, respectively. The antibacterial activities and synergistic effects between these essential oils were further analysed. The combination of A. verum Blackw and Z. limonella (Dennst.) Alston essential oils showed a synergistic effect against all bacterial strains, while the other essential oil combinations showed additive, antagonistic effects, and no interaction. The synergistic effect of the combination between A. verum Blackw and Z. limonella (Dennst.) Alston essential oils could be resulted from 1,8-cineole and limonene which was evaluated to possess strong antibacterial activity.

Natural Medicine a Promising Candidate in Combating Microbial Biofilm

Studies on biofilm-related infections are gaining prominence owing to their involvement in most clinical infections and seriously threatening global public health. A biofilm is a natural form of bacterial growth ubiquitous in ecological niches, considered to be a generic survival mechanism adopted by both pathogenic and non-pathogenic microorganisms and entailing heterogeneous cell development within the matrix. In the ecological niche, quorum sensing is a communication channel that is crucial to developing biofilms. Biofilm formation leads to increased resistance to unfavourable ecological effects, comprising resistance to antibiotics and antimicrobial agents. Biofilms are frequently combated with modern conventional medicines such as antibiotics, but at present, they are considered inadequate for the treatment of multi-drug resistance; therefore, it is vital to discover some new antimicrobial agents that can prevent the production and growth of biofilm, in addition to minimizing the side effects of such therapies. In the search for some alternative and safe therapies, natural plant-derived phytomedicines are gaining popularity among the research community. Phytomedicines are natural agents derived from natural plants. These plant-derived agents may include flavonoids, terpenoids, lectins, alkaloids, polypeptides, polyacetylenes, phenolics, and essential oils. Since they are natural agents, they cause minimal side effects, so could be administered with dose flexibility. It is vital to discover some new antimicrobial agents that can control the production and growth of biofilms. This review summarizes and analyzes the efficacy characteristics and corresponding mechanisms of natural-product-based antibiofilm agents, i.e., phytochemicals, biosurfactants, antimicrobial peptides, and their sources, along with their mechanism, quorum sensing signalling pathways, disrupting extracellular matrix adhesion. The review also provides some other strategies to inhibit biofilm-related illness. The prepared list of newly discovered natural antibiofilm agents could help in devising novel strategies for biofilm-associated infections.

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.

Antimicrobial Properties of Essential Oils Obtained from Autochthonous Aromatic Plants

The aim of this work was to determine the antimicrobial activity of the essential oils of six plants widely distributed in the Dehesa of Extremadura, such as Calendula officinalis, Cistus ladanifer, Cistus salviifolius, Cistus multiflorus, Lavandula stoechas, and Rosmarinus officinalis. The content of total phenolic compounds (TPC) and the antimicrobial activity of the essential oils against pathogenic and spoilage bacteria and yeasts as well as aflatoxin-producing molds were determined. A great variability was observed in the composition of the essential oils obtained from the six aromatic plants. The Cistus ladanifer essential oil had the highest content of total phenols (287.32 ppm), followed by the Cistus salviifolius essential oil; and the Rosmarinus officinalis essential oil showed the lowest amount of these compounds. The essential oils showed inhibitory effects on the tested bacteria and also yeasts, showing a maximum inhibition diameter of 11.50 mm for Salmonella choleraesuis and Kregervanrija fluxuum in the case of Cistus ladanifer and a maximum diameter of 9 mm for Bacillus cereus and 9.50 mm for Priceomyces carsonii in the case of Cistus salviifolius. The results stated that antibacterial and antiyeast activity is influenced by the concentration and the plant material used for essential oil preparation. In molds, aflatoxin production was inhibited by all the essential oils, especially the essential oils of Cistus ladanifer and Cistus salviifolius. Therefore, it can be concluded that the essential oils of native plants have significant antimicrobial properties against pathogenic and spoilage microorganisms, so they could be studied for their use in the industry as they are cheap, available, and non-toxic plants that favor the sustainability of the environment of the Dehesa of Extremeña.

Biofilm formation of pathogenic bacteria isolated from aquatic animals

Bacterial biofilm formation is one of the dynamic processes, which facilitates bacteria cells to attach to a surface and accumulate as a colony. With the help of biofilm formation, pathogenic bacteria can survive by adapting to their external environment. These bacterial colonies have several resistance properties with a higher survival rate in the environment. Especially, pathogenic bacteria can grow as biofilms and can be protected from antimicrobial compounds and other substances. In aquaculture, biofilm formation by pathogenic bacteria has emerged with an increased infection rate in aquatic animals. Studies show that Vibrio anguillarum, V. parahaemolyticus, V. alginolyticus, V. harveyi, V. campbellii, V. fischeri, Aeromonas hydrophila, A. salmonicida, Yersinia ruckeri, Flavobacterium columnare, F. psychrophilum, Piscirickettsia salmonis, Edwardsiella tarda, E. ictaluri, E. piscicida, Streptococcus parauberis, and S. iniae can survive in the environment by transforming their planktonic form to biofilm form. Therefore, the present review was intended to highlight the principles behind biofilm formation, major biofilm-forming pathogenic bacteria found in aquaculture systems, gene expression of those bacterial biofilms and possible controlling methods. In addition, the possibility of these pathogenic bacteria can be a serious threat to aquaculture systems.

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.

Microscopic visualization of the antibiofilm potential of essential oils against Staphylococcus aureus and Klebsiella pneumoniae

Biofilms are known to pose great risks in clinical settings, drinking water systems, and food industries as they show considerable resistance to various environmental stresses. This study investigates the antibiofilm potential of different essential oils against the test organisms Staphylococcus aureus (ATCC 25923) and Klebsiella pneumoniae (ATCC 13883). Moreover, different stages of biofilm formation were also assessed using light microscopic assays. For determining the antibiofilm activity, a total of five essential oils namely cinnamon (Cinnamomum Verum), tea tree (Melaleuca alternifolia), lavender (Lavandula), peppermint (Mentha piperita), and lemongrass (Cymbopogon citratus) were tested for their ability to inhibit the initial attachment of microbial cells as well as the eradication of mature biofilm using the microtitre plate assay. For both the test strains (S. aureus and K. pneumoniae) the concentration of 30 μl/100 μl of cinnamon oil exhibited the highest antibiofilm activity followed by the activity of peppermint oil at the same concentration. These results were further validated by employing the light microscopy assay for observing the antibiofilm potential of cinnamon and peppermint essential oils.

Nanoemulsion as an Effective Inhibitor of Biofilm-forming Bacterial Associated Drug Resistance: An Insight into COVID Based Nosocomial Infections

Antibiotic overuse has resulted in the microevolution of drug-tolerant bacteria. Understandably it has become one of the most significant obstacles of the current century for scientists and researchers to overcome. Bacteria have a tendency to form biofilm as a survival mechanism. Biofilm producing microorganism become far more resistant to antimicrobial agents and their tolerance to drugs also increases. Prevention of biofilm development and curbing the virulency factors of these multi drug resistant or tolerant bacterial pathogens is a newly recognised tactic for overcoming the challenges associated with such bacterial infections and has become a niche to be addressed. In order to inhibit virulence and biofilm from planktonic bacteria such as, Pseudomonas aeruginosa, Acinetobacter baumannii, and others, stable nanoemulsions (NEs) of essential oils (EOs) and their bioactive compounds prove to be an interesting solution. These NEs demonstrated significantly greater anti-biofilm and anti-virulence activity than commercial antibiotics. The EO reduces disease-causing gene expression, which is required for pathogenicity, biofilm formation and attachment to the surfaces. Essential NE and NE-loaded hydrogel surface coatings demonstrates superior antibiofilm activity which can be employed in healthcare-related equipments like glass, plastic, and metal chairs, hospital beds, ventilators, catheters, and tools used in intensive care units. Thus, anti-virulence and anti-biofilm forming strategies based on NEs-loaded hydrogel may be used as coatings to combat biofilm-mediated infection on solid surfaces.

Quorum Sensing Orchestrates Antibiotic Drug Resistance, Biofilm Formation, and Motility in Escherichia coli and Quorum Quenching Activities of Plant-derived Natural Products: A Review

Quorum sensing (QS) is a type of cell-to-cell communication that is influenced by an increase in signaling molecules known as autoinducers, which is correlated to the increase in the density of microbial communities. In this review, we aim to discuss and provide updates on the different signaling molecules used by Escherichia coli, such as acyl-homoserine lactone (AHL), autoinducer-2 (AI-2), and indole to influence key phenotypes such as antibiotic drug resistance, biofilm formation, and motility during quorum sensing. Based on the literature, E. coli signaling molecules have different functions during cell-to-cell communication such that the increase in AHL and indole was found to cause the modulation of antibiotic resistance and inhibition of biofilm formation and motility. Meanwhile, AI-2 is known to modulate biofilm formation, antibiotic resistance, and motility. On the other hand, in the existing literature, we found that various plants possess phytochemicals that can be used to alter QS and its downstream key phenotypes such as biofilm formation, swimming and swarming motility, and genes related to motility, curli and AI-2 production. However, the exact physiological and molecular mechanisms of these natural compounds are still understudied. Understanding the mechanisms of those phytochemicals during QS are therefore highly recommended to conduct as a necessary step for future scholars to develop drugs that target the actions of QS-signaling molecules and receptors linked to antibiotic resistance, biofilm formation, and motility without putting bacteria under stress, thereby preventing the development of drug resistance.

A Review of Essential Oils as Antimicrobials in Foods with Special Emphasis on Fresh Produce

ABSTRACT

Consumer safety concerns over established fresh produce washing methods and the demand for organic and clean-label food has led to the exploration of novel methods of produce sanitization. Essential oils (EOs), which are extracted from plants, have potential as clean-label sanitizers because they are naturally derived and act as antimicrobials and antioxidants. In this review, the antimicrobial effects of EOs are explored individually and in combination, as emulsions, combined with existing chemical and physical preservation methods, incorporated into films and coatings, and in vapor phase. We examined combinations of EOs with one another, with EO components, with surfactants, and with other preservatives or preservation methods to increase sanitizing efficacy. Components of major EOs were identified, and the chemical mechanisms, potential for antibacterial resistance, and effects on organoleptic properties were examined. Studies have revealed that EOs can be equivalent or better sanitizing agents than chlorine; nevertheless, concentrations must be kept low to avoid adverse sensory effects. For this reason, future studies should address the maximum permissible EO concentrations that do not negatively affect organoleptic properties. This review should be beneficial to food scientists or industry personnel interested in the use of EOs for sanitization and preservation of foods, including fresh produce.

HIGHLIGHTS

Chemical Composition, Antioxidant, Antibacterial, and Antibiofilm Activities of Backhousia citriodora Essential Oil

The essential oil of Backhousia citriodora, commonly known as lemon myrtle oil, possesses various beneficial properties due to its richness in bioactive compounds. This study aimed to characterize the chemical profile of the essential oil isolated from leaves of Backhousia citriodora (BCEO) and its biological properties, including antioxidant, antibacterial, and antibiofilm activities. Using gas chromatography-mass spectrometry, 21 compounds were identified in BCEO, representing 98.50% of the total oil content. The isomers of citral, geranial (52.13%), and neral (37.65%) were detected as the main constituents. The evaluation of DPPH radical scavenging activity and ferric reducing antioxidant power showed that BCEO exhibited strong antioxidant activity at IC50 of 42.57 μg/mL and EC50 of 20.03 μg/mL, respectively. The antibacterial activity results showed that BCEO exhibited stronger antibacterial activity against Gram-positive bacteria (Staphylococcus aureus and Staphylococcus epidermidis) than against Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae). For the agar disk diffusion method, S. epidermidis was the most sensitive to BCEO with an inhibition zone diameter of 50.17 mm, followed by S. aureus (31.13 mm), E. coli (20.33 mm), and K. pneumoniae (12.67 mm). The results from the microdilution method showed that BCEO exhibited the highest activity against S. epidermidis and S. aureus, with the minimal inhibitory concentration (MIC) value of 6.25 μL/mL. BCEO acts as a potent antibiofilm agent with dual actions, inhibiting (85.10% to 96.44%) and eradicating (70.92% to 90.73%) of the biofilms formed by the four tested bacteria strains, compared with streptomycin (biofilm inhibition, 67.65% to 94.29% and biofilm eradication, 49.97% to 89.73%). This study highlights that BCEO can potentially be a natural antioxidant agent, antibacterial agent, and antibiofilm agent that could be applied in the pharmaceutical and food industries. To the best of the authors' knowledge, this is the first report, on the antibiofilm activity of BCEO against four common nosocomial pathogens.

Activity of Essential Oils Against Multidrug-Resistant Salmonella enteritidis

We have investigated the antibacterial, anti-biofilm, and anti-quorum sensing potencies of six Essential Oils (EOs) obtained from cinnamon (Cinnamomum verum), thyme (Thymus vulgaris), clove (Eugenia caryophyllata), curcuma (Curcuma longa L.), rosemary (Rosmarinus officinalis L.), and sage (Salvia officinalis). The study was conducted on 20 multidrug-resistant (MDR) S. enteritidis clinical strains. Minimum inhibitory concentrations and minimum bactericide concentrations were displayed by microdilution. The effect on biofilm formation was tested on polystyrene plates. The anti-quorum sensing effect was determined by measuring the inhibition of violacein production by Chromobacterium violaceum CV026. The influence of EOs on the adhesion of Salmonella strains to HT-29 cells was studied. The potency of S. enteritidis to infect and kill Caenorhabditis elegans was evaluated. The cinnamon, thyme, and clove EOs showed remarkable antibacterial properties. Biofilm formation was significantly reduced by the six EOs: 99.10% for cinnamon, 97.64% for clove, 95.90% for thyme, 79.84% for rosemary, 28.98% for curcuma, and 15.55% for sage. The MIC/2 of clove EO exhibited the highest percentage of inhibition of violacein production (99.03%), followed by thyme (91.68%) and cinnamon (84.13%) EOs. Thyme extracts exhibited an important anti-adhesive potency. Clove EO behaves as an effective regulator of Salmonella virulence in nematodes.

The impact of aromatic plant-derived bioactive compounds on seafood quality and safety

Plant-derived bioactive compounds have been extensively studied and used within food industry for the last few decades. Those compounds have been used to extend the shelf-life and improve physico-chemical and sensory properties on food products. They have also been used as nutraceuticals due to broad range of potential health-promoting properties. Unlike the synthetic additives, the natural plant-derived compounds are more acceptable and often regarded as safer by the consumers. This chapter summarizes the extraction methods and sources of those plant-derived bioactives as well as recent findings in relation to their health-promoting properties, including cardio-protective, anti-diabetic, anti-inflammatory, anti-carcinogenic, immuno-modulatory and neuro-protective properties. In addition, the impact of applying those plant-derived compounds on seafood products is also investigated by reviewing the recent studies on their use as anti-microbial, anti-oxidant, coloring and flavoring agents as well as freshness indicators. Moreover, the current limitations of the use of plant-derived bioactive compounds as well as future prospects are discussed. The discoveries show high potential of those compounds and the possibility to apply on many different seafood. The compounds can be applied as individual while more and more studies are showing synergetic effect when those compounds are used in combination providing new important research possibilities.

The ameliorative efficacy of Thymus vulgaris essential oil against Escherichia coli O157:H7-induced hematological alterations, hepatorenal dysfunction and immune-inflammatory disturbances in experimentally infected rats

The purpose of the present study was to evaluate the possible ameliorative role of Thymus vulgaris (T. vulgaris) essential oil against Escherichia coli O157:H7 (E. coli O157:H7) deleterious effects in both blood and different tissues of rats by assessing the hematological, biochemical and immune-inflammatory parameters besides the histopathological alterations in the different organs. Forty male rats were randomly divided into four equal groups as follows: group I served as control, group II orally inoculated with E. coli O157:H7 at a dose of 1.0 × 10⁹ cfu/ml, group III orally received 250 mg/kg BW T. vulgaris oil daily for 7 days and group IV orally inoculated with E. coli O157:H7 as the same dose of group II and orally received T. vulgaris oil as the same dose and duration of group III. Bacterial challenge in groups II and IV was once at the beginning of experiment and administration of oil began after 72 h from bacterial inoculation. At the end of the study, blood was sampled and complete blood picture, liver and kidney function alongside immunoglobulins and cytokines concentrations were estimated and tissues of large intestine (colon), liver and kidneys were collected for histopathological examinations. The results revealed that there was an increase of red blood cells count, hematocrit value and hemoglobin concentration besides white blood cells and thrombocytes counts and substantial increment of serum markers of hepatorenal damage such as the activities of transaminases and concentrations of bilirubin (total, direct and indirect), total proteins, albumin, creatinine and urea in E. coli O157:H7-challenged group. Also, there was a considerable increase in serum immunoglobulins M and G, interleukin 6 and 8 and tumor necrosis factor alpha as well as decreased serum alkaline phosphatase activity. Moreover, T. vulgaris oil could partially improve the hematological, biochemical and histopathological alterations induced by E. coli O157:H7 without any significant alterations in all measured parameters when used alone. The study concluded that the T. vulgaris oil relatively diminished the alterations in hematological parameters, hepatic and renal function markers and immune-inflammatory variables alongside the histopathological changes in different organs induced by E. coli O157:H7. The ameliorative effects of T. vulgaris oil are mediated through its anti-inflammatory, antioxidant and immunomodulatory activities.

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.

GC-MS Profiling, Vibriocidal, Antioxidant, Antibiofilm, and Anti-Quorum Sensing Properties of Carum carvi L. Essential Oil: In Vitro and In Silico Approaches

The main objectives of the present study were to investigate anti-Vibrio spp., antibiofilms, and anti-quorum-sensing (anti-QS) properties of caraway essential oil in relation to their phytochemical composition. The results obtained show the identification of twelve compounds, with carvone (58.2%) and limonene (38.5%) being the main ones. The obtained essential oil (EO) is particularly active against all Vibrio spp. species, with bacteriostatic action against all tested strains (MBC/MIC ratio ≥ 4) and with inhibition zones with high diameters of growth, ranging from 8.66 ± 0.58 mm for V. furnisii ATCC 35016 to 37.33 ± 0.58 mm for V. alginolyticus ATCC 17749. Caraway essential oil (Carvone/limonene chemotype) exhibits antioxidant activities by using four tests (DPPH = 15 ± 0.23 mg/mL; reducing power = 7.8 ± 0.01 mg/mL; β-carotene = 3.9 ± 0.025 mg/mL; chelating power = 6.8 ± 0.05 mg/mL). This oil is particularly able to prevent cell-to-cell communication by inhibiting swarming motility, production of elastase and protease in Pseudomonas aeruginosa PAO1, and violacein production in C. violaceum in a concentration-dependent manner. A molecular docking approach shows good interaction of the identified bioactive molecules in caraway EO, with known target enzymes involved in antioxidant, antibacterial, and anti-QS activities having high binding energy. Overall, the obtained results highlight the possible use of caraway essential oil against pathogenic Vibrio species and to attenuate the secretion of virulence-related factors controlled by QS systems in Gram-negative bacteria. Therefore, this oil can be used by food industries to prevent biofilm formation on abiotic surfaces by Vibrio strains.

Progress in Alternative Strategies to Combat Antimicrobial Resistance: Focus on Antibiotics

Antibiotic resistance, and, in a broader perspective, antimicrobial resistance (AMR), continues to evolve and spread beyond all boundaries. As a result, infectious diseases have become more challenging or even impossible to treat, leading to an increase in morbidity and mortality. Despite the failure of conventional, traditional antimicrobial therapy, in the past two decades, no novel class of antibiotics has been introduced. Consequently, several novel alternative strategies to combat these (multi-) drug-resistant infectious microorganisms have been identified. The purpose of this review is to gather and consider the strategies that are being applied or proposed as potential alternatives to traditional antibiotics. These strategies include combination therapy, techniques that target the enzymes or proteins responsible for antimicrobial resistance, resistant bacteria, drug delivery systems, physicochemical methods, and unconventional techniques, including the CRISPR-Cas system. These alternative strategies may have the potential to change the treatment of multi-drug-resistant pathogens in human clinical settings.

Essential oils as antimicrobial and anti-adhesion agents against bacteria Salmonella Typhimurium and Staphylococcus aureus, and yeasts Candida albicans and Saccharomyces cerevisiae

A serious global problem with the increasing resistance of microorganisms to currently used antimicrobials has opened up the promotional research in the identification of new, more effective drugs with a broad spectrum of antimicrobial activities. Plant essential oils, due to the large biological and structural diversity of their components, are known to have many potential benefits. This study aimed to evaluate the antimicrobial and anti-adhesion activity of fifteen essential oils and their compounds against two bacterial and two yeast species responsible for food spoilage and infectious diseases. Antimicrobial activity was determined by testing the minimum inhibitory concentration (MIC), the minimum bactericidal concentration (MBC) and the minimum fungicidal concentration (MFC) of essential oils and compounds. The essential oils of Cinnamomum zeylanicum and Eugenia caryophyllus showed the highest antimicrobial activity with MICs ranging from 0.078 to 1.25 mg/mL, and 0.039 to 1.25 mg/mL, respectively. On the other hand, essential oils of Eucalypti aetheroleum and Salvia officinalis had significantly weaker antimicrobial properties than the others. Further, MICs were used to assess the inhibition of adhesion of bacteria Salmonella Typhimurium ATCC 25923 and Staphylococcus aureus ATCC 14208, and yeasts Candida albicans ATCC 10231 and Saccharomyces cerevisiae ATCC 9763 in a microtiter plate using the crystal violet staining method. Based on the percentage of adhesion inhibition, yeast S. cerevisiae ATCC 9763 showed a high level of antimicrobial resistance. E. caryophyllus had the strongest effect with inhibition up to 73%. Consistent with the antimicrobial susceptibility results, the most active anti-adhesion compounds were carvacrol and thymol. Considering the role of biofilm in food spoilage and clinical diseases, inhibition of the initial phase of biofilm formation by natural antimicrobial agents may be an alternative to commonly used synthetic ones.

Essential oils as antimicrobial and anti-adhesion agents against bacteria Salmonella Typhimurium and Staphylococcus aureus, and yeasts Candida albicans and Saccharomyces cerevisiae

A serious global problem with the increasing resistance of microorganisms to currently used antimicrobials has opened up the promotional research in the identification of new, more effective drugs with a broad spectrum of antimicrobial activities. Plant essential oils, due to the large biological and structural diversity of their components, are known to have many potential benefits. This study aimed to evaluate the antimicrobial and anti-adhesion activity of fifteen essential oils and their compounds against two bacterial and two yeast species responsible for food spoilage and infectious diseases. Antimicrobial activity was determined by testing the minimum inhibitory concentration (MIC), the minimum bactericidal concentration (MBC) and the minimum fungicidal concentration (MFC) of essential oils and compounds. The essential oils of Cinnamomum zeylanicum and Eugenia caryophyllus showed the highest antimicrobial activity with MICs ranging from 0.078 to 1.25 mg/mL, and 0.039 to 1.25 mg/mL, respectively. On the other hand, essential oils of Eucalypti aetheroleum and Salvia officinalis had significantly weaker antimicrobial properties than the others. Further, MICs were used to assess the inhibition of adhesion of bacteria Salmonella Typhimurium ATCC 25923 and Staphylococcus aureus ATCC 14208, and yeasts Candida albicans ATCC 10231 and Saccharomyces cerevisiae ATCC 9763 in a microtiter plate using the crystal violet staining method. Based on the percentage of adhesion inhibition, yeast S. cerevisiae ATCC 9763 showed a high level of antimicrobial resistance. E. caryophyllus had the strongest effect with inhibition up to 73%. Consistent with the antimicrobial susceptibility results, the most active anti-adhesion compounds were carvacrol and thymol. Considering the role of biofilm in food spoilage and clinical diseases, inhibition of the initial phase of biofilm formation by natural antimicrobial agents may be an alternative to commonly used synthetic ones.

The synergistic antibacterial effect and inhibition of biofilm formation of nisin in combination with terpenes against Listeria monocytogenes

This study was to investigate the synergistic antibacterial effect and inhibition of biofilm formation of nisin in combination with terpenes (carvacrol, cinnamaldehyde, citral, and thymol) against Listeria monocytogenes. The bactericidal ranking of terpenes combined with nisin was carvacrol > cinnamaldehyde, citral > thymol. The minimum inhibitory concentration assay (MIC) of nisin and carvacrol when used together were determined to be 0.1563 mg/ml + 0.0195 mg/ml (nisin at MIC/2 + carvacrol at MIC/16). The addition of nisin at MIC/2 + carvacrol at MIC/2 caused more decrease in membrane potential than carvacrol or nisin at MIC individually. The decrease rates of hlyA and plcA gene expressions caused by nisin at MIC/2 + carvacrol at MIC/2 were significantly higher than those caused by carvacrol or nisin at MIC individually (P < 0.05). Nisin combined with carvacrol showed the highest inhibition activity to formation of L. monocytogenes biofilm on stainless steel and lettuce. The inhibition effect of nisin at MIC/2 + carvacrol at MIC/16 was significantly higher than that of nisin at MIC/2 and carvacrol at MIC/16 (P < 0.05).