Anti-biofilm activities of essential oils rich in carvacrol and thymol against Salmonella Enteritidis

A carrier-free, injectable, and self-assembling hydrogel based on carvacrol and glycyrrhizin exhibits high antibacterial activity and enhances healing of MRSA-infected wounds

Inspired by glycyrrhizin's strong pharmacological activities and the directed self-assembly into hydrogels, we created a novel carrier-free, injectable hydrogel (CAR@glycygel) by combining glycyrrhizin with carvacrol (CAR), without any other chemical crosslinkers, to promote wound healing on bacteria-infected skin. CAR appeared to readily dissolve and load into CAR@glycygel. CAR@glycygel had a dense, porous, sponge structure and strong antioxidant characteristics. In vitro, it showed better antibacterial ability than free CAR. For methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus aureus, and Escherichia coli, the diameter of inhibition zone values of CAR@glycygel were 3.80 ± 0.04, 3.31 ± 0.20 and 3.12 ± 0.24 times greater, respectively, than those of free CAR. The MICs for CAR@glycygel was 156.25 μg/mL while it was 1250.00 μg/mL for free CAR to these three bacteria. Its antibacterial mechanism appeared to involve destruction of the integrity of the bacterial cell wall and biomembrane, leading to a leakage of AKP and inhibition of biofilm formation. In vivo, CAR@glycygel effectively stopped bleeding. When applied to skin wounds on rats infected with MRSA, CAR@glycygel had strong bactericidal activity and improved wound healing. The wound healing rates for CAR@glycygel were 49.59 ± 15.78 %, 93.02 ± 3.09 % and 99.02 ± 0.55 % on day 3, day 7, and day 11, respectively, which were much better than blank control and positive control groups. Mechanisms of CAR@glycygel accelerating wound healing involved facilitating epidermis remolding, promoting the growth of hair follicles, stimulating collagen deposition, mitigating inflammation, and promoting angiogenesis. Overall, CAR@glycygel showed great potential as wound dressing for infected skin wounds.

Exploring the Antibacterial Potential of Lamiaceae Plant Extracts: Inhibition of Bacterial Growth, Adhesion, Invasion, and Biofilm Formation and Degradation in Pseudomonas aeruginosa PAO1

In response to the global rise in antibiotic resistance and the prevalence of bacterial biofilm-related infections, the antibacterial efficacy of methanolic, ethanolic, and aqueous extracts of 18 Lamiaceae plants from Serbia was evaluated. The total coumarins and triterpenes were detected spectrophotometrically, while a microdilution assay measured their effects on bacterial growth. Additionally, the impact of these extracts was assessed on Pseudomonas aeruginosa PAO1 adhesion and invasion in human fibroblasts and biofilm formation and degradation. The alcoholic extracts had the highest phytochemical content, with Teucrium montanum and Lavandula angustifolia being the richest in coumarins and triterpenes, respectively. Gram-positive bacteria, particularly Bacillus subtilis, were more susceptible to the extracts. Hyssopus officinalis ethanolic and Sideritis scardica methanolic extracts inhibited bacterial growth the most efficiently. Although the extracts did not inhibit bacterial adhesion, most ethanolic extracts significantly reduced bacterial invasion. Origanum vulgare and H. officinalis ethanolic extracts significantly inhibited biofilm formation, while Teucrium chamaedrys extract was the most active in biofilm degradation. This study significantly contributes to the literature by examining the antibacterial activity of Lamiaceae extracts, addressing major literature gaps, and underscoring their antibacterial potential, particularly Satureja montana and O. vulgare ethanolic extracts, linking their efficacy to coumarins and triterpenes.

Screening and selection of essential oils for an intranasal spray against bovine respiratory pathogens based on antimicrobial, antiviral, immunomodulatory, and antibiofilm activities

Introduction

The rise in antibiotic resistant pathogens associated with bovine respiratory disease (BRD) poses a serious challenge, particularly to the beef feedlot industry, as they currently depend on antibiotics to prevent BRD to mitigate the financial burden (approx. $1 billion annual loss) inflicted by BRD-associated high mortality and morbidity in feedlot cattle. Thus, there is an impetus need for the development of antimicrobial alternative strategies against BRD. This study aimed to screen and select candidate essential oils (EOs) for the development of an intranasal EO spray that can inhibit BRD pathogens and promote microbiota-mediated respiratory health.

Methods

The effects of selected EOs (ajowan, cinnamon leaf, citronella, grapefruit, fennel, and thyme) on a bovine nasopharyngeal microbiota culture were evaluated using 16S rRNA gene sequencing. The microbiota culture was enriched by incubating nasopharyngeal swabs obtained from finishing beef heifers in brain heart infusion broth with and without EOs (0.025%, v/v). These EOs were then also evaluated for their immunomodulatory effects on bovine turbinate (BT) cells by analyzing the concentrations of 15 cytokines and chemokines in cell culture after 24 h incubation. The crystal violet assay was done to assess the antibiofilm activity of EOs against Escherichia coli UMN026 strain. Finally, 15 EOs were screened for their antiviral activity against the bovine viral diarrhea virus 1 (BVDV-1) using BT cells and a fluorescence-based method.

Results

Ajowan, fennel, and thyme resulted in a moderate reduction of overall nasopharyngeal microbiota growth with significant alterations of both alpha and beta diversity, and the relative abundance of predominant bacterial families (e.g., increasing Enterobacteriaceae and decreasing Moraxellaceae) compared to the control (p < 0.05). Co-incubation of BT cells with selected EOs resulted in minimal alterations in cytokine and chemokine levels (p > 0.05). Ajowan, thyme, fennel, and cinnamon leaf exhibited antibiofilm activity at concentrations of 0.025 and 0.05%. Reduction of BVDV-1 replication in BT cells was observed with thyme (strong), and ajowan and citronella (moderate) at 0.0125% concentration.

Discussion

Accordingly, ajowan, thyme, fennel, cinnamon leaf, and citronella EOs were selected for further development as an intranasal EO spray to prevent and control of BRD pathogens in feedlot cattle.

Biofilm busters: Exploring the antimicrobial and antibiofilm properties of essential oils against Salmonella Enteritidis

This study delves into an exploration of the antimicrobial and antibiofilm properties of the essential oils (EOs) of cinnamon, garlic, and onion on Salmonella Enteritidis. Firstly, disc diffusion and minimum inhibitory concentration (MIC) techniques were employed to assess the antibacterial activity of the EOs. Additionally, the study explored the effect of these EOs on both initial cell attachment and 24 h-preformed biofilms. The crystal violet assay was implemented to evaluate biofilm biomass. The findings revealed that cinnamon EO exhibited the highest anti-biofilm activity. Furthermore, initial cell attachment inhibition at MIC ranged between 50 and 65% for the three oils, while inhibition rates on preformed structures were lower than 40% for all EOs at this MIC concentration. The study also found that the effects of these oils were dosage- and time-dependent (p < 0.05), thereby urging the adoption of these natural extracts as effective strategies for combating Salmonella biofilms.

Essential Oil from Tagetes minuta Has Antiquorum Sensing and Antibiofilm Potential against Pseudomonas aeruginosa Strain PAO1

Biofilms are complex communities of microorganisms that are enclosed in a matrix that shows increased resistance to antimicrobial and immunological encounters. Mostly, the traditional methods to control biofilm are exhausted; therefore, the aim is to evaluate the potential of essential oil (EO) from Tagetes minuta to encounter biofilm and other related virulence factors. The EO of T. minuta was extracted through steam-distillation, analyzed on gas chromatography-mass spectrometry, and the biofilm inhibition assays were performed with various concentrations of EO. Mainly the EO from T. minuta contains cis-β-ocimene (29.1%), trans-tagetenone (23.1%), and cis-tagetenone (17.7%). The virulence factors were monitored while applying different concentrations of EO and it was recorded that the EO from T. minuta significantly inhibited the virulence factors linked with quorum sensing (QS), such as pyocyanin production, protease production, and swarming motility. Biofilm formation is one of the most important virulence factors associated with the QS pathway and was inhibited up to 79% in the presence of EO. Antibacterial activity against the PAO1 of EO was not so promising particularly and it has high MIC (325 μg/mL) and MBC (5000 μg/mL). EO is quite efficient to inhibit biofilm in a very small concentration of 20 μg/mL, which confirms that the biofilm inhibition by EO is not by killing bacterial cells but by inhibiting the QS pathway. The study on PAO1 constructs carrying various QS reported genes confirmed that the EO interferes with the QS pathway that ultimately controls various virulence factors caused by PAO1.

Biofilm formation in food processing plants and novel control strategies to combat resistant biofilms: the case of Salmonella spp

Salmonella is one of the pathogens that cause many foodborne outbreaks throughout the world, representing an important global public health problem. Salmonella strains with biofilm-forming abilities have been frequently isolated from different food processing plants, especially in poultry industry. Biofilm formation of Salmonella on various surfaces can increase their viability, contributing to their persistence in food processing environments and cross-contamination of food products. In recent years, increasing concerns arise about the antimicrobial resistant and disinfectant tolerant Salmonella, while adaptation of Salmonella in biofilms to disinfectants exacerbate this problem. Facing difficulties to inhibit or remove Salmonella biofilms in food industry, eco-friendly and effective strategies based on chemical, biotechnological and physical methods are in urgent need. This review discusses biofilm formation of Salmonella in food industries, with emphasis on the current available knowledge related to antimicrobial resistance, together with an overview of promising antibiofilm strategies for controlling Salmonella in food production environments.

Emerging Insights into the Applicability of Essential Oils in the Management of Acne Vulgaris

The occurrence of pustules, comedones, nodules, and cysts defines acne vulgaris, a prevalent chronic inflammatory dermatological condition. In the past few decades, essential oils extracted from varied natural sources have acquired recognition due to their potential medicinal applications in acne therapy. However, there is not yet sufficient medical data to fully characterize this interaction. Multiple factors contribute to the development of acne vulgaris, including excessive sebaceous production, inflammatory processes, hyperkeratinization, and infection with Cutibacterium acnes. Essential oils, including oregano, lavender, lemon grass, myrtle, lemon, thyme, eucalyptus, rosemary, and tea tree, have been found to possess anti-inflammatory, antioxidant, and antimicrobial properties, which may target the multifactorial causes of acne. Analytical methods for determining antioxidant potential (i.e., total phenolic content, diphenyl-1-picrylhydrazyl free radical scavenging assay, reducing power assay, ferrous ion chelating activity, thiobarbituric acid reactive species assay, β-carotene bleaching assay, etc.) are essential for the evaluation of these essential oils, and their method optimization is crucial. Further studies could include the development of novel acne treatments incorporating essential oils and an assessment of their efficacy in large clinical trials. In addition, further research is necessary to ascertain the mechanisms of action of essential oils and their optimal doses and safety profiles for optimal implementation in the management of acne vulgaris.

Antibiofilm Effect of Lavandula multifida Essential Oil: A New Approach for Chronic Infections

Fungal infections are associated with high morbidity and mortality rates, being highly prevalent in patients with underlying health complications such as chronic lung disease, HIV, cancer, and diabetes mellitus. To mitigate these infections, the development of effective antifungals is imperative, with plants standing out as promising sources of bioactive compounds. In the present study, we focus on the antibiofilm potential of Lavandula multifida essential oil (EO) against dermatophyte strains and Candida albicans. The EO was characterized using GC and GC-MS, and its antifungal effect was assessed on both biofilm formation and disruption. Biofilm mass, extracellular matrix, and viability were quantified using crystal violet, safranin, and XTT assays, respectively, and morphological alterations were confirmed using optical and scanning electron microscopy. L. multifida EO showed very high amounts of carvacrol and was very effective in inhibiting and disrupting fungal biofilms. The EO significantly decreased biofilm mass and viability in all tested fungi. In addition, a reduction in dermatophytes' extracellular matrix was observed, particularly during biofilm formation. Morphological alterations were evident in mature biofilms, with a clear decrease in hypha diameter. These promising results support the use of L. multifida EO in the development of effective plant-based antifungal products.

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.

Chemical Composition, Antibacterial and Antibiofilm Actions of Oregano (Origanum vulgare subsp. hirtum) Essential Oil against Salmonella Typhimurium and Listeria monocytogenes

Essential oils (EOs) are plant mixtures that are known to present strong bioactivities, including a wide antimicrobial action. Biofilms are microbial sessile structures that represent the default mode of growth of microorganisms in most environments. This study focused on the antimicrobial action of the EO extracted from one of the most representative oregano species, that is, Origanum vulgare (subsp. hirtum), against two important foodborne pathogens, Salmonella enterica (serovar Typhimurium) and Listeria monocytogenes. For this, the minimum inhibitory concentrations of the EO against the planktonic and biofilm growth of each bacterium were determined (MICs, MBICs), together with the minimum bactericidal and biofilm eradication concentrations (MBCs, MBECs). The EO was also analyzed for its chemical composition by gas chromatography-mass spectrometry analysis (GC-MS). The influence of EO exposure on the expression of some important virulence genes (hly, inlA, inlB and prfA) was also studied in L. monocytogenes. Results revealed a strong antibacterial and antibiofilm action with MICs and MBICs ranging from 0.03% to 0.06% (v/v) and from 0.06% to 0.13% (v/v), respectively. The application of the EO at 6.25% (v/v) for 15 min resulted in the total eradication of the biofilm cells of both pathogens. The EO was mainly composed of thymol, p-cymene, γ-terpinene and carvacrol. The 3 h exposure of L. monocytogenes planktonic cells to the EO at its MBIC (0.06% v/v) resulted in the significant downregulation of all the studied genes (p < 0.05). To sum, the results obtained advocate for the further exploitation of the antimicrobial action of oregano EO in food and health applications.

Inhibition of Salmonella Enteritidis by Essential Oil Components and the Effect of Storage on the Quality of Chicken

This research investigates the antibacterial potential of plant essential oil components including thymol, carvacrol, citral, cinnamaldehyde, limonene, and β-pinene against Salmonella Enteritidis (S. Enteritidis). Through the determination of minimum inhibitory concentration, three kinds of natural antibacterial agents with the best inhibitory effect on S. Enteritidis were determined, namely thymol (128 μg/mL), carvacrol (256 μg/mL), and cinnamaldehyde (128 μg/mL). Physical, chemical, microbial, and sensory characteristics were regularly monitored on days 0, 2, 4, and 6. The findings of this study reveal that both thymol at MIC of 128 μg/mL and carvacrol at MIC of 256 μg/mL not only maintained the sensory quality of chicken, but also decreased the pH, moisture content, and TVB-N value. Additionally, thymol, carvacrol and cinnamaldehyde successfully inhibited the formation of S. Enteritidis biofilm, thereby minimizing the number of S. Enteritidis and the total aerobic plate count in chicken. Hence, thymol, carvacrol, and cinnamaldehyde have more effective inhibitory activities against S. Enteritidis, which can effectively prevent the spoilage of chicken and reduce the loss of its functional components.

Comparison of the Efficiency of Selected Disinfectants against Planktonic and Biofilm Populations of Escherichia coli and Staphylococcus aureus

The aim of this study is to compare the efficacy of selected food disinfectants on planktonic populations of Staphylococcus aureus and Escherichia coli and on the same microorganisms (MOs) incorporated in a biofilm. Two disinfectants were used for treatment: peracetic acid-based disinfectant (P) and benzalkonium chloride-based disinfectant (D). Testing of their efficacy on the selected MO populations was performed using a quantitative suspension test. The standard colony counting procedure was used to determine their efficacy on bacterial suspensions in tryptone soy agar (TSA). The germicidal effect (GE) of the disinfectants was determined based on the decimal reduction ratio. For both MOs, 100% GE was achieved at the lowest concentration (0.1%) and after the shortest exposure time (5 min). Biofilm production was confirmed with a crystal violet test on microtitre plates. Both E. coli and S. aureus showed strong biofilm production at 25 °C with E. coli showing significantly higher adherence capacity. Both disinfectants show a significantly weaker GE on 48 h biofilms compared to the GE observed after application of the same concentrations on planktonic cells of the same MOs. Complete destruction of the viable cells of the biofilms was observed after 5 min of exposure to the highest concentration tested (2%) for both disinfectants and MOs tested. The anti-quorum sensing activity (anti-QS) of disinfectants P and D was determined via a qualitative disc diffusion method applied to the biosensor bacterial strain Chromobacterium violaceum CV026. The results obtained indicate that the disinfectants studied have no anti-QS effect. The inhibition zones around the disc therefore only represent their antimicrobial effect.

Antibacterial and Biofilm Production Inhibition Activity of Thymus vulgaris L. Essential Oil against Salmonella spp. Isolates from Reptiles

Salmonellosis is an infectious disease affecting both animals and humans. Antimicrobial resistant (AMR) and biofilm-producing Salmonella spp., frequently detected in reptiles (who can then act as asymptomatic carriers for warm-blooded animals), have developed resistance to biocides; this represents a warning for the emergence of biocide/antimicrobial cross-resistance. The aim of this study was to evaluate the efficacy of Thymus vulgaris L. essential oil (TEO) in inhibiting bacterial growth and biofilm production of Salmonella spp., which had been isolated from wild reptiles housed in a Zoo in Italy. The resistance profile against different classes of antibiotics showed that all the isolates were susceptible to the tested antibiotics, despite the presence of several AMR genes. All the isolates were also tested with aqueous solutions of TEO at different dilutions (5% to 0.039%). Interestingly, TEO proved effective both in inhibiting bacterial growth at low dilutions, with MIC and MBC values ranging between 0.078% and 0.312%, and in inhibiting biofilm production, with values ranging from 0.039% to 0.156%. TEO demonstrated effective bioactivity against the biofilm producer Salmonella spp., proving to be a valid disinfectant for the prevention of salmonellosis from reptiles, a possible source of infection for humans exposed to the reptiles' environment.

Salmonella antimicrobials inherited and the non-inherited resistance: mechanisms and alternative therapeutic strategies

Salmonella spp. is one of the most important foodborne pathogens. Typhoid fever and enteritis caused by Salmonella enterica are associated with 16-33 million infections and 500,000 to 600,000 deaths annually worldwide. The eradication of Salmonella is becoming increasingly difficult because of its remarkable capacity to counter antimicrobial agents. In addition to the intrinsic and acquired resistance of Salmonella, increasing studies indicated that its non-inherited resistance, which commonly mentioned as biofilms and persister cells, plays a critical role in refractory infections and resistance evolution. These remind the urgent demand for new therapeutic strategies against Salmonella. This review starts with escape mechanisms of Salmonella against antimicrobial agents, with particular emphasis on the roles of the non-inherited resistance in antibiotic failure and resistance evolution. Then, drug design or therapeutic strategies that show impressive effects in overcoming Salmonella resistance and tolerance are summarized completely, such as overcoming the barrier of outer membrane by targeting MlaABC system, reducing persister cells by limiting hydrogen sulfide, and applying probiotics or predatory bacteria. Meanwhile, according to the clinical practice, the advantages and disadvantages of above strategies are discussed. Finally, we further analyze how to deal with this tricky problems, thus can promote above novel strategies to be applied in the clinic as soon as possible. We believed that this review will be helpful in understanding the relationships between tolerance phenotype and resistance of Salmonella as well as the efficient control of antibiotic resistance.

The action of phytochemicals in biofilm control

Covering: 2009 to 2021Antimicrobial resistance is now rising to dangerously high levels in all parts of the world, threatening the treatment of an ever-increasing range of infectious diseases. This has becoming a serious public health problem, especially due to the emergence of multidrug-resistance among clinically important bacterial species and their ability to form biofilms. In addition, current anti-infective therapies have low efficacy in the treatment of biofilm-related infections, leading to recurrence, chronicity, and increased morbidity and mortality. Therefore, it is necessary to search for innovative strategies/antibacterial agents capable of overcoming the limitations of conventional antibiotics. Natural compounds, in particular those obtained from plants, have been exhibiting promising properties in this field. Plant secondary metabolites (phytochemicals) can act as antibiofilm agents through different mechanisms of action from the available antibiotics (inhibition of quorum-sensing, motility, adhesion, and reactive oxygen species production, among others). The combination of different phytochemicals and antibiotics have revealed synergistic or additive effects in biofilm control. This review aims to bring together the most relevant reports on the antibiofilm properties of phytochemicals, as well as insights into their structure and mechanistic action against bacterial pathogens, spanning December 2008 to December 2021.

Effects of Essential Oils and Hydrolates on the Infectivity of Murine Norovirus

The use of natural substances with antiviral properties might reduce foodborne viral diseases. In this study, we evaluated the virucidal effect of Citrus limon and Thymus serpyllum essential oils (EOs) and of Citrus Limon, Thymus serpyllum and Thymus vulgaris hydrolates on murine norovirus (MNV), a human norovirus surrogate. To assess the virucidal effect of these natural substances, the reduction in viral infectivity was estimated by comparing the TCID50/mL of untreated viral suspension and the viral suspension treated with hydrolates and EOs at different concentrations. The results showed a natural loss of infectivity of the untreated virus after 24 h of approx. 1 log. The EO (1%) of T. serpyllum, and hydrolates (1% and 2%) of T. serpyllum and T. vulgaris immediately caused a reduction in MNV infectivity of about 2 log but did not provide a further significant decrease after 24 h. Instead, the EO (1%) and hydrolate (1% and 2%) of C. limon exerted an immediate reduction in the viral infectivity of about 1.3 log and 1 log, respectively, followed by a further reduction in infectivity of 1 log after 24 h for the hydrolate. These results will allow for the implementation of a depuration treatment based on the use of these natural compounds.

Antibacterial and Antibiofilm Efficacy of Thyme (Thymus vulgaris L.) Essential Oil against Foodborne Illness Pathogens, Salmonella enterica subsp. enterica Serovar Typhimurium and Bacillus cereus

Nowadays, the wide spread of foodborne illness and the growing concerns about the use of synthetic food additives have shifted the focus of researchers towards essential oils (EOs) as possible antimicrobials and preservatives of natural origin. Thanks to their antimicrobial properties against pathogenic and food spoilage microorganisms, EOs have shown good potential for use as alternative food additives, also to counteract biofilm-forming bacterial strains, the spread of which is considered to be among the main causes of the increase in foodborne illness outbreaks. In this context, the aim of this study has been to define the antibacterial and antibiofilm profile of thyme (Thymus vulgaris L.) essential oil (TEO) against widespread foodborne pathogens, Salmonella enterica subsp. enterica serovar Typhimurium and Bacillus cereus. TEO chemical composition was analyzed through gas chromatography-mass spectrometry (GC-MS). Preliminary in vitro antibacterial tests allowed to qualitatively verify TEO efficacy against the tested foodborne pathogens. The subsequent determination of minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values allowed to quantitatively define the bacteriostatic and bactericidal effects of TEO. To evaluate the ability of essential oils to inhibit biofilm formation, a microplate assay was performed for the bacterial biofilm biomass measurement. Results suggest that TEO, rich in bioactive compounds, is able to inhibit the growth of tested foodborne bacteria. In addition, the highlighted in vitro anti-biofilm properties of TEO suggest the use of this natural agent as a promising food preservative to counteract biofilm-related infections in the food industry.

Exploring Possible Ways to Enhance the Potential and Use of Natural Products through Nanotechnology in the Battle against Biofilms of Foodborne Bacterial Pathogens

Biofilms enable pathogenic bacteria to survive in unfavorable environments. As biofilm-forming pathogens can cause rapid food spoilage and recurrent infections in humans, especially their presence in the food industry is problematic. Using chemical disinfectants in the food industry to prevent biofilm formation raises serious health concerns. Further, the ability of biofilm-forming bacterial pathogens to tolerate disinfection procedures questions the traditional treatment methods. Thus, there is a dire need for alternative treatment options targeting bacterial pathogens, especially biofilms. As clean-label products without carcinogenic and hazardous potential, natural compounds with growth and biofilm-inhibiting and biofilm-eradicating potentials have gained popularity as natural preservatives in the food industry. However, the use of these natural preservatives in the food industry is restricted by their poor availability, stability during food processing and storage. Also there is a lack of standardization, and unattractive organoleptic qualities. Nanotechnology is one way to get around these limitations and as well as the use of underutilized bioactives. The use of nanotechnology has several advantages including traversing the biofilm matrix, targeted drug delivery, controlled release, and enhanced bioavailability, bioactivity, and stability. The nanoparticles used in fabricating or encapsulating natural products are considered as an appealing antibiofilm strategy since the nanoparticles enhance the activity of the natural products against biofilms of foodborne bacterial pathogens. Hence, this literature review is intended to provide a comprehensive analysis of the current methods in nanotechnology used for natural products delivery (biofabrication, encapsulation, and nanoemulsion) and also discuss the different promising strategies employed in the recent and past to enhance the inhibition and eradication of foodborne bacterial biofilms.

Evaluation of the antimicrobial effect of the Origanum vulgare L essential oil on strains of Klebsiella pneumoniae

Bacteria may be the initial cause of certain pathologies as well as a secondary agent responsible for the development of complications such as pressure ulcer infections. Pressure ulcers are a persistent health problem, especially in immunocompromised patients, and associated with infection by opportunistic microorganisms with antimicrobial resistance, such as Klebsiella pneumoniae, highlight the need for the development of new antimicrobial approaches. Thus, the aim of this study was to evaluate the antibacterial and anti-adherent activity of Origanum vulgare L. (oregano) essential oil against Klebsiella pneumoniae strains, as well as the effect of its association with synthetic antimicrobials. To this end, the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) analyses were performed on microdilution plates. The assay of the Minimum Inhibitory Adherence Concentration (MIAC), with test tubes. As well as, the association study through the infusion disc method containing ampicillin (AMP), gentamicin (GEN), ciprofloxacin (CIP) and ceftriaxone (CEF). Therefore, it was possible to obtain that the essential oil of oregano presents antimicrobial and bactericidal activity, with MIC ranging between 128μg/mL and 256 μg/mL and MBC between 256 μg/mL and 512 μg/mL, on the tested K. pneumoniae strains. When used in association with ampicillin and gentamicin, oregano essential oil showed synergistic effect for some strains. Therefore, it is observed that the tested essential oil can act as a promising antibacterial in the treatment of diseases caused by K. pneumoniae.

Chemical Composition, Antioxidant, and Antibiofilm Properties of Essential Oil from Thymus capitatus Plants Organically Cultured on the Greek Island of Lemnos

Essential oils (EOs) are mixtures of volatile plant secondary metabolites and have been exploited by humans for thousands of years for various purposes because of their many bioactivities. In this study, the EO from Thymus capitatus, a thyme species organically cultured on the Greek Island of Lemnos, was analyzed for its chemical composition (through GC-FID and GC-MS), antioxidant activity (AA), and total phenolic content (TPC), as well as its antimicrobial and antibiofilm actions against three important foodborne bacterial pathogens (Salmonella enterica ser. Typhimurium, Listeria monocytogenes, and Yersinia enterocolitica). For the latter investigations, the minimum inhibitory concentrations (MICs) and minimum biofilm inhibitory concentrations (MBICs) of the EO against the planktonic and biofilm growth of each pathogen were determined, together with the minimum biofilm eradication concentrations (MBECs). Results revealed that T. capitatus EO was rich in thymol, p-cymene, and carvacrol, presenting high AA and TPC (144.66 μmol Trolox^TM equivalents and 231.32 mg gallic acid equivalents per g of EO, respectively), while its MICs and MBICs ranged from 0.03% to 0.06% v/v and 0.03% to 0.13% v/v, respectively, depending on the target pathogen. The EO was able to fully destroy preformed (mature) biofilms of all three pathogenic species upon application for 15 min, with MBECs ranging from 2.00 to 6.25% v/v. Overall, the results demonstrate that the EO of organically cultured T. capitatus presents strong antioxidant, antibacterial, and antibiofilm properties and could, therefore, be further exploited as a functional and antimicrobial natural formulation for food and health applications.

Raspberry Ketone-Mediated Inhibition of Biofilm Formation in Salmonella enterica Typhimurium-An Assessment of the Mechanisms of Action

Salmonella enterica is an important foodborne pathogen that causes gastroenteritis and systemic infection in humans and livestock. Salmonella biofilms consist of two major components-amyloid curli and cellulose-which contribute to the prolonged persistence of Salmonella inside the host. Effective agents for inhibiting the formation of biofilms are urgently needed. We investigated the antibiofilm effect of Raspberry Ketone (RK) and its mechanism of action against Salmonella Typhimurium 14028 using the Congo red agar method, Calcofluor staining, crystal violet method, pellicle assay, and the TMT-labeled quantitative proteomic approach. RK suppressed the formation of different types of Salmonella biofilms, including pellicle formation, even at low concentrations (200 µg/mL). Furthermore, at higher concentrations (2 mg/mL), RK exhibited bacteriostatic effects. RK repressed cellulose deposition in Salmonella biofilm through an unknown mechanism. Swimming and swarming motility analyses demonstrated reduced motility in RK-treated S. typhimurium. Proteomics analysis revealed that pathways involved in amyloid curli production, bacterial invasion, flagellar motility, arginine biosynthesis, and carbohydrate metabolism, were targeted by RK to facilitate biofilm inhibition. Consistent with the proteomics data, the expressions of csgB and csgD genes were strongly down-regulated in RK-treated S. typhimurium. These findings clearly demonstrated the Salmonella biofilm inhibition capability of RK, justifying its further study for its efficacy assessment in clinical and industrial settings.

The LL-37 Antimicrobial Peptide as a Treatment for Systematic Infection of Acinetobacter baumannii in a Mouse Model

BACKGROUND

The antimicrobial peptides (AMPs) played a critical role in the innate immunity of the host and are considered natural sources illustrating a broad-spectrum antimicrobial activity with high specificity and low cytotoxicity. AMPs generally possess a net positive charge and have amphipathic structures. Thus, AMPs can bind and interact with negatively charged bacterial cell membranes, leading to destructive defects in biomembranes and ending in cell death. LL37 is the only human cathelicidin-derived antimicrobial peptide that shows a broad spectrum of antimicrobial activity.

MATERIALS AND METHODS

To determine the antibacterial efficiency of LL37 in a mouse model of systemic A. baumannii infection, LL37 corresponding gene was expressed in E. coli, purification and refolding situations were optimized. The antimicrobial performance of produced LL-37 against A. baumannii was evaluated in vitro via MIC and Time Kill assays, and its destructive effects on the bacterial cell were confirmed by SEM image.

RESULTS

The recombinant LL37 showed strong antibacterial function against A. baumannii at 1.5 μg/mL concentration. Time kill assay showed a sharp reduction of cell viability during the first period of exposure, and complete cell death was recorded after 40 min exposure.

CONCLUSION

Furthermore, in vivo results represented a significant ability of LL37 in the treatment of systematic infected mouse models, and all infected mice receiving LL37 protein survived without no trace of bacteria in their blood samples.

Antibiofilm Action of Plant Terpenes in Salmonella Strains: Potential Inhibitors of the Synthesis of Extracellular Polymeric Substances

Salmonella can form biofilms that contribute to its resistance in food processing environments. Biofilms are a dense population of cells that adhere to the surface, creating a matrix composed of extracellular polymeric substances (EPS) consisting mainly of polysaccharides, proteins, and eDNA. Remarkably, the secreted substances, including cellulose, curli, and colanic acid, act as protective barriers for Salmonella and contribute to its resistance and persistence when exposed to disinfectants. Conventional treatments are mostly ineffective in controlling this problem; therefore, exploring anti-biofilm molecules that minimize and eradicate Salmonella biofilms is required. The evidence indicated that terpenes effectively reduce biofilms and affect their three-dimensional structure due to the decrease in the content of EPS. Specifically, in the case of Salmonella, cellulose is an essential component in their biofilms, and its control could be through the inhibition of glycosyltransferase, the enzyme that synthesizes this polymer. The inhibition of polymeric substances secreted by Salmonella during biofilm development could be considered a target to reduce its resistance to disinfectants, and terpenes can be regarded as inhibitors of this process. However, more studies are needed to evaluate the effectiveness of these compounds against Salmonella enzymes that produce extracellular polymeric substances.

Essential Oils in the Treatment of Various Types of Acne-A Review

Acne is a chronic, common disease that poses a significant therapeutic, psychological and social problem. The etiopathogenesis of this disease is not fully understood. Drugs used in general and external therapy should have anti-seborrhoeic, anticomadogenic, bactericidal, bacteriostatic, and anti-inflammatory properties. Acne treatment is often associated with the long-term use of antibiotics, contributing to the global antibiotic resistance crisis. In order to solve this problem, attention has been paid to essential oils and their terpene components with potent antimicrobial, anti-inflammatory, and antioxidant properties. Research shows that certain essential oils effectively reduce inflammatory acne lesions through mechanisms related to the sebaceous glands, colonization of Cutibacterium acnes, and reactive oxygen species (ROS). An example is tea tree oil (TTO), a more commonly used topical agent for treating acne. TTO has antimicrobial and anti-inflammatory activity. The paper presents the latest scientific information on the activity and potential use of specific essential oils in treating acne. Evidence of antibacterial, anti-inflammatory, and antioxidant activity of several essential oils and their main components was presented, indicating the possibility of using them in the treatment of acne.

Variation of Salvia officinalis L. Essential Oil and Hydrolate Composition and Their Antimicrobial Activity

This study aimed to investigate the chemical composition of steam distillate essential oil and corresponding hydrolate obtained from S. officinalis grown in Serbia, as well as the influence of weather conditions (temperature and precipitations) on their chemical profiles. Furthermore, their antimicrobial activity was investigated in vitro. The main compounds in essential oil were cis-thujone, followed by camphor, trans-thujone, and 1,8-cineole, while hydrolate was slightly different from the essential oil, with camphor, cis-thujone, and 1,8-cineole as the main compounds. Among the eight respiratory-associated microorganisms, Klebsiella oxytoca was the most sensitive to the tested EOs (minimum inhibitory concentration (MIC)/minimal bactericidal/fungicidal concentration (MBC/MFC) were 14.20 and 28.4 μL mL−1, respectively). MIC and MBC values of other tested bacteria ranged between 28.40 and 227.25 μL mL−1 while for Candida albicans MIC/MFC ranged from 28.40/56.81 to 56.81–113.63 μL mL−1. Antibiotic susceptibility patterns for the analyzed eight respiratory-associated microorganisms showed an intermediate level of resistance to commonly used antibiotics such as ampicillin, levofloxacin, and ciprofloxacin. As a preliminary approach to the antimicrobial profiling of the tested EO, the obtained results revealed that the tested samples possess remarkable antibacterial activities and could be used to develop pharmaceutical formulations as an alternative to conventional antibiotic therapy.

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.

Prospecting of essential oils in combination with florfenicol against motile Aeromonas isolated from tambaqui (Colossoma macropomum)

Natural products with antimicrobial activity and their association with synthetic antimicrobials are a sustainable option in fish farming. The objective of this study was to determine antimicrobial activity, antibiofilm potential and synergism of five essential oils (EOs) with florfenicol against motile Aeromonas isolated from Amazonian Colossoma macropomum. As their major constituent, the EOs of the species of Aloysia triphylla, Croton cajucara (red and white morphotype), Cymbopongo citratus and Lippia gracilis present β-pinene (22.1%), germacrene D (11.5%), linalool (23%), geranial (45.7%) and carvacrol (42.2%), respectively. The EOs of L. gracilis and C. citratus showed the best antimicrobial activities against the Aeromonas strains (5 mg mL^-1). All EOs interfered with biofilm formation and consolidated biofilm. The EOs of A. triphylla, C. citratus and L. gracilis showed a synergistic effect with florfenicol, reducing the amount of the chemical into the water systems while treatment.

Design and Synthesis of Menthol and Thymol Derived Ciprofloxacin: Influence of Structural Modifications on the Antibacterial Activity and Anticancer Properties

Sixteen new Ciprofloxacin derivatives were designed and successfully synthesized. In an in silico experiment, lipophilicity was established for obtained compounds. All compounds were screened for antimicrobial activity using standard and clinical strains. As for Gram-positive hospital microorganisms, all tested derivatives were active. Measured MICs were in the range 1–16 µg/mL, confirming high antimicrobial potency. Derivative 12 demonstrated activity against all standard Gram-positive Staphylococci, within the range of 0.8–1.6 µg/mL and was confirmed as the leading structure with MICs 1 µg/mL for S. pasteuri KR 4358 and S. aureus T 5591 (clinical strains). All compounds were screened for their in vitro cytotoxic properties via the MTT method. Three of the examined compounds (3, 11 and 16) showed good activity against cancer cells, and in parallel were found not to be cytotoxic toward normal cells. Doxorubicin SI ranged 0.14–1.11 while the mentioned three ranged 1.9–3.4. Selected Ciprofloxacin derivatives were docked into the crystal structure of topoisomerase II (DNA gyrase) in complex with DNA (PDB ID: 5BTC). In summary, leading structures were established (3, 11, 12 and 16). We have observed poor results in preformed studies for disubstituted derivatives, suggesting that 3-oxo-4-carboxylic acid core is the active DNA-gyrase binding site, and when structural changes were made in this fragment, there was an observed decrease in antibacterial potency.

nor 3′-Demethoxyisoguaiacin from Larrea tridentata Is a Potential Alternative against Multidrug-Resistant Bacteria Associated with Bovine Mastitis

Bovine mastitis is one of the most common diseases in dairy cows, and it causes significant economic losses in dairy industries worldwide. Gram-positive and Gram-negative bacteria can cause bovine mastitis, and many of them have developed antimicrobial resistance. There is an urgent need for novel therapeutic options to treat the disease. Larrea tridentata-derived compounds represent an important potential alternative treatment. The aim of the present study was to isolate and characterize antibacterial compounds from Larrea tridentata against multidrug-resistant bacteria associated with bovine mastitis. The L. tridentata hydroalcoholic extract (LTHE) exhibited antibacterial activity. The extract was subjected to a bipartition, giving an aqueous fraction (moderate antibacterial activity) and an organic fraction (higher antibacterial activity). Chromatographic separation of the organic fraction enabled us to obtain four active sub-fractions. Chemical analyses through HPLC techniques were conducted for the LTHE, fractions, and sub-fraction Ltc1-F3, from which we isolated two compounds, characterized by ¹H and ¹³C NMR analyses. Compound nor-3 demethoxyisoguaiacin exhibited the best antibacterial activity against the evaluated bacteria (MIC: 0.01–3.12 mg/mL; MBC: 0.02–3.12 mg/mL). The results indicated that nor-3 demethoxyisoguaiacin can be used as an alternative treatment for multidrug-resistant bacteria associated with mastitis.

Salmonella spp. in low water activity food: Occurrence, survival mechanisms, and thermoresistance

The occurrence of disease outbreaks involving low-water-activity (a_w ) foods has gained increased prominence due in part to the fact that reducing free water in these foods is normally a measure that controls the growth and multiplication of pathogenic microorganisms. Salmonella, one of the main bacteria involved in these outbreaks, represents a major public health problem worldwide and in Brazil, which highlights the importance of good manufacturing and handling practices for food quality. The virulence of this pathogen, associated with its high ability to persist in the environment, makes Salmonella one of the main challenges for the food industry. The objectives of this article are to present the general characteristics, virulence, thermoresistance, control, and relevance of Salmonella in foodborne diseases, and describe the so-called low-water-activity foods and the salmonellosis outbreaks involving them.

Chemical Composition, Antioxidant and Antibacterial Activity of Two Different Essential Oils Against Mastitis Associated Pathogens

Mastitis is one of the most common and costly diseases affecting dairy cows worldwide. Since antibiotic resistance has become a global threat to both animal and human health, it is becoming more urgent to continuously search for new therapeutical alternatives for the control and treatment of bovine mastitis. Hence, our research aimed to test the therapeutic use of two essential oils (EOs) based on their chemical composition, antibacterial and antioxidant potential. The present study was conducted by collecting milk samples from the cows diagnosed with clinical or subclinical mastitis with the aim of isolating and identifying bacterial strains. The antioxidant potential of essential oils of Menthae piperitae (MP) and Melissa officinalis (MO) was evaluated in several in vitro assays. In the MP EO, a total of 38 compounds were identified, with menthol as the dominant compound, whereas in MO EO 51 compounds were identified. Furthermore, the values of minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) have been used to quantitatively measure the antibacterial activity of each essential oil. In accordance with which, MP EO samples exhibited a higher degree of antibacterial activity than MO EO. Thus, EOs have been shown to be promising alternatives to antibiotics because of their availability, biodegradability, and lower risk of side effects as compared with conventional, antimicrobial treatment. Nevertheless, further clinical studies are needed to test the potential role of EOs in treating mastitis in dairy cows.

New Perspective of Origanum vulgare L. and Satureja montana L. Essential Oils as Bovine Mastitis Treatment Alternatives

Mastitis represents a heavy burden for the dairy sector worldwide with high economic and animal welfare impact. Antibiotic treatment is an important component of mastitis control programs. However, emergence and transfer of antimicrobial-resistant (AMR) bacteria is becoming a growing concern. Therefore, the development of novel agents is required for prevention and treatment of mastitis. Hence, our aim was to assess the antibacterial properties of two essential oils (EOs) obtained from oregano (Origanum vulgare L., Lamiaceae) and mountain savory (Satureja montana L., Lamiaceae) against mastitis-associated bacteria in Serbia. The chemical composition and antioxidant potential of these EOs were also evaluated. The present study was conducted on strains derived from aseptic milk samples collected from Holstein-Friesian cows with clinical or subclinical mastitis, during the morning milking. Clinical mastitis was assessed by clinical examination, while subclinical mastitis was confirmed using somatic cell count in the milk samples. The microdilution method was used to determine the antibacterial activity, while antioxidant potential of the EOs was evaluated in several in vitro assays. The values of minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) were used to quantitatively measure the antibacterial activity of each EO. MIC/MBC ranged from 0.78/6.25 and 0.39/0.78 mg/mL for oregano and mountain savory, respectively. A total of 25 compounds were identified in the oregano EO, while 47 were identified in winter savory EO, among which aromatic oxygenated monoterpenes were the most abundant compounds. The tested EOs have shown promising antimicrobial activity and could be considered as one of the treatment approaches in mastitis-affected cows.

Effectiveness of selected essential oils and one hydrolate to prevent and remove Listeria monocytogenes biofilms on polystyrene and stainless steel food-contact surfaces

AIMS

This study aimed to evaluate the effectiveness of selected essential oils (EOs) and hydrolates (Hs) against Listeria monocytogenes biofilms on polystyrene (PS) and stainless steel (SS) surfaces.

METHODS AND RESULTS

Among others, Origanum hirtum EO, Corydothymus capitatus EO and Citrus aurantium H were selected to treat L. monocytogenes biofilms during and after biofilm formation. Sub-minimum inhibitory concentrations (MICs) of C. capitatus EO (0.31 µl/ml) showed the highest inhibiting effect against biofilm formation on PS, while on SS no significant differences between the EOs were observed (43.7%-88.7% inhibition). Overall, the tested biosanitizers showed limited activity as biofilm removal agents. Although generally less effective, C. aurantium H exhibited good biofilm inhibition performance at 62.5 µl/ml, particularly on PS. Confocal laser scanning microscopy proved that sub-MICs of the biosanitizers drastically changed L. monocytogenes biofilm architecture, with bacterial cells elongation in the presence of C. capitatus EO.

CONCLUSIONS

Our findings suggest that the tested EOs and H are able to control Listeria biofilms, particularly preventing biofilm formation on both materials. Considering its mild aroma and hydrophilicity, the H exhibited promising perspectives of application.

SIGNIFICANCE AND IMPACT OF STUDY

This study raises the possibility of applying EOs and Hs to control biofilms on different surfaces in the food industry.

Encapsulation of Natural Bioactive Compounds by Electrospinning-Applications in Food Storage and Safety

Packaging is used to protect foods from environmental influences and microbial contamination to maintain the quality and safety of commercial food products, to avoid their spoilage and to extend their shelf life. In this respect, bioactive packaging is developing to additionally provides antibacterial and antioxidant activity with the same goals i.e., extending the shelf life while ensuring safety of the food products. New solutions are designed using natural antimicrobial and antioxidant agents such as essential oils, some polysaccharides, natural inorganic nanoparticles (nanoclays, oxides, metals as silver) incorporated/encapsulated into appropriate carriers in order to be used in food packaging. Electrospinning/electrospraying are receiving attention as encapsulation methods due to their cost-effectiveness, versatility and scalability. The electrospun nanofibers and electro-sprayed nanoparticles can preserve the functionality and protect the encapsulated bioactive compounds (BC). In this review are summarized recent results regarding applications of nanostructured suitable materials containing essential oils for food safety.

Effect of Essential Oils on the Inhibition of Biofilm and Quorum Sensing in Salmonella enteritidis 13076 and Salmonella typhimurium 14028

The emergence of multidrug-resistant microorganisms represents a global challenge that has led to a search for new antimicrobial compounds. Essential oils (EOs) from medicinal aromatic plants are a potential alternative for conventional antibiotics. In this study, the antimicrobial and anti-biofilm potential of 15 EOs was evaluated on planktonic and biofilm-associated cells of Salmonella enterica serovar Enteritidis ATCC 13076 (S. enteritidis) and Salmonella enterica serovar Typhimurium ATCC 14028 (S. typhimurium). In total, 4 out of 15 EOs showed antimicrobial activity and 6 EOs showed anti-biofilm activity against both strains. The EO from the Lippia origanoides chemotype thymol-carvacrol II (LTC II) presented the lowest minimum inhibitory concentration (MIC₅₀ = 0.37 mg mL^-1) and minimum bactericidal concentration (MBC = 0.75 mg mL^-1) values. This EO also presented the highest percentage of biofilm inhibition (>65%) on both microorganisms, which could be confirmed by scanning electron microscopy (SEM) images. Transcriptional analysis showed significant changes in the expression of the genes related to quorum sensing and the formation of the biofilm. EOs could inhibit the expression of genes involved in the quorum sensing mechanism (luxR, luxS, qseB, sdiA) and biofilm formation (csgA, csgB,&nbsp;csgD, flhD, fliZ, and motB), indicating their potential use as anti-biofilm antimicrobial agents. However, further studies are needed to elucidate the action mechanisms of essential oils on the bacterial cells under study.

Thymus vulgaris Essential Oil and Its Biological Activity

Thymus vulgaris essential oil has potential good biological activity. The aim of the research was to evaluate the biological activity of the T. vulgaris essential oil from the Slovak company. The main components of T. vulgaris essential oil were thymol (48.1%), p-cymene (11.7%), 1,8-cineole (6.7), γ-terpinene (6.1%), and carvacrol (5.5%). The antioxidant activity was 85.2 ± 0.2%, which corresponds to 479.34 ± 1.1 TEAC. The antimicrobial activity was moderate or very strong with inhibition zones from 9.89 to 22.44 mm. The lowest values of MIC were determined against B. subtilis, E. faecalis, and S. aureus. In situ antifungal analysis on bread shows that the vapor phase of T. vulgaris essential oil can inhibit the growth of the microscopic filamentous fungi of the genus Penicillium. The antimicrobial activity against S. marcescens showed 46.78-87.80% inhibition at concentrations 62.5-500 µL/mL. The MALDI TOF MS analyses suggest changes in the protein profile of biofilm forming bacteria P. fluorescens and S. enteritidis after the fifth and the ninth day, respectively. Due to the properties of the T. vulgaris essential oil, it can be used in the food industry as a natural supplement to extend the shelf life of the foods.

Antimicrobial and Antibiofilm Effect of ε-Polylysine against Salmonella Enteritidis, Listeria monocytogenes, and Escherichia coli in Tryptic Soy Broth and Chicken Juice

ε-Polylysine (ε-PL) is a safe food additive that is used in the food industry globally. This study evaluated the antimicrobial and antibiofilm activity of antibacterial peptides (ε-PL) against food poisoning pathogens detected in chicken (Salmonella Enteritidis, Listeria monocytogenes, and Escherichia coli). The results showed that minimum inhibitory concentrations (MICs) ranged between 0.031-1.0 mg/mL, although most bacterial groups (75%) showed MICs of 1.0 mg/mL. The reduction in the cell viability of pathogens due to ε-PL depended on the time and concentration, and 1/2 × MIC of ε-PL killed 99.99% of pathogens after 10 h of incubation. To confirm biofilm inhibition and degradation effects, crystal violet assay and confocal laser scanning microscopy (CLSM) were used. The biofilm formation rates of four bacterial groups (Salmonella, Listeria, E. coli, and multi-species bacteria) were 10.36%, 9.10%, 17.44%, and 21.37% at 1/2 × MIC of ε-PL, respectively. Additionally, when observed under a CLSM, ε-PL was found to induce biofilm destruction and bacterial cytotoxicity. These results demonstrated that ε-PL has the potential to be used as an antibiotic and antibiofilm material for chicken meat processing.

The Herbal Compound Thymol Targets Multiple Salmonella Typhimurium Virulence Factors for Lon Protease Degradation

Many important bacterial pathogens are using the type III secretion system to deliver effectors into host cells. Salmonella Typhimurium (S. Typhimurium) is a pathogenic Gram-negative bacterium with the type III secretion system as its major virulence factor. Our previous studies demonstrated that thymol, a monoterpene phenol derivative of cymene, inhibited S. Typhimurium invasion into mammalian cells and protected mice from infection. However, the antibacterial mechanism of thymol is not clear. In this study, we revealed that thymol interferes with the abundance of about 100 bacterial proteins through proteomic analysis. Among the 42 proteins whose abundance was reduced, 11 were important virulence factors associated with T3SS-1. Further analyses with SipA revealed that thymol directly interacts with this protein to induce conformational changes, which makes it susceptible to the Lon protease. In agreement with this observation, thymol effectively blocks cell invasion by S. Typhimurium. Thus, thymol represents a class of anti-virulence compounds that function by targeting pathogenic factors for degradation.

Salvinia auriculata: chemical profile and biological activity against Staphylococcus aureus isolated from bovine mastitis

The aquatic plant Salvinia auriculata has been shown to possess promising properties for the treatment of Staphylococcus aureus bovine mastitis. The disease affects cattle health and compromises dairy cattle productivity, resulting in reduced milk production and higher mortality rates. The aim of this study was to evaluate the antimicrobial activity, antibiofilm activity, and toxicity of S. auriculata root extracts using bovine mammary epithelial cells (MAC-T); determine the chemical composition of the most active extract; and develop an S. auriculata antiseptic solution for pre- and post-milking teat disinfection. Plants were collected during the four seasons of the year. The most active hexane extract was subjected to bioguided fractionation, which resulted in the isolation of six known compounds, stigmast-22-ene-3,6-dione, stigmasterol, friedelinol, β-sitosterol, octadecyl alcohol, and octadecanoic acid. The antimicrobial and antibiofilm activities of the most active extract and isolated compounds were determined against nine S. aureus strains isolated from cows with mastitis. The efficacy of the S. auriculata teat dip formulation was tested using an excised teat model (ex vivo), and promising results were obtained. The S. auriculata extract formulation proved to be as effective as commercial antimicrobials in reducing log counts in excised teats.

Thymus serpyllum Essential Oil and Its Biological Activity as a Modern Food Preserver

The aim of this study was to analyze the chemical composition and biological and antibiofilm activity of the essential oil (EO) of Thymus serpyllum with the use of a MALDI-TOF MS Biotyper. The main compounds of the EO were thymol, 18.8%; carvacrol, 17.4%; o-cymene, 15.4%; and geraniol, 10.7%. It was found that free-radical scavenging activity was high. The highest antimicrobial activity was observed against Pseudomonas aeruginosa, Salmonella enteritidis, and biofilm-forming bacteria. The changes in the biofilm structure after T. serpyllum EO application confirmed the inhibitory action and the most pronounced effect was observed on Bacillus subtilis biofilm. The antifungal activity of the vapor phase was the most effective against Penicillium crustosum. T. serpyllum should be a suitable alternative to synthetic antioxidants as well as antimicrobials. The EO of T. serpyllum can be used in the vapor phase in the storage of root vegetables as well as a growth inhibitor of Penicillium on bread.

Chemical Composition and Biological Activities of the Essential Oils of Chrysophyllum albidum G. Don (African Star Apple)

The volatile compounds of the fruit and leaf essential oils of the African star fruit, Chrysophyllum albidum G. Don, were characterized by gas chromatography-mass spectrometry in this study. The antimicrobial, antibiofilm, and antioxidant activities of the essential oils were also investigated. Thirty-five and thirty-four compounds, representing 97.84% and 97.87%, were identified in the leaf and fruit essential oils, respectively. The antimicrobial activity of the oils was evaluated in vitro against eight pathogens using the broth microdilution method. The fruit essential oil exhibited broad-spectrum antimicrobial activity in the antimicrobial susceptibility test, with minimum inhibitory concentrations (MICs) ranging from 0.195 to 6.250 mg/mL, while the leaf essential oils showed antimicrobial activity with MICs in the range of 6.875–13.750 mg/mL. The antibiofilm activity was assessed via the crystal violet staining assay, with Pseudomonas aeruginosa as the model organism. The concentrations of the leaf and fruit essential oil required for half-maximal inhibition of biofilm formation (BIC₅₀) were 6.97 ± 0.56 and 4.78 ± 0.21 mg/mL, respectively. In evaluating antioxidant activity, the total antioxidant capacity obtained from the phosphomolybdenum assay was 104.8 ± 2.4 and 101.6 ± 0.8 μg/g AAE for leaf and fruit essential oils, respectively. The IC₅₀ values obtained from the hydrogen peroxide scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging, and inhibition of lipid peroxidation assays were 301.8 ± 0.7 and 669.2 ± 2.1 μg/mL, 1048.0 ± 0.3 and 1454.0 ± 0.3 μg/mL, and 460.1 ± 2.7 and 457.4 ± 0.3 μg/mL for both leaf and fruit essential oils, respectively. The results obtained in this study suggest that the leaf and fruit essential oil of Chrysophyllum albidum G. Don could find potential use in the food, cosmetic, and pharmaceutical industries as preservative and pharmaceutical agents.

Synthesis of sulfonate derivatives of carvacrol and thymol as anti-oomycetes agents

Two series of sulfonate derivatives of carvacrol and thymol were synthesized and screened in vitro for their anti-oomycete activity against Phytophthora capsici, respectively. Among all of 32 derivatives, five compounds 3a, 4a, 4k, 3n, and 4n exhibited more potent anti-oomycete activity against P. capsici with EC₅₀ values of 66.66, 62.94, 68.65, 61.24, and 52.91 mg/L, respectively. This suggested that introduction of different substitutions at the hydroxyl position of 1/2 could have remarkable effect on anti-oomycete activity. Overall, when R¹ = isopropyl and R² = methyl, the anti-oomycete activities of the compounds were higher than that of the corresponding compounds of R¹ = methyl and R² = isopropyl.[Formula: see text].

Effects of the Quinone Oxidoreductase WrbA on Escherichia coli Biofilm Formation and Oxidative Stress

The effects of natural compounds on biofilm formation have been extensively studied, with the goal of identifying biofilm formation antagonists at sub-lethal concentrations. Salicylic and cinnamic acids are some examples of these compounds that interact with the quinone oxidoreductase WrbA, a potential biofilm modulator and an antibiofilm compound biomarker. However, WrbA’s role in biofilm development is still poorly understood. To investigate the key roles of WrbA in biofilm maturation and oxidative stress, Escherichia coli wild-type and ∆wrbA mutant strains were used. Furthermore, we reported the functional validation of WrbA as a molecular target of salicylic and cinnamic acids. The lack of WrbA did not impair planktonic growth, but rather affected the biofilm formation through a mechanism that depends on reactive oxygen species (ROS). The loss of WrbA function resulted in an ROS-sensitive phenotype that showed reductions in biofilm-dwelling cells, biofilm thickness, matrix polysaccharide content, and H₂O₂ tolerance. Endogenous oxidative events in the mutant strain generated a stressful condition to which the bacterium responded by increasing the catalase activity to compensate for the lack of WrbA. Cinnamic and salicylic acids inhibited the quinone oxidoreductase activity of purified recombinant WrbA. The effects of these antibiofilm molecules on WrbA function was proven for the first time.