Effect of essential oils on pathogenic bacteria

Effect of Thymus vulgaris L. essential oil and thymol on the microbiological properties of meat and meat products: A review

Since foodborne diseases are often considered as one of the biggest public health threats worldwide, effective preservation strategies are needed to inhibit the growth of undesirable microorganisms in food commodities. Up to now, several techniques have been adopted for the production of safe and high-quality products. Although the traditional methods can improve the reliability, safety, and shelf-life of food, some of them cannot be applied without rising health concerns. Thereby, the addition of various phytochemicals has gained much attention during the last decades, especially for meat products that may be contaminated with pathogenic and spoilage organisms.

Thyme (Thymus vulgaris L.), as an important medicinal and culinary herb, is a promising source of bioactive compounds that have a great impact on the microbiological stability of meat by suppressing the undesirable microflora. However, the use of these antimicrobials is still facing difficulties due to their aromatic properties and variable efficacy against targeted species.

In this paper, we provide an overview on the potential effects of thyme essential oil (EO) and thymol as bio-preservative agents in meat products. Furthermore, this paper provides insights into the limitations and current challenges of the addition of EOs and their constituents to meat commodities and suggests viable solutions that can improve the applicability of these phytochemicals.

An overview of the natural antimicrobial alternatives for sheep meat preservation

Sheep meat is consumed and appreciated all over the world for its nutritional value and flavor. However, this meat is very perishable and easily subjected to the action of both spoilage and pathogenic microorganisms. For this reason, in combination with cold storage, effective preservation techniques are required. There is increasing interest in the application of natural antimicrobials, such as essential oils, extracts, spices, and by-products of the food industry. This review analyses the studies on natural antimicrobials in sheep meat and sheep meat products and gathers evidence about the encouraging results achieved on the reduction and/or elimination of spoilage and pathogenic microorganisms. The use of these natural antimicrobial alternatives might open up important perspectives for industrial application, considering that this specific meat is often traded over long distances. In fact, on the basis of scientific literature, natural antimicrobials can be considered a sustainable and affordable alternative to extend the shelf life of sheep meat and guarantee its safety, although many factors need to be further investigated, such as the sensory impact, potential toxicity, and economic aspects. For all these issues, investigated in some of the studies reviewed here, it is fundamental to obtain the antimicrobial effect with the minimum amount of effective substance to avoid sensory modifications, toxic effects, and unbearable costs. This study sets foundations for the possible direction of future studies, which will contribute to identify effective solutions for industrial applications of natural antimicrobials in the sheep meat industry.

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

Nanogels Containing Foeniculum vulgare Mill. and Mentha piperita L. Essential Oils: Mosquitoes’ Repellent Activity and Antibacterial Effect

Foeniculum vulgare Mill. and Mentha piperita L. are two common medicinally important plants with a wide range of biological activities such as insecticide and antibacterial effects. In this study, the chemical composition of their essential oils was investigated using GC-MS analysis. After that, their nanoemulsions were prepared; optimum samples with droplet sizes of 74 ± 7 and 136 ± 5 nm were gelified. The viscosity of the prepared nanogels and the successful loading of the essential oil in them were investigated. The efficacy of the nanogel containing M. piperita essential oil as a repellent and antibacterial agent was more potent than the nanogel containing F. vulgare essential oil. Its completely protected time against Anopheles stephensi, the main malaria mosquito vector, was 120 ± 8 min. Moreover, the growth of Escherichia coli and Staphylococcus aureus after treatment with 5000 µg/mL of nanogel containing M. piperita essential oil was reduced by 100 and 65%, respectively. Considering natural constituents, a straightforward preparation method, and high efficacy, the nanogel containing M. piperita essential oil could be introduced for further investigation against other mosquitoes and bacterial species.

Chemical Analysis and Investigation of Biological Effects of Salvia officinalis Essential Oils at Three Phenological Stages

Salvia officinalis is a medicinal plant used to treat some diseases, including microbial infections and diabetes. Different studies showed the biological and pharmacological properties of this species. The aim of this study was the determination of the chemical compounds of S. officinalis essential oils and the investigation of their antimicrobial, antioxidant, antidiabetic, and anti-inflammatory properties. The chemical compounds of S. officinalis were determined by GC-MS analysis. The antioxidant activity was assessed by DPPH, ABTS, H₂O₂, and FRAP assays. The in vitro antidiabetic effect was evaluated by the inhibition of α-amylase, α-glucosidase, and lipase activities, and the anti-inflammatory effect was evaluated using the 5-lipoxygenase assay. Moreover, antibacterial activity was assessed against six bacterial strains using agar well diffusion assay and microdilution method. The main compounds in essential oils of S. officinalis at three phenological stages were naphthalenone, camphor, 1.8-cineole, and α-thujone. The full flowering stage essential oil showed the best antioxidant activity with different IC₅₀ values according to the used tests. This oil also exhibited important inhibitory effects at the full flowering stage against α-amylase (IC₅₀ = 69.23 ± 0.1 μg/mL), α-glucosidase (IC₅₀ = 22.24 ± 0.07 μg/mL), and lipase (IC₅₀ = 37.3 ± 0.03 μg/mL). The 5-lipoxygenase inhibitory effect was the best at the full flowering stage (IC₅₀ = 9.24 ± 0.03 μg/mL). The results of the antibacterial evaluation revealed that, at three seasonal periods, S. officinalis essential oil demonstrated strong antibacterial activity. Although the full flowering stage had the best antibacterial activity, there were no significant differences between the three stages. Additionally, the essential oils showed bactericidal effects on Listeria monocytogenes, Staphylococcus aureus, Bacillus subtilis, Proteus mirabilis, Escherichia coli, and Salmonella typhimurium, respectively. The findings of this work showed remarkably that S. officinalis synthesizes essential oils according to different developmental stages. Moreover, it has exhibited interesting biological and pharmacological properties justifying its medicinal effects and suggesting it as a very important source of natural drugs.

Welfare issues and potential solutions for laying hens in free range and organic production systems: A review based on literature and interviews

In free-range and organic production systems, hens can make choices according to their needs and desires, which is in accordance with welfare definitions. Nonetheless, health and behavioral problems are also encountered in these systems. The aim of this article was to identify welfare challenges observed in these production systems in the EU and the most promising solutions to overcome these challenges. It is based on a review of published literature and research projects complemented by interviews with experts. We selected EU specific information for welfare problems, however, the selected literature regarding solutions is global. Free range use may increase the risk of infection by some bacteria, viruses and parasites. Preventive methods include avoiding contamination thanks to biosecurity measures and strengthening animals' natural defenses against these diseases which can be based on nutritional means with new diet components such as insect-derived products, probiotics and prebiotics. Phytotherapy and aromatherapy can be used as preventive and curative medicine and vaccines as alternatives to antibiotics and pesticides. Bone quality in pullets and hens prevents keel deviations and is favored by exercise in the outdoor range. Free range use also lead to higher exposure to variable weather conditions and predators, therefore shadow, fences and guard animals can be used to prevent heat stress and predation respectively. Granting a free range provides opportunities for the expression of many behaviors and yet many hens usually stay close to the house. Providing the birds with trees, shelters or attractive plants can increase range use. Small flock sizes, early experiences of enrichment and personality traits have also been found to enhance range use. Severe feather pecking can occur in free range production systems, although flocks using the outdoor area have better plumage than indoors. While many prevention strategies are facilitated in free range systems, the influence of genetics, prenatal and nutritional factors in free range hens still need to be investigated. This review provides information about practices that have been tested or still need to be explored and this information can be used by stakeholders and researchers to help them evaluate the applicability of these solutions for welfare improvement.

Enterotoxigenic Escherichia coli infection of weaned pigs: Intestinal challenges and nutritional intervention to enhance disease resistance

Enterotoxigenic Escherichia coli (ETEC) infection induced post-weaning diarrhea is one of the leading causes of morbidity and mortality in newly weaned pigs and one of the significant drivers for antimicrobial use in swine production. ETEC attachment to the small intestine initiates ETEC colonization and infection. The secretion of enterotoxins further disrupts intestinal barrier function and induces intestinal inflammation in weaned pigs. ETEC infection can also aggravate the intestinal microbiota dysbiosis due to weaning stress and increase the susceptibility of weaned pigs to other enteric infectious diseases, which may result in diarrhea or sudden death. Therefore, the amount of antimicrobial drugs for medical treatment purposes in major food-producing animal species is still significant. The alternative practices that may help reduce the reliance on such antimicrobial drugs and address animal health requirements are needed. Nutritional intervention in order to enhance intestinal health and the overall performance of weaned pigs is one of the most powerful practices in the antibiotic-free production system. This review summarizes the utilization of several categories of feed additives or supplements, such as direct-fed microbials, prebiotics, phytochemicals, lysozyme, and micro minerals in newly weaned pigs. The current understanding of these candidates on intestinal health and disease resistance of pigs under ETEC infection are particularly discussed, which may inspire more research on the development of alternative practices to support food-producing animals.

Essential Oil-Based Nanoparticles as Antimicrobial Agents in the Food Industry

The use of essential oils (EO) loaded with nanoparticles is the most promising alternative to increase food quality and safety. Interesting works describe the antimicrobial properties of EO for pathogen control in natural and processed foods for human health and animal production, also contributing to sustainability. Their association with different nanosystems allows novel developments in the micronutrition, health promotion, and pathogen control fields, preventing the aggravation of bacterial microevolution and combating antibiotic resistance. Benefits to the environment are also provided, as they are biodegradable and biocompatible. However, such compounds have some physicochemical properties that prevent commercial use. This review focuses on recent developments in antimicrobial EO-based nanoparticles and their application in different food matrices.

In Silico Evaluation of the Antimicrobial Activity of Thymol-Major Compounds in the Essential Oil of Lippia thymoides Mart. & Schauer (Verbenaceae)

In this paper, we evaluated the drug-receptor interactions responsible for the antimicrobial activity of thymol, the major compound present in the essential oil (EO) of Lippia thymoides (L. thymoides) Mart. & Schauer (Verbenaceae). It was previously reported that this EO exhibits antimicrobial activity against Candida albicans (C. albicans), Staphylococcus aureus (S. aureus), and Escherichia coli (E. coli). Therefore, we used molecular docking, molecular dynamics simulations, and free energy calculations to investigate the interaction of thymol with pharmacological receptors of interest to combat these pathogens. We found that thymol interacted favorably with the active sites of the microorganisms’ molecular targets. MolDock Score results for systems formed with CYP51 (C. albicans), Dihydrofolate reductase (S. aureus), and Dihydropteroate synthase (E. coli) were −77.85, −67.53, and −60.88, respectively. Throughout the duration of the MD simulations, thymol continued interacting with the binding pocket of the molecular target of each microorganism. The van der Waals (ΔE_vdW = −24.88, −26.44, −21.71 kcal/mol, respectively) and electrostatic interaction energies (ΔE_ele = −3.94, −11.07, −12.43 kcal/mol, respectively) and the nonpolar solvation energies (ΔG_NP = −3.37, −3.25, −2.93 kcal/mol, respectively) were mainly responsible for the formation of complexes with CYP51 (C. albicans), Dihydrofolate reductase (S. aureus), and Dihydropteroate synthase (E. coli).

Chemical composition and antimicrobial activity of essential oils from Mentha pulegium and Rosmarinus officinalis against multidrug-resistant microbes and their acute toxicity study

This article aimed to study the antimicrobial activity, chemical composition, and acute oral toxicity of essential oils (EOs) of Mentha pulegium and Rosmarinus officinalis, two aromatic and medicinal plants widely used in the traditional Moroccan pharmacopeia. The average content of EOs was 3.2 and 2.5% for M. pulegium and R. officinalis, respectively. The chemical characterization showed a richness in some compounds identified by gas chromatography coupled with mass spectrometry (GC/MS): R(+)-Pulegone (45.48%), Menthone (14.2%), Piperitone (8.15%), and Isomenthone (7.18%) in M. pulegium and 1,8-Cineole (46.32%), Camphene (13.4%), and α-Pinene (9.52%) in R. officinalis. These metabolites showed a significant antimicrobial effect against the tested strains (bacteria and yeasts isolated from the hospital environment) compared to synthetic antibiotics that seem to be ineffective against resistant microorganisms. Based on lethal concentration LD50 >5,000 mg/kg (body weight), the oil was found to be marginally safe according to OECD guidelines and can be further explored (bio-product with low risk).

Antimicrobial Activity of Essential Oils Evaluated In Vitro against Escherichia coli and Staphylococcus aureus

The spread of extended-spectrum β-lactamase-producing Escherichia coli and methicillin-resistant Staphylococcus aureus has caused a reduction in antibiotic effectiveness and an increase in mortality rates. Essential oils (EOs), known for their therapeutic efficacy, can be configured as novel broad-spectrum biocides. Accordingly, the bacteriostatic–bactericidal activity of Citrus Lemon (LEO), Pinus Sylvestris (PEO), Foeniculum Vulgaris (FEO), Ocimum Basilicum (BEO), Melissa Officinalis (MEO), Thymus Vulgaris (TEO), and Zingiber Officinalis Rosc. (GEO), at concentrations ranging from 1.25 to 40% (v/v), were tested in vitro against different E. coli and S. aureus strains using minimal inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs). The chemical compositions of the EOs were analyzed using GC/MS. The major components of all seven tested oils were limonene, α-pinene, anethole, estragole, citral, thymol, and zingiberene, respectively. We found that the bacteriostatic–bactericidal activity of the EOs was related to their chemotypes and concentrations, as well as the strain of the bacteria. A dose–effect correlation was found when testing GEO against S. aureus strains, whilst FEO was found to have no activity regardless of concentration. PEO, MEO, and BEO were found to have bactericidal effect with a MIC and MBC of 1.25% (v/v) against S. aureus strains, and LEO was found to have values of 1.25% (v/v) and 5% (v/v) against ATCC and clinical isolate, respectively. Interestingly, the antimicrobial activity of TEO was not related to oil concentration and the complete inhibition of growth across all E. coli and S. aureus was observed. Although preliminary, our data demonstrate the efficacy of EOs and pave the way for further investigations on their potential synergistic use with traditional drugs in the human and veterinary fields.

Antimicrobial mechanisms of spice essential oils and application in food industry

Spice essential oils (SEOs) are commonly used in food flavoring and are considered an effective food preservative. It has a broad range of applications and promising development prospects. As a natural food additive, SEOs' antimicrobial effects have been widely studied and utilized towards food preservation. Many SEOs have exhibited significant antimicrobial activities against food-borne pathogenic and food spoilage microorganisms. We reviewed the antibacterial and antifungal properties of SEOs, the active components, their corresponding mechanisms of actions, as well as their application in the food industry, providing a theoretical basis for SEOs' further development and application as natural preservatives.

In Vitro Activity of Water Extracts of Olive Oil against Planktonic Cells and Biofilm Formation of Arcobacter-like Species

Extra-virgin olive oils contain many bioactive substances that are phenolic compounds. The survival of Arcobacter-like strains in non-buffered (WEOO) and buffered (BEOO) extracts of olive oils were studied. Time kill curves of different strains were measured in the environment of olive oil extracts of different grades. The activity of the extracts was also monitored for biofilm formation using the Christensen method. In vitro results revealed that extra-virgin olive oil extracts exhibited the strongest antimicrobial effects, especially non-buffered extracts, which exhibited strain inhibition after only 5 min of exposure. The weakest inhibitory effects were observed for olive oil extracts. A decrease in biofilm formation was observed in the environment of higher WEOO concentrations, although at lower concentrations of extracts, increased biofilm formation occurred due to stress conditions. The dialdehydic forms of oleuropein derivatives, hydroxytyrosol, and tyrosol were the main compounds detected by HPLC-CoulArray. The results indicate that not all olive oils had a similar bactericidal effect, and that bioactivity primarily depended on the content of certain phenolic compounds.

Phosphorylated Curdlan Gel/Polyvinyl Alcohol Electrospun Nanofibres Loaded with Clove Oil with Antibacterial Activity

Fibrous membranes based on natural polymers obtained by the electrospinning technique are a great choice for wound dressings. In order to promote an efficient wound repair, and to avoid antibiotics, antibacterial plant extracts can be incorporated. In the present work, the new electrospun nanofibre membranes based on monobasic phosphate curdlan (PCurd) and polyvinyl alcohol (PVA) were obtained for the first time. To establish the adequate mixing ratio for electrospinning, the behaviour of the PCurd and PVA mixture was studied by viscometry and rheology. In order to confer antimicrobial activity with the nanofibre membrane, clove essential oil (CEO) was incorporated into the electrospun solution. Well-defined and drop-free nanofibres with a diameter between 157 nm and 110 nm were obtained. The presence of CEO in the obtained nanofibres was confirmed by ATR–FTIR spectroscopy, by the phenolic and flavonoid contents, and by the antioxidant activity of the membranes. In physiological conditions, CEO was released from the membrane after 24 h. The in vivo antimicrobial tests showed a good inhibitory activity against E. coli and higher activity against S. aureus. Furthermore, the viability cell test showed the lack of cytotoxicity of the nanofibre membrane with and without CEO, confirming its potential use in wound treatment.

Impact of Sub-MIC Eugenol on Klebsiella pneumoniae Biofilm Formation via Upregulation of rcsB

The Rcs phosphorelay system is present in many members of the Enterobacteriaceae. The aim of this study was to illustrate the possible mechanisms of eugenol on ultimate targets of Klebsiella pneumoniae (K. pneumoniae) Rcs phosphorelay, rcsB, and impact on biofilm formation. The minimum inhibitory concentration (MIC) of eugenol against K. pneumoniae KP1 and KP1 ΔrcsB strain was determined using the 2-fold micro-dilution method. Biofilm was measured by crystal violet staining. Transcriptome sequencing was performed to investigate sub-MIC eugenol on K. pneumoniae, and gene expression at mRNA level was analyzed by RT-qPCR. In vitro biofilm formation test and molecular docking were used to evaluate the effect of eugenol and to predict potential interactions with RcsB. MicroScale Thermophoresis (MST) was conducted for further validation. MIC of eugenol against K. pneumoniae KP1 and KP1 ΔrcsB strain was both 200 μg/ml. Transcriptome sequencing and RT-qPCR results indicated that rpmg, degP, rnpA, and dapD were downregulated, while rcsB, rcsD, rcsA, yiaG, and yiaD were upregulated in the eugenol-treated group. ΔrcsB exhibited a weakened biofilm formation capacity. Additional isopropyl-β-d-thiogalactoside (IPTG) hinders biofilm formation, while sub-MIC eugenol could promote biofilm formation greatly. Docking analysis revealed that eugenol forms more hydrophobic bonds than hydrogen bonds. MST assay also showed a weak binding affinity between eugenol and RcsB. These results provide significant evidence that rcsB plays a key role in K. pneumoniae biofilm formation. Sub-MIC eugenol facilitates biofilm formation to a large extent instead of inhibiting it. Our findings reveal the potential risk of natural anti-biofilm ingredients at sub-MIC to treat drug-resistance bacteria.

Antibacterial activities of polyphenols against foodborne pathogens and their application as antibacterial agents

Polyphenols are secondary metabolites produced in higher plants. They are known to possess various functional properties in the human body. Polyphenols also exhibit antibacterial activities against foodborne pathogens. Their antibacterial mechanism is based on inhibiting bacterial biofilm formation or inactivating enzymes. Food-derived polyphenols with such antibacterial activity are natural preservatives and can be used as an alternative to synthetic preservatives that can cause side effects, such as allergies, asthma, skin irritation, and cancer. Studies have reported that polyphenols have positive effects, such as decreasing harmful bacteria and increasing beneficial bacteria in the human gut microbiota. Polyphenols can also be used as natural antibacterial agents in food packaging system in the form of emitting sachets, absorbent pads, and edible coatings. We summarized the antibacterial activities, mechanisms and applications of polyphenols as antibacterial agents against foodborne bacteria.

Microencapsulation of carvacrol as an efficient tool to fight Pseudomonas aeruginosa and Enterococcus faecalis biofilms

Biofilms are involved in serious problems in medical and food sectors due to their contribution to numerous severe chronic infections and foodborne diseases. The high resistance of biofilms to antimicrobial agents makes their removal as a big challenge. In this study, spray-drying was used to develop microcapsules containing carvacrol, a natural antimicrobial agent, to enhance its activity against P. aeruginosa and E. faecalis biofilms. The physicochemical properties and microscopic morphology of the realized capsules and cells were characterized. The minimum inhibitory concentration of encapsulated carvacrol (E-CARV) (1.25 mg mL^-1) was 4-times lower than that of free carvacrol (F-CARV) (5 mg mL^-1) against P. aeruginosa, while it remained the same against E. faecalis (0.625 mg mL^-1). E-CARV was able to reduce biofilm below the detection limit for P. aeruginosa and by 5.5 log CFU ml^-1 for E. faecalis after 15 min of treatment. Results also showed that F-CARV and E-CARV destabilize the bacterial cell membrane leading to cell death. These results indicate that carvacrol exhibited a strong antimicrobial effect against both bacterial biofilms. In addition, spray-drying could be used as an effective tool to enhance the antibiofilm activity of carvacrol, while reducing the concentrations required for disinfection of abiotic surfaces.

Antimicrobial mechanism of linalool against Brochothrix thermosphacta and its application on chilled beef

This work aimed to explore the antibacterial ability and potential mechanism of linalool against Brochothrix thermosphacta (B. thermosphacta), providing knowledge of the preservation of chilled beef with linalool. The results found that linalool had an encouraging inhibitory effect on B. thermosphacta with a minimum inhibitory concentration (MIC) of 1.5 mL/L. Results of FESEM and zeta potential combined with probe labeling confirmed that linalool destroyed the cell structure thereby causing the leakage of intracellular components (AKP, protein, nucleic acid and ion). In addition, linalool caused respiratory disturbance by measuring the key enzyme activities including PK, SDH, MDH and ATPase. Energy limitation also appeared under linalool stress as seen from changes in ATP content (decreased by 56.06% and 69.24% in MIC and 2MIC groups, respectively). The respiratory inhibition rate of linalool to B. thermosphacta was 23.58% and the superposing rate with malonic acid was minimal (35.52%), suggesting that respiratory depression was mainly caused by the TCA cycle. Furthermore, accumulation of ROS and increase in MDA content (increased by 71.17% and 78.03% in MIC and 2MIC groups, respectively) accompanied by decreased activities of detoxification enzymes CAT and POD suggested that oxidative stress contributed to the bactericidal mechanism. Finally, linalool has been shown to effectively inhibit quality deterioration of chilled beef during storage by measuring pH, TVB-N and TVC without affecting sensory acceptability. All these highlight the great promise of using linalool as natural preservative for food industry.

Controlled Release of Volatile Antimicrobial Compounds from Mesoporous Silica Nanocarriers for Active Food Packaging Applications

Essential oils and their active components have been extensively reported in the literature for their efficient antimicrobial, antioxidant and antifungal properties. However, the sensitivity of these volatile compounds towards heat, oxygen and light limits their usage in real food packaging applications. The encapsulation of these compounds into inorganic nanocarriers, such as nanoclays, has been shown to prolong the release and protect the compounds from harsh processing conditions. Nevertheless, these systems have limited shelf stability, and the release is of limited control. Thus, this study presents a mesoporous silica nanocarrier with a high surface area and well-ordered protective pore structure for loading large amounts of natural active compounds (up to 500 mg/g). The presented loaded nanocarriers are shelf-stable with a very slow initial release which levels out at 50% retention of the encapsulated compounds after 2 months. By the addition of simulated drip-loss from chicken, the release of the compounds is activated and gives an antimicrobial effect, which is demonstrated on the foodborne spoilage bacteria Brochothrixthermosphacta and the potentially pathogenic bacteria Escherichia coli. When the release of the active compounds is activated, a ≥4-log reduction in the growth of B. thermosphacta and a 2-log reduction of E. coli is obtained, after only one hour of incubation. During the same one-hour incubation period the dry nanocarriers gave a negligible inhibitory effect. By using the proposed nanocarrier system, which is activated by the food product itself, increased availability of the natural antimicrobial compounds is expected, with a subsequent controlled antimicrobial effect.

Adaptation insights from comparative transcriptome analysis of two Opisthopappus species in the Taihang mountains

Opisthopappus is a major wild source of Asteraceae with resistance to cold and drought. Two species of this genus (Opisthopappus taihangensis and O. longilobus) have been employed as model systems to address the evolutionary history of perennial herb biomes in the Taihang Mountains of China. However, further studies on the adaptive divergence processes of these two species are currently impeded by the lack of genomic resources. To elucidate the molecular mechanisms involved, a comparative analysis of these two species was conducted. Among the identified transcription factors, the bHLH members were most prevalent, which exhibited significantly different expression levels in the terpenoid metabolic pathway. O. longilobus showed higher level of expression than did O. taihangensis in terms of terpenes biosynthesis and metabolism, particularly monoterpenoids and diterpenoids. Analyses of the positive selection genes (PSGs) identified from O. taihangensis and O. longilobus revealed that 1203 genes were related to adaptative divergence, which were under rapid evolution and/or have signs of positive selection. Differential expressions of PSG occurred primarily in the mitochondrial electron transport, starch degradation, secondary metabolism, as well as nucleotide synthesis and S-metabolism pathway processes. Several PSGs were obviously differentially expressed in terpenes biosynthesis that might result in the fragrances divergence between O. longilobus and O. taihangensis, which would provide insights into adaptation of the two species to different environments that characterized by sub-humid warm temperate and temperate continental monsoon climates. The comparative analysis for these two species in Opisthopappus not only revealed how the divergence occurred from molecular perspective, but also provided novel insights into how differential adaptations occurred in Taihang Mountains.

Transcriptomic Profile Analysis of Streptococcus mutans Response to Acmella paniculata Flower Extracts

Background

Acmella paniculata has been used as a traditional medicine to treat oral health diseases such as dental caries and periodontitis. Streptococcus mutans is a common bacterium that initiates dental caries at an early stage.

Aim

The aim of this study was to determine the mode of action of A. paniculata (extracts) against S. mutans growth.

Methods

Time-kill assay has been done to investigate the rate of kill and effectiveness of Acmella paniculata (AP) extracts against S. mutans growth. Phytochemical analysis was done to identify major compounds in AP extracts using gas chromatography mass spectrometry (GCMS). Scanning and transmission electron microscopy (SEM and TEM) have been done to observe the morphological changes of treated bacteria. Transcriptomic profile analysis has been done using Next Gene Sequencing.

Results

AP flower n-hexane (APFH) and AP flower dichloromethane (APFD) extracts acted as bactericidal agents after killing >3 log10 cfu/mL of S. mutans after 24 hours. Oleic and hexadecenoic acids were found to be the major compounds in APFD and APFH extracts, respectively. Photomicrographs from SEM and TEM of treated S. mutans show that the bacterial cell wall has been lysed and the cytoplasm content was decreased. Pathway analysis revealed that the APFD extract significantly affected biosynthesis peptidoglycan, gene expression, RNA processing, and macromolecule metabolism processes in S. mutans.

Conclusion

Data analysis revealed that multiple mechanisms of action were involved in antibacterial activity of A. paniculata extracts toward S. mutans.

Natural Additives Improving Polyurethane Antimicrobial Activity

In recent years, there has been a growing interest in using polymers with antibacterial and antifungal properties; therefore, the present review is focused on the effect of natural compounds on the antibacterial and antifungal properties of polyurethane (PUR). This topic is important because materials and objects made with this polymer can be used as antibacterial and antifungal ones in places where hygiene and sterile conditions are particularly required (e.g., in healthcare, construction industries, cosmetology, pharmacology, or food industries) and thus can become another possibility in comparison to commonly used disinfectants, which mostly show high toxicity to the environment and the human health. The review presents the possibilities of using natural extracts as antibacterial, antifungal, and antiviral additives, which, in contrast to the currently used antibiotics, have a much wider effect. Antibiotics fight bacterial infections by killing bacteria (bactericidal effect) or slowing and stopping their growth (bacteriostatic effect) and effect on different kinds of fungi, but they do not fight viruses; therefore, compounds of natural origin can find wide use as biocidal substances. Fungi grow in almost any environment, and they reproduce easily in dirt and wet spaces; thus, the development of antifungal PUR foams is focused on avoiding fungal infections and inhibiting growth. Polymers are susceptible to microorganism adhesion and, consequently, are treated and modified to inhibit fungal and bacterial growth. The ability of micro-organisms to grow on polyurethanes can cause human health problems during the use and storage of polymers, making it necessary to use additives that eliminate bacteria, viruses, and fungi.

Peppermint essential oil-loaded solid lipid nanoparticle in gelatin coating: Characterization and antibacterial activity against foodborne pathogen inoculated on rainbow trout (Oncorhynchus mykiss) fillet during refrigerated storage

The present study was conducted to determine the characterization and antibacterial activity of peppermint essential oil-loaded solid lipid nanoparticle (PEO-SLN) and its impact on the quality of trout fillet stored at 4 ± 1°C for 12 days. The SLNs were prepared through a bath sonication technique. PEO-SLNs contained 0.2% (w/v) PEO in 2% of lipid phase glycerol monostearate (GMS) and tween 80 (1% w/v) used as a surfactant in the aqueous phase. The characterization parameter of PEO-SLN was evaluated, and the antibacterial activity of PEO-SLNs was conducted under in vitro conditions. Trout samples were analyzed for inoculated Pseudomonas aeruginosa, Listeria monocytogenes, and Escherichia coli O157:H7 during refrigerated storage. The mean particle size of PEO-SLNs was 154.83 ± 1.21 nm with a polydispersity index (PDI) of 0.35 ± 0.01 and zeta potential was about -24.16 ± 0.51 mV. The results indicated that PEO-SLN had higher antibacterial activity than the free form of PEO and also when used in combination with gelatin coating (gel + PEO-SLN) had a significant effect on preventing microbial growth in trout fillets (p < 0.05). The most decreasing rate of P. aeruginosa (1.92 log CFU/g), E. coli O157:H7 (0.71 log CFU/g), and L. monocytogenes count (1.69 log CFU/g) was seen in gel + PEO-SLN. These findings illustrated that PEO-SLNs could potentially be utilized in the food industry to increase the shelf life of fish fillets.

Antimicrobial Properties of Chilean Native Plants: Future Aspects in Their Application in the Food Industry

Food contamination with microorganisms is responsible for food spoilage, deterioration and change of organoleptic properties of foods. Besides, the growth of pathogenic microorganisms can provoke serious health problems if food is consumed. Innovative packaging, such as active packaging, is increasing rapidly in the food industry, especially in applying antimicrobials into delivery systems, such as sachets. Chile is a relevant hotspot for biodiversity conservation and a source of unique bio-resources with antimicrobial potential. In this review, fifteen native plants with antimicrobial properties are described. Their antimicrobial effects include an effect against human pathogens. Considering the emergence of antimicrobial resistance, searching for new antimicrobials to design new strategies for food pathogen control is necessary. Chilean flora is a promising source of antimicrobials to be used in active packaging. However, further studies are required to advance from laboratory tests of their antimicrobial effects to their possible effects and uses in active films.

Terpinen-4-ol, the Main Bioactive Component of Tea Tree Oil, as an Innovative Antimicrobial Agent against Legionella pneumophila

Legionella pneumophila (Lp), responsible for a severe pneumonia called Legionnaires’ disease, represents an important health burden in Europe. Prevention and control of Lp contamination in warm water systems is still a great challenge often due to the failure in disinfection procedures. The aim of this study was to evaluate the in vitro activity of Terpinen-4-ol (T-4-ol) as potential agent for Lp control, in comparison with the essential oil of Melaleuca alternifolia (tea tree) (TTO. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of T-4-ol were determined by broth micro-dilution and a micro-atmosphere diffusion method to investigate the anti-Lp effects of T-4-ol and TTO vapors. Scanning Electron Microscopy (SEM) was adopted to highlight the morphological changes and Lp damage following T-4-ol and TTO treatments. The greatest antimicrobial activity against Lp was shown by T-4-ol with a MIC range of 0.06–0.125% v/v and MBC range of 0.25–0.5% v/v. The TTO and T-4-ol MIC and MBC decreased with increasing temperature (36 °C to 45 ± 1 °C), and temperature also significantly influenced the efficacy of TTO and T-4-ol vapors. The time-killing assay showed an exponential trend of T-4-ol bactericidal activity at 0.5% v/v against Lp. SEM observations revealed a concentration- and temperature- dependent effect of T-4-ol and TTO on cell surface morphology with alterations. These findings suggest that T-4-ol is active against Lp and further studies may address the potential effectiveness of T-4-ol for control of water systems.

Development of active packaging films based on liquefied shrimp shell chitin and polyvinyl alcohol containing β-cyclodextrin/cinnamaldehyde inclusion

To maintain the freshness of fruits and to meet environmental and consumer needs, a biobased packaging film with long-lasting antimicrobial activity was developed in this article. Liquefied ball-milled shrimp shell chitin/polyvinyl alcohol (LBSC/PVA) blend films containing varying concentrations (0, 1, 2, 3, 4, 5 wt%) of the β-cyclodextrin/cinnamaldehyde (β-CD/CA) inclusion were prepared and characterized. The association between β-CD and CA and the sustained release behavior of CA were explored. The physicochemical property, antimicrobial activity and food preservation performance of the films were investigated. Results showed that CA was successfully encapsulated into the cavity of CD by host-guest interactions, which greatly improved the sustained release of CA. The 3 wt% β-CD/CA/LBSC/PVA blend film showed optimized mechanical properties with a tensile strength of 41.5 MPa and an elongation at break of 810 %. In addition, the incorporation of β-CD/CA inclusion significantly enhanced the antimicrobial activity and food preservation performance of the blend films. Moreover, the 3 wt% β-CD/CA/LBSC/PVA blend film exhibited evidently longer lasting antimicrobial activity and cherry tomato preservation performance than the 3 wt% CA/LBSC/PVA blend film, further demonstrating the critical role of β-CD in delaying CA release. These novel β-CD/CA/LBSC/PVA blend films may have a potential use in active food packaging.

Efficacy and Mechanism of Thymol/KGM/LG Edible Coating Solution on Inhibition of Mucor circinelloides Isolated From Okra

With the increasing demand and quality requirement for the natural nutritious food in modern society, okra has attracted much attention because of its high nutritional value and remarkable functionality. However, the occurrence of postharvest diseases of fresh okra severely limited the application and the value of okra. Therefore, in this study, the dominant pathogens causing postharvest diseases such as soft rot were isolated from naturally decaying okra. It was identified as Mucor circinelloides by its morphological characteristics and standard internal transcribed spacer ribosomal DNA sequence. Furthermore, the biological characteristics of M. circinelloides were studied, and the inhibitory effect of thymol/KGM/LG (TKL) edible coating solution on M. circinelloides and its possible mechanism was discussed. In addition, TKL edible coating solution had a dose-dependent inhibitory effect on M. circinelloides, with a 50% inhibitory concentration (EC50) of 113.55 mg/L. The TKL edible coating solution at 960 mg/L of thymol completely inhibited mycelial growth and spore germination of M. circinelloides. The results showed that the best carbon source of M. circinelloides was maltose, the best nitrogen source was beef extract and potassium nitrate, the best pH was 6, the best temperature was 28°C, the best NaCl concentration was 0.5%, and the light was conducive to the growth of M. circinelloides. It was also observed by scanning electron microscope (SEM) that TKL was more likely to destroy the cell wall integrity of M. circinelloides, inhibit spore morphology and change mycelium structure. Meanwhile, the activity of chitinase (CHI), an enzyme related to cell wall synthesis of M. circinelloides, was significantly decreased after being treated by TKL with thymol at 100 mg/L (TKL100). The content of Malondialdehyde (MDA) in M. circinelloides decreased significantly from 12 h to 48 h, which may cause oxidative damage to the cell membrane. The activity polygalacturonase (PG), pectin methylgalacturonase (PMG), and cellulase (Cx) of M. circinelloides decreased significantly. Therefore, the results showed that TKL had a good bacteriostatic effect on okra soft rot pathogen, and the main bacteriostatic mechanism might be the damage of cell membrane, degradation of the cell wall, inhibition of metabolic activities, and reduction of metabolites, which is helpful to further understand the inhibitory effect of TKL on okra soft rot pathogen and its mechanism.

Chemical Composition of Essential Oils of Bulbs and Aerial Parts of Two Cultivars of Allium sativum and Their Antibiofilm Activity against Food and Nosocomial Pathogens

This work aimed to evaluate the chemical composition of the essential oils (EOs) of two cultivars of Allium sativum and their antibiofilm activity against the food pathogens Acinetobacter baumannii, Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus. The crystal violet assay ascertained the susceptibility of the bacterial biofilms, while the MTT assay let to evaluations of the metabolic changes occurring in the bacterial cells within biofilms. Their chemical composition indicated some sulfuric compounds (i.e., allicin, diallyl disulfide, and allyl propyl disulfide), and decene as some of the main components of the EOs. The aerial parts and bulbs’ EOs from the two cultivars showed chemical differences, which seemed to affect the antibiofilm activity. The EOs from aerial parts of ‘Bianco del Veneto’ inhibited the biofilm formation of L. monocytogenes and E. coli (60.55% and 40.33%, respectively). In comparison, the ‘Staravec’ EO inhibited the cellular metabolism of E. coli (62.44%) and S. aureus (51.52%) sessile cells. These results indicate their possible use as preserving agents in the food industry and suggest their potential exploitation in the development of new formulations to avoid or limit nosocomial infections.

Efficient Synthesis of 2-Aminopyridine Derivatives: Antibacterial Activity Assessment and Molecular Docking Studies

A new and suitable multicomponent one-pot reaction was developed for the synthesis of 2-amino-3-cyanopyridine derivatives.

BACKGROUND

This synthesis was demonstrated by the efficient and easy access to a variety of substituted 2-aminopyridines using enaminones as key precursors under solvent-free conditions.

METHODS

A range of spectroscopic techniques was used to determine and confirm the chemical structures (FTIR, ¹H NMR, ¹³C NMR). The antimicrobial potency of synthesized compounds (2a-d) was tested using disk diffusion assays, and the Minimum Inhibitory Concentration (MIC) for the active compounds was determined against a panel of microorganisms, including Gram-positive and Gram-negative bacteria and yeasts. Moreover, a docking analysis was conducted by Molecular Operating Environment (MOE) software to provide supplementary information about the potential, as well as an ADME-T prediction to describe the pharmacokinetic properties of the best compound and its toxicity.

RESULTS

The results of the antimicrobial activity indicated that compound 2c showed the highest activity against Gram-positive bacteria, particularly S. aureus and B. subtilis whose MIC values were 0.039 ± 0.000 µg·mL^-1. The results of the theoretical study of compound 2c were in line with the experimental data and exhibited excellent antibacterial potential.

CONCLUSIONS

On the basis of the obtained results, compound 2c can be used as an antibacterial agent model with high antibacterial potency.

Application of Clove Oil and Sonication Process on the Influence of the Functional Properties of Mung Bean Flour-Based Edible Film

The present study was aimed to investigate the effects of sonication and clove oil incorporation on the improvement of physical, antioxidant, and antimicrobial properties and lipid oxidation inhibiting abilities of mung bean flour (MF)-based films. There were three groups of films tested (1) MF: mung bean flour alone, (2) MFC: MF incorporated with 2% clove oil (C), and (3) MFCU: MFC prepared with sonication (25 kHz, 100% amplitude, 10 min). Film thickness and bulk density showed slight differences, and moisture content, solubility, and water vapor permeability significantly differed between the formulations. Tensile strength, elongation at break, and Young’s modulus were highest for the MFCU films, followed by MFC and MF in rank order. Furthermore, the Fourier-transform infrared spectroscopy results also demonstrated that the clove oil and sonication treatment had improved the interconnections of the biopolymers, thus increasing the physical strength of the film. Phytochemicals in terms of total phenolics and total flavonoids were elevated in the MFCU films and contributed to stronger radical scavenging abilities (p < 0.05). MFC and MFCU films showed a strong antibacterial control of the Gram-positive Staphylococcus aureus (S. aureus) and also of the Gram-negative Campylobacter jejuni (C. jejuni). Overall, the lipid oxidation indicators Thiobarbituric acid reactive substances (TBARS, peroxide value, p-anisidine value, and totox value) showed significantly high inhibition, attributed to radical scavenging activities in the MFCU and MFC samples. The mung bean flour films incorporated with clove oil and prepared with sonication have good potential as packaging materials for food due to strong physical, antimicrobial, and antioxidant properties, as well as lipid oxidation inhibiting abilities.

Phytochemical Analysis, Antibacterial Activity and Modulating Effect of Essential Oil from Syzygium cumini (L.) Skeels

One of the main global problems that affect human health is the development of bacterial resistance to different drugs. As a result, the growing number of multidrug-resistant pathogens has contributed to an increase in resistant infections and represents a public health problem. The present work seeks to investigate the chemical composition and antibacterial activity of the essential oil of Syzygium cumini leaves. To identify its chemical composition, gas chromatography coupled to mass spectrometry was used. The antibacterial activity test was performed with the standard strains Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 25853 and Staphylococcus aureus ATCC 25923 and multidrug-resistant clinical isolates E. coli 06, P. aeruginosa 24 and S. aureus 10. The minimum inhibitory concentration (MIC) was determined by serial microdilution as well as the verification of the modulating effect of the antibiotic effect. In this test, the oil was used in a subinhibitory concentration. The test reading was performed after 24 h of incubation at 37 °C. The results show that the major chemical constituent is α-pinene (53.21%). The oil showed moderate activity against E. coli ATCC 25922, with the MIC of 512 µg/mL; there was no activity against the other strains. The oil potentiated the effect of antibiotics demonstrating possible synergism when associated with gentamicin, erythromycin and norfloxacin against E. coli 06 and S. aureus 10.

Chemical composition, antibiofilm, cytotoxic, and anti-acetylcholinesterase activities of Myrtus communis L. leaves essential oil

BACKGROUND

The potential of essential oils (EOs) and of their principal constituents for eradication of biofilm and at the same time the research of new potential acetylcholinesterase inhibitors is gaining increasing interest in last years. The aims of this study were to determine the chemical composition and to evaluate the antibacterial, cytotoxic, and anti-acetylcholinesterase properties of Myrtus communis leaves essential oil and its main constituents.

METHODS

Essential oil was obtained by hydrodistillation of M. communis L. leaves and was analyzed by GC and GC-MS. The antimicrobial activity was carried out against both gram-negative and gram-positive bacteria. The microdilution method was used to estimate the minimum inhibitory concentrations (MICs). Then, the capacity of essential oil and its main constituent to inhibit biofilm growth, with the method of O'Toole and Kolterand, and the metabolic activity of biofilm cells through the MTT colorimetric method were evaluated at different times. Moreover, was studied the potential cytotoxic activity against SH-SY5Y cell line with MTT assay and the anti-acetylcholinesterase activity using Ellman's assay.

RESULTS

Myrtenyl-acetate, 1,8 cineole, α-pinene, and linalool were the main components in the EO. The myrtle EO, at the minimum tested dose (0.4 mg/ml), inhibited S. aureus biofilm by 42.1% and was capable of inhibiting the biofilm cell metabolism in all tested strains, except Staphylococcus aureus. Moreover, the EO showed good cytotoxic and anti-acetylcholinesterase activities IC₅₀ of 209.1 and 32.8 μg/ml, respectively.

CONCLUSIONS

The results suggest that myrtle EO and its main constituents could be used as possible products that could act against the resistant pathogenic species E. coli, P. aeruginosa, L. monocytogenes and S. aureus, on the other hand, as possible coadjutants in the treatment of neurological diseases.

Exploitation of Marginal Hilly Land in Tuscany through the Cultivation of Lavandula angustifolia Mill.: Characterization of Its Essential Oil and Antibacterial Activity

Lavandula angustifolia Mill., known as one of the best essential oil-bearing plants, is an aromatic plant that is well cultivated in many Mediterranean regions due to its adaptability to variations in climatic and edaphic conditions. Therefore, its essential oil (EO) composition and its antimicrobial activity change as a consequence of abiotic and biotic factors. The chemical composition of L. angustifolia EO collected during four consecutive years of growth was one of the aims of this work. The volatile profile evidenced the prevalence of linalool and linalool acetate even though they switched their positions according to age. Plants in their first year were characterized by a high amount of sesquiterpene compounds (22.1% of the identified fraction). This percentage decreased during plant growth, not representing more than 5.3% in the fourth year. It is interesting to note that both the third- and fourth-year plants showed a content of monoterpenes that exceeded 90% of the total identified constituents. The EO extracted from the oldest plants evidenced higher activity on the studied strains, with more sensitivity on the Gram-positive ones. Tuscan lavender EO, especially that obtained from the four-year-old plants, is of great interest for its potential industrial applications and constitutes an example for the valorization of marginal Tuscan land and good-quality production.

Green Leaf Volatile Trans-2-Hexenal Inhibits the Growth of Fusarium graminearum by Inducing Membrane Damage, ROS Accumulation, and Cell Dysfunction

Fusarium graminearum, the main agent of Fusarium head blight (FHB), can cause serious yield loss and secrete mycotoxins to contaminate grain. Here, the biological activity of trans-2-hexenal (T2H) against F. graminearum was determined and its mode of action (MOA) was investigated. Furthermore, surface plasmon resonance with liquid chromatography-tandem mass spectrometry (SPR-LC-MS/MS), bioinformatic analysis, and gene knockout technique were combined to identify the binding proteins of T2H in F. graminearum cells. T2H exhibited satisfactory inhibitory activity against F. graminearum in vitro. Good lipophilicity greatly enhanced the affinity of T2H to F. graminearum mycelia and further caused membrane damage. The FgTRR (thioredoxin reductase) gene negatively regulates the sensitivity of F. graminearum to T2H by reducing the generation of reactive oxygen species (ROS) induced by T2H. Two mutant strains with FgSLX1 (structure-specific endonuclease subunit) and FgCOPB (coatomer subunit β) genes knockout showed decreased sensitivity to T2H, suggesting that these two genes may be involved in the antimicrobial activity of T2H. Taken together, T2H can inhibit F. graminearum growth by multiple MOAs and can be used as a biofumigant to control the occurrence of FHB in the field.

Biogenic Silver Nanoparticles Strategically Combined With Origanum vulgare Derivatives: Antibacterial Mechanism of Action and Effect on Multidrug-Resistant Strains

Multidrug-resistant bacteria have become a public health problem worldwide, reducing treatment options against several pathogens. If we do not act against this problem, it is estimated that by 2050 superbugs will kill more people than the current COVID-19 pandemic. Among solutions to combat antibacterial resistance, there is increasing demand for new antimicrobials. The antibacterial activity of binary combinations containing bioAgNP (biogenically synthesized silver nanoparticles using Fusarium oxysporum), oregano essential oil (OEO), carvacrol (Car), and thymol (Thy) was evaluated: OEO plus bioAgNP, Car plus bioAgNP, Thy plus bioAgNP, and Car plus Thy. This study shows that the mechanism of action of Thy, bioAgNP, and Thy plus bioAgNP involves damaging the membrane and cell wall (surface blebbing and disruption seen with an electron microscope), causing cytoplasmic molecule leakage (ATP, DNA, RNA, and total proteins) and oxidative stress by enhancing intracellular reactive oxygen species and lipid peroxidation; a similar mechanism happens for OEO and Car, except for oxidative stress. The combination containing bioAgNP and oregano derivatives, especially thymol, shows strategic antibacterial mechanism; thymol disturbs the selective permeability of the cell membrane and consequently facilitates access of the nanoparticles to bacterial cytoplasm. BioAgNP-treated Escherichia coli developed resistance to nanosilver after 12 days of daily exposition. The combination of Thy and bioAgNP prevented the emergence of resistance to both antimicrobials; therefore, mixture of antimicrobials is a strategy to extend their life. For antimicrobials alone, minimal bactericidal concentration ranges were 0.3-2.38 mg/ml (OEO), 0.31-1.22 mg/ml (Car), 0.25-1 mg/ml (Thy), and 15.75-31.5 μg/ml (bioAgNP). The time-kill assays showed that the oregano derivatives acted very fast (at least 10 s), while the bioAgNP took at least 30 min to kill Gram-negative bacteria and 7 h to kill methicillin-resistant Staphylococcus aureus (MRSA). All the combinations resulted in additive antibacterial effect, reducing significantly minimal inhibitory concentration and acting faster than the bioAgNP alone; they also showed no cytotoxicity. This study describes for the first time the effect of Car and Thy combined with bioAgNP (produced with F. oxysporum components) against bacteria for which efficient antimicrobials are urgently needed, such as carbapenem-resistant strains (E. coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa) and MRSA.

Antibiofilm activity of phytochemicals against Enterococcus faecalis: A literature review

Enterococcus faecalis is a leading causative pathogen of recalcitrant infections affecting heart valves, urinary tract, surgical wounds and dental root canals. Its robust biofilm formation, production of virulence factors and antibiotic resistance contribute significantly to its pathogenicity in persistent infections. The decreased effectiveness of most of antibiotics in preventing and/or eradicating E. faecalis biofilms mandates the discovery of alternative novel antibiofilm agents. Phytochemicals are potential sources of antibiofilm agents due to their antivirulence activity, diversity of chemical structure and multiple mechanisms of action. In this review, we describe the phenotypic and genetic attributes that contribute to antimicrobial tolerance of E. faecalis biofilms. We illuminate the benefits of implementing the phytochemicals to tackle microbial pathogens. Finally, we report the antibiofilm activity of phytochemicals against E. faecalis, and explain their mechanisms of action. These compounds belong to different chemical classes such as terpenes, phenylpropenes, flavonoids, curcuminoids and alkaloids. They demonstrate the ability to inhibit the formation of and/or eradicate E. faecalis biofilms. However, the exact mechanisms of action of most of these compounds are not fully understood. Therefore, the future studies should elucidate the underlying mechanisms in detail.