Antibacterial and antibiofilm activities of thyme oil against foodborne multiple antibiotics-resistant Enterococcus faecalis

4-Hydroxyboesenbergin B of Alpinia japonica protected gastrointestinal tract by inhibiting vancomycin-resistant enterococcus and balancing intestinal microbiota

ETHNOPHARMACOLOGICAL RELEVANCE

Alpinia japonica, a traditional herb utilized in Miao medicine in southwestern China, has been employed to alleviate symptoms such as stomachache, diarrhea, and abdominal pain, some of these symptoms may be associated with bacterial infections of the gastrointestinal tract.

AIM OF THE STUDY

To explore antimicrobial compounds related to traditional uses of A. japonica and its potential pathway in vitro and in vivo.

MATERIALS AND METHODS

Bioactive components of A. japonica were isolated by bioguide separation method. The antibacterial bioactivity of 4-hydroxyboesenbergin B (4-HB) was evaluated by time-kill curve and drug resistance induction. The pathway of 4-HB against VRE was investigated through network pharmacological analysis and validated by in vitro experiments and RT-qPCR assays. Moreover, a mouse gastrointestinal tract model was established to validate the antibacterial bioactivity of 4-HB in vivo.

RESULTS

4-HB from A. japonica inhibited VRE (MIC = 16 μg/mL), rapidly killed the bacteria within 4 h at the 4 MIC concentration and exhibited low susceptibility to drug resistance. 4-HB specifically targeted VRE biofilms by down-regulating the expression of AtlA, SgrA, GelE, and Ace. As a result, 4-HB diminished the adhesion and aggregation ability of VRE, reduced the extracellular matrix content, disrupted biofilm structure and morphology, thereby reducing VRE resistance and virulence. Additionally, 4-HB significantly reduced VRE colonization, enhanced intestinal microbiota diversity, and promoted the restoration of intestinal microbiota balance in vivo. Notably, 4-HB enhanced the abundance of beneficial bacteria genera, such as Lactobacillus and Limosilactobacillus.

CONCLUSIONS

4-HB has a significant ability to destroy VRE biofilms and balance intestinal microbiota, which might be responsible for the traditional use of A. japonica partly.

In vitro antibacterial and antibiofilm activities of isobavachalcone against Enterococcus faecalis clinical isolates from China

BACKGROUND

The pharmacological activities of the natural product isobavachalcone, such as antimicrobial activity, reverse transcriptase blockade, and antioxidant property have been extensively reported. Whereas, its antimicrobial and biofilm-inhibitory effects on clinical E. faecalis strains in China, along with its potential mechanisms, are still not fully clear. This research is intended to assess the in vitro antibacterial and anti-biofilm effects of isobavachalcone against clinical E. faecalis isolates sourced from China. Moreover, it further explores the potential target site of it within E. faecalis.

RESULTS

It was found that the minimum inhibitory concentrations (MICs) of isobavachalcone ranged from 6.25 to 12.5 µM against 220 E. faecalis clinical strains obtained from a tertiary hospital in China. The antibiofilm activity of it with sub-MIC concentration ( 1/2 × MIC ) against the biofilm formation of E. faecalis was demonstrated and Time -killing curve assay revealed the quick bactericidal effect of isobavachalcone against E. faecalis planktonic cells. However, no synergetic bactericidal activity of isobavachalcone co-administered with vancomycin, or ampicillin was observed for eradicating the biofilm. Moreover, isobavachalcone-resistant E. faecalis was isolated by in vitro induction of isobavachalcone, and whole genome sequencing was performed to determine the genetic mutations of ten functional proteins in isobavachalcone-resistant E. faecalis, including PurH and FlgJ, with the other eight proteins being related to cell wall or cell membrane biogenesis, DNA synthesis, and energy metabolism. In addition, molecular docking results indicate that there is a potential binding of isobavachalcone and PurH protein in E. faecalis.

CONCLUSION

This research highlights the potential of isobavachalcone as a potent antibacterial agent against E. faecalis clinical isolates, capable of significantly inhibiting biofilm formation at sub-MIC concentrations. PurH protein in E. faecalis might serve as a potential target of isobavachalcone and the specific action mechanism of isobavachalcone needs further study.

Surfactin inhibits enterococcal biofilm formation via interference with pilus and exopolysaccharide biosynthesis

Enterococcus faecalis is a significant pathogen in healthcare settings and is frequently resistant to multiple antibiotics. This resistance is compounded by its ability to form biofilms, dense bacterial communities that are challenging to eliminate via standard antibiotic therapies. As such, targeting biofilm formation is considered a viable strategy for addressing these infections. This study assessed the effectiveness of surfactin, a cyclic lipopeptide biosurfactant synthesized by Bacillus subtilis natto NTU-18, in preventing biofilm formation by E. faecalis. Analytical characterization of surfactin was performed via liquid chromatography‒mass spectrometry (LC‒MS). Additionally, transcriptomic sequencing and quantitative PCR (qPCR) were used to investigate alterations in E. faecalis gene expression following treatment with surfactin. The data revealed notable suppression of crucial virulence-related genes responsible for pilus construction and exopolysaccharide synthesis, both of which are vital for E. faecalis adhesion and biofilm structure. Functional tests confirmed that surfactin treatment substantially reduced E. faecalis attachment to Caco-2 cell monolayers and curtailed exopolysaccharide production. Moreover, confocal laser scanning microscopy revealed significant thinning of the biofilms. These observations support the potential utility of surfactin as a therapeutic agent to manage biofilm-associated infections caused by E. faecalis.

A thermal perspective of the advancements in antibacterial polycaprolactone/graphene scaffolds

Excessive activation of osteoclasts during bone infections can result in destructive bone complications, including non-union and delayed fracture healing. Enterococcus faecalis and Streptococcus pyogenes are known pathogens associated with bone and joint infections, which can lead to severe complications and the deterioration of tissue. This study aimed to investigate the potential of mechano-bacteria intervention in combating these bacteria. Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) tests were conducted on Polycaprolactone (PCL) and PCL/graphene (G) scaffolds containing different concentrations of graphene, namely 0.5, 1.5, and 2.5 wt%, to evaluate the thermal impact on the activity of E. faecalis and S. pyogenes. Furthermore, the Kirby Bauer Method was used to assess the antibacterial activity against both bacteria. The analysis of the average inhibition zone showed a correlation between the antibacterial effect and the concentration of G within the scaffolds. The highest inhibition zone was observed when 2.5 wt% G was used for both E. faecalis and S. pyogenes. The higher Tmax from Thermogravimetric Analysis showed PCL/G with 2.5 wt% G was due to the greater heat energy required to break down sp2 hybridized carbon atoms in a hexagonal framework. The TGA results indicate that higher graphene content (2.5 wt%) requires more energy for thermal decomposition compared to lower concentrations (0.5 wt% and 1.5 wt%) and PCL while the DSC results also showed that presence of G had a significant impact on Tg (glass transition temperature), Tc (crystallization temperature), and Tm (melting temperature), as the temperature increased with the addition of G. Based on the result of this study, it was concluded that G had potential for inhibiting bacteria growth.

Contribution of Phosphorylation Modification to Stability and Antibacterial Activity of Egg White Protein Nanogels Loaded with Cinnamon Bark Essential Oil

This study evaluated the potential usage of phosphorylated egg white protein (P-EWP) nanogels fabricated via microwave-induced phosphorylation modification and gel process and further ultrasonic nanometrization as novel delivery systems for cinnamon bark essential oil (CBEO). Compared to EWP-CBEO nanogels without chemical phosphorylation, the obtained P-EWP-CBEO nanogels have shown smaller average hydrodynamic diameter (133.6 nm), relatively uniform size distribution (polydispersity index around 0.265), enhanced negative surface charge (-35.4 mV), and improved stability under the conditions of high temperature (up to 90 °C) and ionic strength (up to 200 mM NaCl). Moreover, P-EWP-CBEO nanogels, with hydrophobic interactions and disulfide bonds as the main intermolecular forces, exhibited a remarkable conformational change in microstructures. In addition, the results of the antibacterial experiments on Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes showed that the MIC values of P-EWP-CBEO nanogels were two times lower than those of EWP-CBEO nanogels and could completely inhibit the growth of pathogenic bacteria within 108 h. Hence, we have suggested that P-EWP-CBEO nanogels are successfully fabricated with improved physicochemical properties as novel potential natural preservatives in the food industry.

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

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

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

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

Contemporary strategies and approaches for characterizing composition and enhancing biofilm penetration targeting bacterial extracellular polymeric substances

Extracellular polymeric substances (EPS) constitutes crucial elements within bacterial biofilms, facilitating accelerated antimicrobial resistance and conferring defense against the host's immune cells. Developing precise and effective antibiofilm approaches and strategies, tailored to the specific characteristics of EPS composition, can offer valuable insights for the creation of novel antimicrobial drugs. This, in turn, holds the potential to mitigate the alarming issue of bacterial drug resistance. Current analysis of EPS compositions relies heavily on colorimetric approaches with a significant bias, which is likely due to the selection of a standard compound and the cross-interference of various EPS compounds. Considering the pivotal role of EPS in biofilm functionality, it is imperative for EPS research to delve deeper into the analysis of intricate compositions, moving beyond the current focus on polymeric materials. This necessitates a shift from heavy reliance on colorimetric analytic methods to more comprehensive and nuanced analytical approaches. In this study, we have provided a comprehensive summary of existing analytical methods utilized in the characterization of EPS compositions. Additionally, novel strategies aimed at targeting EPS to enhance biofilm penetration were explored, with a specific focus on highlighting the limitations associated with colorimetric methods. Furthermore, we have outlined the challenges faced in identifying additional components of EPS and propose a prospective research plan to address these challenges. This review has the potential to guide future researchers in the search for novel compounds capable of suppressing EPS, thereby inhibiting biofilm formation. This insight opens up a new avenue for exploration within this research domain.

Effects of essential oils on economically important characteristics of ruminant species: A comprehensive review

Essential oils derived from plants can provide biological impacts to livestock species. Scientific studies researching essential oils in livestock have investigated various essential oils for prevention and treatment of microbial infection and parasites as well as to enhance milk production, animal performance and rumen function. Despite the availability of several commercial products containing essential oils to promote animal health and production, the vast amount of essential oils, modes of application, and effective concentrations of the essential oils suggest there are more opportunities for essential oils to be utilized in commercial livestock production and veterinary medicine. The objective of this review is to contribute to the understanding of the value that essential oils can provide to the ruminant diet and to examine the biological impact of various essential oils on economically important production traits of ruminant species.

Study on the formation and anti-biofilm properties of cinnamon essential oil inclusion complexes by the structure of modified β-cyclodextrins

Essential oils (EOs), which are plant-oriented anti-biofilm agents, are extensively encapsulated by cyclodextrins to overcome their aqueous solubility and chemical instability, and achieve slow release during long-term storage. However, the biological activities of EOs decreased after initial encapsulation in CDs. In this study, modified-β-cyclodextrins (β-CDs) were screened as wall materials to maintained the initial anti-biofilm effect of pure CEO. The inhibitory and bactericidal activities of CEO encapsulated in five types of β-CDs with different substituents (primary hydroxyl, maltosyl, hydroxypropyl, methyl, and carboxymethyl) against Staphylococcus aureus biofilm were evaluated. Crystal violet assay and 3D-View observations suggested that CEO and its inclusion complexes (CEO-ICs) inhibited Staphylococcus aureus biofilm formation through the inhibition of colonising spreading, exopolysaccharide synthesis, and cell surface properties. Molecular docking revealed the causes of the decrease in the anti-biofilm effect after encapsulation, and quantitative structure-activity relationship assays provided MIC and MBIC prediction equation for modified-β-cyclodextrins inclusion complexes. Maltosyl-β-CD was screened as the best wall material to retained the anti-biofilm activities as pure cinnamon essential oil in initial stage, and its inclusion complexes can effectively inhibited biofilm formation in milk. This study provides a theoretical guidance for the selection β-CDs to encapsulate CEO as plant-oriented anti-biofilm agents to inhibit bacterial biofilm formation.

Antibacterial and Antibiofilm Efficacy and Mechanism of Ginger (Zingiber officinale) Essential Oil against Shewanella putrefaciens

Ginger (Zingiber officinale) has unique medicinal value and can be used to treat colds and cold-related diseases. The chemical composition and antibacterial activity of ginger essential oil (GEO) against Shewanella putrefaciens were determined in the present study. Zingiberene, α-curcumene, and zingerone were the main active compounds of GEO. GEO displayed significant antibacterial activity against S. putrefaciens, with a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 2.0 and 4.0 μL/mL, respectively. Changes in intracellular ATP content, nucleic acid and protein structure, exopolysaccharides (EPS) content, and extracellular protease production indicated that GEO disrupted the membrane integrity of S. putrescens. At the same time, changes in biofilm metabolic activity content and the growth curve of biofilm showed that GEO could destroy the biofilm. Both scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) observations confirmed that GEO destroyed the cell membrane and lead to the leakage of the constituents. The above results indicate that GEO entered the cells via contact with bacterial membranes, and then inhibited the growth of S. putrefaciens and its biofilms by increasing membrane permeability and inhibiting various virulence factors such as EPS. The findings showed that GEO could destroy the structure of cell membrane and biofilm of tested S. putrefaciens, indicating its potential as a natural food preservative.

Antimicrobial and Antibiofilm Potential of Thymus vulgaris and Cymbopogon flexuosus Essential Oils against Pure and Mixed Cultures of Foodborne Bacteria

The spread of pathogenic and food spoilage microorganisms through the food chain still faces major mitigation challenges, despite modern advances. Although multiple cleaning and disinfection procedures are available for microbial load reduction in food-related settings, microbes can still remain on surfaces, equipment, or machinery, especially if they have the ability to form biofilms. The present study assessed the biofilm-forming properties of pure and mixed cultures of foodborne and spoilage bacteria (Listeria monocytogenes, Enterococcus faecalis, Aeromonas hydrophila, Brochothrix thermosphacta), using polystyrene and stainless steel contact surfaces. Subsequently, the antimicrobial and antibiofilm properties of Thymus vulgaris and Cymbopogon flexuosus essential oils—EOs—were evaluated against these bacteria. Moreover, in silico prediction of the absorption and toxicity values of the EOs’ major constituents was also performed, perceiving the putative application in food-related settings. Overall, biofilm formation was observed for all microbes under study, at different temperatures and both contact surfaces. In polystyrene, at 25 °C, when comparing pure with mixed cultures, the combination Listeria–Aeromonas achieved the highest biofilm biomass. Moreover, at 4 °C, increased biofilm formation was detected in stainless steel. Regarding thyme, this EO showed promising antimicrobial features (especially against A. hydrophila, with a MIC of 0.60 µg/µL) and antibiofilm abilities (MBEC of 110.79 µg/µL against L. monocytogenes, a major concern in food settings). As for lemongrass EO, the highest antimicrobial activity, with a MIC of 0.49 µg/µL, was also observed against L. monocytogenes. Overall, despite promising results, the in situ effectiveness of these essential oils, alone or in combination with other antimicrobial compounds, should be further explored.

Beyond the Risk of Biofilms: An Up-and-Coming Battleground of Bacterial Life and Potential Antibiofilm Agents

Microbial pathogens and their virulence factors like biofilms are one of the major factors which influence the disease process and its outcomes. Biofilms are a complex microbial network that is produced by bacteria on any devices and/or biotic surfaces to escape harsh environmental conditions and antimicrobial effects. Due to the natural protective nature of biofilms and the associated multidrug resistance issues, researchers evaluated several natural anti-biofilm agents, including bacteriophages and their derivatives, honey, plant extracts, and surfactants for better destruction of biofilm and planktonic cells. This review discusses some of these natural agents that are being put into practice to prevent biofilm formation. In addition, we highlight bacterial biofilm formation and the mechanism of resistance to antibiotics.

The Anti-Biofilm Activity and Mechanism of Apigenin-7-O-Glucoside Against Staphylococcus aureus and Escherichia coli

Introduction

This study aimed to examine the anti-biofilm activity and mechanism of gallic acid (GA), kaempferol-7-O-glucoside (K7G) and apigenin-7-O-glucoside (A7G) against Staphylococcus aureus and Escherichia coli.

Methods

The antibacterial activity of the natural compounds was determined by serial dilution method. The inhibitory activity of natural compounds on biofilms was determined by crystal violet staining method. The effects and mechanisms of natural compounds on bacterial biofilms were analyzed by atomic force microscopy.

Results

In our study, compared with GA and K7G, A7G was found to exhibit the strongest anti-biofilm and antibacterial activities. The minimum biofilm inhibitory concentration (MBIC) of A7G against S. aureus and E. coli was 0.20 mg/mL and 0.10 mg/mL, respectively. The inhibition rates of 1/2 MIC of A7G on biofilms of S. aureus and E. coli were 88.9%, and 83.2% respectively. Moreover, atomic force microscope (AFM) images showed the three-dimensional biofilm morphology of S. aureus and E. coli, and the results indicated that A7G was highly effective in biofilm inhibition.

Discussion

It was found that the inhibition of A7G on biofilm was achieved through inhibiting on exopolysaccharides (EPS), quorum sensing (QS), and cell surface hydrophobicity (CSH). A7G exerted strong anti-biofilm activities by inhibiting EPS production, QS, and CSH. Hence, A7G, as a natural substance, could be a promising novel antibacterial and anti-biofilm agent for control of biofilm in food industry.

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.

The Antimicrobial and Antibiofilm Activity of Oregano Essential Oil against Enterococcus faecalis and Its Application in Chicken Breast

Oregano essential oil (OEO) possesses anti-inflammatory, antioxidant, and cancer-suppressive properties. Enterococcus faecalis is a foodborne opportunistic pathogen that can be found in nature and the food processing industry. The goal of this investigation was to explore the antimicrobial action and mechanism of OEO against E. faecalis, inactivation action of OEO on E. faecalis in mature biofilms, and its application in chicken breast. The minimum inhibitory concentration (MIC) of OEO against E. faecalis strains (ATCC 29212 and nine isolates) ranged from 0.25 to 0.50 μL/mL. OEO therapy reduced intracellular adenosine triphosphate (ATP) levels, caused cell membrane hyperpolarization, increased the intracellular reactive oxygen species (ROS), and elevated extracellular malondialdehyde (MDA) concentrations. Furthermore, OEO treatment diminished cell membrane integrity and caused morphological alterations in the cells. In biofilms on stainless-steel, OEO showed effective inactivation activity against E. faecalis. OEO reduced the number of viable cells, cell viability and exopolysaccharides in the biofilm, as well as destroying its structure. Application of OEO on chicken breast results in a considerable reduction in E. faecalis counts and pH values, in comparison to control samples. These findings suggest that OEO could be utilized as a natural antibacterial preservative and could effectively control E. faecalis in food manufacturing.

Multi-responsive poly N-isopropylacrylamide/poly N-tert-butylacrylamide nanocomposite hydrogel with the ability to be adsorbed on the chitosan film as an active antibacterial material

Nanocomposite hydrogel composed of Poly N-isopropylacrylamide (PNIPAM), poly N-tert-Butylacrylamide (PBAM) and poly acrylic acid (PAA) was synthesized by free radical polymerization, and then thymol was embedded in it, to design an active antibacterial material that could control release. The characterization of products used SEM, AFM, FTIR, Zeta sizer to analyze the sensitivity of nanoparticles to pH, temperature and salt ions, and the agar diffusion method was used to determine the antibacterial effect of the polymers. The results showed that nanoparticles had pH, temperature and salt ion responsiveness, PNIPAM/PBAM (65:35) nanoparticles loaded thymol had longer release time (more than 24 h) at lower temperature than that (around 6 h) at high temperature. In addition, the nanoparticles could also be adsorbed on the chitosan film, which makes it have a wider range of applications. All thymol-loaded nanoparticles showed antibacterial activity against both B. subtilis and E. coli, while the chitosan film adsorbed nanoparticles showed weak effect, which was related to the controlled and slow release of bacteriostatic agents. Thus, these copolymers have potential value in the development and application of bacteriostatic packaging films for food.

The Antimicrobial Effect of Melissa officinalis L. Essential Oil on Vibrio parahaemolyticus: Insights Based on the Cell Membrane and External Structure

The study was to evaluate the antimicrobial impacts on Melissa officinalis L. essential oil (MOEO) against Vibrio parahaemolyticus. The minimum inhibitory concentration (MIC) of MOEO on Vibrio parahaemolyticus was 1 μL⋅mL^–1. The kill-time curve exhibited that MOEO had good antimicrobial activity. The analysis of cellular ingredients leakage and cell viability illustrated that MOEO has destruction to the morphology of the cell membrane. The damage to the membrane integrity by MOEO has been confirmed by transmission and scanning electron microscopy, obvious morphological and ultrastructural changes were observed in the treated bacterial cells. The MOEO at 0.5 μL⋅mL^–1 can inhibit the biofilm formation, biofilm motility, and extracellular polysaccharide production. Meanwhile, the qPCR results exhibited MOEO inhibited the expression of virulence genes. The findings showed that MOEO exerted its antimicrobial effect mainly by destroying the membrane, which indicated its potential as a natural food preservative.

The Effect of Lemon Essential Oil on Halitosis

OBJECTIVES

To evaluate the effect of lemon essential oil (LEO) on salivary bacteria and volatile sulfur compound (VSC) production of patients with halitosis.

MATERIALS AND METHODS

Saliva of five patients with halitosis was collected, after adding different concentrations (0.563-9 mg/ml) of LEO, detecting the growth of salivary bacteria, the formation of biofilm, and VSC production, and compare the difference of different concentrations of LEO on bacterial growth and VSC production. 48 volunteers were randomly divided into 4 groups. After gargling with LEO, cetylpyridinium chloride (CPC), chlorhexidine (CHX), and hydrogen peroxide (H₂ O₂ ) separately measure changes of VSC production and pH values at 30, 45, 60, 90, and 120 min and then compare the differences at different time points within group.

RESULTS

Compared with the negative control group, under subinhibitory concentrations of LEO (0.563-2.25 mg/ml), the biofilm formation and VSC production of salivary bacteria in LEO group were significantly inhibited (p < 0.05). Compared with the baseline, the VSC production of subjects decreased after rinsing with the LEO in 60 min (p < 0.05). After gargling with LEO, the pH value rose significantly in 30 min and reverted to the baseline level at 120 min (p < 0.05).

CONCLUSIONS

Lemon essential oil can inhibit the growth of salivary bacteria and reduce VSC production of patients with halitosis.

Bacillus subtilis natto Derivatives Inhibit Enterococcal Biofilm Formation via Restructuring of the Cell Envelope

Enterococcus faecalis is considered a leading cause of hospital-acquired infections. Treatment of these infections has become a major challenge for clinicians because some E. faecalis strains are resistant to multiple clinically used antibiotics. Moreover, the presence of E. faecalis biofilms can make infections with E. faecalis more difficult to eradicate with current antibiotic therapies. Thus, our aim in this study was to investigate the effects of probiotic derivatives against E. faecalis biofilm formation. Bacillus subtilis natto is a probiotic strain isolated from Japanese fermented soybean foods, and its culture fluid potently inhibited adherence to Caco-2 cell monolayers, aggregation, and biofilm production without inhibiting the growth of E. faecalis. An apparent decrease in the thickness of E. faecalis biofilms was observed through confocal laser scanning microscopy. In addition, exopolysaccharide synthesis in E. faecalis biofilms was reduced by B. subtilis natto culture fluid treatment. Carbohydrate composition analysis also showed that carbohydrates in the E. faecalis cell envelope were restructured. Furthermore, transcriptome sequencing revealed that the culture fluid of B. subtilis natto downregulated the transcription of genes involved in the WalK/WalR two-component system, peptidoglycan biosynthesis and membrane glycolipid biosynthesis, which are all crucial for E. faecalis cell envelope synthesis and biofilm formation. Collectively, our work shows that some derivatives present in the culture fluid of B. subtilis natto may be useful for controlling E. faecalis biofilms.

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.

Trans-Cinnamaldehyde Attenuates Enterococcus faecalis Virulence and Inhibits Biofilm Formation

Enterococcus faecalis as an important nosocomial pathogen is critically implicated in the pathogenesis of endocarditis, urinary tract, and persistent root canal infections. Its major virulence attributes (biofilm formation, production of proteases, and hemolytic toxins) enable it to cause extensive host tissue damage. With the alarming increase in enterococcal resistance to antibiotics, novel therapeutics are required to inhibit E. faecalis biofilm formation and virulence. Trans-cinnamaldehyde (TC), the main phytochemical in cinnamon essential oils, has demonstrated promising activity against a wide range of pathogens. Here, we comprehensively investigated the effect of TC on planktonic growth, biofilm formation, proteolytic and hemolytic activities, as well as gene regulation in E. faecalis. Our findings revealed that sub-inhibitory concentrations of TC reduced biofilm formation, biofilm exopolysaccharides, as well as its proteolytic and hemolytic activities. Mechanistic studies revealed significant downregulation of the quorum sensing fsr locus and downstream gelE, which are major virulence regulators in E. faecalis. Taken together, our study highlights the potential of TC to inhibit E. faecalis biofilm formation and its virulence.

Use of Essential Oils in Veterinary Medicine to Combat Bacterial and Fungal Infections

Essential oils (EOs) are secondary metabolites of plants employed in folk medicine for a long time thanks to their multiple properties. In the last years, their use has been introduced in veterinary medicine, too. The study of the antibacterial properties of EOs is of increasing interest, because therapies with alternative drugs are welcome to combat infections caused by antibiotic-resistant strains. Other issues could be resolved by EOs employment, such as the presence of antibiotic residues in food of animal origin and in environment. Although the in vitro antimicrobial activity of EOs has been frequently demonstrated in studies carried out on bacterial and fungal strains of different origins, there is a lack of information about their effectiveness in treating infections in animals. The scientific literature reports some studies about in vitro EOs' activity against animal clinical bacterial and fungal isolates, but in vivo studies are very scanty. The use of EOs in therapy of companion and farm animals should follow careful studies on the toxicity of these natural products in relation to animal species and route of administration. Moreover, considering the different behavior of EOs in relation to both species and strain pathogen, before starting a therapy, an aromatogram should be executed to choose the oil with the best antimicrobial activity.

Potential Application of Apilactobacillus kunkeei for Human Use: Evaluation of Probiotic and Functional Properties

Apilactobacillus kunkeei is an insect symbiont with documented beneficial effects on the health of honeybees. It belongs to fructophilic lactic acid bacteria (FLAB), a subgroup of lactic acid bacteria (LAB) notably recognized for their safe status. This fact, together with its recurrent isolation from hive products that are traditionally part of the human diet, suggests its possible safe use as human probiotic. Our data concerning three strains of A. kunkeei isolated from bee bread and honeybee gut highlighted several interesting features, such as the presence of beneficial enzymes (β-glucosidase, β-galactosidase and leucine arylamidase), the low antibiotic resistance, the ability to inhibit P. aeruginosa and, for one tested strain, E. faecalis, and an excellent viability in presence of high sugar concentrations, especially for one strain tested in sugar syrup stored at 4 °C for 30 d. This datum is particularly stimulating, since it demonstrates that selected strains of A. kunkeei can be used for the probiotication of fruit preparations, which are often used in the diet of hospitalized and immunocompromised patients. Finally, we tested for the first time the survival of strains belonging to the species A. kunkeei during simulated gastrointestinal transit, detecting a similar if not a better performance than that showed by Lacticaseibacillus rhamnosus GG, used as probiotic control in each trial.