Antibacterial mechanisms of thyme essential oil nanoemulsions against Escherichia coli O157:H7 and Staphylococcus aureus: Alterations in membrane compositions and characteristics

Chickpea-Derived Modified Antimicrobial Peptides KTA and KTR Inactivate Staphylococcus aureus via Disrupting Cell Membrane and Interfering with Peptidoglycan Synthesis

The widespread bacterial contamination caused by foodborne pathogens has continuously driven the development of advanced and potent food antimicrobial agents. In this study, two novel antimicrobial peptides (AMPs) named KTA and KTR were obtained by modifying a natural AMP, Leg2, from chickpea storage protein legumin hydrolysates. They were further predicted to be stable hydrophobic cationic AMPs of α-helical structure with no hemolytic toxicity by several online servers. Moreover, the AMPs exerted superior antibacterial activity against two representative Staphylococcus aureus strains thanks to the increased hydrophobicity and positive charge, with minimum inhibition concentration value (4.74-7.41 μM) significantly lower than that of Leg2 (>1158.70 μM). Further, this study sought to elucidate the specific antimicrobial mechanism against Gram-positive bacteria. It was found that the electrostatic interactions of the AMPs with peptidoglycan were vital for peptide activity in combating Gram-positive bacteria. Subsequently, the cell membrane of S. aureus cells was irreversibly disrupted by increasing permeability and impairing membrane components, which led to the massive release of intracellular substances and eventual cell death. Overall, this work demonstrated that KTA and KTR were active against Gram-positive bacteria via peptidoglycan targeting and membrane-disruptive mechanisms and paved the way for expanding their application potential to alleviate food contamination.

Inhibitory mechanisms of promising antimicrobials from plant byproducts: A review

Plant byproducts and waste present enormous environmental challenges and an opportunity for valorization and industrial application. Due to consumer demands for natural compounds, the evident paucity of novel antimicrobial agents against foodborne pathogens, and the urgent need to improve the arsenal against infectious diseases and antimicrobial resistance (AMR), plant byproduct compounds have attracted significant research interest. Emerging research highlighted their promising antimicrobial activity, yet the inhibitory mechanisms remain largely unexplored. Therefore, this review summarizes the overall research on the antimicrobial activity and inhibitory mechanisms of plant byproduct compounds. A total of 315 natural antimicrobials from plant byproducts, totaling 1338 minimum inhibitory concentrations (MIC) (in μg/mL) against a broad spectrum of bacteria, were identified, and a particular emphasis was given to compounds with high or good antimicrobial activity (typically <100 μg/mL MIC). Moreover, the antimicrobial mechanisms, particularly against bacterial pathogens, were discussed in-depth, summarizing the latest research on using natural compounds to combat pathogenic microorganisms and AMR. Furthermore, safety concerns, relevant legislation, consumer perspective, and current gaps in the valorization of plant byproducts-derived compounds were comprehensively discussed. This comprehensive review covering up-to-date information on antimicrobial activity and mechanisms represents a powerful tool for screening and selecting the most promising plant byproduct compounds and sources for developing novel antimicrobial agents.

Advances in Controllable Release Essential Oil Microcapsules and Their Promising Applications

Essential oils (EOs) have emerged as natural and popular ingredients used in the preparation of safe and sustainable products because of their unique characteristics, such as antibacterial and antioxidant activity. However, due to their high volatility, poorly solubility in water, and susceptibility to degradation and oxidation, the application of EOs is greatly limited. One of the promising strategies for overcoming these restrictions is encapsulation, which involves in the entrapment of EOs inside biocompatible materials to utilize their controllable release and good bioavailability. In this review, the microencapsulation of the controllable release EOs and their applications are investigated. The focus is on the antimicrobial mechanism of various EOs on different bacteria and fungi, release mechanism of microencapsulated EOs, and preparation research progress of the controllable EOs microcapsules. In addition, their applications are introduced in relation to the food, textiles, agriculture, and medical fields.

Effects of monolauroyl-galactosylglycerol on membrane fatty acids and properties of Bacillus cereus

The purpose of this study was to provide new ideas for the antibacterial mechanism of monolauroyl-galactosylglycerol (MLGG) from the perspective of cell membranes. The changes in cell membrane properties of Bacillus cereus (B. cereus) CMCC 66,301 exposed to different concentrations (1 × MIC (minimum inhibitory concentration), 2 × MIC, 1 × MBC (minimum bacterial concentration)) of MLGG were evaluated. It was found that the lag phase of B. cereus cells was prolonged at low concentration MLGG (1 × MIC and 2 × MIC), while about 2 log CFU/mL reduction in B. cereus populations were observed when exposed to high concentration MLGG (1 × MBC). MLGG treated B. cereus displayed obvious membrane depolarization, while membrane permeability had no change using PI (propidium iodide) staining. Significant increase in the membrane fluidity in response to MLGG exposure occurred, which was consistent with the modification of membrane fatty acids compositions, where the relative content of straight-chain fatty acids (SCFAs) and unsaturated fatty acids (UFAs) increased, while branched-chain fatty acids (BCFAs) decreased significantly. The decreased transition T_m value and cell surface hydrophobicity was also observed. Additionally, effect of MLGG on bacterial membrane compositions were explored at the submolecular level by infrared spectroscopy. Resistance tests of B. cereus to MLGG had demonstrated the advantages of MLGG as a bacteriostatic agent. Collectively, these studies indicate that modifying the fatty acid composition and properties of cellular membranes through MLGG exposure is crucial for inhibiting bacteria growth, providing new insights into the antimicrobial mechanisms of MLGG. KEY POINTS: • Monolauroyl-galactosylglycerol inserted into B. cereus lipid bilayer membrane • Monolauroyl-galactosylglycerol treatment caused B. cereus membrane depolarization • Monolauroyl-galactosylglycerol resulted in B. cereus membrane fatty acids alteration.

Preparation of lemon essential oil nanoemulsion and its effect on the microbial community of pork patties

The purpose of this study was to prepare an essential oil nanoemulsion and apply it to meat products to achieve antimicrobial effect. The nanoemulsion of lemon essential oil was produced by high power ultrasonication. The influences of ultrasonic power, ultrasonic time, and mass ratio of sodium caseinate to essential oil on the particle size were examined. The optimal conditions for preparing nanoemulsion were ultrasonic power 327 W, ultrasonic time 18 min, and sodium caseinate to essential oil mass ratio 4.23:1. Lower temperature was more conducive to the preservation of nanoemulsion. Compared to control and essential oil group, the nanoemulsion could decrease the total volatile basic nitrogen content and total bacterial colony in pork patties. When applied to pork patties, the nanoemulsion decreased the microbial diversity and inhibited the growth of a variety of microorganisms such as Bacillus, extending the storage time of pork patties. This study developed a novel and workable nanoemulsion for inhibiting bacteria of meat products.

Antibacterial Activity and Mechanism of Oxidized Bacterial Nanocellulose with Different Carboxyl Content

Oxidized bacterial nanocellulose (OBC) is reported to prevent microbial growth, but its antibacterial characteristics and mechanism are still unclear. Here, the antibacterial mechanism of OBC is explored by detecting and assessing the interaction of OBC with different carboxyl content on Staphylococcus aureus and Escherichia coli. The results show that OBC has strong antibacterial activity and antibiofilm activity against S. aureus and E. coli, which is positively correlated with the carboxyl content of OBC. After OBC treatment, the bacteria adhesion is inhibited and the cell membrane is destroyed leading to increased permeability. Further investigation reveals that the concentration of cyclic diguanosine monophosphate (c-di-GMP) that induced biofilm formation is significantly decreased to 1.81 pmol mg^-1 after OBC treatment. In addition, OBC inactivates mature biofilms, with inactivation rates up to 79.3%. This study suggests that OBC has excellent antibacterial and antiadhesion properties, which can increase the cell membrane permeability and inhibit c-di-GMP formation. In addition, OBC also has a strong inactivation effect on mature biofilm, which can be used as an effective antibiofilm agent.

Recent Advances in Using Natural Antibacterial Additives in Bioactive Wound Dressings

Wound care is a global health issue with a financial burden of up to US $96.8 billion annually in the USA alone. Chronic non-healing wounds which show delayed and incomplete healing are especially problematic. Although there are more than 3000 dressing types in the wound management market, new developments in more efficient wound dressings will require innovative approaches such as embedding antibacterial additives into wound-dressing materials. The lack of novel antibacterial agents and the misuse of current antibiotics have caused an increase in antimicrobial resistance (AMR) which is estimated to cause 10 million deaths by 2050 worldwide. These ongoing challenges clearly indicate an urgent need for developing new antibacterial additives in wound dressings targeting microbial pathogens. Natural products and their derivatives have long been a significant source of pharmaceuticals against AMR. Scrutinising the data of newly approved drugs has identified plants as one of the biggest and most important sources in the development of novel antibacterial drugs. Some of the plant-based antibacterial additives, such as essential oils and plant extracts, have been previously used in wound dressings; however, there is another source of plant-derived antibacterial additives, i.e., those produced by symbiotic endophytic fungi, that show great potential in wound dressing applications. Endophytes represent a novel, natural, and sustainable source of bioactive compounds for therapeutic applications, including as efficient antibacterial additives for chronic wound dressings. This review examines and appraises recent developments in bioactive wound dressings that incorporate natural products as antibacterial agents as well as advances in endophyte research that show great potential in treating chronic wounds.

Potential Application of Luteolin as an Active Antibacterial Composition in the Development of Hand Sanitizer Products

Antibacterial hand sanitizers could play a prominent role in slowing down the spread and infection of hand bacterial pathogens; luteolin (LUT) is potentially useful as an antibacterial component. Therefore, this study elucidated the antibacterial mechanism of LUT against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) and developed an antibacterial hand sanitizer. The results showed that LUT had excellent antibacterial activity against both E. coli (minimum inhibitory concentration (MIC) = 312.5 μg/mL, minimal bactericidal concentration (MBC) = 625 μg/mL), and S. aureus (MIC = 312.5 μg/mL, MBC = 625 μg/mL). Furthermore, LUT induced cell dysfunction in E. coli and S. aureus, changed membrane permeability, and promoted the leakage of cellular contents. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) analysis showed that LUT treatment affected cell structure and disrupted cell membrane integrity. The Fourier transform infrared analysis (FTIR) also confirmed that the LUT acted on the cell membranes of both E. coli and S. aureus. Overall, the application of LUT in hand sanitizer had better inhibition effects. Therefore, this study could provide insight into expanding the application of LUT in the hand sanitizer markets.

Inhibitory Effect of Sodium Alginate Nanoemulsion Coating Containing Myrtle Essential Oil (Myrtus communis L.) on Listeria monocytogenes in Kasar Cheese

The present study aimed to characterize the physical properties of nanoemulsion-based sodium alginate edible coatings containing myrtle (Myrtus communis L.) essential oil and to determine its inhibitory effects on Listeria monocytogenes in fresh Kasar cheese during the 24-day storage at 4 °C. The GC-MS analysis showed that the main components of myrtle essential oil were 1,8-cineol (38.64%), α-pinene (30.19%), d-limonene (7.51%), and α-ocimene (6.57%). Myrtle essential oil showed an inhibitory effect on all tested L. monocytogenes strains and this effect significantly increased after ultrasonication. Minimum inhibitory and minimum bactericidal concentrations of myrtle essential oil nanoemulsion were found to be 4.00-4.67 mg/mL and 5.00-7.33 mg/mL, respectively. The antibacterial activity of myrtle essential oil nanoemulsion against L. monocytogenes was confirmed by the membrane integrity and FESEM analyses. Nanoemulsion coatings containing myrtle essential oil showed antibacterial activity against L. monocytogenes with no adverse effects on the physicochemical properties of cheese samples. Nanoemulsion coatings containing 1.0% and 2.0% myrtle essential oil reduced the L. monocytogenes population in cheese during the storage by 0.42 and 0.88 log cfu/g, respectively. These results revealed that nanoemulsion-based alginate edible coatings containing myrtle essential oil have the potential to be used as a natural food preservative.

Natural Emulsions Based on Essential Oils as Antifungal and Antimycotoxicogenic Agents on Wheat for Bakery Industry

This study aimed to investigate the antifungal and antimycotoxicogenic effect of binary and tertiary mixtures of Thymus vulgaris, Origanum sativum, and Coriandrum sativum essential oils (EOs), as well as emulsions based on EO mixtures, on fungi developed on wheat grains destined for the bakery industry. The chemical composition of the EO mixtures, the physical characteristics of the emulsions, and the influence of treatments on the proximate composition of wheat seeds were also studied. The methods used included the microbiological analysis of fungi developed on wheat seeds, the ELISA technique for determining the deoxynivalenol content (DON), gas chromatography coupled with mass spectrometry (GC-MS) to detect the chemical composition of the EOs, Zetasizer to analyse the particle sizes and their electric charge at the surface, and NIR analysis of the proximate composition of wheat. The chemical composition analysis revealed that thymol and o-cymene were the major components in the binary mixture of the EOs with thyme, linalool in the binary mixtures of the EOs with coriander and carvacrol, and o-cymene in the binary mixtures of the EOs with oregano. The results showed that, based on the zeta potential, the tertiary mixture ensured maximum emulsion stability, while the emulsion based on thyme and oregano was the less stable system. Regarding the antifungal and antimycotoxicogenic effect, the results showed that the highest inhibition potential on fungi was observed with the binary mixtures of the EOs based on thyme and oregano, and on deoxynivalenol (DON) when the binary emulsion based on the same EOs was applied to wheat seeds. The proximate composition of wheat seeds contaminated with DON showed an increase in protein content and mineral substances, and there were changes in the colour of the wheat seeds after treatment with the EOs. In conclusion, the results obtained in this study showed the possibility of using binary/tertiary mixtures of EOs and emulsions as healthy and environmentally friendly alternatives in the bakery industry.

Thermal, structural, antimicrobial, and physicochemical characterisation of thyme essential oil encapsulated in β- and γ-cyclodextrin

The present work aimed to encapsulate the thyme essential oil (TEO) in β-cyclodextrin (BCD) and γ-cyclodextrin (GCD) complexes in two selected cyclodextrin (CD) to TEO ratios (85/15 and 80/20 w/w) and compare the physicochemical, antioxidant, and antimicrobial properties of the encapsulated powders. The inclusion complexes between CD and TEO were prepared by blending aqueous CD and TEO in ethanol followed by freeze-drying. The powder properties were assessed by measuring particle size and microstructure using SEM, FTIR, and XRD. The median values of the particle sizes (GCD: 92.0 ± 4.69 and BCD: 46.2 ± 2.56-mm) significantly influenced the encapsulation efficiency, resulting in a higher encapsulation efficiency of the GCD (92.02 ± 10.79%) than that of the BCD (56.30 ± 12.19%). The encapsulated GCD/TEO (80/20) showed higher antioxidant activity and an antimicrobial inhibitory effect against Listeria monocytogenes and Salmonella enterica sv. typhimurium. Overall, the GCD acts as a superior wall material to the BCD in the TEO encapsulation.