A green approach to develop zeolite-thymol antimicrobial composites: analytical characterization and antimicrobial activity evaluation

Influence of silver coated zeolite fillers on the chemical and mechanical properties of 3D-printed polyphenylene sulfone restorations

OBJECTIVES

To investigate the chemical and mechanical properties of polyphenylene sulfone (PPSU) depending on its composition and manufacturing.

METHODS

Unfilled-PPSU1 and with antimicrobial silver coated zeolites filled-PPSU2 specimens were made of granulate-GR, filament-FI, or printed-3D. Scanning microscopy and X-ray spectroscopy were performed. Martens hardness-HM, elastic indentation modulus-EIT and flexural strength-FS were determined initially and after aging. Shear bond strength-SBS to veneering and luting composite after conditioning with 7 adhesive systems were examined after aging. Silver leaching was tested after 1-, 3-, 7-, 14-, 21-, 28- and 42 days. Analyses of variance, Kolmogorov-Smirnov, Kruskal-Wallis, Mann-Whitney U, unpaired t-tests and Weibull modulus were computed (p < 0.05).

RESULTS

Zeolites were homogeneously distributed. PPSU1-GR and PPSU1-FI showed the highest HM/EIT, followed by PPSU2-GR, PPSU1-3D and PPSU2-3D. PPSU2-FI presented the lowest HM/EIT, displaying micro pits. Aging showed reduced HM/EIT in PPSU1 and no impact on PPSU2, while FS increased (PPSU1) or decreased (PPSU2). PPSU2-3D presented lower FS than PPSU1-3D. High SBS to the luting (7.0-16.2 MPa) and veneering composite (11.8-22.2 MPa), except for adhesive system PR, were observed. PPSU2-3D showed the highest silver release (9.6%), with all compositions dispensing silver over 42 days.

CONCLUSIONS

For the examined period of 6 weeks, antimicrobial silver ions were released from filled PPSU. The high SBS between PPSU and veneering/luting composite confirmed the feasibility of esthetically veneering and luting filled PPSU. To achieve mechanical properties like unfilled PPSU, the processing parameters of filled PPSU require refinement.

CLINICAL SIGNIFICANCE

This investigation provides proof of principle that PPSU can be successfully doped with silver-coated zeolites. The combination of 3D-printing with an antimicrobial thermoplastic constitutes a great opportunity in the field of prosthetic dentistry. Potential applications include clasps for removable dental prostheses, provisional or permanent fixed dental prostheses and implant abutments.

Analytical and Antimicrobial Characterization of Zn-Modified Clays Embedding Thymol or Carvacrol

Carvacrol and thymol are broad-spectrum natural antimicrobial agents. To reduce their volatility and improve their antimicrobial performance, synergistic systems were prepared loading the active molecules in zinc-modified clays. Montmorillonite (MMT) and zeolite (ZEO) were modified with zinc ions (ZnMMT and ZnZEO), with well-known antimicrobial properties, and then with carvacrol or thymol, reaching the 26 ± 3% and 33 ± 2% w/w of loading, respectively. The resulting hybrid materials were characterized by FT-IR, XPS, XRD, TGA, and GC-MS to evaluate carvacrol/thymol release in simulating food matrices. Antimicrobial assays carried out using spoiler and pathogenic bacterial strains showed that the antimicrobial activity of both thymol and carvacrol was largely preserved once they were loaded into Zn-modified clays. However, MMT hybrids showed an antibacterial activity significantly higher than ZEO hybrids at 50 mg/mL of thymol and carvacrol. For this reason, deeper antimicrobial evaluations were carried out only for ZnMMT composites. ZnMMT loaded with thymol or carvacrol produced inhibition zones against most of the target strains, also at 3.12 mg/mL, while the positive controls represented by the single molecule thymol or carvacrol were not active. The hybrid materials can be useful for applications in which the antimicrobial activity of natural molecules need to be displayed over time as requested for the control of microbial pathogens and spoilage bacteria in different applications, such as active packaging, biomaterials, and medical devices.

Antimicrobial, Probiotic, and Immunomodulatory Potential of Cannabis sativa Extract and Delivery Systems

The compounds present in hemp show multidirectional biological activity. It is related to the presence of secondary metabolites, mainly cannabinoids, terpenes, and flavonoids, and the synergy of their biological activity. The aim of this study was to assess the activity of the Henola Cannabis sativae extract and its combinations with selected carriers (polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer, magnesium aluminometasilicate, and hydroxypropyl-β-cyclodextrin) in terms of antimicrobial, probiotic, and immunobiological effects. As a result of the conducted research, the antimicrobial activity of the extract was confirmed in relation to the following microorganisms: Clostridium difficile, Listeria monocytogenes, Enterococcus faecalis, Staphylococcus aureus, Staphylococcus pyrogenes, Escherichia coli, Klebsiella pneumoniae, Salmonella typhimurium, Pseudomonas aereuginosa, and Candida albicans (microorganism count was reduced from ~102 CFU mL-1 to <10 CFU mL-1 in most cases). Additionally, for the system with hydroxypropyl-β-cyclodextrin, a significant probiotic potential against bacterial strains was established for strains Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus rhamnosus, Lactobacillus reuteri, Pediococcus pentosaceus, Lactococcus lactis, Lactobacillus fermentum, and Streptococcus thermophilus (microorganism count was increased from ~102 to 104-107). In terms of immunomodulatory properties, it was determined that the tested extract and the systems caused changes in IL-6, IL-8, and TNF-α levels.

Pore engineering of micro/mesoporous nanomaterials for encapsulation, controlled release and variegated applications of essential oils

Essential oils have become increasingly popular in fields of medical, food and agriculture, owing to their strongly antimicrobial, anti-inflammation and antioxidant effects, greatly meeting demand from consumers for healthy and safe natural products. However, the easy volatility and/or chemical instability of active ingredients of essential oils (EAIs) can result in the loss of activity before realizing their functions, which have greatly hindered the widely applications of EAIs. As an emerging trend, micro/mesoporous nanomaterials (MNs) have drawn great attention for encapsulation and controlled release of EAIs, owing to their tunable pore structural characteristics. In this review, we briefly discuss the recent advances of MNs that widely used in the controlled release of EAIs, including zeolites, metal-organic frameworks (MOFs), mesoporous silica nanomaterials (MSNs), and provide a comprehensive summary focusing on the pore engineering strategies of MNs that affect their controlled-release or triggered-release for EAIs, including tailorable pore structure properties (e.g., pore size, pore surface area, pore volume, pore geometry, and framework compositions) and surface properties (surface modification and surface functionalization). Finally, the variegated applications and potential challenges are also given for MNs based delivery strategies for EAIs in the fields of healthcare, food and agriculture. These will provide considerable instructions for the rational design of MNs for controlled release of EAIs.

Thymol as a Component of Chitosan Systems-Several New Applications in Medicine: A Comprehensive Review

Thymol, a plant-derived monoterpene phenol known for its broad biological activity, has often been incorporated into chitosan-based biomaterials to enhance therapeutic efficacy. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, we conducted a systematic literature review from 2018 to 2023, focusing on the biomedical implications of thymol-loaded chitosan systems. A review of databases, including PubMed, Scopus, and Web of Science was conducted using specific keywords and search criteria. Of the 90 articles, 12 were selected for the review. Thymol-loaded chitosan-based nanogels (TLCBS) showed improved antimicrobial properties, especially against multidrug-resistant bacterial antagonists. Innovations such as bipolymer nanocarriers and thymol impregnated with photosensitive chitosan micelles offer advanced bactericidal strategies and show potential for bone tissue regeneration and wound healing. The incorporation of thymol also improved drug delivery efficiency and biomechanical strength, especially when combined with poly(dimethylsiloxane) in chitosan-gelatin films. Thymol-chitosan combinations have also shown promising applications in oral delivery and periodontal treatment. This review highlights the synergy between thymol and chitosan in these products, which greatly enhances their therapeutic efficacy and highlights the novel use of essential oil components. It also highlights the novelty of the studies conducted, as well as their limitations and possible directions for the development of integrated substances of plant and animal origin in modern and advanced medical applications.

Chemical Compositions of Essential Oil Extracted from Eight Thyme Species and Potential Biological Functions

Thymus is an herbaceous perennial or subshrub of the Lamiaceae family and is widely distributed worldwide. Essential oils extracted from thymus have attracted much attention, owing to their potential biological functions. Here, we evaluated the chemical compositions of eight thyme essential oils (TEOs) using gas chromatography mass spectrometry and assessed their antioxidant activity. The results showed that (1) the main components in eight TEOs were monoterpene hydrocarbons and oxygenated monoterpenes (84.26-92.84%), and the chemical compositions of the TEOs were affected by the specie factor; (2) eight TEOs could be divided into three groups (thymol-, geraniol-, and nerol acetate-types), and thymol was the main type; (3) eight TEOs had some common compounds, such as thymol and p-cymene, which were the main components in seven TEOs; (4) eight TEOs had antioxidant activity, and Thymus pulegioides, Thymus thracicus, and Thymus serpyllum EOs had stronger antioxidant activity than vitamin E (0.07-0.27 fold) at a concentration of 1 mg/mL, while Thymus quinquecostatus and Thymus longicaulis EOs had relatively weak antioxidant activity. In addition, three chemical type standards were used to evaluate potential roles in antibacterial and tumor therapy. The results showed that thymol had strong antibacterial activity against the growth of Escherichia coli and Staphylococcus aureus, and antimigratory activity for A549 cell. Overall, our results can provide a theoretical basis for further exploring the function of natural products from thyme essential oils.

Production and In Situ Modification of Bacterial Cellulose Gels in Raisin Side-Stream Extracts Using Nanostructures Carrying Thyme Oil: Their Physicochemical/Textural Characterization and Use as Antimicrobial Cheese Packaging

We report the production of BC gels by Komagataeibacter sucrofermentans in synthetic (Hestrin and Schramm; HS) and natural media (raisin finishing side-stream extracts; RFSE), and their in situ modification by natural zeolite (Zt) and activated carbon (AC) nanostructures (NSs) carrying thyme oil (Th). The NS content for optimum BC yield was 0.64 g/L for both Zt-Th (2.56 and 1.47 g BC/L in HS and RFSE, respectively), and AC-Th (1.78 and 0.96 g BC/L in HS and RFSE, respectively). FTIR spectra confirmed the presence of NS and Th in the modified BCs, which, compared to the control, had reduced specific surface area (from 5.7 to 0.2-0.8 m2/g), average pore diameter (from 264 to 165-203 Å), cumulative pore volume (from 0.084 to 0.003-0.01 cm3/g), crystallinity index (CI) (from 72 to 60-70%), and crystallite size (from 78 to 72-76%). These values (except CI and CS), slightly increased after the use of the BC films as antimicrobial coatings on white cheese for 2 months at 4 °C. Tensile properties analysis showed that the addition of NSs resulted in a decrease of elasticity, tensile strength, and elongation at break values. The best results regarding an antimicrobial effect as cheese coating were obtained in the case of the RFSE/AC-Th BC.

Comparison of Antibacterial Activity of Phytochemicals against Common Foodborne Pathogens and Potential for Selection of Resistance

Antimicrobial resistance is now commonly observed in bacterial isolates from multiple settings, compromising the efficacy of current antimicrobial agents. Therefore, there is an urgent requirement for efficacious novel antimicrobials to be used as therapeutics, prophylactically or as preservatives. One promising source of novel antimicrobial chemicals is phytochemicals, which are secondary metabolites produced by plants for numerous purposes, including antimicrobial defence. In this report, we compare the bioactivity of a range of phytochemical compounds, testing their ability to directly inhibit growth or to potentiate other antimicrobials against Salmonella enterica Typhimurium, Pseudomonas aeruginosa, Listeria monocytogenes, and Staphylococcus aureus. We found that nine compounds displayed consistent bioactivity either as direct antimicrobials or as potentiators. Thymol at 0.5 mg/mL showed the greatest antimicrobial effect and significantly reduced the growth of all species, reducing viable cell populations by 66.8%, 43.2%, 29.5%, and 70.2% against S. enterica Typhimurium, S. aureus, P. aeruginosa, and L. monocytogenes, respectively. Selection of mutants with decreased susceptibility to thymol was possible for three of the pathogens, at a calculated rate of 3.77 × 10-8, and characterisation of S. enterica Typhimurium mutants showed a low-level MDR phenotype due to over-expression of the major efflux system AcrAB-TolC. These data show that phytochemicals can have strong antimicrobial activity, but emergence of resistance should be evaluated in any further development.

Application of Thymol Vapors to Control Postharvest Decay Caused by Penicillium digitatum and Lasiodiplodia theobromae in Grapefruit

Two of the major postharvest diseases impacting grapefruit shelf life and marketability in the state of Florida (USA) are stem-end rot (SER) caused by Lasiodiplodia theobromae and green mold (GM) caused by Penicillium digitatum. Here, we investigated the in vitro and in vivo efficacy of vapors of thymol, a natural compound found in the essential oil of various plants and the primary constituent of thyme (Thymus vulgaris) oil, as a potential solution for the management of GM and SER. Thymol vapors at concentrations lower than 10 mg L-1 significantly inhibited the mycelial growth of both pathogens, causing severe ultrastructural damage to P. digitatum conidia. In in vivo trials, the incidence and lesion area of GM and SER on inoculated grapefruit were significantly reduced after a 5 d exposure to 50 mg L-1 thymol vapors. In addition, the in vitro and in vivo sporulation of P. digitatum was suppressed by thymol. When applied in its vapor phase, thymol had no negative effect on the fruit, neither introducing perceivable off-flavor nor causing additional weight loss. Our findings support the pursuit of further studies on the use of thymol, recognized as safe for human health and the environment, as a promising strategy for grapefruit postharvest disease management.

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

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

Plant Antimicrobials for Food Quality and Safety: Recent Views and Future Challenges

The increasing demand for natural, safe, and sustainable food preservation methods drove research towards the use of plant antimicrobials as an alternative to synthetic preservatives. This review article comprehensively discussed the potential applications of plant extracts, essential oils, and their compounds as antimicrobial agents in the food industry. The antimicrobial properties of several plant-derived substances against foodborne pathogens and spoilage microorganisms, along with their modes of action, factors affecting their efficacy, and potential negative sensory impacts, were presented. The review highlighted the synergistic or additive effects displayed by combinations of plant antimicrobials, as well as the successful integration of plant extracts with food technologies ensuring an improved hurdle effect, which can enhance food safety and shelf life. The review likewise emphasized the need for further research in fields such as mode of action, optimized formulations, sensory properties, safety assessment, regulatory aspects, eco-friendly production methods, and consumer education. By addressing these gaps, plant antimicrobials can pave the way for more effective, safe, and sustainable food preservation strategies in the future.

Essential Oils Encapsulated in Zeolite Structures as Delivery Systems (EODS): An Overview

Essential oils (EO) obtained from plants have proven industrial applications in the manufacturing of perfumes and cosmetics, in the production and flavoring of foods and beverages, as therapeutic agents in aromatherapy, and as the active principles or excipients of medicines and pharmaceutics due to their olfactory, physical-chemical, and biological characteristics. On behalf of the new paradigm of a more natural and sustainable lifestyle, EO are rather appealing due to their physical, chemical, and physiological actions in human beings. However, EO are unstable and susceptible to degradation or loss. To tackle this aspect, the encapsulation of EO in microporous structures as zeolites is an attractive solution, since these host materials are cheap and non-toxic to biological environments. This overview provides basic information regarding essential oils, including their recognized benefits and functional properties. Current progress regarding EO encapsulation in zeolite structures is also discussed, highlighting some representative examples of essential oil delivery systems (EODS) based on zeolites for healthcare applications or aromatherapy.

Nanohybrid of Thymol and 2D Simonkolleite Enhances Inhibition of Bacterial Growth, Biofilm Formation, and Free Radicals

Due to the current concerns against opportunistic pathogens and the challenge of antimicrobial resistance worldwide, alternatives to control pathogen growth are required. In this sense, this work offers a new nanohybrid composed of zinc-layered hydroxide salt (Simonkolleite) and thymol for preventing bacterial growth. Materials were characterized with XRD diffraction, FTIR and UV–Vis spectra, SEM microscopy, and dynamic light scattering. It was confirmed that the Simonkolleite structure was obtained, and thymol was adsorbed on the hydroxide in a web-like manner, with a concentration of 0.863 mg thymol/mg of ZnLHS. Absorption kinetics was described with non-linear models, and a pseudo-second-order equation was the best fit. The antibacterial test was conducted against Escherichia coli O157:H7 and Staphylococcus aureus strains, producing inhibition halos of 21 and 24 mm, respectively, with a 10 mg/mL solution of thymol–ZnLHS. Moreover, biofilm formation of Pseudomonas aeruginosa inhibition was tested, with over 90% inhibition. Nanohybrids exhibited antioxidant activity with ABTS and DPPH evaluations, confirming the presence of the biomolecule in the inorganic matrix. These results can be used to develop a thymol protection vehicle for applications in food, pharmaceutics, odontology, or biomedical industries.