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Using existing adrentimicrobials with essential oil components to prevent antimicrobial resistance is an alternative strategy. This study aimed to evaluate the resistance status, synergistic combinations, and in vitro biofilm formation activities of clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), Stenotrophomonas maltophilia and Candida albicans against antimicrobial agents and cinnamaldehyde, carvacrol, eugenol, limonene and eucalyptol. Antimicrobial activities were evaluated by microdilution, cytotoxicity by XTT, synergy by checkerboard and time-kill, and biofilm inhibition by microplate methods. Cinnamaldehyde and carvacrol showed strong antimicrobial activity. Synergistic effects were observed when using all essential oils with antimicrobials. Only two C. albicans isolates showed antagonism with cinnamaldehyde and fluconazole. The constituents showed cytotoxic effects in the L929 cell line (except limonene). A time-kill analysis revealed a bacteriostatic effect on S. maltophilia and MRSA isolates and a fungicidal effect on C. albicans isolates. These results are important for further research to improve antimicrobial efficacy or to develop new agents.

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 Brochothrix thermosphacta 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.

Population growth directly affects the global food supply, demanding a higher production efficiency without farmland expansion - in view of limited land resources and biodiversity loss worldwide. In such scenario, intensive agriculture practices have been widely used. A commonly applied method to maximize yield in animal production is the use of subtherapeutic doses of antibiotics as growth promoters. Because of the strong antibiotic selection pressure generated, the intense use of antibiotic growth promoters (AGP) has been associated to the rise of antimicrobial resistance (AMR). Also, cross-resistance can occur, leading to the emergence of multidrug-resistant pathogens and limiting treatment options in both human and animal health. Thereon, alternatives have been studied to replace AGP in animal production. Among such alternatives, essential oils and essential oil components (EOC) stand out positively from others due to, besides antimicrobial effectiveness, improving zootechnical indexes and modulating genes involved in resistance mechanisms. This review summarizes recent studies in essential oils and EOC for zoonotic bacteria control, providing detailed information about the molecular-level effects of their use in regard to AMR, and identifying important gaps to be filled within the animal production area.

This study aimed to evaluate possible synergistic interactions on antimicrobial and antioxidant efficacy of clove and cinnamon oil components in combination and characterization of compounds responsible for synergistic interactions using TLC bioautography followed by checkerboard titration, isobologram analysis, and spectrometric characterization. Among the combinations tested, cinnamaldehyde from cinnamon oil and eugenol from clove oil in combination showed a synergistic antimicrobial interaction against foodborne microbes Listeria monocytogenes (fractional inhibitory concentration index (FICI): 0.31), Salmonella typhimurium (FICI: 0.41), and Aspergillus niger (FICI: 0.48), and synergistic antioxidant efficacy (combination index: 0.78) in in vitro model. Cinnamaldehyde/eugenol blend did not show any cytotoxic effect (IC 50 > 1000 μg/ml) in human normal keratinocyte cell line. The results provide evidence that the cinnamaldehyde/eugenol blend may help in designing a more potent novel natural antimicrobial and antioxidant agent in food and pharmaceutical industries.

Available disinfection methods and therapies against Helicobacter pylori have multiple disadvantages, such as increased prevalence of antibiotic-resistant strains, which requires the search for novel effective antimicrobial agents against H. pylori. Among them, naturally-occurring antimicrobial compounds, like essential oil components (EOCs), have been reported as substances with anti-H. pylori potential. To avoid the disadvantages associated with using EOCs in their free form, including volatility, low water solubility and intense sensory properties, their immobilisation in inert supports has recently been developed. This study sought to evaluate the inhibitory properties of EOCs immobilised on silica microparticles against H. pylori and to elucidate the mechanism of action of the immobilised antimicrobials. After the preparation and characterisation of the antimicrobial supports, the susceptibility of H. pylori in the presence of the immobilised compounds was assessed by plate count, fluorescent viability staining and direct viable count-fluorescent in situ hybridisation analyses. The antimicrobial supports were found to inhibit H. pylori growth, and to induce morphological and metabolic alterations to the H. pylori membrane, with a minimum bactericidal concentration value between 25 and 50 μg/ml according to the tested EOC. These findings indicate that immobilised EOCs can be used as potential antimicrobial agents for H. pylori clearance and treatment.

The hydro-distilled essential oils obtained from aerial parts of the wild and cultivated Echinophora tenuifolia subsp. sibthorpiana have been analyzed by GC-MS and screened for antimicrobial activity. In total, 28 compounds representing more than 99% of the oils were identified. α-phellandrene (13.22% and 55.27%), δ-3-carene (49.29% and 4.03%), and methyl eugenol (22.59–25.69%) were found as the main components for the wild and cultivated oils, respectively. EOs of the wild and cultivated plants differed significantly in both the percentage of the main components and antifungal effect. α-phellandrene was more dominant in cultivated plants (55.27%) than in wild ones (13.22%), while δ-3-carene was more abundant in the wild plants (49.29%). In the antifungal assays, both oils displayed moderate to high activity against three phytopathogenic fungi; Fusarium oxysporum, Rhizoctonia solani, and Alternaria alternata. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the presence of histamine-forming bacteria in cheeses, and to assess the impact of naturally-occurring antimicrobials on isolates' viability and histamine-forming potential. Cheese isolates' ability to produce histamine was evaluated by incubation in the presence of the histamine precursor; qualitative detection with a pH indicator and a quantitative analysis by high-performance liquid chromatography. Eight of the 114 isolates were able to produce histamine, but only one was capable of generating histamine at high concentrations. Histamine-producing isolates were identified by matrix-assisted laser desorption ionisation-time of flight mass spectrometry. Isolated strain C_MRSV_25A_4 was the microorganism with the highest capacity to produce histamine, and was identified as Lacticaseibacillus rhamnosus. The antimicrobial potential of natural antimicrobials was tested against this isolate. The results showed that carvacrol, cinnamaldehyde, eugenol, thymol and nisin exhibited remarkable bactericidal activity. These compounds' inhibitory potential was evaluated against the histamine-generating ability of strain C_MRSV_25A_4 at three concentrations of interest: minimum bactericidal concentration (MBC), MBC/2 and MBC/4. The results on histamine-forming capability at sub-bactericidal concentrations were promising. Given these results, we propose novel antimicrobial formulations based on natural antimicrobials as efficient strategies to reduce potential microbial contamination and histamine accumulation throughout cheese production. [Display omitted] • Bacteria responsible to generate histamine were isolated from commercial cheeses. • Natural compounds had an antimicrobial effect against histamine-forming isolates. • Sub-bactericidal concentrations partially inhibited decarboxylase activity. • Using sub-bactericidal concentrations could control histamine content in cheese. • Antimicrobials may reduce microbial growth to prevent histamine formation in cheese. [ABSTRACT FROM AUTHOR]

Available disinfection methods and therapies against Helicobacter pylori have multiple disadvantages, such as increased prevalence of antibiotic-resistant strains, which requires the search for novel effective antimicrobial agents against H. pylori. Among them, naturally-occurring antimicrobial compounds, like essential oil components (EOCs), have been reported as substances with anti-H. pylori potential. To avoid the disadvantages associated with using EOCs in their free form, including volatility, low water solubility and intense sensory properties, their immobilisation in inert supports has recently been developed. This study sought to evaluate the inhibitory properties of EOCs immobilised on silica microparticles against H. pylori and to elucidate the mechanism of action of the immobilised antimicrobials. After the preparation and characterisation of the antimicrobial supports, the susceptibility of H. pylori in the presence of the immobilised compounds was assessed by plate count, fluorescent viability staining and direct viable count–fluorescent in situ hybridisation analyses. The antimicrobial supports were found to inhibit H. pylori growth, and to induce morphological and metabolic alterations to the H. pylori membrane, with a minimum bactericidal concentration value between 25 and 50 μg/ml according to the tested EOC. These findings indicate that immobilised EOCs can be used as potential antimicrobial agents for H. pylori clearance and treatment. [ABSTRACT FROM AUTHOR]

Essential oil components (EOCs) are potent natural antimicrobial agents, but their high volatility and reactivity limit their potential applications. Here, we report the preparation of a series of nanomaterials containing EOCs (i.e., allyl isothiocyanate, carvacrol, cinnamaldehyde, diallyl disulphide, eugenol and thymol). The materials were prepared by simple adsorption of the EOCs onto a montmorillonite nanoclay. The antimicrobial activities of these materials were assessed against Aspergillus niger and Staphylococcus aureus as typical models of agricultural fungal pathogens and foodborne bacterial pathogens, respectively. In addition, the activities of the encapsulated EOCs were compared with those of the corresponding free forms with or without Tween‐80 in two types of assays: microdilution assays for determining the minimum inhibitory concentration (MIC) and agar‐based assays mimicking surface treatment. Enhanced antifungal activity of the encapsulated form was observed for all EOCs. In addition, against S. aureus, the MICs of all EOCs were remarkably lower in encapsulated form than in free form. These results indicate that EOCs encapsulated in low‐cost nanoclays have favourable potential as antimicrobials compared with the pure compounds. Antimicrobial activity of the nanoclay‐encapsulated essential oil components were compared with their free forms. Prolonged activity of the encapsulated forms was observed against Aspergillus niger, while remarkably lower MICs were achieved against S. aureus. [ABSTRACT FROM AUTHOR]

In the present study, seven thyme species Origanum onites, O. vulgare var. hirtum, O. vulgare var. gracile, O. syriacum, Satureja hortensis, Thymbra spicata, and Thymus vulgaris were used. The essential oils of these plants were obtained by the hydrodistillation method. Antimicrobial activities of the essential oils against microorganisms, including multiple antibiotic-resistant bacteria, were investigated using the disc diffusion method. All the essential oils used in this study were very effective against Gram-positive and Gram-negative bacteria, which included multiple resistant strains. All essential oils tested were especially very effective against Streptococcus pyogenes. The maximum antimicrobial activity was observed with the essential oils of S. hortensis. The antimicrobial activities of the essential oils varied depending on the species. In fact, the essential oils of some thyme species showed different levels of antimicrobial activities. The antioxidant activity results show that the percentage of inhibition values ranged from 28.32 to 94.55%. Among essential oils, O. vulgare var. gracile oil showed the lowest antioxidant capacity (28.32%), while S. hortensis showed the highest one (94.55%). Generally, the data suggest that different thyme species oil possesses useful antimicrobial and antioxidant properties and may be utilized in the food industry and as a dietary supplement. [ABSTRACT FROM AUTHOR]

Rhynchosia heynei Wt. & Arn. (Fabaceae) is an endemic medicinal plant found in the forests of Eastern Ghats of India. The essential oil obtained from the leaves by steam distillation was studied for antimicrobial activity and chemical characterization. The essential oil exhibited a broad spectrum of antimicrobial activity on eight bacterial and three fungal strains. The essential oil was characterized chemically using gas chromatography with flame ionization detector. The majority of the components of the essential oil of R. heynei are oxygenated terpenes, such as, terpineol, camphene hydrate, germacrene-D, humulene, and linalool. etc. [ABSTRACT FROM AUTHOR]

Abstract: The possible use of antimicrobials from seven plant essential oils as food preservatives was studied by examining their effects on the growth kinetics of activated Bacillus cereus INRA L2104 spores inoculated into tyndallized carrot broth. The effects of various concentrations of borneol, carvacrol, cinnamaldehyde, eugenol, menthol, thymol, and vanillin were determined. Five microliters of cinnamaldehyde, 15 μl of carvacrol, or 30 mg of thymol per 100 ml of inoculated carrot broth completely inhibited bacterial growth for more than 60 days at 16 °C. Lower concentrations of the three antimicrobials prolonged the lag phase and reduced both the exponential growth rate and the final population densities of cultures. The study of the sensory characteristics of the supplemented broths suggested that low concentration of cinnamaldehyde enhanced the taste of carrot broth, and that it did not have any adverse effect on the taste and smell of carrot broth at concentrations less than 6 μl 100 ml−1. [Copyright &y& Elsevier]

The essential oil of Tanacetum macrophyllum growing wild in Turkey was obtained by hydrodistillation, and antimicrobial activity of the essential oil was tested against six bacteria and two yeasts including Candida albicans and Aspergillus niger by disc diffusion method. Further the oil of this plant was analyzed by CC and CC/MS technique. Best effect of the oil was against pseudomonas earuginosa. Twenty-eight components, representing 95.6% of the total oil, were identified. The main component of the oil was β-eudesmol (89.5%). The antioxidant activity of the essential oil was measured by the ferric reducing antioxidant power (FRAP) assay. [ABSTRACT FROM AUTHOR]