Antimicrobial effect of food-grade GML microemulsions against Staphylococcus aureus

Dietary lauric acid promoted antioxidant and immune capacity by improving intestinal structure and microbial population of swimming crab (Portunus trituberculatus)

Lauric acid (LA), a saturated fatty acid with 12 carbon atoms, is widely regarded as a healthy fatty acid that plays an important role in disease resistance and improving immune physiological function. The objective of this study was to determine the effects of dietary lauric acid on the growth performance, antioxidant capacity, non-specific immunity and intestinal microbiology, and evaluate the potential of lauric acids an environmentally friendly additive in swimming crab (Portunus trituberculatus) culture. A total of 192 swimming crabs with an initial body weight of 11.68 ± 0.02 g were fed six different dietary lauric acid levels, the analytical values of lauric acid were 0.09, 0.44, 0.80, 1.00, 1.53, 2.91 mg/g, respectively. There were four replicates per treatment and 8 juvenile swimming crabs per replicate. The results indicated that final weight, percent weight gain, specific growth rate, survival and feed intake were not significantly affected by dietary lauric acid levels; however, crabs fed diets with 0.80 and 1.00 mg/g lauric acid showed the lowest feed efficiency among all treatments. Proximate composition in hepatopancreas and muscle were not significantly affected by dietary lauric acid levels. The highest activities of amylase and lipase in hepatopancreas and intestine were found at crabs fed diet with 0.80 mg/g lauric acid (P < 0.05), the activity of carnitine palmityl transferase (CPT) in hepatopancreas and intestine significantly decreased with dietary lauric acid levels increasing from 0.09 to 2.91 mg/g (P < 0.05). The lowest concentration of glucose and total protein and the activity of alkaline phosphatase in hemolymph were observed at crabs fed diets with 0.80 and 1.00 mg/g lauric acid among all treatments. The activity of GSH-Px in hepatopancreas significantly increased with dietary lauric acid increasing from 0.09 to 1.53 mg/g, MDA in hepatopancreas and hemolymph was not significantly influenced by dietary lauric acid levels. The highest expression of cat and gpx in hepatopancreas were exhibited in crabs fed diet with 1.00 mg/g lauric acid, however, the expression of genes related to the inflammatory signaling pathway (relish, myd88, traf6, nf-κB) were up-regulated in the hepatopancreas with dietary lauric acid levels increasing from 0.09 to 1.00 mg/g, moreover, the expression of genes related to intestinal inflammatory, immune and antioxidant were significantly affected by dietary lauric acid levels (P < 0.05). Crabs fed diet without lauric acid supplementation exhibited higher lipid drop area in hepatopancreas than those fed the other diets (P < 0.05). The expression of genes related to lipid catabolism was up-regulated, however, and the expression of genes related to lipid synthesis was down-regulated in the hepatopancreas of crabs fed with 0.80 mg/g lauric acid. Lauric acid improved hepatic tubular integrity, and enhanced intestinal barrier function by increasing peritrophic membrane (PM) thickness and upregulating the expression of structural factors (per44, zo-1) and intestinal immunity-related genes. In addition, dietary 1.00 mg/g lauric acid significantly improved the microbiota composition of the intestinal, increased the abundance of Actinobacteria and Rhodobacteraceae, and decreased the abundance of Vibrio, thus maintaining the microbiota balance of the intestine. The correlation analysis showed that there was a relationship between intestinal microbiota and immune-antioxidant function. In conclusion, the dietary 1.00 mg/g lauric acid is beneficial to improve the antioxidant capacity and intestinal health of swimming crab.

A review of the antimicrobial activity of thermodynamically stable microemulsions

Microemulsions are thermodynamically stable, transparent, isotropic mixtures of oil, water and surfactant (and sometimes a co-surfactant), which have shown potential for widespread application in disinfection and self-preservation. This is thought to be due to an innate antimicrobial effect. It is suggested that the antimicrobial nature of microemulsions is the result of a combination of their inherent kinetic energy and their containing surfactants, which are known to aid the disruption of bacterial membranes. This review examines the contemporary evidence in support of this theory.

Nanoemulsions: The rising star of antiviral therapeutics and nanodelivery system-current status and prospects

Nanoemulsions (NEs) of essential oil (EO) have significant potential to target microorganisms, especially viruses. They act as a vehicle for delivering antiviral drugs and vaccines. Narrowing of drug discovery pipeline and the emergence of new viral diseases, especially, coronavirus disease, have created a niche to use NEs for augmenting currently available therapeutic options. Published literature demonstrated that EOs have an inherent broad spectrum of activity across bacterial, fungal, and viral pathogens. The emulsification process significantly improved the efficacy of the active ingredients in the EOs. This article highlights the research findings and patent developments in the last 2 years especially, in EO antiviral activity, antiviral drug delivery, vaccine delivery, viral resistance development, and repurposing EO compounds against SARS-CoV-2.

Influence of polysorbates (Tweens) on structural and antimicrobial properties for microemulsions

Polysorbates (Tweens) are one of the most used excipients for essential oils encapsulation. In this work, the polysorbate based microemulsions (PMEs) for R-(+)-limonene (LMN) encapsulation were investigated for the structural and antimicrobial properties. PMEs were constructed using the pseudoternary phase diagrams, and then characterized for electrical conductivity, rheology, size distribution and particle geometry. Conductivity and rheological measurement results showed that Tween 80 and Tween 60 based microemulsions have identical phase transitions. Dynamic light scattering demonstrated that hydrodynamic diameters of oil-in-water microemulsions decreased from 30 nm to 25 nm during the dilution, while small-angle X-ray scattering indicated that their spherical geometries were maintained. PMEs exhibited enhanced antimicrobial efficiencies in vitro against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Interestingly, when Tween 80 was replaced by Tween 60, PME was observed more effective against S. aureus. The two PMEs structural analogues exhibited different antimicrobial efficiencies corresponding to the bioactivity of polysorbates. In conclusion, PMEs can be considered as a desirable system for LMN encapsulation to enhance its solubility and antimicrobial efficiency. Furthermore, the difference in the antimicrobial efficiency suggested that the choice of emulsifiers should be concerned to improve further applications.

Essential oil micro- and nanoemulsions: promising roles in antimicrobial therapy targeting human pathogens

Antimicrobial resistance is a major health concern worldwide. A narrowing of the antibiotic development pipeline and a resurgence in public opinion towards 'natural' therapies have renewed the interest in using essential oils as antimicrobial agents. The drawbacks of bulk dosing of essential oils can be mitigated by formulating them as micro- and nanoemulsions. These emulsions have an added advantage as they are in the nanometre size range whose thermodynamic properties enable them to be used as an effective drug delivery system. This review describes the current work on the antimicrobial activities of essential oil micro- and nanoemulsions and their role as drug delivery vehicles.

Studies on the kinetics of killing and the proposed mechanism of action of microemulsions against fungi

Microemulsions are physically stable oil/water clear dispersions, spontaneously formed and thermodynamically stable. They are composed in most cases of water, oil, surfactant and cosurfactant. Microemulsions are stable, self-preserving antimicrobial agents in their own right. The observed levels of antimicrobial activity associated with microemulsions may be due to the direct effect of the microemulsions themselves on the bacterial cytoplasmic membrane. The aim of this work is to study the growth behaviour of different microbes in presence of certain prepared physically stable microemulsion formulae over extended periods of time. An experiment was designed to study the kinetics of killing of a microemulsion preparation (17.3% Tween-80, 8.5% n-pentanol, 5% isopropyl myristate and 69.2% sterile distilled water) against selected test microorganisms (Candida albicans, Aspergillus niger, Schizosaccharomyces pombe and Rhodotorula spp.). Secondly, an experiment was designed to study the effects of the microemulsion preparation on the cytoplasmic membrane structure and function of selected fungal species by observation of 260 nm component leakage. Finally, the effects of the microemulsion on the fungal membrane structure and function using S. pombe were studied using transmission electron microscopy. The results showed that the prepared microemulsions are stable, effective antimicrobial systems with effective killing rates against C. albicans, A. niger, S. pombe and Rhodotorula spp. The results indicate a proposed mechanism of action of significant anti-membrane activity, resulting in the gross disturbance and dysfunction of the cytoplasmic membrane structure which is followed by cell wall modifications, cytoplasmic coagulation, disruption of intracellular metabolism and cell death.