Tannic Acid Tailored-Made Microsystems for Wound Infection

Chitosan-coated PLGA microemulsion loaded with tannic acid against Escherichia coli in vitro and in vivo

The overuse of antibiotics has resulted in a surge of drug-resistant bacteria, making the pursuit of natural antimicrobials an urgent and significant trend. Encapsulation and nanoparticulation are effective ways to enhance the antibacterial properties of natural drugs. In this study, we encapsulated tannic acid (TA) with chitosan (CS) and poly (lactide-co-glycolide) (PLGA) using the emulsion-solvent evaporation method to enhance the antimicrobial effect of TA. We prepared a bilayer membrane spherical nanoemulsion of TA-PLGA-CS (TPC) with uniform size of 559.87 ± 1.16 nm, and zeta potential of 59.53 ± 1.07 mV. TPC could be stably stored for 90 days at 4°C without affecting the properties of the emulsion, and the minimum bactericidal concentration against four strains of Escherichia coli (E. coli) remained unchanged for 60 d. The results indicated that TPC enhanced the inhibitory effect of TA against E. coli. Scanning electron microscope images revealed that TPC treatment caused damage to the bacterial cell membrane. In addition, in vivo experiments indicated that TPC exhibited a superior therapeutic effect on artificial colibacillosis in chickens infested with Avian pathogenic Escherichia coli, as evidenced by the changes in body weight and a reduction bacterial load in heart. Furthermore, TPC reversed the down-regulation of catalase, glutathione peroxidase1 (GPX1), and GPX7 gene expression levels in intestinal tissues. Compared to the model group, TPC treatment elevated serum glutathione peroxidase activities and lowered myeloperoxidase and lactate dehydrogenase levels, offering antioxidant protection that was slightly better than that of doxycycline hydrochlorid group. In summary, we prepared a novel TA antimicrobial preparation with significant antioxidant potential and inhibitory effect against E. coli both in vitro and in vivo.

Anti-staphylococcal activity of a polyphenol-rich citrus extract: synergy with β-lactams and low proficiency to induce resistance

Introduction

Antibiotic resistance represents one of the most significant threats to public health in the 21st century. Polyphenols, natural molecules with antibacterial activity produced by plants, are being considered as alternative antimicrobial strategies to manage infections caused by drug-resistant bacteria. In this study, we investigated the antibacterial activity of a polyphenol mixture extracted from citrus fruits, against both antibiotic-susceptible and resistant strains of Staphylococcus aureus and Staphylococcus epidermidis.

Methods

Broth microdilution and time-kill curve experiments were used to test the extract anti-staphylococcal activity. Cytotoxicity was assessed by the hemolysis assay. The interaction between the mixture and antibiotics was investigated by the checkerboard assay. The effect of B alone and in combination with oxacillin on the membrane potential was investigated by the 3,3'-dipropylthiadicarbocyanine iodide assay. The ability of the extract to induce the development of resistance was verified by propagating S. aureus for 10 transfers in the presence of sub-inhibitory concentrations.

Results

The citrus extract was found to be active against all Staphylococcus strains at remarkably low concentrations (0.0031 and 0.0063%), displaying rapid bactericidal effects without being toxic on erythrocytes. In particular, B was found to rapidly cause membrane depolarization. When combined with methicillin, meropenem, and oxacillin, the mixture displayed synergistic activity exclusively against methicillin-resistant strains. We additionally show that the sequential exposure of S. aureus to sub-inhibitory concentrations did not induce the development of resistance against the extract.

Discussion

Overall, these findings support the potential use of the citrus extract as promising option to manage staphylococcal infections and suggest that it may counteract the mechanism behind methicillin-resistance.

Walnut By-Products and Elderberry Extracts-Sustainable Alternatives for Human and Plant Health

A current alternative for sustainable development through green chemistry is the replacement of synthetic compounds with natural ones through the superior capitalization of natural resources, with numerous applications in different fields. The benefits of walnuts (Juglans regia L.) and elderberries (Sambucus nigra L.) have been known since ancient times, due to the presence of phytochemicals such as flavonoids, polyphenols, carotenoids, alkaloids, nitrogen-containing compounds, tannins, steroids, anthocyanins, etc. These active compounds have multiple biological activities for human health, including benefits that are antibacterial, antioxidant, anti-inflammatory, antidiabetic, hepatoprotective, antihypertensive, neuroprotective, etc. Like other medicinal plants, the walnut and the elderberry possess important phytosanitary properties (antibacterial, antifungal, and insecticidal) and their extracts can also be used as environmentally safe biopesticides, with the result that they constitute a viable and cheap alternative to environmentally harmful synthetic products. During recent years, walnut by-products and elderberries have attracted the attention of researchers, and investigations have focused on the species' valuable constituents and active properties. Comparing the information from the literature regarding the phytochemical profile and biological activities, it is highlighted that, apart from the predominant specific compounds, the walnut and the elderberry have common bioactive compounds, which come from six classes (phenols and derivatives, flavonoids, hydroxycinnamic acids, tannins, triterpenoids, and phytosteroids), and act on the same microorganisms. From this perspective, the aim of this review is to provide an overview of the bioactive compounds present in the different constitutive parts of walnut by-products and elderberries, which present a specific or common activity related to human health and the protection of agricultural crops in the context of sustainable development.