Nanoparticles—Attractive Carriers of Antimicrobial Essential Oils

Microbial pathogens are the most prevalent cause of chronic infections and fatalities around the world. Antimicrobial agents including antibiotics have been frequently utilized in the treatment of infections due to their exceptional outcomes. However, their widespread use has resulted in the emergence of multidrug-resistant strains of bacteria, fungi, viruses, and parasites. Furthermore, due to inherent resistance to antimicrobial drugs and the host defence system, the advent of new infectious diseases, chronic infections, and the occurrence of biofilms pose a tougher challenge to the current treatment line. Essential oils (EOs) and their biologically and structurally diverse constituents provide a distinctive, inexhaustible, and novel source of antibacterial, antiviral, antifungal, and antiparasitic agents. However, due to their volatile nature, chemical susceptibility, and poor solubility, their development as antimicrobials is limited. Nanoparticles composed of biodegradable polymeric and inorganic materials have been studied extensively to overcome these limitations. Nanoparticles are being investigated as nanocarriers for antimicrobial delivery, antimicrobial coatings for food products, implantable devices, and medicinal materials in dressings and packaging materials due to their intrinsic capacity to overcome microbial resistance. Essential oil-loaded nanoparticles may offer the potential benefits of synergism in antimicrobial activity, high loading capacity, increased solubility, decreased volatility, chemical stability, and enhancement of the bioavailability and shelf life of EOs and their constituents. This review focuses on the potentiation of the antimicrobial activity of essential oils and their constituents in nanoparticulate delivery systems for a wide range of applications, such as food preservation, packaging, and alternative treatments for infectious diseases.

De-novo fabrication of sunlight irradiated silver nanoparticles and their efficacy against E. coli and S. epidermidis

Silver nanoparticles (AgNPs) gained significant attention due to their activity against microbial pathogens, cancer cells, and viral particles etc. Traditional fabrication methods require hazardous chemicals as reducing agents and their usage and disposal pose a significant hazard to environmental ecosystem. Here, a de novo, robust, cost effective and an eco-friendly method is reported to fabricate AgNPs irradiated with sunlight (SL) while using Salvadora persica root extract (SPE) as reducing agent. Sunlight (SL) irradiated S. persica silver nanoparticles (SpNPs) i.e., SL-SpNPs were characterized using multiple techniques and their antibacterial efficacy was evaluated. The SL-SpNPs were synthesized in 10 min. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) analysis revealed their spherical morphology with a size range of 4.5–39.7 nm, while surface plasmon resonance (SPR) peaked at 425 nm. Fourier transform infrared spectroscopy (FTIR) analysis suggested that the reduction of SL-SpNPs was due to the presence of phytochemicals in the SPE. Furthermore, X-ray powder diffraction (P-XRD) pattern depicted the crystal structure of SL-SpNPs, hence proving the presence of AgNPs. Further the antibacterial studies were carried out against Escherichia coli (ATCC 11229) and Staphylococcus epidermidis (ATCC 12228) using Kirby Bauer method. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for E. coli were determined to be 1.5 μg/mL and 3.0 μg/mL respectively while MIC and MBC values for S. epidermidis were found to be 12.5 μg/mL and 25 μg/mL respectively. The solar irradiation-based fabrication method and resulting SL-SpNPs can find their utility in many biomedical and environmental applications.

Plant-Based Vaccines: Antigen Design, Diversity, and Strategies for High Level Production

Vaccines for human use have conventionally been developed by the production of (1) microbial pathogens in eggs or mammalian cells that are then inactivated, or (2) by the production of pathogen proteins in mammalian and insect cells that are purified for vaccine formulation, as well as, more recently, (3) by using RNA or DNA fragments from pathogens. Another approach for recombinant antigen production in the last three decades has been the use of plants as biofactories. Only have few plant-produced vaccines been evaluated in clinical trials to fight against diseases, of which COVID-19 vaccines are the most recent to be FDA approved. In silico tools have accelerated vaccine design, which, combined with transitory antigen expression in plants, has led to the testing of promising prototypes in pre-clinical and clinical trials. Therefore, this review deals with a description of immunoinformatic tools and plant genetic engineering technologies used for antigen design (virus-like particles (VLP), subunit vaccines, VLP chimeras) and the main strategies for high antigen production levels. These key topics for plant-made vaccine development are discussed and perspectives are provided.

Solvent-Free Synthesis, In Vitro and In Silico Studies of Novel Potential 1,3,4-Thiadiazole-Based Molecules against Microbial Pathogens

A new series of 1,3,4-thiadiazoles was synthesized by the reaction of methyl 2-(4-hydroxy-3-methoxybenzylidene) hydrazine-1-carbodithioate (2) with selected derivatives of hydrazonoyl halide by grinding method at room temperature. The chemical structures of the newly synthesized derivatives were resolved from correct spectral and microanalytical data. Moreover, all synthesized compounds were screened for their antimicrobial activities using Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Bacillus subtilis, Staphylococcus aureus, and Candida albicans. However, compounds 3 and 5 showed significant antimicrobial activity against all tested microorganisms. The other prepared compounds exhibited either only antimicrobial activity against Gram-positive bacteria like compounds 4 and 6, or only antifungal activity like compound 7. A molecular docking study of the compounds was performed against two important microbial enzymes: tyrosyl-tRNA synthetase (TyrRS ) and N-myristoyl transferase (Nmt). The tested compounds showed variety in binding poses and interactions. However, compound 3 showed the best interactions in terms of number of hydrogen bonds, and the lowest affinity binding energy (–8.4 and –9.1 kcal/mol, respectively). From the in vitro and in silico studies, compound 3 is a good candidate for the next steps of the drug development process as an antimicrobial drug.

Microbial pathogens induce neurodegeneration in Alzheimer’s disease mice: protection by microglial regulation

Background Neurodegeneration is considered the consequence of misfolded proteins’ deposition. Little is known about external environmental effects on the neurodegenerative process. Infectious agent-derived pathogen-associated molecular patterns (PAMPs) activate microglia, key players in neurodegenerative diseases. We hypothesized that systemic microbial pathogens may accelerate neurodegeneration in Alzheimer’s disease (AD) and that microglia play a central role in this process. Methods We examined the effect of an infectious environment and of microbial Toll-like receptor (TLR) agonists on cortical neuronal loss and on microglial phenotype in wild type versus 5xFAD transgenic mice, carrying mutated genes associated with familial AD. Results We examined the effect of a naturally bred environment on the neurodegenerative process. Earlier and accelerated cortical neuron loss occurred in 5xFAD mice housed in a natural (“dirty”) environment than in a specific-pathogen-free (SPF) environment, without increasing the burden of Amyloid deposits and microgliosis. Neuronal loss occurred in a microglia-rich cortical region but not in microglia-poor CA regions of the hippocampus. Environmental exposure had no effect on cortical neuron density in wild-type mice. To model the neurodegenerative process caused by the natural infectious environment, we injected systemically the bacterial endotoxin lipopolysaccharide (LPS), a TLR4 agonist PAMP. LPS caused cortical neuronal death in 5xFAD, but not wt mice. We used the selective retinoic acid receptor α agonist Am580 to regulate microglial activation. In primary microglia isolated from 5xFAD mice, Am580 markedly attenuated TLR agonists-induced iNOS expression, without canceling their basic immune response. Intracerebroventricular delivery of Am580 in 5xFAD mice reduced significantly the fraction of (neurotoxic) iNOS + microglia and increased the fraction of (neuroprotective) TREM2 + microglia. Furthermore, intracerebroventricular delivery of Am580 prevented neurodegeneration induced by microbial TLR agonists. Conclusions Exposure to systemic infections causes neurodegeneration in brain regions displaying amyloid pathology and high local microglia density. AD brains exhibit increased susceptibility to microbial PAMPs’ neurotoxicity, which accelerates neuronal death. Microglial modulation protects the brain from microbial TLR agonist PAMP-induced neurodegeneration.

Non-neutralizing antibodies targeting the immunogenic regions of HIV-1 envelope reduce mucosal infection and virus burden in humanized mice

Antibodies are principal immune components elicited by vaccines to induce protection from microbial pathogens. In the Thai RV144 HIV-1 vaccine trial, vaccine efficacy was 31% and the sole primary correlate of reduced risk was shown to be vigorous antibody response targeting the V1V2 region of HIV-1 envelope. Antibodies against V3 also were inversely correlated with infection risk in subsets of vaccinees. Antibodies recognizing these regions, however, do not exhibit potent neutralizing activity. Therefore, we examined the antiviral potential of poorly neutralizing monoclonal antibodies (mAbs) against immunodominant V1V2 and V3 sites by passive administration of human mAbs to humanized mice engrafted with CD34+ hematopoietic stem cells, followed by mucosal challenge with an HIV-1 infectious molecular clone expressing the envelope of a tier 2 resistant HIV-1 strain. Treatment with anti-V1V2 mAb 2158 or anti-V3 mAb 2219 did not prevent infection, but V3 mAb 2219 displayed a superior potency compared to V1V2 mAb 2158 in reducing virus burden. While these mAbs had no or weak neutralizing activity and elicited undetectable levels of antibody-dependent cellular cytotoxicity (ADCC), V3 mAb 2219 displayed a greater capacity to bind virus- and cell-associated HIV-1 envelope and to mediate antibody-dependent cellular phagocytosis (ADCP) and C1q complement binding as compared to V1V2 mAb 2158. Mutations in the Fc region of 2219 diminished these effector activities in vitro and lessened virus control in humanized mice. These results demonstrate the importance of Fc functions other than ADCC for antibodies without potent neutralizing activity.

Scavenger receptors in host defense: from functional aspects to mode of action

Scavenger receptors belong to a superfamily of proteins that are structurally heterogeneous and encompass the miscellaneous group of transmembrane proteins and soluble secretory extracellular domain. They are functionally diverse as they are involved in various disorders and biological pathways and their major function in innate immunity and homeostasis. Numerous scavenger receptors have been discovered so far and are apportioned in various classes (A-L). Scavenger receptors are documented as pattern recognition receptors and known to act in coordination with other co-receptors such as Toll-like receptors in generating the immune responses against a repertoire of ligands such as microbial pathogens, non-self, intracellular and modified self-molecules through various diverse mechanisms like adhesion, endocytosis and phagocytosis etc. Unlike, most of the scavenger receptors discussed below have both membrane and soluble forms that participate in scavenging; the role of a potential scavenging receptor Angiotensin-Converting Enzyme-2 has also been discussed whereby only its soluble form might participate in preventing the pathogen entry and replication, unlike its membrane-bound form. This review majorly gives an insight on the functional aspect of scavenger receptors in host defence and describes their mode of action extensively in various immune pathways involved with each receptor type.

Identification of the Host Substratome of Leishmania-Secreted Casein Kinase 1 Using a SILAC-Based Quantitative Mass Spectrometry Assay

Leishmaniasis is a severe public health problem, caused by the protozoan Leishmania. This parasite has two developmental forms, extracellular promastigote in the insect vector and intracellular amastigote in the mammalian host where it resides inside the phagolysosome of macrophages. Little is known about the virulence factors that regulate host-pathogen interactions and particularly host signalling subversion. All the proteomes of Leishmania extracellular vesicles identified the presence of Leishmania casein kinase 1 (L-CK1.2), a signalling kinase. L-CK1.2 is essential for parasite survival and thus might be essential for host subversion. To get insights into the functions of L-CK1.2 in the macrophage, the systematic identification of its host substrates is crucial, we thus developed an easy method to identify substrates, combining phosphatase treatment, in vitro kinase assay and Stable Isotope Labelling with Amino acids in Cell (SILAC) culture-based mass spectrometry. Implementing this approach, we identified 225 host substrates as well as a potential novel phosphorylation motif for CK1. We confirmed experimentally the enrichment of our substratome in bona fide L-CK1.2 substrates and showed they were also phosphorylated by human CK1δ. L-CK1.2 substratome is enriched in biological processes such as “viral and symbiotic interaction,” “actin cytoskeleton organisation” and “apoptosis,” which are consistent with the host pathways modified by Leishmania upon infection, suggesting that L-CK1.2 might be the missing link. Overall, our results generate important mechanistic insights into the signalling of host subversion by these parasites and other microbial pathogens adapted for intracellular survival.

In Vitro Antimicrobial and Cytotoxicity Activities of Some Medicinal Plant Extracts against Oral Microbial Pathogens

Introduction: Medicinal plants have long been of great interest to scientists in the search for the best treatment of diseases, especially the infectious diseases. In recent years, the use of herbal medicines has become more well-known because of their antimicrobial, antifungal, anti-cancer and less side effects. Aim: The aim of this study was to investigate the antimicrobial and antifungal effects of Urtica dioica, Equisetum arvense, and Punica Granatum peel extracts on two common oral microorganisms, Streptococcus mutans and Candida albicans. Materials and methods: The study investigated the hydro-alcoholic extract of the plants. The antimicrobial activity of the extracts was evaluated using the method of measuring the inhibition of microorganisms, and the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were determined using different concentrations of the extracts and also biofilm assay and SEM were determined. Also cell viability was assessed by MTT assay on human gingival fibroblast cells. Results: The lowest MIC against S. mutants and C. albicans was related to the hydro-alcoholic extract of U. dioica. There was a significant reduction in the microbial biofilms by all three extracts. Among them, U. dioica could decrease the biofilms of S. mutans and C. albicans more than other extracts. In addition, the best results for growth inhibition zone were the hydro-alcoholic extracts of E. arvense and U. dioica with 35 and 30 mm growth zone, respectively. The results of SEM showed that P. granatum peel, U. dioica and E. arvense could destroy microbial biofilms without exerting any cytotoxic effects on HGF cell. Conclusions: The results of the study suggest that U. dioica, E. arvense, and P. Granatum peel extracts can be used as mouthwash with the least significant difference with routine mouthwashes. Also, the plant-based mouthwashes may be more suitable substitutes for chemical types in the future.