The agar microdilution method - a new method for antimicrobial susceptibility testing for essential oils and plant extracts

Preparation and antibacterial activity of coronarin E derivatives

Coronarin E is a main diterpene ever isolated from Hedychium yunnanense. With the aim to enlarge its potential application, four butenolide derivatives (compounds 4a, 4b, 5a and 5b) were obtained from coronarin E via synthetic method, and their antibacterial effects were also evaluated. It is noteworthy that compounds 5a and 5b exhibited stronger antibacterial activities against most of the tested bacterial strains than ampicillin and kanamycin, two first- and second-line antimicrobials in clinical. For example, minimum inhibitory concentration (MIC) of 5a, 5b, ampicillin and kanamycin against Acinetobacter baumanii were 2, 1, 8 and 4 μg/mL, respectively, and MIC of the four compounds mentioned above against Klebsiella pneumonia were 1, 0.5, 16 and 4 μg/mL, respectively. The current studies not only enrich the structural diversity of diterpenes derived from Hedychium genus, but also provide potent candidates for the development of antibacterial medicines.

Journey of technological advancements in the detection of antimicrobial resistance

Increased uses rather an extensive misuse of antibiotics due to easy availability and easy access have resulted in antibiotic resistance as a global crisis. The speed of discovery of new antibiotics has slowed down recently. Therefore, there is a need to reduce the rate of increase in resistance against the presently available antibiotics, or else many infections may be left untreatable or difficult to be treated due to the high prevalence of resistance. The judicious use of broad-spectrum antibiotics can control the increase in resistance profile. Various techniques are presently being used for the detection of antibiotic resistance. Conventional phenotypic methods are preferred that are highly reliable but are much more time-consuming. The patients cannot spare more time as the infection keeps increasing. The results with genotypic methods are obtained within 24 h as compared to phenotypic methods. Hence, recent molecular methods like qPCR can be used for detection. In this review, we present an overview of various methods useful for the detection of antibiotic resistance, with emphasis on their advantages and limitations. The review also emphasizes qPCR to be the most preferred method out of all because of various advantageous factors.

Biofilm busters: Exploring the antimicrobial and antibiofilm properties of essential oils against Salmonella Enteritidis

This study delves into an exploration of the antimicrobial and antibiofilm properties of the essential oils (EOs) of cinnamon, garlic, and onion on Salmonella Enteritidis. Firstly, disc diffusion and minimum inhibitory concentration (MIC) techniques were employed to assess the antibacterial activity of the EOs. Additionally, the study explored the effect of these EOs on both initial cell attachment and 24 h-preformed biofilms. The crystal violet assay was implemented to evaluate biofilm biomass. The findings revealed that cinnamon EO exhibited the highest anti-biofilm activity. Furthermore, initial cell attachment inhibition at MIC ranged between 50 and 65% for the three oils, while inhibition rates on preformed structures were lower than 40% for all EOs at this MIC concentration. The study also found that the effects of these oils were dosage- and time-dependent (p < 0.05), thereby urging the adoption of these natural extracts as effective strategies for combating Salmonella biofilms.

Phytochemical Profile, Antioxidant Potential, Antimicrobial Activity, and Cytotoxicity of Dry Extract from Rosa damascena Mill

Dry rose extract (DRE) obtained industrially by aqueous ethanol extraction from R. damascena flowers and its phenolic-enriched fraction, obtained by re-extraction with ethyl acetate (EAE) were the subject of this study. 1H NMR of DRE allowed the identification and quantitation of fructose and glucose, while the combined use of HPLC-DAD-ESIMS and HPLC-HRMS showed the presence of 14 kaempferol glycosides, 12 quercetin glycosides, 4 phenolic acids and their esters, 4 galloyl glycosides, 7 ellagitannins, and quinic acid. In addition, the structures of 13 of the flavonoid glycosides were further confirmed by NMR. EAE was found to be richer in TPC and TFC and showed better antioxidant activity (DPPH, ABTS, and FRAP) compared to DRE. Both extracts displayed significant activity against Propionibacterium acnes, Staphylococcus aureus, and S. epidermidis, but showed no activity against Candida albicans. Toxicity tests on normal human skin fibroblasts revealed low toxicity for both extracts with stronger effects observed at 24 hours of treatment that were compensated for over the following two days. Human hepatocarcinoma (HepG2) cells exhibited an opposite response after treatment with a concentration above 350 µg/mL for EAE and 500 µg/mL for DRE, showing increased toxicity after the third day of treatment. Lower concentrations were non-toxic and did not significantly affect the cell cycle parameters of either of the cell lines.

Antioxidant, Antimicrobial, and Insecticidal Properties of Chemically Characterized Essential Oils Extracted from Mentha longifolia: In Vitro and In Silico Analysis

The present study aimed to explore the phytochemical profile, and evaluate the antioxidant, antimicrobial, and insecticidal properties, of Moroccan Mentha longifolia L. essential oil (ML-EO) using in vitro and in silico assays. Noteworthily, as chromatography (GC-MS/MS) revealed that ML-EO is majorly composed of piperitenone oxide (53.43%), caryophyllene (20.02%), and (-) germacrene D (16.53%). It possesses excellent antioxidant activity with an IC50 of 1.49 ± 0.00 for DPPH and 0.051 ± 0.06 μg/mL for ABTS. Moreover, the RP and TAC activities were 0.80 ± 0.01 μg/mL and 315.532 ± 0.00 mg EAA/g, respectively. ML-EO exhibited a potent antimicrobial effect, specifically against Pseudomonas aeruginosa. It also exhibited strong antifungal ability, especially against Candida albicans. Regarding insecticidal activity, for ML-EO, a dose of 20 µL/mL produced a complete reduction in fecundity, fertility, and emergence of adult C. maculatus with mortality rates reaching 100%. In silico results showed that the antioxidant activity is mostly attributed to α-Cadinol, the antibacterial efficiency is attributed to piperitenone oxide, and antifungal capacity is related to cis-Muurola-4(15),5-diene and piperitenone oxide. Accordingly, ML-EO has high potential to be used as an alternative for preserving food and stored grain and protecting them against microbes and insect pests in the food and pharmaceutical sectors.

Efficacy of various extracting solvents on phytochemical composition, and biological properties of Mentha longifolia L. leaf extracts

The current work attempts to explore the influence of three extraction solvents on phytochemical composition, content of polyphenols, antioxidant potential, and antibacterial capacity of hydroethanolic, acetonic, and aqueous extracts from Moroccan Mentha longifolia leaves. To achieve this goal, the chemical composition was identified using an HPLC-DAD examination. The contents of polyphenols were assessed, while the total antioxidant capacity (TAC), the DPPH test, and the reducing power test (RP) were utilized to determine antioxidant capacity. To assess the antibacterial activity, the microdilution technique was carried out to calculate the minimum inhibitory (MIC) and minimum bactericidal concentrations (MBC) of extracts against four nosocomial bacteria (Bacillus cereus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus). Additionally, the antibacterial and antioxidant activities of all tested extracts were examined in silico against the proteins NADPH oxidase and Bacillus cereus phospholipase C. Study reveals that M. longifolia extracts contain high phenolic and flavonoids. Additionally, the hydroethanolic extract contained the highest amounts of phenolic and flavonoid content, with values of 23.52 ± 0.14 mg Gallic acid equivalent/g dry weight and 17.62 ± 0.36 mg Quercetin Equivalent/g dry weight, respectively compared to the other two extracts. The same extract showed the best antioxidant capacity (IC50 = 39 µg/mL ± 0.00), and the higher RP (EC50 of 0.261 ± 0.00 mg/mL), compared to the acetonic and aqueous extract regarding these tests. Furthermore, the hydroethanolic and acetonic extracts expressed the highest TAC (74.40 ± 1.34, and 52.40 ± 0.20 mg EAA/g DW respectively), compared with the aqueous extract. Regarding antibacterial activity, the MIC value ranges between 1.17 and 12.50 mg/mL. The in-silico results showed that the antibacterial activity of all extracts is principally attributed to kaempferol and ferulic acid, while antioxidant capacity is attributed to ferulic acid.

Green Synthesized Iron-Coated Silver Nanoparticles: Economic Bimetallic Nanoparticles Potential Against Methicillin-Resistance Staphylococcus aureus

Iron coating was introduced as one of the novel techniques to improve physicochemical and biological properties of silver nanoparticles (AgNPs). In the current experiment, impact of iron coating on the antimicrobial potency of AgNPs was investigated against methicillin-resistance Staphylococcus aureus (MRSA). To obtain more accurate data about the antimicrobial potency of examined nanostructures, the experiment was done on the 10 isolates of MRSA which were isolated from skin lesions. AgNPs and iron-coated AgNPs (Fe@AgNPs) were fabricated based on a green one-pot reaction procedure. Minimal inhibitory concentration (MIC) of Fe@AgNPs was not significantly different with MIC of AgNPs against eight out of 10 examined MRSA isolates. Also, by iron coating a reduction in the minimal inhibitory concentration (MIC) of AgNPs was observed against two MRSA isolates. The average MIC of AgNPs against 10 MRSA isolates was calculated to be 2.16 ± 0.382 mg/mL and this value was reduced to 1.70 ± 0.638 mg/mL for Fe@AgNPs. However, this difference was not considered significant statistically (P-value > 0.05). From productivity point of view, it was found that iron coating would improve the productivity of the synthesis reaction more than fivefold. Productivity of AgNPs was calculated to be 1.02 ± 0.07 g/L, meanwhile this value was 5.25 ± 0.05 g/L for Fe@AgNPs. Iron coating may provide another economic benefit to reduce final price of AgNPs. It is obvious that the price of a particular nanostructure made of silver and iron is significantly lower than that of pure silver. These findings can be considered for the fabrication of economic and potent antimicrobial nanoparticles.

Current Landscape of Methods to Evaluate Antimicrobial Activity of Natural Extracts

Natural extracts have been and continue to be used to treat a wide range of medical conditions, from infectious diseases to cancer, based on their convenience and therapeutic potential. Natural products derived from microbes, plants, and animals offer a broad variety of molecules and chemical compounds. Natural products are not only one of the most important sources for innovative drug development for animal and human health, but they are also an inspiration for synthetic biology and chemistry scientists towards the discovery of new bioactive compounds and pharmaceuticals. This is particularly relevant in the current context, where antimicrobial resistance has risen as a global health problem. Thus, efforts are being directed toward studying natural compounds' chemical composition and bioactive potential to generate drugs with better efficacy and lower toxicity than existing molecules. Currently, a wide range of methodologies are used to analyze the in vitro activity of natural extracts to determine their suitability as antimicrobial agents. Despite traditional technologies being the most employed, technological advances have contributed to the implementation of methods able to circumvent issues related to analysis capacity, time, sensitivity, and reproducibility. This review produces an updated analysis of the conventional and current methods to evaluate the antimicrobial activity of natural compounds.

Comparative evaluation of the antifungal efficacy of sodium hypochlorite, chlorhexidine, and silver nanoparticles against Candida albicans

Candida albicans is a microorganism that causes root canal infections. However, it cannot be eliminated with conventional irrigation solutions. Recently, silver nanoparticles (AgNPs) have become popular for their superior antimicrobial effects. The purpose of this study was to evaluate the antifungal effect of AgNPs to C. albicans comparing with 5.25% sodium hypochlorite (NaOCl) and 2% chlorhexidine (CHX). Silver nanoparticles were synthesized by chemical reduction method. Minimum inhibitory concentration and minimum fungicidal concentration of AgNPs against C. albicans strain were determined according to microdilution method reported by Clinical Laboratory Standards Institute. C. albicans biofilm layer was formed on the dentin blocks for 10 days. The biofilm structure was observed by scanning electron microscopy. Statistical analysis was performed with one way analysis of variance analysis and group comparisons were performed with Tukey test. AgNPs showed the highest antifungal effect among the groups. 5.25% NaOCl showed the lowest antifungal effect among the groups. While the 2% CHX solution had a statistically lower antifungal effect than AgNPs, it was found to have a higher effect than NaOCl (p < .016). Nanoparticles present a wide research field as an alternative irrigation solution in root canal treatment. The antifungal effect of AgNPs against C. albicans was confirmed in this study. Further in vivo studies should evaluate the conditions of use and long-term prognosis of AgNPs.

Antibacterial and Antifungal Silver Nanoparticles with Tunable Size Embedded in Various Cellulose-Based Matrices

The aim of this study was to synthesize silver nanoparticles (AgNPs) using cellulose derivatives and to evaluate their antimicrobial potential. As effective reducing and stabilizing agents for AgNPs, cellulose derivatives, such as hydroxypropyl cellulose (HPC), methylcellulose (MC), ethylcellulose (EC), and cellulose acetate (CA), were used. Their ability to reduce silver ions as well as the size of the resulting AgNPs were compared. The formation and stability of the reduced AgNPs in the solution were monitored using UV-Vis analysis. The size, morphology, and charge of the AgNPs were evaluated. We found that, when using cellulosic derivatives, AgNPs with sizes ranging from 17 to 89 nm and different stabilities were obtained. The parameters, such as size and ζ potential indicate the stability of AgNPs, with AgNPs-CA and AgNPs-HPC being considered more stable than AgNPs-EC and AgNPs-MC since they show higher ζ potential values. In addition, the AgNPs showed antimicrobial activity against all reference strains and clinical isolates. MIC values between 0.0312 and 0.125 mM had a bactericidal effect on both Gram-positive and Gram-negative bacteria. The fungicidal effect was obtained at a MIC value of 0.125 mM. These results may provide rational support in the design of medical gauze products, including gauze pads, rolls, and sponges.

Evaluation of Usnea barbata (L.) Weber ex F.H. Wigg Extract in Canola Oil Loaded in Bioadhesive Oral Films for Potential Applications in Oral Cavity Infections and Malignancy

Usnea lichens are known for their beneficial pharmacological effects with potential applications in oral medicine. This study aims to investigate the extract of Usnea barbata (L.) Weber ex F.H. Wigg from the Călimani Mountains in canola oil as an oral pharmaceutical formulation. In the present work, bioadhesive oral films (F-UBO) with U. barbata extract in canola oil (UBO) were formulated, characterized, and evaluated, evidencing their pharmacological potential. The UBO-loaded films were analyzed using standard methods regarding physicochemical and pharmacotechnical characteristics to verify their suitability for topical administration on the oral mucosa. F-UBO suitability confirmation allowed for the investigation of antimicrobial and anticancer potential. The antimicrobial properties against Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27353, Candida albicans ATCC 10231, and Candida parapsilosis ATCC 22019 were evaluated by a resazurin-based 96-well plate microdilution method. The brine shrimp lethality assay (BSL assay) was the animal model cytotoxicity prescreen, followed by flow cytometry analyses on normal blood cells and oral epithelial squamous cell carcinoma CLS-354 cell line, determining cellular apoptosis, caspase-3/7 activity, nuclear condensation and lysosomal activity, oxidative stress, cell cycle, and cell proliferation. The results indicate that a UBO-loaded bioadhesive film’s weight is 63 ± 1.79 mg. It contains 315 µg UBO, has a pH = 6.97 ± 0.01, a disintegration time of 124 ± 3.67 s, and a bioadhesion time of 86 ± 4.12 min, being suitable for topical administration on the oral mucosa. F-UBO showed moderate dose-dependent inhibitory effects on the growth of both bacterial and fungal strains. Moreover, in CLS-354 tumor cells, F-UBO increased oxidative stress, diminished DNA synthesis, and induced cell cycle arrest in G0/G1. All these properties led to considering UBO-loaded bioadhesive oral films as a suitable phytotherapeutic formulation with potential application in oral infections and neoplasia.

Aroma Profile and Biological Effects of Ochradenus arabicus Essential Oils: A Comparative Study of Stem, Flowers, and Leaves

The present analysis explores the chemical constituents and determines the in vitro antimicrobial, antidiabetic, and antioxidant significance of the essential oils (EOs) of the stem, leaves, and flowers of Ochradenus arabicus for the first time. The EOs of the flowers presented seventy-four constituents contributing to 81.46% of the total EOs, with the major compounds being 24-norursa-3,12-diene (13.06%), 24-norursa-3,12-dien-11-one (6.61%), and 24-noroleana-3,12-diene (6.25%). The stem EOs with sixty-one compounds contributed 95.95% of the total oil, whose main bioactive compounds were (+)-camphene (21.50%), eremophilene (5.87%), and δ-selinene (5.03%), while a minimum of fifty-one compounds in the leaves’ EOs (98.75%) were found, with the main constituents being n-hexadecanoic acid (12.32%), octacosane (8.62%), tetradecanoic acid (8.54%), and prehydro fersenyl acetone (7.27%). The antimicrobial activity of the EOs of O. arabicus stem, leaves, and flowers was assessed against two bacterial strains (Escherichia coli and Streptococcus aureus) and two fungal strains (Penicillium simplicissimum and Rhizoctonia solani) via the disc diffusion assay. However, the EOs extracted from the stem were found effective against one bacterial strain, E. coli, and one fungal strain, R. Solani, among the examined microbes in comparison to the standard and negative control. The tested EOs samples of the O. arabicus stem displayed a maximum potential to cure diabetes with an IC50 = 0.40 ± 0.10 µg/mL, followed by leaves and flowers with an IC50 = 0.71 ± 0.11 µg/mL and IC50 = 10.57 ± 0.18 µg/mL, respectively, as compared to the standard acarbose (IC50 = 377.26 ± 1.20 µg/mL). In addition, the EOs of O. arabicus flowers had the highest antioxidant activity (IC50 = 106.40 ± 0.19 µg/mL) as compared to the standard ascorbic acid (IC50 = 73.20 ± 0.17 µg/mL) using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. In the ABTS assay, the EOs of the same sample (flower) depicted the utmost potential to scavenge the free radicals with an IC50 = 178.0 ± 0.14 µg/mL as compared with the ascorbic acid, having an IC50 of 87.34 ± 0.10 µg/mL the using 2,2-Azino-Bis-3-Ethylbenzothiazoline-6-Sulfonic acid (ABTS) assay. The EOs of all parts of O. arabicus have useful bioactive components due to which they present antidiabetic and antioxidant significance. Furthermore, additional investigations are considered necessary to expose the responsible components of the examined biological capabilities, which would be effective in the production of innovative drugs.

Synthesis of mesoporous antimicrobial herbal nanomaterial-carrier for silver nanoparticles and antimicrobial sensing

Herbal nanoparticles (HNPs) were introduced as a novel generation of antimicrobial nanoparticles. But in the battle against superbugs we need nanostructures with boosted antimicrobial potency. So in the current experiment, for the first time a green approach was developed for the silver functionalization of HNPs which were fabricated from an antimicrobial herb Thymus vulgaris. Silver functionalized HNPs (AgHNPs) were found to be mesoporous and were further fortified with antimicrobial compounds. The resulted structures were re-tested against MRSA and P. aeruginosa as superbugs. It was found that silver functionalization can provide eight-fold increase in the antimicrobial potency of HNPs. Moreover, MIC was reduced from 20 mg/mL to 2.5 mg/mL. Another eight-fold reduction in the MIC (0.3 mg/mL) was achieved by fortification with antimicrobial compounds. So, the antimicrobial potency of HNPs was successfully increase approximately up to 64-folds. Obtained results illustrated that silver functionalization and fortification with antimicrobial compounds can be considered as effective approaches to achieve HNPs with boosted antimicrobial potency. These nanostructures have the potency to be loaded with other antimicrobial compound such as antibiotics toward synergistic effects of AgNPs and antibiotics. Resulted nanostructures can be employed in the formulation of powerful topical and surface disinfectants against superbugs. Also, these particles can be considered as a next generation of boosted antimicrobial nanostructures.

The Tagetes lucida Cav. essential oil and the mixture of its main compounds are antibacterial and modulate antibiotic resistance in multi-resistant pathogenic bacteria

We evaluated an essential oil (EO) of Tagetes lucida Cav. and the mixture of its main compounds against multi-drug resistant bacteria. We found that EO and the partially reconstituted blend of its main components have antibacterial activity and inhibit antibiotic resistance (ampicillin, chloramphenicol, nalidixic acid, vancomycin, and imipenem) in strains of Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa HIM-MR01. The T. lucida EO alone or added to the antibiotics showed antimicrobial activity against S. aureus and P. aeruginosa. The EO main bioactive compounds were methyl eugenol (46.15%), estragole (32.93%), linalool (2.48%), and geraniol (0.33%). The mixture (PREO) of those compounds at those proportions inhibited the growth of P. aeruginosa in 45% at 683.62 µg mL^-1 and that of S. aureus in 51.7% at 39.04 µg mL^-1 . The PREO had higher antibacterial and modulatory activities than the original EO. In conclusion, we overcame the unpredictability of EO activity (due to their natural variability) by determining which EO components inhibited bacteria and then producing a PREO to generate a reproducible mixture with predictable antibacterial and modulation of resistance activities. Thus, the PREO, and its components, show potential as alternatives to manage multidrug-resistant pathogens.

Antidiarrheal, antimicrobial, and toxic effects of the aqueous and methanolic leaf and fruit extracts of Cucumis dipsaceus (Ehrenb. Ex Spach.)

Introduction: Cucumis dipsaceus is used to treat diarrhoea, microbial infections, among other diseases across the world; however, there is insufficient empirical data to validate its efficacy, toxicity, and safety. Accordingly, we investigated the antidiarrheal, antimicrobial, and toxic effects of the aqueous and methanolic leaf and fruit extracts of C. dipsaceus.Methods: Antidiarrheal activities of the aqueous and methanolic leaf and fruit extracts of C. dipsaceus were investigated using the castor oil-induced diarrhoea technique in a Wistar rat model. The disk diffusion and broth microdilution methods were adopted to determine the antimicrobial activities of the studied plant extracts. The acute oral toxicity effects of the studied plant extracts were investigated in Wistar rats according to the Organisation for Economic Co-operation and Development (OECD) guidelines.Results: The aqueous and methanolic leaf and fruit extracts of C. dipsaceus significantly (P < 0.05) inhibited diarrhoea in a dose-dependent manner in experimental rats. Besides, the studied extracts significantly (P < 0.05) inhibited the growth of Salmonella enteritidis, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Candida albicans in varying degrees, as depicted by their growth inhibition zones (>6.00 mm) and minimum inhibitory concentrations (MICs <1000 μg/mL). Moreover, the studied extracts did not cause any observable acute oral toxicity effects in the experimental rats across the 14-day experimental period.Conclusion: The aqueous and methanolic leaf and fruit extracts of C. dipsaceus present a potential source of safe and efficacious lead compounds for developing antidiarrheal and antimicrobial therapies.

Antimicrobial Susceptibility Testing: A Comprehensive Review of Currently Used Methods

Antimicrobial resistance (AMR) has emerged as a major threat to public health globally. Accurate and rapid detection of resistance to antimicrobial drugs, and subsequent appropriate antimicrobial treatment, combined with antimicrobial stewardship, are essential for controlling the emergence and spread of AMR. This article reviews common antimicrobial susceptibility testing (AST) methods and relevant issues concerning the advantages and disadvantages of each method. Although accurate, classic technologies used in clinical microbiology to profile antimicrobial susceptibility are time-consuming and relatively expensive. As a result, physicians often prescribe empirical antimicrobial therapies and broad-spectrum antibiotics. Although recently developed AST systems have shown advantages over traditional methods in terms of testing speed and the potential for providing a deeper insight into resistance mechanisms, extensive validation is required to translate these methodologies to clinical practice. With a continuous increase in antimicrobial resistance, additional efforts are needed to develop innovative, rapid, accurate, and portable diagnostic tools for AST. The wide implementation of novel devices would enable the identification of the optimal treatment approaches and the surveillance of antibiotic resistance in health, agriculture, and the environment, allowing monitoring and better tackling the emergence of AMR.

Investigating the Production of Antimicrobial Nanoparticles by Chlorella vulgaris and the Link to Its Loss of Viability

Chlorella vulgaris from Al-Ahsa, KSA was proved to be an active silver and gold nanoparticle producer. Nanogold and nanosilver particles were characterized using UV-visible spectroscopy, Fourier-transform infrared spectroscopy, and scanning electronmicroscopy. Both nanoparticles were used in the antimicrobial bioassay. The two nanoparticles showed antibacterial activities, with the silver nanoparticles being the most effective. To investigate the argumentative nature of their biosynthesis (i.e., whether it is a biotic or abiotic process), we isolated total ribonucleic acid RNA as an indicator of vitality. RNA was completely absent in samples taken after one week of incubation with silver nitrate and even after one or two days. However, successful extraction was only achievable in samples taken after incubation for one and four hours with silver nitrate. Most importantly, the gel image showed recognizable shearing of the nucleic acid after 4 h as compared to the control. An assumption can be drawn that the synthesis of nanoparticles may start biotically by the action of enzyme(s) and abiotically by action of reducing entities. Nonetheless, with prolonged incubation, excessive nanoparticle accumulation can be deadly. Hence, their synthesis continues abiotically. From the RNA banding profile, we suggest that nanosilver production starts both biotically and abiotically in the first few hours of incubation and then continues abiotically. Nanosilver particles proved to have more of an antimicrobial impact than nanogold and hence are recommended for different applications as antibacterial agents.

Bioprospecting for antituberculosis natural products – A review

There has been an increase in the reported cases of tuberculosis, a disease caused by Mycobacterium tuberculosis, which is still currently affecting most of the world’s population, especially in resource-limited countries. The search for novel antitubercular chemotherapeutics from underexplored natural sources is therefore of paramount importance. The renewed interest in studies related to natural products, driven partly by the growing incidence of MDR-TB, has increased the prospects of discovering new antitubercular drug leads. This is because most of the currently available chemotherapeutics such as rifampicin and capreomycin used in the treatment of TB were derived from natural products, which are proven to be an abundant source of novel drugs used to treat many diseases. To meet the global need for novel antibiotics from natural sources, various strategies for high-throughput screening have been designed and implemented. This review highlights the current antitubercular drug discovery strategies from natural sources.

The impact of essential oils on the qualitative properties, release profile, and stimuli-responsiveness of active food packaging nanocomposites

Food industries attempt to introduce a new food packaging by blending essential oils (EOs) into the polymeric matrix as an active packaging, which has great ability to preserve the quality of food and increase its shelf life by releasing active compounds within storage. The main point in designing the active packaging is controlled-release of active substances for their enhanced activity. Biopolymers are functional substances, which suggest structural integrity to sense external stimuli like temperature, pH, or ionic strength. The controlled release of EOs from active packaging and their stimuli-responsive properties can be very important for practical applications of these novel biocomposites. EOs can affect the uniformity of the polymeric matrix and physical and structural characteristics of the composites, such as moisture content, solubility in water, water vapor transmission rate, elongation at break, and tensile strength. To measure the ingredients of EOs and their migration from food packaging, chromatographic methods can be used. A head-space-solid phase micro-extraction coupled to gas chromatography (HS-SPME-GC-MS) technique is as a good process for evaluating the release of Eos. Therefore, the aims of this review were to evaluate the qualitative characteristics, release profile, and stimuli-responsiveness of active and smart food packaging nanocomposites loaded with essential oils and developing such multi-faceted packaging for advanced applications.

Challenges to antimicrobial susceptibility testing of plant-derived polyphenolic compounds

As multidrug resistance gains momentum, the last two decades have seen an ever-growing interest in the antimicrobial properties of plant extracts and plant-derived compounds. Most of the focus is on polyphenols – a large and diverse group of phytochemicals with strong antibacterial activity. Testing methods provide reliable results as long as they follow standard procedures. However, methods and procedures used in antimicrobial susceptibility testing (AST) are often too diverse to allow comparison of results. The lack of uniformity and comparability is much owed to the absence of guidelines. The focus of this review is to give a critical overview of different methods used in the assessment of polyphenols antimicrobial efficacy and to highlight the importance of their standardisation.

Different Responses in Mandarin Cultivars Uncover a Role of Cuticular Waxes in the Resistance to Citrus Canker

'Okitsu' is a mandarin cultivar showing substantial resistance to X. citri subsp. citri (X. citri). We have previously shown that this cultivar has significantly lower canker incidence and severity than 'Clemenules', particularly during early stages of leaf development in the field. This differential response is only seen when the leaves are inoculated by spraying, suggesting that leaf surface contributes to resistance. In this work, we have studied structural and chemical properties of leaf surface barriers of both cultivars. Ultrastructural analysis showed a thicker cuticle covering epidermal surface and guard cells in young 'Okitsu' leaves than in 'Clemenules'. This thicker cuticle was associated with a smaller stomatal aperture and reduced cuticle permeability. These findings correlated with an accumulation of cuticular wax components, including primary alcohols, alkanes, and fatty acids. None of these differences were observed in mature leaves, where both cultivars are equally resistant to the bacterium. Remarkably, mechanical alteration of cuticular thickness of young 'Okitsu' leaves allows canker development. Furthermore, cuticular waxes extracted from young 'Okitsu' leaves have higher antibacterial activity against X. citri than 'Clemenules'. Taken together, these data suggest that a faster development of epicuticular waxes in 'Okitsu' leaves play a central role in its resistance to X. citri.

Pimenta Oil as A Potential Treatment for Acinetobacter Baumannii Wound Infection: In Vitro and In Vivo Bioassays in Relation to Its Chemical Composition

Bacterial biofilm contributes to antibiotic resistance. Developing antibiofilm agents, more favored from natural origin, is a potential method for treatment of highly virulent multidrug resistant (MDR) bacterial strains; The potential of Pimenta dioica and Pimenta racemosa essential oils (E.Os) antibacterial and antibiofilm activities in relation to their chemical composition, in addition to their ability to treat Acinetobacter baumannii wound infection in mice model were investigated; P. dioica leaf E.O at 0.05 µg·mL⁻¹ efficiently inhibited and eradicated biofilm formed by A. baumannii by 85% and 34%, respectively. Both P. diocia and P. racemosa leaf E.Os showed a bactericidal action against A. baumanii within 6h at 2.08 µg·mL⁻¹. In addition, a significant reduction of A. baumannii microbial load in mice wound infection model was found. Furthermore, gas chromatography mass spectrometry analysis revealed qualitative and quantitative differences among P. racemosa and P. dioica leaf and berry E.Os. Monoterpene hydrocarbons, oxygenated monoterpenes, and phenolics were the major detected classes. β-Myrcene, limonene, 1,8-cineole, and eugenol were the most abundant volatiles. While, sesquiterpenes were found as minor components in Pimenta berries E.O; Our finding suggests the potential antimicrobial activity of Pimenta leaf E.O against MDR A. baumannii wound infections and their underlying mechanism and to be further tested clinically as treatment for MDR A. baumannii infections.

Targeting a critical step in fungal hexosamine biosynthesis

Aspergillus fumigatus is a human opportunistic fungal pathogen whose cell wall protects it from the extracellular environment including host defenses. Chitin, an essential component of the fungal cell wall, is synthesized from UDP-GlcNAc produced in the hexosamine biosynthetic pathway. As this pathway is critical for fungal cell wall integrity, the hexosamine biosynthesis enzymes represent potential targets of antifungal drugs. Here, we provide genetic and chemical evidence that glucosamine 6-phosphate N-acetyltransferase (Gna1), a key enzyme in this pathway, is an exploitable antifungal drug target. GNA1 deletion resulted in loss of fungal viability and disruption of the cell wall, phenotypes that could be rescued by exogenous GlcNAc, the product of the Gna1 enzyme. In a murine model of aspergillosis, the Δgna1 mutant strain exhibited attenuated virulence. Using a fragment-based approach, we discovered a small heterocyclic scaffold that binds proximal to the Gna1 active site and can be optimized to a selective submicromolar binder. Taken together, we have provided genetic, structural, and chemical evidence that Gna1 is an antifungal target in A. fumigatus.

Garlic, Onion, and Cinnamon Essential Oil Anti-biofilms' Effect against Listeria monocytogenes

Biofilms represent a serious problem for food industries due to their persistence in processing surfaces, from which they can cause food spoilage or, even worse, lead to foodborne diseases. Microorganisms immersed in biofilms are more resistant to biocides. The search for natural effective alternatives for the prevention and the control of biofilms has increased lately. The aim of this research was to test the antibacterial and the anti-biofilm activities of cinnamon, onion, and garlic essential oils against Listeria monocytogenes. The methodology highlighted first the effect of these essential oils on L. monocytogenes using disc diffusion and minimum inhibitory concentration (MIC) methods and then on initial cell attachment and six hours preformed biofilms. The inhibition of biofilms was assessed by crystal violet assay. Sulfides were the most abundant compounds present in onion and garlic essential oils, while cinnamaldehyde was predominant in cinnamon essential oil. MIC values were of 0.025 mg mL-1 for onion essential oil and 0.100 mg mL-1 for cinnamon and garlic. Onion essential oil inhibited initial cell attachment by 77% at 0.5 of the MIC dose, while at MIC, cinnamon and garlic essential oils inhibited the initial microbial adhesion completely. All three essential oils completely inhibited initial cell attachment when applied at 2 MIC. On the contrary, preformed biofilms were more resistant, and the inhibition rate ranged from 33% to 78%. In summary, this investigation revealed that the essential oils of garlic, onion, and cinnamon show an effective antibiofilm activity against L. monocytogenes and are promising natural antimicrobial alternatives for food processing facilities.

Testing the Antimicrobial Characteristics of Wood Materials: A Review of Methods

Some wood species have antimicrobial properties, making them a better choice over inert surfaces in certain circumstances. However, the organic and porous nature of wood raises questions regarding the use of this material in hygienically important places. Therefore, it is reasonable to investigate the microbial survival and the antimicrobial potential of wood via a variety of methods. Based on the available literature, this review classifies previously used methods into two broad categories: one category tests wood material by direct bacterial contact, and the other tests the action of molecules previously extracted from wood on bacteria and fungi. This article discusses the suitability of these methods to wood materials and exposes knowledge gaps that can be used to guide future research. This information is intended to help the researchers and field experts to select suitable methods for testing the hygienic safety and antimicrobial properties of wood materials.

Headspace gas chromatographic method for antimicrobial screening: Minimum inhibitory concentration determination

The headspace gas chromatographic method has been widely used to detect volatile metabolites to reflect the growth state of microorganisms, however, it has never been used for the determination of the minimum inhibitory concentration in antibacterial drugs. This paper reports a new method for evaluating the antimicrobial activity of drugs by measuring the amount of CO₂ produced by bacterial metabolism after treatment with drugs. According to the amount of CO₂ produced by bacterial metabolism, a proper amount of bacterial liquid is selected and added to a drug-containing culture medium as compared with bacteria without drugs in parallel. The amount of CO₂ produced by bacteria is measured by using a headspace gas chromatograph coupled with a thermal conductivity detector to measure the bacteriostasis rate and the minimum bacteriostasis concentration of the tested drug, so as to evaluate its antibacterial activity. The accuracy of this method was verified by comparison with the standard method (the OD method), which indicated that the precision was less than 3 % (expressed by relative standard deviation), the inhibition rate (R² = 0.968) was consistent with the reference method above. This method is simple in operation and can avoid the error caused by the properties of the sample such as volatility, solubility and color in the determination of the minimum inhibitory concentration. It is suitable for the determination of antibacterial activity of drugs, especially natural drugs.

Encapsulation of cinnamon oil in cyclodextrin nanosponges and their potential use for antimicrobial food packaging

The main goal of this work is the encapsulation of cinnamon essential oil in cyclodextrin nanosponges and the assessment of their antimicrobial activity against foodborne pathogens. After nanosponge synthesis, a headspace-solid phase microextraction coupled to gas chromatography-mass spectrometry (HS-SPME-GC-MS) method was validated to quantify essential oil major compounds. Results showed that essential oil was successfully encapsulated in cyclodextrin nanosponges with α-NS and β-NS being able to encapsulate higher essential oil amounts. Cinnamon essential oil, alone and encapsulated in nanosponges, proved to have antimicrobial activity against foodborne bacteria. Time-kill assays proved that the essential oil, alone or encapsulated, had a bacteriostatic effect against all bacteria tested, with the exception of Y. enterocolitica where a bactericidal action was observed. Furthermore, the controlled release achieved by its encapsulation, allowed cinnamon essential oil to be effective at a much lower concentration in culture medium than when solely dissolved in culture medium. Thus, the results described herein encourage the use of cyclodextrin nanosponges as encapsulating agents for active food packaging applications.

Phytochemical standardization and biological activities of certain desert plants growing in Saudi Arabia

The phytochemical screening, antimicrobial and antitumor activities of Calendula tripterocarpa, Centarea sinaica, Centaurea pseudosinaica, Koelpinia linearis, Plectranthus arabicus, Plectranthus asirensis and Tripleurospermum auriculatum determined. The best antibacterial activity; 41.8 ± 0.23 mm, 39.7 ± 0.25 mm, 35.8 ± 0.58 mm, 34.7 ± 0.51 mm and 32.7 ± 0.25 mm was obtained by Plectranthus arabicus against Klebsiella pneumonia, Tripleurospermum auriculatum against Bacillus subtilis, Centaurea pseudosinaica against Bacillus subtilis, Centaurea pseudosinaica against Stroptococcus pyogenes and Plectranthus arabicus against Staphylococcus epidermidis, respectively. While the highest antifungal activity; 35.9 ± 1.15 mm, 34.6 ± 0.34, 30.6 ± 0.26 mm and 29.9 ± 0.63 mm was obtained by Tripleurospermum auriculatum against Geotricum candidum, Candida albicans, C. tropicalis and Aspergillus fumigatus, respectively. The antitumor activity (IC₅₀) obtained by Centarea sinaica; 3.1 ± 6.9 µg/ml, 14.3 ± 3.1 µg/ml and 22.7 ± 4.1 µg/ml was better than activity of vinblastine sulphate; 5.9 ± 0.4 µg/ml, 59.7 ± 2.1 µg/ml and 30.3 ± 1.4 µg/ml against breast carcinoma (MCF-7), cervical carcinoma (Hela) and colorectal carcinoma (CACO), respectively. Plectranthus arabicus alcoholic extract showed higher antitumor activity; 15.3 ± 5.3 µg/ml, 28.6 ± 3.6 µg/ml and 24.3 ± 4.1 µg/ml than vinblastine; 21.2 ± 0.9 µg/ml, 59.7 ± 2.1 µg/ml and 30.3 ± 1.4 µg/ml against prostate carcinoma (Pc3), cervical carcinoma (Hela) and colorectal carcinoma (CACO), respectively. Also, the antitumor activity of Plectranthus asirensis against cervical carcinoma (Hela) (37.1 ± 2.6 µg/ml) was potent than vinblastine sulphate (59.7 ± 2.1 µg/ml). The obtained results of LD₅₀ and sub-chronic toxicity revealed that the plants have no toxicity.