In Vitro and In Silico Approaches for the Evaluation of Antimicrobial Activity, Time-Kill Kinetics, and Anti-Biofilm Potential of Thymoquinone (2-Methyl-5-propan-2-ylcyclohexa-2,5-diene-1,4-dione) against Selected Human Pathogens

Thymoquinone (2-methyl-5-propan-2-ylcyclohexa-2,5-diene-1,4-dione; TQ), a principal bioactive phytoconstituent of Nigella sativa essential oil, has been reported to have high antimicrobial potential. Thus, the current study evaluated TQ’s antimicrobial potential against a range of selected human pathogens using in vitro assays, including time-kill kinetics and anti-biofilm activity. In silico molecular docking of TQ against several antimicrobial target proteins and a detailed intermolecular interaction analysis was performed, including binding energies and docking feasibility. Of the tested bacteria and fungi, S. epidermidis ATCC 12228 and Candida albicans ATCC 10231 were the most susceptible to TQ, with 50.3 ± 0.3 mm and 21.1 ± 0.1 mm zones of inhibition, respectively. Minimum inhibitory concentration (MIC) values of TQ are in the range of 12.5–50 µg/mL, while minimum biocidal concentration (MBC) values are in the range of 25–100 µg/mL against the tested organisms. Time-kill kinetics of TQ revealed that the killing time for the tested bacteria is in the range of 1–6 h with the MBC of TQ. Anti-biofilm activity results demonstrate that the minimum biofilm inhibitory concentration (MBIC) values of TQ are in the range of 25–50 µg/mL, while the minimum biofilm eradication concentration (MBEC) values are in the range of 25–100 µg/mL, for the tested bacteria. In silico molecular docking studies revealed four preferred antibacterial and antifungal target proteins for TQ: D-alanyl-D-alanine synthetase (Ddl) from Thermus thermophilus, transcriptional regulator qacR from Staphylococcus aureus, N-myristoyltransferase from Candida albicans, and NADPH-dependent D-xylose reductase from Candida tenuis. In contrast, the nitroreductase family protein from Bacillus cereus and spore coat polysaccharide biosynthesis protein from Bacillus subtilis and UDP-N-acetylglucosamine pyrophosphorylase from Aspergillus fumigatus are the least preferred antibacterial and antifungal target proteins for TQ, respectively. Molecular dynamics (MD) simulations revealed that TQ could bind to all four target proteins, with Ddl and NADPH-dependent D-xylose reductase being the most efficient. Our findings corroborate TQ’s high antimicrobial potential, suggesting it may be a promising drug candidate for multi-drug resistant (MDR) pathogens, notably Gram-positive bacteria and Candida albicans.

Chemical Differentiation and Antimicrobial Potential of Four Brassica napus L Seed Oils

The conducted study compares the phytochemical and the antimicrobial potential of four varieties of Brassica napus seed oils. The plant seeds were cultivated during the winter growing season. Soxhlet extractor and Gas Chromatography-Mass Spectrometer (GC-MS) were used for essential oil analysis. The micro broth dilutionassay was applied to test the antimicrobial potential (MIC: Minimum inhibitory concentration, MBC: Minimum bactericidal concentration) of the extracted essential oils against different bacterial strains. A total of 56 phytochemicals were found, including 23 and 25 compounds in the oils of Pactol and Rapifera seed varieties,respectively, and 21 compounds in each of Bacara and Rally seed oils. Oleic acid constituted about 35.79 %, 15.62%, 7%, and 2.41 % for Rally, Bacara, Rapifera, and Pactol seed oils, respectively. Gram-positive bacteria, Streptococcus pyogenes and Streptococcus agalactiae, showed lower resistance potentials (MIC= 0.78%, 3.125%respectively) (MBC=1.36%, 6.25% respectively) to the essential oils compared with Staphylococcus aureus. Escherichia coli showed higher sensitivity (6.25% and 12.5% for MIC and MBC, respectively) than Klebsiella pneumonia and Pseudomonas aeruginosa to the B. napus seed oils. Gram-positive bacteria weremore sensitive to the tested essential oils than Gram-negative bacteria. Overall, four different seed varieties have important chemicals and fatty acids. Oleic acid was the most common carboxylic acid (fatty acid) and 2,4-decadienal with hexanal were the most prevalent aldehydes in four seed oils. Tested B. napus seed essential oilsshowed antimicrobial activities against various Gram-positive and negative bacteria and Candida albicans, with Pactol seed oils exerting the highest activity.

Synthesis, Characterisation and Antimicrobial Potential of Novel N-Alkylated Pyrrole Derivatives of Chitosan

Chitosan, a cationic biopolymer is a major derivative of chitin. It is biocompatible, non-toxic and environ-friendly material and has broad spectrum antimicrobial activity. However, it is less effective in neutral or basic conditions due to its solubility only in acidic medium. Therefore, chemical modification with suitable groups is necessary to enhance the potency of chitosan. The present study was mainly conducted to explore the effect of structural modifications on antimicrobial potential of chitosan. N-Methyl, N-Ethyl and N-Propyl pyrrole were reacted with N-chloroacyl-6-O-triphenylmethylchitosan prepared by stepwise modification of chitosan to form N-Methyl, N-Ethyl and N-Propyl pyrrole derivatives of chitosan. Structural characterization of these pyrrole derivatives was done by IR, NMR, XRD, DSC and Elemental Analysis. The gram-negative bacterium Escherichia coli, gram-positive bacterium Staphylococcus aureus were selected for antibacterial activity and the fungus C. albicans was selected for antifungal activity by agar diffusion method and MIC method. Antimicrobial activity of the N-Methyl, N-Ethyl and N-Propyl pyrrole derivatives on E. coli, S. aureus and C. albicans showed an inhibitory effect on all the organisms. The potency of inhibition was found to be varied with the substitutions. The maximum activity was shown by N-pyrrolylpropylchitosan against E. coli (zone of inhibition 1.2±0.05cm, MIC 0.15±0.03mg/ml), S. aureus (zone of inhibition 1.4±0.03cm, MIC 0.15±0.01mg/ml), C. albicans (zone of inhibition 0.8±0.03cm, MIC 0.2±0.03mg/ml). The study also confirmed that all the three derivatives exhibited higher inhibition than that of chitosan against E. coli (zone of inhibition 0.7±0.03cm, MIC 0.09±0.02mg/ml), S. aureus (zone of inhibition 0.8±0.03cm, MIC 0.09±0.02mg/ml), C. albicans (zone of inhibition 0.6±0.03cm, MIC 0.09±0.03mg/ml). Results demonstrated that these three N-alkylpyrrole chitosan derivatives exhibited improved potency and hence can have the more applicability as antimicrobials.

Essential-Oil-Loaded Nanoemulsion Lipidic-Phase Optimization and Modeling by Response Surface Methodology (RSM): Enhancement of Their Antimicrobial Potential and Bioavailability in Nanoscale Food Delivery System

Nanoencapsulation is an attractive technique used for incorporating essential oils in foods. Thus, our main goal was to formulate a novel nanoemulsion (NE) with nanoscale droplet size and lowest interfacial tension in the oil–water interface, contributing positively to the stability and the enhancement of essential oil potential. Thereby, response surface methodology (RSM), with mixture design was used to optimize the composition of the NE lipid phase. The essential oil combinations were encapsulated through high-pressure homogenization (HPH) with the binary emulsifier system (Tween 80: Gum Arabic). Then, the electrophoretic and physical properties were evaluated. We also conducted a follow-up stability and antimicrobial study that examined the stabilization mechanism of optimal NE. Thereafter, the effect of nanoencapsulation on the essential oil composition was assessed. The RSM results were best fitted into polynomial models with regression coefficient values of more than 0.95. The optimal NE showed a nanometer-sized droplet (270 nm) and lower interfacial tension (~11 mN/m), favoring negative ζ-potential (−15 mV), showing good stability under different conditions—it synergistically enhances the antimicrobial potential. GC-MS analysis showed that the use of HPH affected the active compounds, consistent with the differences in linalool and 2-Caren-10-al content. Hence, the novel nanometric delivery system contributes to food industry fortification.

Phytochemical, In vitro Anti-inflammatory and Antimicrobial Potential of Hugonia mystax L.

Hugonia mystax L., (Linaceae), is commonly distributed in the thorny scrubs and tropical dry evergreen forests of Tamil Nadu, which has been valued for centuries in traditional system of medicine for the treatment of various ailments. In the present study was an attempt to investigate the phytochemical nature and anti-inflammatory, antimicrobial potential by adopting suitable methods. Phytochemical analysis of Hugonia mystax L., plant extracts revealed the presence of various biochemical compounds such as alkaloids, flavonoids, glycosides, triterpenoids and saponins etc. Since triterpenoids and flavonoids have remarkable anti-inflammatory activity, so our present work aims at evaluating in vitro anti inflammatory activity of Hugonia mystax L., by HRBC membrane stabilization method. The inhibition of hypotonicity induced HRBC membrane lysis was taken as a measure of the anti-inflammatory activity. The percentage of membrane stabilization for ethanolic extracts and Diclofenac sodium were done at different concentrations. The maximum membrane stabilization of Hugonia mystax L., extracts was found to be 94.97 % at a dose of 2000 μg/ml. Therefore, our studies support the isolation and the use of active constituents from Hugonia mystax L., in treating inflammations.