Antimicrobial and Alpha-Amylase Inhibitory Activities of Organic Extracts of Selected Sri Lankan Bryophytes.

Medicinal plants have been the main focus of natural product research. However, recent research has revealed that lower plants including bryophytes are also a major resource of biologically active compounds with novel structures. Sri Lanka is considered as a biodiversity hotspot with a higher degree of endemism flora including bryophytes. In this study, different species of bryophytes were investigated for their antimicrobial and alpha-amylase inhibitory activities. The air-dried plant materials of 6 different bryophyte species, Marchantia sp., Fissidens sp., Plagiochila sp., Sematophyllum demissum, Hypnum cupressiforme, and Calymperes motley, were subjected to sequential cold extraction with 3 different organic solvents. All three types of organic crude extracts were subjected to screening of antimicrobial bioassays using the disc-diffusion method against 3 bacterial strains and 1 fungal strain. According to the results obtained, 6 extracts out of 18 showed antibacterial activity for tested Gram-positive bacteria and 1 active against Gram-negative bacteria. Two extracts showed activity against the pathogenic fungus strain. Extracts from some plants were active against tested bacterial as well as fungal species. TLC-based bioautographic study was carried out to identify the corresponding active bands which is useful for active compound isolation. Furthermore, the ethyl acetate extracts were subjected to evaluate alpha-amylase inhibitory activity where three extracts out of six extracts showed moderate inhibitory activity for alpha-amylase with IC50 ranging 8-30%.

Curcumin loaded zinc oxide nanoparticles for activity-enhanced antibacterial and anticancer applications.

Zinc oxide nanoparticles and curcumin have been shown to be excellent antimicrobial agents and promising anticancer agents, both on their own as well as in combination. Together, they have potential as alternatives/supplements to antibiotics and traditional anticancer drugs. In this study, different morphologies of zinc oxide-grafted curcumin nanocomposites (ZNP-Cs) were synthesized and characterized using SEM, TGA, FTIR, XRD and UV-vis spectrophotometry. Antimicrobial assays were conducted against both Gram negative and Gram-positive bacterial stains. Spherical ZnO-curcumin nanoparticles (SZNP-Cs) and rod-shaped ZnO-curcumin nanoparticles showed the most promising activity against tested bacterial strains. The inhibition zones for these curcumin-loaded ZnO nanocomposites were consistently larger than their bare counterparts or pure curcumin, revealing an additve effect between the ZnO and curcumin components. The potential anticancer activity of the synthesized nanocomposites was studied on the rhabdomyosarcoma RD cell line via MTT assay, while their cytotoxic effects were tested against human embryonic kidney cells using the resazurin assay. SZNP-Cs exhibited the best balance between the two, showing the lowest toxicity against healthy cells and good anticancer activity. The results of this investigation demonstrate that the nanomatrix synthesized can act as an effective, additively-enhanced combination delivery/therapeutic agent, holding promise for anticancer therapy and other biomedical applications.

Drug-Loaded Halloysite Nanotube-Reinforced Electrospun Alginate-Based Nanofibrous Scaffolds with Sustained Antimicrobial Protection.

Halloysite nanotube (HNT)-reinforced alginate-based nanofibrous scaffolds were successfully fabricated by electrospinning to mimic the natural extracellular matrix (ECM) structure which is beneficial for tissue regeneration. An antiseptic drug, cephalexin (CEF)-loaded HNT, was incorporated into the alginate-based matrix to obtain sustained antimicrobial protection and robust mechanical properties, the key criteria for tissue engineering applications. Electron microscopic imaging and drug release studies revealed that CEF had penetrated into the lumen space of the HNT and also deposited on the outer walls, with a total loading capacity of 30 wt %. Moreover, the diameter of alginate-based nanofibers of the scaffolds ranged from 40 to 522 nm with well-aligned HNTs, resulting in superior mechanical properties. For instance, the addition of 5% (w/w) HNT improved the tensile strength (σ) and elastic modulus by 3-fold and 2-fold, respectively, compared to those of the alginate-based scaffolds without HNT. The fabricated scaffolds exhibited remarkable antimicrobial properties against both Gram-negative and Gram-positive bacteria, and the cytotoxicity studies confirmed the nontoxicity of the fabricated scaffolds. Drug release kinetics showed that CEF inside HNTs diffuses within 24 h and that the diffusion of the drug is delayed by 7 days once the CEF-loaded HNTs are incorporated into the alginate-based nanofibers. These fabricated alginate-based electrospun scaffolds with enhanced mechanical properties and sustained antimicrobial protection hold great potential to be used as artificial ECM scaffolds for tissue engineering applications.

Antimicrobial activities of endophytic fungi of the Sri Lankan aquatic plant Nymphaea nouchali and chaetoglobosin A and C, produced by the endophytic fungus Chaetomium globosum.

Twenty distinct endophytic fungi were isolated from the surface-sterilized plant parts of Nymphaea nouchali and were identified using morphological and molecular techniques. At 300 µg/disc concentration, eight of the 20 fungal extracts exhibited antimicrobial activities against Staphylococcus aureus (ATCC 25923) and Bacillus cereus (ATCC 11778) while two within the eight showed activity against Pseudomonas aeruginosa (ATCC 9027) and Escherichia coli (ATCC 35218). Furthermore, investigation of the crude extract of Chaetomium globosum resulted in the isolation of two known cytochalasans, chaetoglobosin A and C, and their structures were elucidated and confirmed by mass and nuclear magnetic resonance (NMR) (1H, 13C, COSY, HSQC, HMBC and tROESY) spectral data. Chaetoglobosin A showed antibacterial activities against Bacillus subtilis (MIC 16 µg mL-1), Staphylococcus aureus (MIC 32 µg mL-1) and methicillin-resistant Staphylococcus aureus (MRSA, MIC 32 µg mL-1). This is the first study to report the isolation, identification and antimicrobial properties of endophytic fungi of N. nouchali in Sri Lanka.