Browsing by Author "Lazarova-Zdravkova N."

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    Anti-Coronavirus Activity of Chitosan-Stabilized Liposomal Nanocarriers Loaded with Natural Extracts from Bulgarian Flora
    (2024-09-01) Gyurova A.; Milkova V.; Iliev I.; Lazarova-Zdravkova N.; Rashev V.; Simeonova L.; Vilhelmova-Ilieva N.
    Disease’s severity, mortality rates, and common failures to achieve clinical improvement during the unprecedented COVID-19 pandemic exposed the emergency need for new antiviral therapeutics with higher efficacy and fewer adverse effects. This study explores the potential to encapsulate multi-component plant extracts in liposomes as optimized delivery systems and to verify if they exert inhibitory effects against human seasonal betacoronavirus OC43 (HCoV-OC43) in vitro. The selection of Sambucus nigra, Potentilla reptans, Allium sativum, Aesculus hippocastanum, and Glycyrrhiza glabra L. plant extracts was based on their established pharmacological and antiviral properties. The physicochemical characterization of extract-loaded liposomes was conducted by DLS and electrokinetics. Encapsulated amounts of the extract were evaluated based on the total flavonoid content (TFC) and total polyphenol content (TPC) by colorimetric methods. The BALB 3T3 neutral red uptake (NRU) phototoxicity/cytotoxicity assay was used to estimate compounds’ safety. Photo irritation factors (PIFs) of the liposomes containing extracts were <2 which assigned them as non-phototoxic substances. The antiviral capacities of liposomes containing medicinal plant extracts against HCoV-OC43 were measured by the cytopathic effect inhibition test in susceptible HCT-8 cells. The antiviral activity increased by several times compared to “naked” extracts’ activity reported previously. A. hippocastanum extract showed 16 times higher inhibitory properties reaching a selectivity index (SI) of 58.96. Virucidal and virus-adsorption effects were investigated using the endpoint dilution method and ∆lgs comparison with infected and untreated controls. The results confirmed that nanoparticles do not directly affect the viral surface or cell membrane, but only serve as carriers of the active substances and the observed protection is due solely to the intracellular action of the extracts.
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    Antibacterial activity of microencapsulated via spouted-bed hydro-alcoholic rosemary extracts
    (2020-01-01) Lazarova-Zdravkova N.; Terzieva T.; Peshev D.; Georgieva N.
    In this study the antibacterial activity of microencapsulated rosemary hydro-alcoholic extracts against Escherichia coli K12 was observed. The tested microcapsules were previously produced in five batches varying the type of the inert core and shell material as well as the content of fresh or concentrated rosemary extract. Batch 1 and batch 3 contained equal amount of non-concentrated rosemary extract where batch 2 and batch 4 consisted of the same amount of concentrated rosemary extract. Microcapsules from the last batch 5 were impregnated with three times higher quantity of the non-concentrated rosemary extract than the previous four batches. All five types of microcapsules were tested by the agar diffusion method and showed inhibitory effect against the bacterial strain. The highest antibacterial activity was obtained for batch 5 followed by the samples with concentrated extract (batch 2 and batch 4) and the least inhibitory effect was observed by the microcapsules with non-concentrated extract (batch 1 and batch 3).
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    EFFECT OF STORAGE STABILITY ON THE ANTIMICROBIAL ACTIVITY OF MICROENCAPSULATED VIA SPOUTED-BED ROSEMARY EXTRACTS
    (2020-01-01) Lazarova-Zdravkova N.; Peshev D.; Georgieva N.
    Long-term stability of microencapsulated via spouted-bed rosemary hydro-alcoholic extracts was studied regarding their antibacterial activity. The samples were stored in dark place at 4°C for 10 months. Five batches with variation in the incorporated extracts and composition of the coating agent were tested by means of the agar diffusion method against two model strains, the Gram-negative Escherichia coli K12 and the Gram-positive Bacillus subtilis 356. Inhibitory effect was obtained from all five samples against the Gram-positive bacteria. None of the studied products showed activity against the Gram-negative strain. The most prominent effect against B. subtilis 356 was detected by microcapsules of batch 5 containing the highest amount of fresh rosemary extract, followed by the samples with concentrated extract (batch 2 and 4). The least inhibitory effect was observed by the microcapsules of batch 1 and 3, containing a lower quantity of fresh non-concentrated extract
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    Preparation, Characterization, and Antibacterial Properties of Cu-Fibreboards
    (2023-11-01) Aleksandrov L.; Rangelova N.; Lazarova-Zdravkova N.; Georgieva N.; Dragnevska M.; Nenkova S.
    In the present study, copper modified fibreboards were prepared and their existing phase, morphology, and antibacterial behaviour were investigated. The copper content and the physical and mechanical properties of fibreboards (thickness, bending strength, and swelling) were determined. X-ray diffraction analysis (XRD) showing diffraction peaks typical for cellulose, Cu2S, and Na2SO4, depended on the preparation conditions. The average size of the Cu2S crystals varied between 20 and 50 nm. The morphology of the obtained fibreboards, as well as the size and shape of copper particles, were observed by scanning electron microscopy (SEM) and transition electron microscopy (TEM). The antibacterial activity was tested against Gram-positive (Bacillus subtilis 3562) and Gram-negative (Escherichia coli K12 407) bacteria. The tests showed that the materials had higher antibacterial activity against E. coli, which depended on their preparation conditions. Based on these results, the obtained copper fibreboards can be used as antibacterial agents in the packaging and building industry.