Browsing by Author "Georgieva N."
Now showing 1 - 20 of 40
Results Per Page
Sort Options
Item ANTIBACTERIAL ACTIVITY AND STRUCTURE OF SOL-GEL BASED SiO2/HPC/Zn NANOCOMPOSITES(2020-01-01) Angelova T.; Rangelova N.; Aleksandrov L.; Georgieva N.The present paper reports an investigation of the antibacterial activity of sol-gel derived silica/hydroxypropyl cellulose zinc doped nanocomposites. The thermal analysis shows that the crosslinking between cellulose ether and zinc ions is more thermally stable than the crosslinking of the precursors in the matrix. The optical investigation and the transmission electron microscopy (TEM) observation verify the existence of nano-dimentional zinc particles. The antibacterial properties of the composites are investigated by measuring the inhibition zones formed around the materials of a different zinc content in presence of reference strains of Gram-positive bacteria - Bacillus subtilis 3562 and Gram-negative bacteria - Escherichia coli K12 and by calculating the growth decrease percentage.Item 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).Item Antibacterial activity of SiO 2/hydroxypropyl cellulose hybrid materials containing silver nanoparticles(2012-07-01) Angelova T.; Rangelova N.; Yuryev R.; Georgieva N.; Müller R.Silica hybrid materials containing tetraethyl orthosilicate (TEOS) as SiO 2 precursor, hydroxypropyl cellulose (HPC) as an organic compound with incorporation of silver were prepared, and their structure and surface morphology were examined by FTIR measurements and SEM. The quantity of organic substance was 5 wt.% and the silver concentration varied from 0.5 to 2.5 wt.%. It is suggested that the main structural units build an amorphous network of synthesized hybrids from depolymerized [SiO 4] tetrahedra giving strong bands at 1050 and 790 cm - 1. The surface morphology changed from smooth to rough with the increasing amount of silver. The possible antibacterial behavior of the hybrid materials was also studied. The results indicate pronounced antibacterial performance against Escherichia coli and Bacillus subtilis. Highest antibacterial activity was detected against B. subtilis. The increase of silver concentration up to 2.5 wt.% Ag leads to stronger antibacterial effects with both strains. © 2012 Elsevier B.V. All rights reserved.Item Antifungal effect of SiO2/cellulose ethers/Ag hybrid nanomaterials on the growth of Penicillium chrysogenum 2303(2016-01-01) Angelova T.; Mohamed R.A.A.E.; Rangelova N.; Georgieva N.Three types of silica hybrid nanomaterials, doped with silver, were studied for their antifungal effect against fungi Penicillium chrysogenum strain 2303. The hybrid nanomaterials based on SiO2 and cellulose ethers - hydroxypropyl cellulose, hydroxypropylmethyl cellulose and carboxymethyl cellulose, and silver were prepared by sol-gel method. The antifungal effect was quantified against P. chrysogenum 2303 based on the inhibition zone measurement by the agar diffusion test. The results showed that the hybrid nanomaterials containing hydroxypropylmethyl cellulose, doped with the highest silver concentration of 2.5 mass % Ag, have the most prominent antifungal effect towards the fungi in comparison to the other nanomaterials.Item Antimicrobial activity of (KLAKLAK)–NH2 analogs against pathogenic microbial strains(2024-01-01) Jaber S.; Evstatieva Y.; Nemska V.; Nikolova D.; Naydenova E.; Georgieva N.; Danalev D.Many microorganisms pose a threat to human health due to the ever-increasing bacterial resistance to conventional drugs. Nowadays, searching for new alternatives to conventional antibiotics to fight bacterial resistance is a main task. Thus, natural molecules such as amino acids and peptides arise as possible solutions to the problem. The antimicrobial activity of targeted compounds was studied by the agar-diffusion method, using the prepared working solutions of the targeted peptides with the corresponding concentrations. The results of the antimicrobial activity against different test pathogens show specificity, as antimicrobial activity against the used test microorganisms was not found in the investigated short-chain synthetic peptides Si6, Si3 and Si13. Antimicrobial activity against Bacillus cereus, Staphylococcus aureus, Staphylococcus epidermidis, Propionibacterium acnes, Escherichia coli, Pseudomonas aeruginosa, and the yeasts Malassezia furfur and Candida albicans was established for the long-chain synthetic peptides Si1, Si5 and Si16, except Si5 which does not show activity against pathogenic fungal strain C. albicans. The compound Si16 where natural Leu in (KLAKLAK)2-NH2 is replaced by unnatural Nle is the best candidate for medical drug due to the combined antibacterial and antiproliferative effect as well as long hydrolytic stability.Item ANTIMICROBIAL ACTIVITY OF AMINO ACID DERIVATIVES OF MEMANTINE(2022-01-01) Tencheva A.; Stankova I.; Angelova T.; Nemska V.; Georgieva N.; Danalev D.Memantine is adamantane derivative used in medicinal practice. It is well-proven inhibitors of the M2 ion channel of influenza virus. In addition, it is applied for treatment of patients with Alzheimer’s disease. Herein, we report the antimicrobial activity of specifically designed memantine derivatives containing spatially compact (Gly, Ala, β-Ala) and bulky (Val and Phe) amino acids. New compounds were synthesized in a solution using 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethylaminium tetrafluoroborate (TBTU) as a coupling agent. All derivatives were obtained with good yields. Newly synthesized molecules at concentration 100 mM were tested for their antimicrobial activity using model strains of Gram-positive (Bacillus subtilis NBIMCC 3562), Gram-negative (Escherichia coli NBIMCC K12 407) microorganisms and fungal strain Candida albicans NBIMCC 74. The active compounds against model G+ microorganism are Val-MEM followed by Ala-MEM and Gly-MEM. All compounds show good activity against model G-microorganism. Introducing of bulky amino acid Phe, containing aromatic core, and Val, containing aliphatic core, leads to good antifungal activityItem Antimicrobial activity of SiO2/cellulose ethers/Ag hybrid materials against Saccharomyces cerevisiae 537(2016-01-01) Angelova T.; Georgieva N.; Müller R.The antimicrobial effect against Saccharomyces cerevisiae 537 of silica hybrid materials based on tetraethylorthosilicate, cellulose derivates (hydroxypropyl cellulose and hydroxypropyl methyl cellulose) and silver was investigated. The silver concentration in the hybrid materials varied from 0.5 wt % to 2.5 wt %. The antimicrobial effect was quantified on ground of the inhibition zone measurement and determination of the growth of the synthesized hybrid materials inhibitory effect. The results showed 80 % and 92 % decrease of cell growth by hydroxypropyl cellulose hybrid materials and hydroxypropyl methyl cellulose, respectively, in presence of the highest silver concentration of 2.5 wt %. The lowest silver concentration of 0.5 wt % Ag had no effect on the tested strain viability as the cells observed were not inactivated.Item ANTIMICROBIAL PROFILE OF EXTRACTS FROM THE FUNGUS SPECIES LEPISTA PERSONATA(2023-01-01) Nemska V.; Yaneva S.; Georgieva N.; Danalev D.Nowadays, mushrooms are widely studied due to the various bioactive substances they produce. They define their antibacterial, antifungal, antioxidant, antitumor, cytostatic and anti-inflammatory properties which are beneficial for human health. This study aimed to determine the antimicrobial activity of different (hot and cold ethanol/ dichloromethane/ hexane) extracts from the fungus species Lepista personata against two test microorganisms: Escherichia coli NBIMCC K12 407 and Bacillus subtilis NBIMCC 3562. The antimicrobial assays were performed applying the classical disc diffusion method. The sensitivity of test microorganisms was determined according to the zone of inhibition which appeared around the discs after 24 h of incubation at 30°C - 37°C. All extracts were dissolved in 200 mM dimethyl sulfoxide, which was used as a control sample. Results showed that E. coli NBIMCC K12 407 is susceptible to dimethyl sulfoxide whereas B. subtilis NBIMCC 3562 showed no growth inhibition. All mushroom extracts also showed no inhibitory activity against B. subtilis NBIMCC 3562. At the same time, only the dichloromethane extract obtained after hot extraction inhibited the growth of E. coli NBIMCC K12 407.Item ANTIMICROBIAL PROPERTIES OF SILICA/HYDROXYPROPYLCELLULOSE HYBRIDS DOPED WITH COPPER IONS(2022-01-01) Foteva T.; Georgieva N.The subject of intense research is the creation of innovative materials with antimicrobial effect, which would find potential application in various fields such as food industry, pharmacy, medicine, agriculture, wastewater treatment. In the present study silica/hydroxypropylcellulose hybrids doped with copper ions from Cu(NO3)2 × 3H2O were obtained using sol-gel technique. The copper concentration in the hybrids varied from 0.5 wt. % to 5 wt. %. The antimicrobial potential of materials was investigated using reference strains for Gram-positive bacteria (Bacillus subtilis NBIMCC 3562), Gram-negative bacteria (Escherichia coli K12 NBIMCC 407) and yeast (Candida albicans NBIMCC 74). The experiments were based on the measurement of formed inhibition zones by agar well diffusion test and determination of cells growth in presence of studied materials.Item BIOCOMPATIBILITY AND ANTIFUNGAL ACTIVITY OF SILVER DOPED SiO2/PECTIN COMPOSITE MATERIALS(2021-01-01) Angelova T.; Uzunova V.; Rangelova N.; Georgieva N.; Momchilova A.; Tzoneva R.The purpose of the study was to evaluate the biocompatibility and antifungal activity of silver doped SiO2/citrus pectin composite materials. The effect of the amount of silver content (0 - 2.5 wt. %) on biocompatibility using L929 fibroblast cells and antifungal activity against Candida albicans 74 was observed. It was established that composites containing 0.5 wt. % and 1 wt. % Ag exhibited biocompatibility as well as revealed low cytotoxicity, good cell adhesion and spreading and luck of apoptosis. The antifungal activity of the composites demonstrated that the size of formed inhibition zones depends on the amount of silver in the materials. Based on the obtained results, silver doped SiO2/ pectin composite materials were proven to be efficient for use as in vivo implants in tissue engineering applications.Item Cytotoxicity and antibiofilm activity of SiO2/cellulose derivative hybrid materials containing silver nanoparticles(2016-01-01) Angelova T.; Rangelova N.; Uzunova V.; Georgieva N.; Andreeva T.; Momchilova A.; Tzoneva R.; Müller R.Hybrid materials based on tetraethyl orthosilicate (TEOS), hydroxypropyl cellulose (HPC), or hydroxypropyl methyl cellulose (HPMC) with silver nanoparticles were synthesized. They were analyzed and characterized using differential thermal analysis and thermogravimetry, atomic force microscopy, and static contact angle measurements. It was experimentally demonstrated that the silverdoped hybrid materials have pronounced antibacterial behavior by studying the reduction of Pseudomonas aeruginosa PAO1 biofilm formation on the tested materials. The results revealed biofilm reduction of 35.7% and 30% by SiO2/HPC/2.5% Ag and SiO2/HPMC/2.5% Ag hybrid materials, respectively, compared to the control. Cytotoxicity of examined materials and actin cytoskeleton organization of fibroblasts seeded on the materials was studied as a function of material properties as the type of surface functional groups and silver content. The obtained hybrid materials with low silver content proved efficient in tissue engineering applications since they showed good antibacterial and noncytotoxic properties for eukaryotic cells.Item CYTOTOXICITY OF COPPER DOPED SiO2-HYDROXYPROPYL CELLULOSE COMPOSITES ON CANCER AND NON-CANCEROUS CELLS(2023-01-01) Foteva T.; Vukova T.; Rangelova N.; Georgieva N.; Tzoneva R.In the present paper the cytotoxicity of series of sol-gel based copper doped SiO2/HPC composites on lung cancer cell line (A549) and primary human umbilical cord endothelial cells (HUVEC) was investigated. Hydroxypropyl cellulose (HPC), tetraethyl ortosilicate (TEOS) were used for preparation of amorphous matrix in which the copper was added as Cu(NO3)2*3H2O or CuSO4*5H2O in concentration range of 0 - 5 wt. %. We observed that the composite materials at low concentration of Cu (0.5 wt. %) showed no toxic effects on both cell types. The composite material with CuSO4*5H2O was found relatively more toxic, and furthermore, cancer cells are more sensitive to the copper concentration increase to non-cancer cells. The concentration of Cu ions of 2.5 and 5 wt. % were toxic to both cancer and non-cancer cells at 24th hour. At 72th hour of incubation some restoration of cell viability was observedItem Development and validation of HPLC-DAD methodology for simultaneous qualitative and quantitative determination of thirteen substances with a steroid structure(2023-01-01) Zaharieva Z.; Atanasova S.; Danalev D.; Jaber S.; Foteva T.; Nemska V.; Tanev D.; Georgieva N.Using supplements in different sports is a common practice for many athletes. Unfortunately, the growth of this market has entailed some speculations, such as the addition of excessive doses of potentially toxic ingredients. Sometimes the doses listed on the package do not correspond to the real content. Some nutritional supplements on sale may contain undeclared ingredients. Some of those supplements are prohibited substances according to different regulations. Herein, a simple HPLC/DAD procedure that is easy to apply in conventional laboratory practice was developed for the simultaneous determination of 13 substances with steroid structure in nutritional supplements for sport: testosterone, testosterone propionate, testosterone enanthate, methyltestosterone, nandrolone, nandrolone propionate, nandrolone decanoate, methandienone, androstenedione, trenbolone, trenbolone acetate, trenbolone enanthate and boldenone undecylenate. The methodology includes gradient elution with mobile phase A: MeOH:ddH2O (55:45) and mobile phase B: 100% MeOH in a standard HPLC system containing a Halo 90 Å, C18 (150 x 4.6 mm, 2.7 µm) column, flow rate 0.6 mL/min, UV wavelength of 254 nm, temperature of 40 °C and 20 μL injection volume. The developed methodology was validated according to the corresponding official documents. The key parameters used for the selection of the optimal HPLC conditions were the ability of the mobile phase and solvents to be used with both an HPLC/MS and a GC/MS chromatographic system. The obtained total run time, the reproducibility of the retention times, the separation of all peaks and peak characteristics meet all requirements.Item Drug mass transfer mechanism, thermodynamics, and in vitro release kinetics of antioxidant-encapsulated zeolite microparticles as a drug carrier system(2018-10-01) Yaneva Z.; Georgieva N.; Bekirska L.; Lavrova S.The aim of the present study was to develop a new vitamin E-zeolite drug carrier system, and investigate the mass transfer mechanism of the antioxidant encapsulation and release on/from the mineral matrix by thermodynamic and kinetics sorption/desorption experiments and mathematical modelling of the experimental data. The surface, morphological and spectral characteristics of the vitamin and the zeolite were determined by Boehm titration, SEM, FTIR and UV/Vis spectrophotometric analyses. Intraparticle diffusion was not the only rate-limiting mechanism, as the mixed-order kinetics model gave the highest regression coefficient (R2) and lowest SSE, MSE, RMSE, and AICC values. The thermodynamic study confirmed the endothermic nature of the spontaneous encapsulation process and increased degrees of randomness at the solid-liquid interface. The in vitro release results were best modelled by the zero-order and sigmoidal models. The results obtained are essential for the development of innovative vitamin E-carrier systems for application in human and veterinary medicine.Item Effect of B2O3 on the Structure, Properties and Antibacterial Abilities of Sol-Gel-Derived TiO2/TeO2/B2O3 Powders(2023-10-01) Bachvarova-Nedelcheva A.; Iordanova R.; Stoyanova A.; Georgieva N.; Nemska V.; Foteva T.This paper studies the influence of B2O3 on the structure, properties and antibacterial abilities of sol-gel-derived TiO2/TeO2/B2O3 powders. Titanium(IV) butoxide, telluric(VI) acid and boric acid were used as precursors. Differences were observed in the degree of decomposition of Ti butoxide in the presence of H3BO3 and H6TeO6 acids. The phase transformations of the obtained gels in the temperature range of 200–700 °C were investigated by XRD. Composite materials containing an amorphous phase and different crystalline phases (metallic Te, α-TeO2, anatase, rutile and TiTe3O8) were prepared. Heating at 400 °C indicated a crystalline-to-amorphous-phase ratio of approximately 3:1. The scanning electron microscopy (SEM) analysis showed the preparation of plate-like TiO2 nanoparticles. The IR results showed that the short-range order of the amorphous phases that are part of the composite materials consists of TiO6, BO3, BO4 and TeO4 structural units. Free B2O3 was not detected in the investigated compositions which could be related to the better connectivity between the building units as compared to binary TiO2/B2O3 compositions. The UV-Vis spectra of the investigated gels exhibited a red shift of the cut-off due to the presence of boron and tellurium units. The binary sample achieved the maximum photodegradation efficiency (94%) toward Malachite green dye under UV irradiation, whereas the ternary sample photoactivity was very low. The compositions exhibited promising antibacterial activity against E. coli NBIMCC K12 407.Item 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 extractItem Enzyme profile of lactobacilli from traditional Bulgarian fermented milk products(2019-01-01) Nemska V.; Danova S.; Georgieva N.In recent years, scientific community has focused the attention on the non-starter lactic acid microbiota of home-made dairy products as a source of new candidate-probiotic strains. Lactic acid bacteria (LAB) and in particular Lactobacillus spp. play a major role in acquiring the specific taste and aroma of the final product during the fermentation. For this purpose, 43 Lactobacillus strains, isolated from traditional Bulgarian katak, curd, yoghurt, white-brined and yellow cheese, were subjected to screening of their enzyme capacity. Twenty-five of the strains were pre-selected for determination of their enzyme profile by API ZYM system. It was established that most of the strains showed high leucine and valine arylamidase, β-galactosidase and α-glucosidase activity. Only a few strains showed N-acetyl-β-glucosaminidase, α-galactosidase, β-glucosidase and Naphtol-AS-BI-phospho-hydrolase activity. Alkaline phosphatase, trypsin, α-chymotrypsin, α-mannosidase, lipase (except L. lactis OC2), β-glucuronidase (except L. salicinus KC2) and α-fucosidase (except L. plantarum BS41 and L. lactis OC2) activity were not observed. In order to complete the obtained results, two qualitative tests for determination of the β-galactosidase and proteolytic activity of more than 30 Lactobacillus strains were also applied. Most of the investigated lactobacilli showed moderate proteolytic activity. According to their β-galactosidase activity, 34 % could be defined as active lactose fermenters, 23 %-as late lactose fermenters and 43 %-could not ferment lactose. The investigated Lactobacillus strains showed strain-specific enzyme capacity.Item Functional characteristics of lactobacilli from traditional bulgarian fermented milk products(2019-01-01) Nemska V.; Logar P.; Rasheva T.; Sholeva Z.; Georgieva N.; Danova S.After oral administration, probiotic lactobacilli meet a number of protection systems in the human body, such as exposure to gastric, pancreatic, and small intestinal juices. Overcoming these detrimental barriers allows living bacteria to adhere to the intestinal epithelium and permanently colonize the gastrointestinal tract (GIT), providing health benefits to the host. Based on this, the transit tolerance of 25 candidate probiotic lactobacilli from katak, yoghurt, and white-brined and yellow cheese to simulated bile and small intestinal juices of variable pH was investigated. To establish their resistance, in vitro model systems based on modified MRS media and a longer duration of action (up to 24 h of incubation) were designed. Six of the strains studied were found to show strain-specific survival capacity with low viability in conditions simulating stomach acidity and high resistance to bile and intestinal juices. In addition, the adherence capability (autoaggregation and hydrophobicity) of the strains was determined. Obtained results allowed to select Lactobacillus strains with high survival ratios while passing through the GIT and good adherence properties, which make them suitable for the development of new probiotics.Item Immobilization of trichosporon cutaneum R57 on PVA/TEOS/ MPTEOS hybrid matrices for removal of manganese ions(2013-10-17) Georgieva N.; Bryaskova R.; Lazarova N.; Racheva R.New hybrid materials based on polyvinyl alcohol (PVA), 3-mercaptopropyltriethoxysilane (MPTEOS) and tetraethoxysilane (TEOS) were prepared, using a sol-gel process. Thermogravimetric analysis (TGA) was performed to determine the thermal stability of the hybrid materials. MPTEOS, as a precursor, ensured the presence of SH-groups, thus providing additional binding places for cell immobilization. Based on good adhesive behavior, the hybrid materials were tested as matrices for immobilization of Trichosporon cutaneum R57 for removal of manganese ions from aqueous solutions. Maximum Mn2+ removal was achieved by cells immobilized onto materials with higher MPTEOS concentration. The synthesized PVA/TEOS/MPTEOS hybrid materials proved to be efficient for use in biosorption applications. © Biotechnol. & Biotechnol. Eq.Item IN VITRO ASSESSMENT OF LACTOBACILLUS SPP. TO GROW IN THE PRESENCE OF DIFFERENT CARBON SOURCES IN THE MEDIUM(2022-01-01) Nemska V.; Danova S.; Georgieva N.The selection of suitable media plays a central role in attempts to improve the production of biomass from lactobacilli and the yield of products during fermentation. For this purpose, the growth capacity of 41 candidate probiotic lactobacilli from katak, yoghurt and white-brined and yellow cheese in the presence of different carbon sources in the medium was investigated. To access their abilities, in vitro model systems based on modified MRS broth, containing different carbon sources (2 % and 5 % (w/v) lactose or 2 % (w/v) glucose, prebiotics (inulin, galactooligosaccharides, glucooligosaccharides and fructooligosaccharides) and 30 % (w/v) sucrose) were designed. It was established that Lactiplantibacillus plantarum S8 and S10 had the highest growth rate in modified MRS with 2 % (w/v) glucose, whereas Lactobacillus delbrueckii subsp. bulgaricus Ro34 showed the highest growth rate in modified MRS broth with 5 % (w/v) lactose. In the presence of modified MRS, containing 20 % (w/v) prebiotics, most Lactobacillus strains showed complete utilisation towards galactooligosaccharides, followed by inulin, fructooligosaccharides and glucooligosaccharides. Seventy-three per cent of strains could grow in the presence of 30 % (w/v) sucrose in the medium and were determined as possible exopolysaccharide producers. In addition, the biofilm-formation capacity of the lactobacilli, cultivated in these media, was tested. Lactiplantibacillus plantarum OC1 and BS32 demonstrated good biofilm-formation in the presence of galactooligosaccharides, whereas Ligilactobacillus salivarius subsp. salicinus KC2 formed stable biofilms in the presence of galactooligosaccharides and fructooligosaccharides.