Iva Tsvetkova

Antimicrobial resistance (AMR) is one of the major threats to human health and is becoming an environmental challenge for water resources too. Our study’s aim was: to assess the AMR of heterotrophic bacteria in drinking water-associated biofilms against six clinically important antibiotics; to compare the prevalence of antibiotic resistant bacteria...

Antimicrobial resistance (AMR) is a worldwide health problem affecting humans, animals, and the environment within the framework of the “One Health” concept. The aim of our study was to evaluate the prevalence of pathogenic strains of the species Escherichia coli (E. coli), their AMR profile, and biofilm-forming potential. The isolated strains from...

The publication examines the properties of the electrochemically activated waters catholyte and anolyte with Electrolyzer device. It is accepted that the acid-alkaline nature of water in the human body has a pH of 7.0. When the pH is above 7.0, the water is alkaline. When the pH is less than 7.0, the water is acidic. The water Catholyte has using w...

In the recent years, electrochemically activated water (ECAW) is considered as an alternative disinfectant used for the decontamination of objects of clinical practice and the environment. Low percentage of aqueous solution of sodium chloride and an electrolytic cell was used for its preparation. The main advantages of ECAW than traditional disinfe...

Finding new green solvents for extraction of bioactive natural compounds is among the first areas of research in green chemistry. Recently, a new kind of "green" solvents, the natural deep eutectic solvents (NADESs), was developed. In a particular combination and ratio natural compounds in solid state (primary metabolites) may generate a eutectic m...

Two new δ-tocotrienol derivatives with oxidized terminal chain: 5,6-dioxo-garcinoic acid (trans-13′-carboxy-5,6-dioxo-δ-tocotrienol) (2) and 5-hydroxy-8b-oxo garcinoic acid (trans-13′-carboxy-5-hydroxy-8b-oxo-δ-tocotrienol) (3), together with one known derivative garcinoic acid (trans-13′-carboxy-δ-tocotrienol) (1) were isolated from a Colombian pr...

In the light of the emerging bacterial resistance to broad-spectrum antibiotics, the search for new antibacterial therapeutics and drug combinations is one of the most challenging topics nowadays. In the present study, we investigated for the first time the antibacterial and biofilm inhibitory effects of the third generation anticancer alkylphospho...

It is reported for first time, that silver modified nanoporous MCM-41 or SBA-15 silicas are promising carriers for the preparation of poplar propolis loaded dermal formulations. MCM-41 or SBA-15 were successfully modified with 5–15 nm sized silver nanoparticles by direct or post synthesis methods. The formed silver nanoparticles are stabilized in t...

Many Geum species are known to be rich in biologically active compounds and therefore could be a source of new natural products with pharmacological potential. The medicinal plant Geum urbanum L. is widespread in Bulgaria and has been used in folk medicine. In the present study, the methanol extracts of the roots and aerial parts of G. urbanum and...

Propolis (bee glue) is a resinous honeybee product having a long history of application in many countries as a traditional remedy for treating wounds, burns, soar throat, stomach disorders, etc. It has been proved to possess beneficial biological effects, including antimicrobial, antioxidant, anti-inflammatory, cytotoxic, antiulcer, and many others...

In vitro activity of nine cyanobacterial and ten microalgal newly isolated or culture collection strains against eight significant food‐borne pathogens has been evaluated and compared. Water extracts and culture liquids of Gloeocapsa sp. and Synechocystis sp. demonstrated the widest spectrum of activity with minimal inhibitory concentration (MIC) r...

From a biologically active extract of Indonesian propolis from East Java, 11 compounds were isolated and identified: four alk(en)ylresorcinols (obtained as an inseparable mixture) (1-4) were isolated for the first time from propolis, along with four prenylflavanones (6-9) and three cycloartane-type triterpenes (5, 10 and 11). The structures of the...

From propolis samples from Kenya, two new arylnaphtalene lignans were isolated, tetrahydrojusticidin B 1 and 6-methoxydiphyllin 2, along with four known phenolic compounds 5-8, found for the first time in propolis. The structures of the compounds were elucidated based on their spectral properties. The geranylstilbenes 7 and 8 demonstrated antibacte...

Seventeen Maltese propolis samples were studied by GC-MS after silylation. They exhibited the typical Mediterranean chemical profile, rich in diterpene compounds (18-92% of TIC, GC-MS): 32 individual diterpenes were identified; 22 of them were present in each specimen. The other abundant compound group was that of sugars and sugar derivatives. In s...

The chemical composition of fresh flowers from Allium ursinum (ramsons, bear's garlic, wild garlic) growing in Bulgaria has been studied. Thymidine (1), adenosine (2), astragalin (kaempferol-3-O-beta-D-glucopyranoside (3), kaempferol-3-O-beta-D-glucopyranosyl-7-O-beta-D-glucopyranoside (4), kaempferol-3-O-beta-D-neohesperoside (5), and kaempferol-3...

From a biologically active extract from the fungus Fomitopsis rosea, two new lanostane triterpenes were isolated, 3alpha-(3'-butylcarboxyacetoxy)oxepanoquercinic acid C 1 and 3alpha-hydroxy-24-methylene-23-oxolanost-8-en-26-carboxylic acid 2, along with three known triterpenes, 3-5, and the epidioxy sterol derivative 6. The structures of the compou...

Chloroform extracts, n-butanol extracts, water extracts, and volatile compounds from seven species belonging to six Black Sea genera of brown algae and 10 species belonging to seven Black Sea genera of red algae were assessed for antibacterial, antiviral, and cytotoxic prop-erties. Most of the extracts showed pronounced effects against the Gram (q)...

Four groups of metabolites from the halophyte plant Stachys maritima Gouan, family Lamiaceae, were investigated: lipids, sterols, volatiles and polar compounds. Most of the metabolites have been previously reported to possess biological activity. Two of the main substances in the volatile fraction--phenidone and naphthalene, unusual for plants--wer...

The antibacterial activity of the medium chain fatty acids and their 1-monoglycerides was evaluated towards several Gram-positive strains belonging to the genera Staphylococcus, Corynebacterium, Bacillus, Listeria and Streptococcus. The 1-monoglycerides were more active than the fatty acids with monolaurin being the most active compound. Interestin...

A large series of chalcones were synthesized and studied against Staphylococcus aureus and Escherichia coli. Chalcones were either unsubstituted in ring A or possessed 4'-chloro or 3',4',5'-trimethoxy groups. Their other ring B was variously substituted. It was found that the anti-staphylococcal activity of chalcones was related to the energy diffe...

Hexane extracts of wild Sideritis scardica Griesb. and of cultivated hybrid S. scardica x S. syriaca were analyzed by (GC-MS and tested for antimicrobial activity. Main components of all the extracts were diterpenes and n-alkanes. Cultivated and wild plant extracts demonstrated significant activity against S. aureus. The results demonstrate the pos...

The antibacterial activity of synthetic aliphatic and aromatic monoacylglycerols (MAGs) was studied against two human pathogens: Staphylococcus aureus and Escherichia coli. The active compounds inhibited selectively S. aureus. The most active compounds amongst them were those with medium size aliphatic chain and aromatic MAGs with electron withdraw...

A novel bacterial strain of Virgibacillus marismoftui was isolated from Lake Pomorie in Bulgaria and characterized by partial sequencing of its 16S rDNA which showed a similarity of 99.6% to this species. The analysis of the cellular fatty acids also showed good correspondence to the profile of the genus Bacillus and related genera. As expected fro...

Validated spectrophotometric procedures were used to quantify three main groups of bioactive substances (phenolics, flavones/flavonols, flavanones/dihydroflavonols) in 114 samples of poplar-type propolis from different geographic origins. From the results, we characterized raw poplar propolis in terms of minimum content of its bioactive components...

A large series of chalcones were synthesized and studied for activity against Candida albicans. The SAR analysis showed that the antifungal activity was highly dependent on the substitution pattern of the aryl rings and correlated to a large extent with the ability of compounds to interact with sulfhydryl groups. The most active were the hydroxylat...

In a new propolis type, red Brazilian propolis, 14 compounds were identified (six of them new for propolis), among them simple phenolics, triterepenoids, isoflavonoids, prenylated benzophenones and a naphthoquinone epoxide (isolated for the first time from a natural source). Three of the major components demonstrated significant antimicrobial activ...

Polar and unpolar extracts from 18 species of the most widespread Bulgarian higher Basidiomycetes were tested for their activity against Staphylococcus aureus, Escherichia coli, and Candida albicans. Most of the studied extracts demonstrated activity against S. aureus but all were inactive against the Gram-negative E. coli and C. albicans. In gener...

The methanol, petroleum ether, ethyl acetate and water-methanol extracts of Ruta graveolens were found to possess antimicrobial and cytotoxic activities.

The chemical composition of the brackish water green alga Cladophora rivularis was investigated. Seven sterols were identified and the stereochemistry of the most com-mon forms was established. Thirty-eight and 21 com-pounds were identified in the volatile and polar fractions, respectively. The main lipid classes were isolated and their fatty acid...

Two new polyisoprenylated benzophenones, 18-ethyloxy-17-hydroxy-17,18-dihydroscrobiculatone A and 18-ethyloxy-17-hydroxy-17,18-dihydroscrobiculatone B, together with the known scrobiculatones A and B, were isolated from Venezuelan propolis. The scrobiculatones A and B showed significant antibacterial activity and moderate toxicity to Artemia salina...

Fourteen aromatic and 24 aliphatic acids were determined by GC-MS analysis of acidic fractions obtained from Paeonia peregrina and Paeonia tenuifolia roots. Benzoic acid and its monohydroxy-, dihydroxy- and trihydroxy-derivatives are the main acid components of both Paeonia species. Some fractions could serve as a source of benzoic, 4-hydroxybenzoi...

Two diterpene glycosides, ent-8(17)-labden-15-O-alpha-L-rhamnoside and ent-8(17)-labden-15-O-(3'-O-acetyl)-alpha-L-rhamnoside (new natural compounds) were isolated from propolis from El Salvador. The compounds showed significant antibacterial activity and moderate toxicity to Artemia salina nauplii. These are the first glycosides reported in bee gl...

Propolis (bee glue) is a resinous hive product collected by bees from plant exudates. It is widely used in medicine, cosmetics and food industry (Marcucci 1995; Matsuda 1994), due to its versatile biological activities. These include antimicrobial, fungicidal, antiviral, immunostimulating, cytostatic and radical-scavenging activities (Marcucci, 199...

Three ent-kaurene diterpenoids, not previously described as constituents of propolis, were isolated from a sample collected by Brazilian native bees Melipona quadrifasciata anthidioides. One of them, kaurenoic acid, as well as the total extract, displayed moderate antibacterial activity.

The chemical composition of propolis from Bulgaria, Turkey, Greece and Algeria was investigated by GC-MS. All of them contained mainly flavonoids and esters of caffeic and ferulic acids, which indicated that their main source are buds of poplars of the taxonomic section Aegieros. Some Turkish samples contained a low percent of diterpenic acids, whi...

Twenty-one propolis samples produced by 12 different Meliponinae species were analyzed by GC-MS. Several chemical types of stingless bees' propolis could be grouped, according to the prevailing type of compounds like: 'gallic acid", "diterpenic" and "triterpenic" types. The results confirm that neither the bee species nor the geographical location...

Propolis samples from different geographic origins were investigated for their antibacterial (against Staphylococcus aureus and Escherichia coli), antifungal (against Candida albicans) and antiviral (against Avian influenza virus) activities. All samples were active against the fungal and Gram-positive bacterial test strains, and most showed antivi...