Synergistic Activity of Antibiotics and Bioactive Plant Extracts: A Study Against Gram-Positive and Gram-Negative Bacteria

The alarming growth of the number of antibiotic resistant bacteria and difficulties in treatment of infections have initiated a search for new antibacterial compounds and develop new alternative strategies in combating bacterial infections. Plant-derived compounds could exhibit a direct antibacterial activity and/or an indirect activity as antibiotic resistance modifying compounds, which, combined with antibiotics, increase their effectiveness. This ability of plant active substances reflects in modification or blocking of resistance mechanism so that bacterium becomes sensitive to antibiotic or the antibiotic acts when in lower concentrations. The systematic screening of plant-derived bioactive compounds, including those which can synergistically act with antibiotics, as resistance modifying agents represents a potential approach to overcome bacterial resistance. Therefore, the goals of this chapter are (i) an update of literature review on synergism between plant extracts and antibiotics, (ii) presentation of experimental results of synergistic activity of selected plant extracts and antibiotics and (iii) concluding remarks

Biological activities of extracts from cultivated Granadilla Passiflora alata

Research conducted in this study showed the influence of ethanol, acetone and ethyl acetate extracts of the outgrowth of cultivated Passiflora alata on microorganisms, as well as the antioxidant activity and the concentrations of total phenols, flavonoids and tannins. In vitro antimicrobial activities of extracts were studied on 27 species of microorganisms, of which 17 species of bacteria and 10 species of fungi. The strongest antimicrobial activity was detected on G+ bacteria while the activities on other species were moderate. Ethyl acetate extract showed the strongest effect. The concentrations of total phenols were examined by using Folin-Ciocalteu reagent and the obtained values ranged from 14.04 to 34.22 mg GA/g. By using aluminium chloride method, the concentrations of flavonoids were obtained and the values ranged from 33.19 to 62.30 mg RU/g. In determining the amount of tannins we used the method with buthanol-HCl reagent and the obtained value was 5.1 % of dry matter. The efficiency of antioxidation, which we identified through the reduction of DPPH, was in the range from 808.69 to 1107.79 μg/ml for a particular IC50, and AAI values were between 0.07 and 0.10. The best parameters were shown by ethanol extract. All data were statistically analyzed. Overall, extracts showed potential for further investigation and use

Freshwater algae Cladophora glomerata and Vaucheria sp. from Serbia as sources of bioactive compounds: chemical analysis and biological activities

We examined potential biological activities of two taxa of freshwater algae, Cladophora glomerata and Vaucheria sp., from Serbia. The total phenolic and pigment contents, antioxidant potential, antimicrobial, antibiofilm activities, and cytotoxicity of the ethanol and acetone extracts were evaluated. The extracts were also subjected to Fourier transform infrared spectroscopy (FTIR) analysis. The levels of total phenolic compounds, chlorophylls a and b, and carotenoids varied based on both the algal taxa and the type of extracts. FTIR analysis showed the presence of lipids, unsaturated fatty acids, protein, carbohydrates, and phenols in the algal extracts. The extracts had moderate DPPH radical scavenging activity and lower reducing power compared with ascorbic acid. The antimicrobial activity expressed as minimum inhibitory concentrations ranged from 0.31 mg/mL to 10 mg/mL. The strains of Staphylococcus aureus and Bacillus cereus isolated from food samples, as well as S. aureus ATCC 25923, were the most sensitive. For the first time, the antibiofilm activity test revealed 98.7% inhibition of S. aureus biofilm formation. The extracts exhibited cytotoxic effects on choriocarcinoma JAR cells but without selectivity on normal fetal lung fibroblast MRC-5 cells. This is the first report on the biological activities of freshwater macroalgae from Serbia

Immortelle (Xeranthemum annum L.) as a natural source of biologically active substances

Antioxidant and antimicrobial effects, total phenolic content and flavonoid concentrations of methanolic, acetone and ethyl acetate extracts from Xeranthemum annuum L. were investigated in this study. The total phenolic content was determined using Folin-Ciocalteu reagent and ranged between 101.33 to 159.48 mg GA/g. The concentration of flavonoids in various X. annuum extracts was determined using spectrophotometric method with aluminum chloride and the results varied from 22.25 to 62.42 mg RU/g. Antioxidant activity was monitored spectrophotometrically using DPPH reagent and expressed in terms of IC50 (μg/ml), and it ranged from 59.25 to 956.81 μg/ml. The highest phenolic content and capacity to neutralize DPPH radicals were found in the acetone extract. In vitro antimicrobial activity was determined by microdilution method. Minimum inhibitory concentration (MIC) and minimum microbicidal concentration (MMC) have been determined. Testing was conducted against 24 microorganisms, including 15 strains of bacteria (standard and clinical strains) and 9 species of fungi. Statistically significant difference in activity between the extracts of X. annuum L. was observed and the acetone extract was found most active. The activity of acetone extract was in accordance with total phenol content and flavonoid concentration measured in this extract. The tested extracts showed significant antibacterial activity against G+ bacteria and weak to moderate activity against other microorganisms. Based on the obtained results, X. annuum can be considered as a rich natural source of polyphenolic compounds with very good antioxidant and antimicrobial activity

Freshwater algae Cladophora glomerata and Vaucheria sp. from Serbia as sources of bioactive compounds: chemical analysis and biological activities

We examined potential biological activities of two taxa of freshwater algae, Cladophora glomerata and Vaucheria sp., from Serbia. The total phenolic and pigment contents, antioxidant potential, antimicrobial, antibiofilm activities, and cytotoxicity of the ethanol and acetone extracts were evaluated. The extracts were also subjected to Fourier transform infrared spectroscopy (FTIR) analysis. The levels of total phenolic compounds, chlorophylls a and b, and carotenoids varied based on both the algal taxa and the type of extracts. FTIR analysis showed the presence of lipids, unsaturated fatty acids, protein, carbohydrates, and phenols in the algal extracts. The extracts had moderate DPPH radical scavenging activity and lower reducing power compared with ascorbic acid. The antimicrobial activity expressed as minimum inhibitory concentrations ranged from 0.31 mg/mL to 10 mg/mL. The strains of Staphylococcus aureus and Bacillus cereus isolated from food samples, as well as S. aureus ATCC 25923, were the most sensitive. For the first time, the antibiofilm activity test revealed 98.7% inhibition of S. aureus biofilm formation. The extracts exhibited cytotoxic effects on choriocarcinoma JAR cells but without selectivity on normal fetal lung fibroblast MRC-5 cells. This is the first report on the biological activities of freshwater macroalgae from Serbia

Great horsetail (Equisetum telmateia Ehrh.)

This paper deals with the antioxidant and antimicrobial activity, total phenolic content and concentrations of flavonoids of Equisetum telmateia extracts. Total phenolic content was determined with Folin-Ciocalteu reagent and it ranged between 129.0 to 262.7 mg GA/g. The concentration of flavonoids in various extracts of E. telmateia was determined using spectrophotometric method with aluminum chloride and obtained results varied from 112.6 to 199.8 mg RU/g. Antioxidant activity was monitored spectrophotometrically and expressed in terms of IC50 (μg/ml), and its values ranged from 33.4 to 982.2 μg/ml. The highest phenolic content, concentrations of flavonoids and capacity to neutralize DPPH radicals were found in the acetone extract. In vitro antimicrobial activity was determined using microdilution method. Minimum inhibitory concentration (MIC) and minimum microbicidal concentration (MMC) were also determined. Testing was performed on 22 microorganisms, including 15 strains of bacteria (standard and clinical strains) and 7 species of fungi. There were statistically significant differences in activity between the extracts of E. telmateia. Different effects were noticed against the bacteria and the methanol extract appeared to be most efficient. All the extracts showed significant antibacterial activity against G+ bacteria and weak to moderate activity against other microorganisms

Synthetic cinnamates as potential antimicrobial agents

This study deals with synthesis of methyl cinnamate, butyl cinnamate, and p-methoxy methyl cinnamate and testing of their in vitro antimicrobial activity. Antimicrobial activity was examined towards 29 microorganisms using microdilution method. It is shown that antimicrobial activity of methyl cinnamate and p-methoxy methyl cinnamate was better than that of butyl cinnamate. Sarcina lutea, Bacillus subtilis ATCC 6633, B. subtilis and B. subtilis IP 5832 (probiotic) were the most sensitive bacteria. It is established that p-methoxy methyl cinnamate can be a new, potential anti-Staphylococcus aureus agent with minimum inhibitory concentration of 62.5 μg/ml. Methyl cinnamate and p-methoxy methyl cinnamate inhibited the growth of Aspergillus restrictus, A. flavus and A. fumigatus in the concentration range from 62.5 μg/ml to 250 μg/ml

Melilotus albus and Dorycnium herbaceum extracts as source of phenolic compounds and their antimicrobial, antibiofilm, and antioxidant potentials

Melilotus albus Medic. and Dorycnium herbaceum Vill. (Fabaceae) acetone, ethyl acetate, and ethanol extracts were investigated for their in vitro antimicrobial, antibiofilm, and antioxidant activity with quantification of phenolic compound contents. In general, D. herbaceum extracts showed better antibacterial and antioxidant activity than M. albus extracts. Bacteria Bacillus subtilis, Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa, and Proteus mirabilis were the most susceptible with the minimum inhibitory concentrations (MICs), determined by microdilution method, between 1.25–10 mg/mL. Antifungal activity was lower with the detectable MICs at 10 mg/mL and 20 mg/mL. The plant extracts, using the crystal violet assay, inhibit P. aeruginosa biofilm formation in concentration range from 5 mg/mL to 20 mg/mL whereas the effect on mature bacterial biofilm was lower. The antioxidant activity was evaluated using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radicals scavenging and reducing power model systems. The intensity of DPPH radicals scavenging activity, expressed as half maximal effective concentration (EC50) values, was from 84.33 μg/mL to >1000 μg/mL. The extracts demonstrated reduced power in a concentration-dependent manner, with ethanol extract as the most active. The total phenols, flavonoids, and proanthocyanidins were determined spectrophotometrically while total extractable tannins were obtained by precipitation method. The phenolic compounds showed differences in their total contents depending on solvents polarities and plant species. Although the plants M. albus and D. herbaceum have not yet been fully explored, these results contribute better understanding of their biotic properties and potential application as antimicrobial and antioxidant agents

In vitro synergistic antibacterial activity of Melissa officinalis L. and some preservatives

The aim of this study was to investigate the antibacterial activity of aqueous, ethanol and ethyl acetate extracts of the species Melissa officinalis L. and their in vitro synergistic action with preservatives, namely: sodium nitrite, sodium benzoate and potassium sorbate against selected food spoiling bacteria, for a potential use in food industry. Synergistic action was noticed in almost every combination between plant extracts and preservatives. This work showed that the active compounds from ethanol, ethyl acetate and aqueous extracts of Melissa officinalis L. significantly enhanced the effectiveness of tested preservatives. Synergism was established at plant extract and preservative concentrations corresponding to 1/4 and 1/8 minimal inhibitory concentration values, which indicated the possibility of avoiding the use of higher concentrations of tested preservatives

In vitro activity of heather [Calluna vulgaris (L.) Hull] extracts on selected urinary tract pathogens

© 2014 ABMSFBIH. Calluna vulgaris L. Hull (Ericaceae) has been used for treatment of urinary tract infections in traditional medicine. In this study we analyzed in vitro antibacterial activity of the plant extracts on different strains of Escherichia coli, Enterococcus faecalis and Proteus vulgaris, as well as the concentrations of total phenols and flavonoids in the extracts. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined. The concentrations of total phenols were examined by using Folin-Ciocalteu reagent and ranged between 67.55 to 142.46 mg GAE/g. The concentrations of flavonoids in extracts were determined using spectrophotometric method with aluminum chloride and the values ranged from 42.11 to 63.68 mg RUE/g. The aqueous extract of C. vulgaris showed a significant antibacterial activity. The values of MIC were in the range from 2.5 mg/ml to 20 mg/ml for this extract. Proteus vulgaris strains were found to be the most sensitive. The results obtained suggest that all tested extracts of C. vulgaris inhibit the growth of human pathogens, especially the aqueous extract