Chemical characterization and antibacterial activities of Brazilian propolis extracts from Apis mellifera bees and stingless bees (Meliponini).

The aim of this study was to evaluate the physicochemical composition and antibacterial activity of Brazilian propolis extracts from different types, concentrations, and extraction solvents and from different regions in Brazil. A total of 21 samples were analyzed, comprising 14 samples from Apis mellifera (12 green, 1 brown, and 1 red) and 7 samples from stingless bees (3 mandaçaia, 2 jataí, 1 hebora, and 1 tubuna). The analyses performed were dry extract, total phenolic content (TPC) and antioxidant activity (DPPH and ABTS). The antibacterial activity was performed by Determination of Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC). The results showed that very low levels of phenolic compounds and antioxidant activity decreased the antimicrobial activity of the propolis extracts from tubuna and jataí. However, there was no correlation between the increase in propolis concentration in the extract, and the increase in antimicrobial activity. The highest TPC and antioxidant activity was obtained for green propolis extract made with 70% raw propolis that presented similar antibacterial activity to the samples formulated with 30% or less raw propolis. The aqueous propolis extract showed lower antimicrobial activity compared to the alcoholic extracts, indicating that ethanol is a better solvent for extracting the active compounds from propolis. It was observed that the MIC (0.06 to 0.2 mg/mL) and MBC (0.2 to 0.5 mg/mL) values for Gram-negative bacteria were higher compared to Gram-positive bacteria (MIC 0.001-0.2 mg/mL, and the MBC 0.02-0.5 mg/mL). The propolis extracts that exhibited the highest antimicrobial activities were from stingless bees hebora from the Distrito Federal (DF) and mandaçaia from Santa Catarina, showing comparable efficacy to samples 5, 6, and 7, which were the green propolis from the DF. Hence, these products can be considered an excellent source of bioactive compounds with the potential for utilization in both the pharmaceutical and food industries.

Characterization and Determination of the Antibacterial Activity of Baccharis dracunculifolia Essential-Oil Nanoemulsions.

The aim of this study was to evaluate the antibacterial activity of nanoemulsions of Baccharis dracunculifolia essential oil. The volatile compounds of the essential oil were identified using gas chromatography-mass spectrometry. The properties of the nanoemulsions (droplet size, polydispersity index, pH, and electrical conductivity) were determined. The antibacterial activities of the essential oil and its nanoemulsions were evaluated using MIC, MBC, and disk diffusion. The microorganisms used were: Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Bacillus cereus ATCC 14579, Streptococcus mutans ATCC 25175, and Enterococcus faecalis ATCC 29212) and Gram-negative bacteria (Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumoniae ATCC BAA-1706, Salmonella enterica ATCC 14028, and Escherichia coli ATCC 25922). The major volatile compounds of the B. dracunculifolia essential oil were limonene (19.36%), (E)-nerolidol (12.75%), bicyclogermacrene (10.76%), and ß-pinene (9.60%). The nanoemulsions had a mean droplet size between 13.14 and 56.84 nm. The nanoemulsions presented lower and statistically significant MIC values compared to the essential oil, indicating enhancement of the bacteriostatic action. The disk diffusion method showed that both the nanoemulsions and the essential oil presented inhibition zones only for Gram-positive bacteria, while there were no results against Gram-negative bacteria, indicating that B. dracunculifolia essential oil has a better antimicrobial effect on Gram-positive microorganisms.