Chemical characterization, antioxidant, cytotoxic and antibacterial activity of propolis extracts and isolated compounds from the Brazilian stingless bees Melipona quadrifasciata and Tetragonisca angustula

Since chemical or pharmacological studies on the propolis of Brazilian native bees are scarce, the aim of this study was to evaluate the chemical profile, the antioxidant, cytotoxic and antibacterial activity of aqueous and hydro-alcoholic extracts and isolated compounds of propolis of the native bees, Melipona quadrifasciata and Tetragonisca angustula, against bacteria with (Gram-positive and Gram-negative) and without cell wall (mollicutes). The extracts presented a peculiar feature between green and yellow propolis. Despite the low content of flavonoid and phenolic compounds, a promising level of antioxidant activity without toxicity in the propolis extracts of M. quadrifasciata was observed. The best antimicrobial activity was that of the hydro-alcoholic extract against Mycoplasma pneumoniae and Ureaplasma urealyticum (MIC 125 μg/ml). We isolated two compounds and identified them from the aqueous and hydro-alcoholic extracts as the flavononol sakuranetin and gallic acid. Sakuranetin and gallic acid presented MICs of 50 and 25 μg/ml against Mycoplasma hominis and Mycoplasma genitalium respectively. Propolis from Brazilian native bees may constitute an alternative and undervalued source of compounds with biological activity. The mollicutes are the smallest self-replicating bacteria that constitute a model of cellular and molecular biology studies due to their small genome and restrict biochemical machinery. This is the first report investigating the potential of antibacterial molecules isolated from propolis of Brazilian native bees using this microorganism model. Our results contribute to a better understanding of the chemical and biological properties of these propolis types and provide evidence for its potential medicinal use.