Antimicrobial and antiproliferative activities of stingless bee Melipona scutellaris geopropolis

Abstract

Background: Geopropolis is a type of propolis containing resin, wax, and soil, collected by threatened stingless bee species native to tropical countries and used in folk medicine. However, studies concerning the biological activity and chemical composition of geopropolis are scarce. In this study, we evaluated the antimicrobial and antiproliferative activity of the ethanolic extract of geopropolis (EEGP) collected by Melipona scutellaris and its bioactive fraction against important clinical microorganisms as well as their in vitro cytotoxicity and chemical profile.

Methods: The antimicrobial activity of EEGP and fractions was examined by determining their minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against six bacteria strains as well as their ability to inhibit Streptococcus mutans biofilm adherence. Total growth inhibition (TGI) was chosen to assay the antiproliferative activity of EEGP and its bioactive fraction against normal and cancer cell lines. The chemical composition of M. scutellaris geopropolis was identified by reversed-phase high-performance liquid chromatography and gas chromatography-mass spectrometry.

Results: EEGP significantly inhibited the growth of Staphylococcus aureus strains and S. mutans at low concentrations, and its hexane fraction (HF) presented the highest antibacterial activity. Also, both EEGP and HF inhibited S. mutans biofilm adherence (p < 0.05) and showed selectivity against human cancer cell lines, although only HF demonstrated selectivity at low concentrations. The chemical analyses performed suggest the absence of flavonoids and the presence of benzophenones as geopropolis major compounds.

Conclusions: The empirical use of this unique type of geopropolis by folk medicine practitioners was confirmed in the present study, since it showed antimicrobial and antiproliferative potential against the cancer cell lines studied. It is possible that the major compounds found in this type of geopropolis are responsible for its properties.

Figure 1

Effect of the ethanolic extract of geopropolis (EEGP) and its hexane fraction (HF) to inhibit the adherence of Streptococcus mutans UA159 growing cells. Each concentration marked with * differs significantly from the vehicle control (p < 0.05, ANOVA, Student-Newman-Keuls).

Figure 2

RP-HPLC chromatograms. Chromatogram of the ethanolic extract of geopropolis (EEGP) (A) and its hexane fraction (HF) (B) using photodiode array detector (SPD-M10AVp) at 254 nm; reversed-phase C18 column (250 mm × 4.6 mm i.d.; 5 μm particle size); mobile phase: water/acetic acid (19:1, v/v) (solvent A) and methanol (solvent B) at a constant flow rate of 1 mL/min. The gradient started with 30% solvent B, changing to 40% of B in 15 min, 50% of B in 30 min, 60% of B in 45 min, 75% of B in 65 min, 75% of B in 85 min, 90% of B in 95 min, 90% of B in 110 min, and 30% of B in 120 min. The column was maintained at 35°C. Constituents are represented only by the absorption spectra in the UV (λ_max): 1: UV λ 241 nm, RT = 2.72 min; 2: UV λ 287 nm, RT = 81.40 min; 3: UV λ 283 nm, RT = 83.31 min; 4: UV λ 279 nm, RT = 100.53 min; 5: UV λ 281 nm, RT = 101.95 min; 6: UV λ 240 nm, RT = 42.54 min; 7: UV λ 282 nm, RT = 87.14 min; 8: UV λ 284 nm, RT = 91.00 min.