In Vitro Biological Profiles and Chemical Contents of Ethanolic Nest Entrance Extracts of Thai Stingless Bees Tetrigona apicalis

Abstract

Tetrigona apicalis is a species of stingless bees found in Lower Northern Thailand. They normally construct their nest entrances as an external structure for protecting themselves from enemies. Their biological properties have not well characterized yet. The objectives of this study were to evaluate the antibacterial, antifungal and anti-proliferative activities of their nest entrances. Samples were collected from four provinces and then extracted using 70% ethanol, finally called as ethanolic Nest Entrances Extracts (eNEEs). Broth microdilution method was applied to determine their antimicrobial effects. The cytotoxicity was examined to evaluate their anti-proliferative effects. The total phenolic and flavonoid concentrations were determined using colorimetric methods. Overall, the MICs were between 6.25 and >12.5 mg/mL against the bacteria tested whereas were between 1.56 and >12.5 mg/mL for the yeasts tested. The IC₅₀ of HeLa cells was lower than that of LEP cells. TPC (19.3-24.1 mg PGE/g dried eNEEs) and TFC (2.4-4.8 mg QE/g dried eNEEs) contained in the eNEEs with the major substances of hydroquinin and quercetin. In conclusion, the Thai ethanolic nest entrance extracts possess the antibacterial, antifungal and anti-proliferative activities.