Antibacterial, Antioxidant, and Anti-Inflammatory Activities of Thai Stingless Bee Propolis Extracts

Propolis is a resinous natural product collected by bees from plant sources to protect the hive. Its chemical composition varies according to bee species and environmental conditions, resulting in differences in its biological activities. This study aimed to evaluate the biological properties of stingless bee propolis collected from different provinces in Thailand, with particular attention to two native species, Tetragonula pegdeni and Tetragonula laeviceps. These two species of Tetragonula are commonly found in tropical regions of the country. The investigation focused on their antioxidant, antimicrobial, and anti-inflammatory activities. The propolis extract from T. laeviceps stingless bee (sample D) exhibited the highest total phenolic and flavonoid contents, at 29.59 mg GAE/g extract and 73.95 mg QUE/g extract, respectively. Among the propolis extracts, T. pegdeni stingless bee propolis extract (sample A) showed the greatest antioxidant activity of 7.08 ± 0.18 GAE/g extract and 75.64 ± 3.07 mg TEAC/g extract by the DPPH and ABTS assays, respectively, together with the highest FRAP value of 48.54 ± 0.48 mg FeSO₄/g extract. The antibacterial efficacy of these extracts was further evaluated against skin pathogenic bacteria, including Staphylococcus aureus, Staphylococcus epidermidis, methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Micrococcus luteus, and Cutibacterium acnes. Inhibition zones ranged from 7.00 to 14.00 mm when determined by the agar disc diffusion method. Moreover, antibacterial activity was investigated by broth dilution assay, and MIC and MBC values ranged from 0.97 to 125 mg/mL. The cytotoxicity test of propolis extracts using RAW264.7 macrophage cells showed cell viability above 70%, and the selected concentrations were used for further anti-inflammatory evaluation. T. pegdeni stingless bee propolis extracts (samples A and B) demonstrated anti-inflammatory activity by reducing NO production and decreasing the expression of iNOS, COX-2, and IL-1β genes in LPS-stimulated RAW264.7 macrophage cells. LC-MS analysis revealed differences in chemical profiles among the propolis extracts and various bioactive compounds, including phenolic acids, flavonoids, xanthones, terpenoids, triterpenoids, and curcuminoids were identified. Therefore, Thai stingless bee propolis demonstrated potential as a natural source of bioactive compounds with antioxidant, antibacterial, and anti-inflammatory properties.