Anti-staphylococcal properties of propolis from Australian stingless bees Tetragonula carbonaria

Bees mix plant resins with their beeswax to produce propolis. Bee propolis has been used as a traditional remedy in ancient civilisations and modern societies of Europe, America and Asia for their antibacterial properties [1]. However, no antimicrobial investigations have been conducted on Australian propolis yet. This study aimed to assess the in vitro anti-staphylococcal properties and cytotoxicity towards Caco-2 and Vero cells of Australian stingless bees (Tetragonula carbonaria) propolis. Propolis was harvested from 14 beehives in Queensland. Ethanol crude extracts were analysed by liquid chromatography-mass spectrometry, and structure elucidation was performed using NMR and HR-ESI-MS. Propolis was fractioned in individual constituents that were purified by repeated column chromatography. Purified constituents and crude extracts were evaluated against 12 strains of Staphylococcus aureus including clinical strains of seven multidrug-resistant types and three methicillin-resistant of different clonal types. Antimicrobial activities were assessed using gel diffusion assay according to CLSI guidelines as well as broth dilution assay with MTT-tetrazolium dye to quantitate the bacterial production of formazan crystals at 570nm. Positive and negative controls were phenol standard and ethanol, respectively. Bactericidal concentrations were identified as 99.9% growth inhibition after replating on fresh agar. Cell viability was tested on Vero and Caco-2 cells seeded at 10⁴ cells/mL, and assessed by MTT and trypan blue assays using bright field microscopy. Propolis constituents were C-methyl flavanones and phloroglucinols originating from the fruit resins of Corymbia torelliana trees [2]. Samples exerted anti-staphylococcal effects at MIC values 6.9 – 511.1 µg/mL, while full cell viabilities were 7.0 – 40.0 µg/mL. Further investigations are warranted on the mode of action by propolis samples against S. aureus strains.

Keywords: flavonoids, Eucalyptus, honey, antimicrobial, phloroglucinol

References:

[1] Inui S, Shimamura Y, Masuda S, Shirafuji K, Moli RT, Kumazawa S. A new prenylflavonoid isolated from propolis collected in the Solomon Islands. Biosci Biotech Biochem. 2012;76(5):1038 – 40.

[2] Massaro C, Katouli M, Grkovic T, Vu H, Quinn RJ, Heard TA, et al. Anti-staphylococcal activity of C-methyl flavanones from propolis of Australian stingless bees (Tetragonula carbonaria) and fruit resins of Corymbia torelliana (Myrtaceae). Fitoterapia. 2014;95:247 – 57.