In vitro antibacterial phenolic extracts from “sugarbag” pot-honeys of Australian stingless bees (Tetragonula carbonaria)

Honey has been used in medicinal preparations since ancient times. Medical research of the antimicrobial effects of honeys can define the potential therapeutic uses [1] further to leads for drug discovery. Medicinal 'man̄uka' honeys from honeybees (Apis mellifera, Apidae) contain the antibacterial methylglyoxal (MGO) [1], and clinical observations showed that honey is effective as a wound dressing [2]. Australian stingless bees Tetragonula carbonaria (Meliponini) produce 'sugarbag-pot-honeys' used by Aboriginal people as gastrointestinal cleansers. The antimicrobial properties of sugarbag honeys were reported [1], while their bioactive factors remained unknown. This study aimed to assess in vitro antibacterial effects of phenolic fractions and peroxide contents from T. carbonaria honeys.

Methods used T. carbonaria honeys harvested in subtropical East Australia. Phenolic extracts were analysed by liquid and gas chromatography mass spectrometry. Antibacterial tests were run against Staphylococcus aureus ATCC 25923 by in vitro agar diffusion (Fig. 1) and broth dilution assays. Controls were ethanol (negative) and phenolic standard solutions (positive).

Results identified natural products ie. 3-phenyllactic acid, flavonoids and norisoprenoids, while no MGO was found. Total antibacterial activities were partially ascribed to hydrogen peroxide contents as well as phytochemicals [3]: phenolic fractions were bactericidal at 1.2 – 1.8 mg/mL; hydrogen peroxide content was 155.8 µM while requiring a bactericidal concentration of 760 µM.

In conclusion, T. carbonaria honey can source bioactive compounds of antimicrobial interest, and may have a role as a medicinal agent to treat chronic wounds.

References:

[1] Boorn K, Khor YY, Sweetman E, Tan F, Heard T, Hammer K. J Appl Micro 2010; 108: 1534 – 1543

[2] Lu J, Turnbull L, Burke CM, Liu M, Carter DA, Schlothauer RC, Whitchurch CB, Harry EJ. PeerJ 2014; 2: e326

[3] Massaro CF, Shelley D, Heard TA, Brooks P. J Agric Food Chem 2014; 62: 12209 – 12217