ORIGINAL ARTICLE Antimicrobial activity of honey from the stingless bee Trigona carbonaria determined by agar diffusion, agar dilution, broth microdilution and time-kill methodology K.L. Boorn 1 , Y.-Y. Khor 2 , E. Sweetman 2 , F. Tan 2 , T.A. Heard 3 and K.A. Hammer 2 1 School of Pathology and Laboratory Medicine, The University of Western Australia, Crawley, Western Australia, Australia 2 Microbiology and Immunology, School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Crawley, Western Australia, Australia 3 CSIRO Entomology, Indooroopilly, Brisbane, Queensland, Australia Introduction The antimicrobial activity of honey has been both researched scientifically and exploited medicinally for many years. The majority of research has focused on honey produced by the European honeybee Apis mellifera and, until recently, relatively little attention has been paid to honey from stingless bees. Stingless bees (Apidae, Meliponini) are native to tropical and subtropical parts of the world such as Central and South America, Africa, Asia and northern Australia (Crane 1990). Like Apis honeybees, most species of eusocial stingless bees, such as Tetragonisca angustula and Melipona quadrifasciata from Brazil (Souza et al. 2006) and Trigona carbonaria from Australia, produce honey. Stingless bee honey is highly valued as a food source by the Aboriginal people of northern Australia and is of cultural significance, playing a role in the social traditions and rituals of the people (Akerman 1979; Isaacs 2000). Stingless bee honey has also been used in traditional medicine in Central and South America, and Africa (Cortopassi-Laurino et al. 2006), suggesting that stingless bee honey may have therapeutic properties that are similar to currently used medicinal honeys such as manuka honey from New Zealand (Cooper et al. 2000; George and Cutting 2007; Adams et al. 2008). Keywords antibacterial, minimum inhibitory concentration, MRSA, wounds. Correspondence Katherine A. Hammer, Microbiology & Immunology (M502), School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia 6009, Australia. E-mail: khammer@cyllene.uwa.edu.au 2009 ⁄ 0970: received 2 June 2009, revised 28 July 2009 and accepted 17 August 2009 doi:10.1111/j.1365-2672.2009.04552.x Abstract Aims: The aim of this study was to determine the spectrum of antimicrobial activity of 11 samples of stingless bee honey compared to medicinal, table and artificial honeys. Methods and Results: Activity was assessed by agar diffusion, agar dilution, broth microdilution and time-kill viability assays. By agar dilution, minimum inhibitory concentration (MIC) ranges were 4% to >10% (w ⁄ v) for Gram-positive bacteria, 6% to >16% (w ⁄ v) for Gram-negative bacteria and 6% to >10% (w ⁄ v) for Candida spp. By broth microdilution, all organisms with the exception of Candida albicans and Candida glabrata were inhibited at £32% (w ⁄ v). Geometric MIC (w ⁄ v) means for stingless bee honeys ranged from 7Æ1% to 16Æ0% and were 11Æ7% for medicinal honey and 26Æ5% for table honey. Treatment of organisms with 20% (w ⁄ v) stingless bee honey for 60 min resulted in decreases of 1–3 log for Staphylococcus aureus, >3 log for Pseudo- monas aeruginosa and <1 log for C. albicans. Similar treatment with each control honey resulted in decreases of <1 log for all organisms. Conclusions: Stingless bee honey has broad-spectrum antibacterial activity although activity against Candida was limited. Stingless bee honey samples varied in activity and the basis for this remains to be determined. Significance and Impact of the Study: Stingless bee honey had similar activity to medicinal honey and may therefore have a role as a medicinal agent. Journal of Applied Microbiology ISSN 1364-5072 1534 Journal compilation ª 2009 The Society for Applied Microbiology, Journal of Applied Microbiology 108 (2010) 1534–1543 ª 2009 The Authors