Minimal inhibitory concentrations (MICs) of Chilean honey against infectious bacteria

The minimal inhibitory concentrations (MICs) of 12 different Chilean honey types, provided by Apicoop, were determined against six infectious bacterial species. Of the standard methods (CLSI standard), the broth dilution assay was applied; using optical density at 595 nm (OD595), bacterial growth was measured in the presence of honey (45.5, 20.7, 9.4, 4.3 and 1.9% [w/w]) after overnight incubation at 35 °C. The observed MICs that inhibited bacterial growth ranged between 1.9 and 45.5% honey. The most effective honey types, with a detected MIC of 1.9%, were: - Honey 10-12/PT FC20 and 10-12/PT TC20 against Acetobacter baumannii - Honey 10-12ME0024/53 against Staphylococcus aureus Pseudomonas aeruginosa, Helicobacter pylori and Streptococcus pyogenes were more resistant against honey, since the majority of the determined MICs were at 9.4 or 20.7% (depending on the honey type). MICs for Cutibacterium acnes (previously known as Propionibacterium acnes) could not be determined. This was due to the relatively slow growth of the microorganism in the assay, combined with anaerobic atmosphere conditions and outgrowth of microorganisms naturally present in honey (presumably anaerobic spores) under these conditions. Notably, the detected bacterial growth inhibition can be, at least partly, caused by a decreased water activity due to the binding of water by honey (due to high sugar content). Further research can be performed on elucidation of the growth inhibiting compound in the honey types.