Propolis-induced exclusion of colloids: Possible new mechanism of biological action

Propolis is a natural product originating from life activity of honeybees. It exhibits wide range of biological properties applicable in medicine, the food industry, and cosmetics. Chemically, propolis is a complex and variable mixture with more than 300 identified biologically active components. Propolis's many health-promoting effects are attributed to different biochemical mechanisms, mediated by often-concerted actions of some of its many constituents. Propolis is considered safe and biocompatible. Yet due to its intrinsic complexity, standardization of propolis preparations for medical use as well as prediction of e.g. pathogen-specific interactions becomes a non-trivial task. In this work we demonstrate a new physical mechanism of propolis action, largely independent of specific nuances of propolis chemistry, which may underlie some of its biological actions. We show that propolis-bearing surfaces generate an extensive exclusion zone (EZ) water layer. EZ is an interfacial region of water capable of excluding solutes ranging from ions to microorganisms. Propolis-generated EZ may constitute an effective barrier, physically disabling the approach of various pathogens to the propolis-functionalized surfaces. We suggest possible implications of this new mechanism for propolis-based prevention of respiratory infections.