Oleuropein has been shown to have strong antimicrobial activity against both Gram- negative and Gram-positive bacteria [1–3] as well as mycoplasma [4]. Phenolic structures similar to Oleuropein seem to produce its antibacterial effect by damaging the bacterial membrane and/or disrupting cell peptidoglycans. Different authors have used biophysical assays to study the interaction between Oleuropein and membrane lipids [5]; however, the exact mechanism of the antimicrobial activity of Oleuropein is still not completely established, although some authors have proposed that it is due to the presence of the ortho-diphenolic system (catechol) [1]. In 2001, Saija and Uccella [6] proposed that the glycoside group modifies the ability to penetrate the cell membrane and get to the target site. Effective interference with the production procedures of certain amino acids necessary for the growth of specific microorganisms has also been suggested. Another mechanism proposed is the direct stimulation of phagocytosis as a response of the immune system to microbes of all types.

Oleuropein and hydrolysis products are able to inhibit the development and production of enterotoxin B by Staphylococcus aureus, the development of Salmonella enteritidis and the germination and consequent development of spores of Bacillus cereus [7-9]. Oleuropein and other phenolic compounds (p-hydroxybenzoic, vanillic and p-coumaric acids) completely inhibit the development of Klebsiella pneumoniae, Escherichia coli and B. cereus [2].

Recently, Sudjana et al. [8] showed the antimicrobial activity of commercial Olea europaea (olive) leaf extracts (abundantly Oleuropein) against Campylobacter jejuni, Helicobacter pylori and methicillin-resistant Staphylococcus aureus (MRSA). The authors also demonstrated these extracts play a role in regulating the composition of the gastric flora by selectively reducing levels of H. pylori and C. jejuni.

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