**1. Introduction**

Extra virgin olive oil (EVOO) is a food extracted by the mechanical pressing of the fruits of the olive tree (*Olea europaea* L.). EVOO and other products from olive tree are central components of the Mediterranean diet, characterized, as it is well known, by a scarce intake of products of terrestrial animal origin, and, concomitantly, by a high intake of fruits, vegetables, cereals, fish, as well as by a moderate wine consumption. Fruits and vegetables, including cereals, are rich in phytochemicals, with proven protective effects in limiting several chronic diseases, such as cancer and cardiovascular illnesses. EVOO represents an important source of nutritionally and healthfully compounds, so that it is considered as a real functional food [1]. Apart from fatty acids (mainly triglycerides, fat-soluble substances and polar compounds, representing 95–98% of the whole EVOO)—pulp and seed of olive contain several other types of compounds, which are present in the final product after the extractive process. Polyphenols are probably one of the most important groups of minor polar components present in the EVOO. The biological importance of polyphenols gives rise from their numerous ascertained biochemical activities, such as the prevention of oxidation reactions to fatty acids. In addition, for this reason they contribute to the stability of the oil over time, delaying rancidity. Polyphenols are also capable of preventing and inhibiting radical-type reactions in the human body, thus limiting the formation of anomalous molecules that might alter the smooth functioning of cell membranes. Generally, EVOO is rich in polyphenols, until 1 g gallic acid equivalents (GAE)/kg of product [2]. The principal subfamilies of polyphenols detectable in the EVOO are phenolic acids,

phenolic alcohols, secoridoids, lignans and flavonoids. Each of the above-mentioned subfamilies can then be differentiated from the others by chemical composition and reactivity, as well as, probably, by its organoleptic characteristics. It is therefore clear that the proportions and rate between the different polyphenols present in the EVOO considerably change its nutraceutical and sensory qualities. Olives and its derived-products, including EVOO, are capable, within certain limits, to resist against the biotic and abiotic stresses, for instance against pathogen attack, affecting the host-pathogen interaction. Such property is mainly due to the presence of polyphenols, which can also exhibit antimicrobial activity [3]. Polyphenols of EVOOs are able to inhibit in vitro, generally in a synergistic way, the growth of pathogens responsible for some intestine and respiratory diseases. Olive polyphenols could contribute in inhibiting the growth of *Helicobacter pylori* [4] and that of some foodborne pathogens, such as *Escherichia coli*, *Listeria monocytogenes* and *Salmonella enteriditis* [5]. EVOO demonstrated a good antimicrobial effect against *Salmonella* Typhi [6]. EVOO polyphenols are considerably absorbed (up to 95%) in humans mainly in the small intestine, where they might exert a significant local action [7]. Therein, they undergo different fate: some of them are directly absorbed; others are metabolized giving rise to other molecules, which can play a double role: act against enteropathogens, for instance, and, among other activities, improve the growth of beneficial microbes, acting as prebiotics [8,9]. Taking also into account the bioavailability of polyphenols, several authors ascertained that the use of EVOO in food might help in supporting the prevention against foodborne pathogens [5,10]. Recently, the inhibitory effect of EVOO polyphenols was demonstrated also against some oral microorganisms, such as oral streptococci, *Porphyromonas gingivalis*, *Fusobacterium nucleatum*, and *Parvimonas micra* [11]. In olive mill wastewater, phenolic compounds and their secoiridoid derivatives present in an ethanol fraction contribute to support the noticeable antimicrobial activity exhibited against the foodborne pathogen *Campylobacter* [12]. Cultivar, genetics, agronomic practices and climatic conditions, as well as the degree of ripening, storage conditions and fruit processing techniques are all factors that may affect the characteristics of EVOO, including the polyphenol profile and the subsequent biological properties [13,14]. The aim of our work was to evaluate the antibacterial activity exhibited by the polyphenol fraction of EVOOs, produced with the fruits of three varieties of *Olea europea* L. (*Ruvea antica*, *Ravece*, and *Ogliarola*) cultivated in Southern Italy. The study evaluated in particular the inhibitory effect of the extracts against several Gram-positive and Gram-negative bacterial strains. Statistical analysis correlated the antibacterial activity to the total polyphenols and to the percentage of the single components identified by a chromatographic approach within the three extracts.
