On the in-vitro antimicrobial activity of oleuropein and hydroxytyrosol

Secoiridoides (oleuropein and derivatives), one of the major classes of pol yphenol contained in olives and olive oil, have recently been shown to inhi bit or delay the rate of growth of a range of bacteria and microfungi but. there are no data in the literature concerning the possible employment of t hese secoiridoides as antimicrobial agents against pathogenic bacteria in m an. In this study five ATCC standard bacterial strains (Haemophilus influenzae ATCC 9006, Moraxella catarrhalis ATCC 8176, Salmonella typhi ATCC 6539, Vib rio parahaemolyticus ATCC 17802 and Staphylococcus aureus ATCC 25923) and 4 4 fresh clinical isolates (Haemophilus influenzae, eight strains, Moraxella catarrhalis, six strains, Salmonella species, 15 strains, Vibrio cholerae, one strain, Vibrio alginolyticus, two strains, Vibrio parahaemolyticus, on e strain, Staphylococcus aureus, five penicillin-susceptible strains and si x penicillin-resistant strains), causal agents of intestinal or respiratory tract infections in man, were tested for in-vitro susceptibility to two ol ive (Olea europaea) secoiridoides, oleuropein (the bitter principle of oliv es) and hydroxytyrosol (derived from oleuropein by enzymatic hydrolysis and responsible for the high stability of olive oil). The minimum inhibitory c oncentrations (MICs) calculated in our study are evidence of the broad anti microbial activity of hydroxytyrosol against these bacterial strains (MIC v alues between 0.24 and 7.85 mu g mL(-1) for ATCC strains and between 0.97 a nd 31.25 mu g mL(-1) for clinically isolated strains). Furthermore oleurope in also inhibited (although to a much lesser extent) the growth of several bacterial strains (MIC values between 62.5 and 500 mu g mL(-1) for ATCC str ains and between 31.25 and 250 mu g mL(-1) for clinical isolates); oleurope in was ineffective against Haemophilus influenzae and Moraxella catarrhalis . These data indicate that in addition to the potential employment of its act ive principles as food additives or in integrated pest-management programs, Olea europaea can be considered a potential source of promising antimicrob ial agents for treatment of intestinal or respiratory tract infections in m an.