Secoiridoides (oleuropein and derivatives), one of the major classes of polyphenol contained in olives and olive oil, have recently been shown to inhibit 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 these secoiridoides as antimicrobial agents against pathogenic bacteria in man. In this study five ATCC standard bacterial strains (Haemophilus influenzae ATCC 9006, Moraxella catarrhalis ATCC 8176, Salmonella typhi ATCC 6539, Vibrio parahaemolyticus ATCC 17802 and Staphylococcus aureus ATCC 25923) and 44 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, one strain, Staphylococcus aureus, five penicillin-susceptible strains and six penicillin-resistant strains), causal agents of intestinal or respiratory tract infections in man, were tested for in-vitro susceptibility to two olive (Olea europaea) secoiridoides, oleuropein (the bitter principle of olives) and hydroxytyrosol (derived from oleuropein by enzymatic hydrolysis and responsible for the high stability of olive oil). The minimum inhibitory concentrations (MICs) calculated in our study are evidence of the broad antimicrobial activity of hydroxytyrosol against these bacterial strains (MIC values between 0.24 and 7.85 microg mL(-1) for ATCC strains and between 0.97 and 31.25 microg mL(-1) for clinically isolated strains). Furthermore oleuropein also inhibited (although to a much lesser extent) the growth of several bacterial strains (MIC values between 62.5 and 500 microg mL(-1) for ATCC strains and between 31.25 and 250 microg mL(-1) for clinical isolates); oleuropein was ineffective against Haemophilus influenzae and Moraxella catarrhalis. These data indicate that in addition to the potential employment of its active principles as food additives or in integrated pest-management programs, Olea europaea can be considered a potential source of promising antimicrobial agents for treatment of intestinal or respiratory tract infections in man.

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The conformational behavior, molecular geometry and electronic structure of quercetin were investigated using the semiempirical AM1 and PM3 methods. Results reveal that quercetin has a nonplanar molecular structure, with cross-conjugation occurring at the C ring. Calculations were also performed for quercetin radical species at the OH groups, showing the presence of three radicals in a narrow range of energy. An interpretation of the antioxidative process mechanism, exerted by quercetin as a free radical scavenger, relies on two isoenergetic radicals with extended electronic delocalization between adjacent rings, also having cross-conjugated systems and being affected by the experimental environment influencing their relative order.

The biological properties and, particularly, the antioxidant activity of plant hydroxycinnamic acids, such as caþ eic and ferulic acids, are well recognised. This preliminary study was designed to estimate the potential utility of caþ eic and ferulic acids to prevent, when topically applied, photooxidative stress in the skin. With this aim we have evaluated the antioxidant activity of ferulic and caþ eic acids in two experimental models : (1) the UV radiation-induced peroxidation in phosphatidylcholine (PC) liposomal membranes ; (2) the scavenging activity against nitric oxide (a radical involved in oxidative reactions). In addition, given that a suitable percutaneous absorption is an essential requirement for successful topical photoprotective agents, we measured their in vitro permeation through excised human skin. Caþ eic and ferulic acids efficiently protected PC liposomes from UV radiation-induced peroxidation and reacted with nitrogen oxides. In addition, caþ eic and ferulic acids were able to permeate through the stratum corneum (the main barrier against the penetration of exogenous substances through the skin). Taken together, these ündings suggest that caþ eic and ferulic acids should be good canditates for successful employment as topical protective agents against UV radiation-induced skin damage.1999 Society of Chemical Industry (

Aims: In this paper the mechanisms involved in the antibacterial effect of six 2E-alkenals [(E)-2-hexenal, (E)-2-eptenal, (E)-2-octenal, (E)-2-nonenal, (E)-2-decenal and (E,E)-2,4-decadienal] were investigated. Methods and Results: We measured the release of carboxyfluorescein (CF) trapped in liposomes of phosphatidylcholine (PC) following exposure to the aldehydes mentioned above, in comparison with that elicited by hexanal and nonanal; the modifications of the thermotropic behaviour of liposomes of dimyristoylphosphatidylcholine (DMPC) induced by (E,E)-2,4-decadienal (the aldehyde endowed with the highest microbicidal activity) were evaluated by means of differential scanning calorimetry. With the exception of hexanal, all aldehydes tested caused rapid CF leakage from PC liposomes. The effectiveness order correlates well with the chain length and the presence of the a,b-double bond. Furthermore (E,E)-2,4-decadienal is able to interact with and cross DMPC bilayers. Conclusions: The present findings suggest that the 2E-alkenals tested elicit, very likely, a gross perturbation of the lipidic fraction of plasmatic membranes and are able to penetrate into bacterial cells. Significance and Impact of the Study: These data represent an interesting background for a rational employment of the plant 2E-alkenals tested as antimicrobial agents.

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