Arianna Scardigli

Global Analysis of Type Three Secretion System and Quorum Sensing Inhibition of Pseudomonas savastanoi by Polyphenols Extracts from Vegetable Residues

Protection of plants against bacterial diseases still mainly relies on the use of chemical pesticides, which in Europe correspond essentially to copper-based compounds. However, recently plant diseases control is oriented towards a rational use of molecules and extracts, generally with natural origin, with lower intrinsic toxicity and a reduced negative environmental impact. In this work, polyphenolic extracts from vegetable no food/feed residues of typical Mediterranean crops, as Olea europaea, Cynara scolymus, and Vitis vinifera were obtained and their inhibitory activity on the Type Three Secretion System (TTSS) and the Quorum Sensing (QS) of the Gram-negative phytopathogenic bacterium Pseudomonas savastanoi pv. nerii strain Psn23 was assessed. Extract from green tea (Camellia sinensis) was used as a positive control. Collectively, the data obtained through gfp-promoter fusion system and real-time PCR show that all the polyphenolic extracts here studied have a high inhibitory activity on both the TTSS and QS of Psn23, without any depressing effect on bacterial viability. Extracts from green tea and grape seeds were shown to be the most active. Such activity was confirmed in planta by a strong reduction in the ability of Psn23 to develop hyperplastic galls on explants from adult oleander plants, as well as to elicit hypersensitive response on tobacco. By using a newly developed Congo red assay and an ELISA test, we demonstrated that the TTSS-targeted activity of these polyphenolic extracts also affects the TTSS pilus assembly. In consideration of the potential application of polyphenolic extracts in plant protection, the absence of any toxicity of these polyphenolic compounds was also assessed. A widely and evolutionary conserved molecular target such as Ca2+-ATPase, essential for the survival of any living organism, was used for the toxicity assessment.

Leishmanicidal activity of green tea leaves and pomegranate peel extracts on L. infantum

Abstract Leishmania infantum is responsible for the cutaneous and visceral form of this zoonotic disease, which is potentially lethal for humans and has dogs as natural reservoir. In the light of the antiparasitic properties displayed by several natural products, L. infantum promastigotes were exposed to green tea (Camellia sinensis) leaves extract (GTE) and pomegranate (Punica granatum) peel extract (PPE). Both extracts, characterized by NMR and HPLC analysis, inhibited parasite proliferation in a dose-dependent manner, as proved by IC50 evaluation determined by MTT assay.Moreover, the reversibility assay showed that GTE and PPE have an aptotosis-mediated leishmanicidal effect, as evidenced by DNA degradation and confirmed by DNA fragmentation and real-time PCR analyses. Finally, for the first time morphological and ultrastructural alterations induced by a P. granatum extract on Leishmania were shown by the use of light, transmission and scanning electron microscopy.