Enterotoxigenic Escherichia coli (ETEC) produces two types of enterotoxins: heat-labile (LT) and heat-stable (STa and STb). These molecules are involved in the induction of secretory diarrhea in animals including humans. This condition is currently treated using a fluid replacement therapy and antibiotics. This treatment is often not available to people in developing countries, and several die from the condition provoke by ETEC. Over the years, plants and plant extracts have been use as traditional medicine to treat various gastrointestinal ailments including diarrhea. Many of these plant products have been claimed to be active against diarrhea, however few have been extensively studied. The main objective of this review was to gather the scattered information on the antidiarrheal activities reported for various plant products on ETEC. This includes two major effects: (1) The inhibitory effect on bacterial growth or viability and (2) The interference with ETEC enterotoxins activity upon the intestinal epithelium. We will focus on plant products and extracts for which we have major indications of their biological activity against ETEC and their enterotoxins. Because Vibrio cholerae toxin (CT) is structurally, antigenically and mechanistically related to LT, it will also be discussed in this review.

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The present work was undertaken to determine safety parameters of selected Mexican medicinal plants chosen on the basis of their frequency of medicinal use and commercial importance. The medicinal herbs included Amphipteryngium adstringens, Hintonia standleyana, Hintonia latiflora, Piper sanctum, Haemathoxylon brasiletto, Iostephane heterophylla, Valeriana procera, Arracacia tolucensis, Brickellia veronicaefolia, Scaphyglottis livida, Exostema caribaeum, Hippocratea excelsa, Ligusticum porteri, Poliomintha longiflora and Gnaphalium sp. In the acute toxicity studies in mice performed according to the Lorke procedure, Exostema caribaeum, Hippocratea excelsa, Ligusticum porteri and Poliomintha longiflora were the most toxic with LD(50) values between 1085 and 2mg/kg. The Ames test revealed that Gnaphalium sp. and Valeriana procera extracts induced mutations of S. typhimurium TA98 with or without the S9 microsomal fraction, and TA100 in the presence of the enzymatic fraction, respectively. The tincture of Valeriana procera, however, was non-mutagenic. Finally, in the Artemia salina lethality test Brickellia veronicaefolia, Arracacia tolucensis, Poliomintha longiflora and Piper sanctum caused significant mortality of the crustacean larvae with LC(50) in the range of 37-227 microg/mL.

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Antibacterial properties of aqueous and methanolic extracts of 26 medicinal plants used in Mexico to treat gastrointestinal disorders were tested against eight different species of enteropathogens: two Escherichia coli species; two Shigella sonnei species; two Shigella flexneri species; and two Salmonella sp. species. The results showed that all crude extracts exhibited antibacterial activity, at least against one of the microorganisms tested, at concentrations of 8 mg/mL or lower. The extracts from Caesalpinia pulcherria, Chiranthodendron pentadactylon, Cocos nucifera, Geranium mexicanum (aerial parts and roots), Hippocratea excelsa, and Punica granatum possessed strong antibacterial activity against most of the pathogens tested. In general, methanolic extracts were more active than aqueous extracts. Their activity was higher than chloramphenicol but did not exceed that of trimethoprim. Shigella sonnei species showed the highest susceptibility to both extracts. This is the first evaluation of these plants against bacterial pathogen isolates, which cause diarrhea and dysentery in Mexican population.

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The aqueous and ethanol extracts of the root bark of Hippocratea excelsa HBK. Locally known as 'Cancerina', showed an important gastroprotective effect in several experimental ulcer models in rats. Fractionation of the methanol extract led to four pools of active fractions (F1-F4). Sitosterol-3-O-beta-glucoside, beta-sitosterol and (-) epicatechin were isolated from the active fractions and showed an important gastroprotective activity (93.4,85.7 and 72.1% of gastroprotection, respectively), whereas bismuth subsalicylate, used as positive control, showed 46.2% of gastroprotection. A mixture of alpha-amyrin and beta-amyrin showed 50% of gastroprotection. Friedelin, canophyllal and canophyllol were isolated from the active fractions, but they were inactive as gastroprotective compounds. These results provide additional support for the popular use of this plant as an antiulcer remedy in the Mexican traditional medicine.

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The ethanol extract of the plant Hippocratea excelsa was examined for its anti-inflammatory effects using several animal models. It produced significant inhibition of carrageenan-induced paw edema and reduced the weight of cotton pellet-induced granuloma at doses of 25-100 mg/kg. The extract was found to exert a protective effect on heat-induced erythrocyte lysis at concentrations of 25, 50 and 100 micrograms/ml. In chronic models of formaldehyde and adjuvant arthritis, its anti-arthritic activity was found to be less than that of phenylbutazone (PNB). It may be inferred that the ethanol extract is effective against both exudative-proliferative and chronic phases of inflammation.

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