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To investigate the antidiarrheal mechanism of quercetin extracted from Psidium guajava L. The effects of quercetin on the contractility of guinea pig ileum in vitro and on the peristaltic motion of mouse small intestine in vivo were observed, and the peak value of contractility and peristaltic distance recorded. The inhibitory effect of quercetin on the permeability of the abdominal capillaries was also observed. Quercetin inhibited the contraction of guinea pig ileum in vitro and the peristaltic motion of mouse small intestine, and reduced the permeability of abdominal capillaries. Quercetin can inhibit the intestinal movement and reduce capillary permeability in the abdominal cavity, which may be the antidiarrheal mechanism of Psidium guajava L extract.
The stimulating effect of subinhibitory concentrations of antibiotics on the production of verocytotoxin (VT) by enterohaemorrhagic Escherichia coli (EHEC) O157:H7 has been claimed. The purpose of this study was to find an alternative, but bioactive medicine for the treatment of this organism. Fifty-eight preparations of aqueous and ethanolic extracts of 38 medicinal plant species commonly used in Thailand to cure gastrointestinal infections were tested for their antibacterial activity against different strains of Escherichia coli, including 6 strains of Escherichia coli O157:H7, Escherichia coli O26:H11, Escherichia coli O111:NM, Escherichia coli O22; 5 strains of Escherichia coli isolated from bovine; and Escherichia coli ATCC 25922. Inhibition of growth was primarily tested by the paper disc agar diffusion method. Among the medicinal plants tested, only 8 species (21.05%) exhibited antimicrobial activity against Escherichia coli O157:H7. Acacia catechu, Holarrhena antidysenterica, Peltophorum pterocarpum, Psidium guajava, Punica granatum, Quercus infectoria, Uncaria gambir, and Walsura robusta demonstrated antibacterial activity with inhibition zones ranging from 7 to 17 mm. The greatest inhibition zone against Escherichia coli O157:H7 (RIMD 05091083) was produced from the ethanolic extract of Quercus infectoria. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined by the agar microdilution method and agar dilution method in petri dishes with millipore filter. Both aqueous and ethanolic extracts of Quercus infectoria and aqueous extract of Punica granatum were highly effective against Escherichia coli O157:H7 with the best MIC and MBC values of 0.09, 0.78, and 0.19, 0.39 mg/ml, respectively. These plant species may provide alternative but bioactive medicines for the treatment of Escherichia coli O157:H7 infection.
Five guava seed glutelin extracts were obtained with different buffer solutions: Na(2)B(4)O(7) alone (Glut.Bo) or containing SDS (Glut. BoSDS), 2-mercaptoethanol (Glut.Bo2-ME), or a combination of both (Glut. BoSDS2-ME) and NaOH (Glut.Na). All borate buffer solutions were at pH 10. The higher yield of glutelins corresponded to the Glut. BoSDS extract (81.9% dry basis) and the lower to Glut.Bo (6.8%). The functional properties of the five guava seed glutelin extracts were determined. Glut. BoSDS, Glut. BoSDS2-ME, and Glut.Na showed high values for several properties, including surface hydrophobicity (7.7, 10.8, and 0.6, respectively), solubility at pH 10 (91.1, 77.9, and 96.7, respectively), water-holding capacity at pH 3.6 (1.7, 2.5, and 2.8, respectively), emulsifying activity index (pH 10; 503.5, 238.2, and 838.0, respectively), and foaming properties (pH 10; V(0) = 0.14, 0.25, and 0.19, respectively; V(max) = 6.1, 5.59, and 4.51, respectively; t(1/2) = 266, 255.3, and 94 s, respectively). These results suggest that the denaturing reagent (SDS or NaOH) during extraction conferred on the proteins a structure that facilitated the development of their functional properties.