Green fluorescent protein-producing Escherichia coli were used to investigate the fate of bacteria in the alimentary tract of sterile grown maggots, Lucilia sericata (Meigen), using a laser scanning confocal microscope. A computer program was used to analyze the intensity of the fluorescence and to quantify the number of bacteria. The crop and the anterior midgut were the most heavily infected areas of the intestine. A significant decrease in the amount of bacteria was observed in the posterior midgut. The number of bacteria decreased even more significantly in the anterior hindgut and practically no bacteria were seen in the posterior end, near the anus. The viability of bacteria in the different gut sections was examined. It was shown that 66.7% of the crops, 52.8% of the midguts, 55.6% of the anterior hindguts, and 17.8% of posterior hindguts harbored living bacteria. In conclusion, during their passage through the digestive tract the majority of E. coli was destroyed in the midgut. Most of the remaining bacteria were killed in the hindgut, indicating that the feces were either sterile or contained only small numbers of bacteria.
Tissue type plasminogen activator (tPA) is a key enzyme in the fibrinolytic cascade. In this paper we report that tPA contains 2 independent epitopes that exert opposite effects on blood vessel tone. Low concentrations of tPA (1 nM) inhibit the phenylephrine (PE)-induced contraction of isolated aorta rings. In contrast, higher concentrations (20 nM) stimulate the contractile effect of PE. The 2 putative vasoactive epitopes of tPA are regulated by the plasminogen activator inhibitor-1 (PAI-1) and by a PAI-1-derived hexapeptide that binds tPA. TNK-tPA, a tPA variant in which the PAI-1 docking site has been mutated, stimulates PE-induced vasoconstriction at all concentrations used. The stimulatory, but not the inhibitory, effect of tPA on the contraction of isolated aorta rings was abolished by anti-low-density lipoprotein receptor-related protein/␣ 2 -macroglobulin receptor (LRP) antibodies. Administering tPA or TNK-tPA to rats regulates blood pressure and cerebral vascular resistance in a dose-dependent mode. In other in vivo experiments we found that the vasopressor effect of PE is more pronounced in tPA knockout than in wildtype mice. Our findings draw attention to a novel role of tPA and PAI-1 in the regulation of blood vessel tone that may affect the course of ischemic diseases.
We have previously identified ␣-defensin in association with medial smooth muscle cells (SMCs) in human coronary arteries. In the present paper we report that ␣-defensin, at concentrations below those found in pathological conditions, inhibits phenylephrine (
Adherence of Mycoplasma fermentans to HeLa cells followed saturation kinetics, required a divalent cation, and was enhanced by preincubation of the organism at 37°C for 1 h in a low-osmolarity solution. Proteolytic digestion, choline phosphate, or anti-choline phosphate antibodies partially inhibited the adherence, supporting the notion that M. fermentans utilizes at least two surface components for adhesion, a protease-sensitive surface protein and a phosphocholine-containing glycolipid. Plasminogen binding to M. fermentans greatly increased the maximal adherence of the organism to HeLa cells. Anti-plasminogen antibodies and free plasminogen inhibited this increase. These observations suggest that in the presence of plasminogen the organism adheres to novel sites on the HeLa cell surface, which are apparently plasminogen receptors. Plasminogen-bound M. fermentans was detected exclusively on the cell surface of the infected HeLa cells. Nevertheless, plasminogen binding in the presence of the urokinase-type plasminogen activator (uPA) promoted the invasion of HeLa cells by M. fermentans. The latter finding indicates that the invasiveness of M. fermentans does not result from binding plasminogen but from activation of the bound plasminogen to plasmin. Cholesterol depletion and sequestration with -cyclodextrin and filipin, respectively, did not affect the capacity of M. fermentans to adhere, but invasion of HeLa cells by uPA-activated plasminogen-bound M. fermentans was impaired, suggesting that lipid rafts are implicated in M. fermentans entry.Mycoplasmas (class Mollicutes) are wall-less prokaryotes that are widely distributed in nature. Most mycoplasmas are parasites, exhibiting strict host and tissue specificities, and almost all of them are bound to the surface of the host cells. Almost all animal mycoplasmas depend on adhesion to host tissues for subsequent colonization and infection (26,31). In these mycoplasmas, adherence is the major virulence factor, and adherence-deficient mutants are avirulent (3, 32). The best-studied adherence system is that of Mycoplasma pneumoniae, the causative agent of primary atypical pneumonia in humans. Adherence of this organism to cells in the respiratory tract is an initial and essential step in tissue colonization and the subsequent development of disease (20). A surface 169-kDa protein designated P1 (18) and a 30-kDa protein designated P30 (11) are densely clustered at the tip organelle of virulent M. pneumoniae and are associated with the adherence process.The human pathogen Mycoplasma fermentans was isolated from the urogenital tract several decades ago (33). Interest in this organism has recently increased because of its possible role in the pathogenesis of rheumatoid arthritis and reports indicating that this organism may function as a cofactor accelerating the progression of human immunodeficiency virus disease (22, 28). Although M. fermentans is a typical extracellular microorganism able to adhere to human epithelial cells, ultrastructural studies performed with engu...
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