Enteroaggregative Escherichia coli an emergent pathogen with different virulence properties.

Enteroaggregative Escherichia coli (EAEC) is an emergent bacterial pathogen. The first studies in developing countries with EAEC strains, showed that this bacterium was associated with persistent diarrhea. However, new studies showed that EAEC may be associated also with acute diarrhea, with both nosocomial and community outbreaks worldwide, and as an important pathogen of diarrheal disease in human immunodeficiency virus-infected adults. EAEC strains are recognized by their characteristic aggregative adherence or "stacked-brick" pattern to epithelial cells. Although the pathogenesis of EAEC infection is not well understood, cellular changes observed in animal models and in vitro assays, suggested that the alterations in the intestinal mucosa during EAEC infection are associated with adherence factors and toxins production. The damage has been associated with the release of inflammatory mediators, which may contribute also to the intestinal illness. The dissemination of the high pathogenicity island from Yersinia pestis evolutionary group to EAEC has been show; different studies suggest that it may contribute to the virulence of EAEC strains. Molecular methods to investigate the presence of plasmid and chromosomal EAEC-associated virulence markers, have been used for the characterization and epidemiological studies of EAEC strains. Although the clinical and epidemiological importance of EAEC have been demonstrated in different studies, Escherichia coli strains with adherent agreggative phenotype are commonly isolated from healthy children and environmental sources. This support the necessity to study virulence factors no related with the cells adherence pattern, that show the specific EAEC pathogenic clones associated whit intestinal disease.

Pet toxin from enteroaggregative Escherichia coli produces cellular damage associated with fodrin disruption.

Pet toxin is a serine protease from enteroaggregative Escherichia coli which has been described as causing enterotoxic and cytotoxic effects. In this paper we show that Pet produces spectrin and fodrin (nonerythroid spectrin) disruption. Using purified erythrocyte membranes treated with Pet toxin, we observed degradation of alpha- and beta-spectrin chains; this effect was dose and time dependent, and a 120-kDa protein fraction was observed as a breakdown product. Spectrin degradation and production of the 120-kDa subproduct were confirmed using specific antibodies against the alpha- and beta-spectrin chains. The same degradation effect was observed in alpha-fodrin from epithelial HEp-2 cells, both in purified cell membranes and in cultured cells which had been held in suspension for 36 h; these effects were confirmed using antifodrin rabbit antibodies. The spectrin and fodrin degradation caused by Pet is related to the Pet serine protease motif. Fluorescence and light microscopy of HEp-2 Pet-treated cells showed morphological alterations, which were associated with irregular distribution of fodrin in situ. Spectrin and fodrin degradation by Pet toxin were inhibited by anti-Pet antibodies and by phenylmethylsulfonyl fluoride. A site-directed Pet mutant, which had been shown to abolish the enterotoxic and cytotoxic effects of Pet, was unable to degrade spectrin in erythrocyte membranes or purified spectrin or fodrin in epithelial cell assays. This is a new system of cellular damage identified in bacterial toxins which includes the internalization of the protease, induction of some unknown intermediate signaling steps, and finally the fodrin degradation to destroy the cell.

In vitro effects of a high-molecular-weight heat-labile enterotoxin from enteroaggregative Escherichia coli.

The pathogenic mechanisms of enteroaggregative Escherichia coli (EAggEC) infection are not fully elucidated. In this work we show that an ammonium sulfate precipitate of culture supernatant of EAggEC strain 049766 increased the potential difference (PD) and the short-circuit current (Isc) in rat jejunal preparations mounted in Ussing chambers. The precipitate contained two major proteins of 108 and 116 kDa, which were partially copurified by chromatography in DEAE-cellulose. This chromatographic fraction (peak I) increased jejunal PD and Isc in a dose-dependent manner, accompanied by a decrease in tissue electrical resistance. These effects were inhibited by incubation of peak I at 75 degreesC for 15 min or for 1 h with proteinase K at 37 degreesC. Rabbit polyclonal antibodies against peak I containing both the 108- and 116-kDa proteins inhibited the enterotoxic effect. Specific polyclonal antibodies raised against the 108-kDa but not against the 116-kDa protein inhibited the enterotoxic effect, suggesting that the 108-kDa protein is the active toxic species. Moreover, another EAggEC strain (065126) producing the 116-kDa protein but not the 108-kDa protein had no effect on rat jejunal mucosa in the Ussing chamber. The >100-kDa fraction derived from prototype EAggEC strain 042, which also expressed both 108- and 116-kDa proteins, also produced an enterotoxic effect on rat jejunal preparations in Ussing chambers; however, the same strain cured of its 65-MDa adherence plasmid did not. A subclone derived from the 65-MDa plasmid expressing the 108-kDa toxin (and not the 116-kDa protein) elicited rises in Isc. Tissue exposed to any preparation containing the 108-kDa toxin exhibited similar histopathologic changes, characterized by increased mucus release, exfoliation of cells, and development of crypt abscesses. Our data suggest that some EAggEC strains produce a ca. 108-kDa enterotoxin/cytotoxin which is encoded on the large virulence plasmid.

Detection of dengue virus from mosquito cell cultures inoculated with human serum in the presence of actinomycin D.

We report the use of cultures of mosquito cells (TRA-284) to detect dengue virus in serum from cases of dengue fever in the state of Puebla, México. Using the conventional procedure 56 of 171 samples (32.7%) were positive. The negative sera (67.3%) were passaged 'blind' in mosquito cell cultures but no virus was detected. However, when these sera were incubated in the presence of actinomycin D (an inhibitor of deoxyribonucleic acid transcription) 20 of the 115 samples (17.4%) became positive. This procedure increased the virus detection rate from 32.7% to 44.4%. Serotypes 1 and 4 were identified for the first time in the state of Puebla, where the transmission of dengue virus is increasing. The addition of actinomycin D to mosquito cell cultures may improve the detection of dengue virus and could be a useful tool for virological surveillance in endemic countries.

[Hemorrhagic fever and the dengue shock syndrome]. / Fiebre hemorrágica y síndrome de choque por dengue.

Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS) are the severe and/or fatal clinical manifestations of dengue fever. Epidemics of DHF/DSS occur mainly in the southeast Asian countries where children are seriously affected and high case-fatality ratio is annually reported. Recently significant epidemics of DHF/DSS have been reported in Cuba, Venezuela and Brazil, which means that reinforcements of the epidemiological surveillance in the countries of the American region that show high virus transmission, are urgently needed. The main purpose of the present article is to review relevant information regarding the clinical manifestations, pathology, diagnostic procedures, treatment of cases, pathophysiologic mechanisms and some data related with specific DHF/DSS epidemics.