Enterotoxigenic Escherichia coli (ETEC), a major cause of infectious diarrhea, produce heat-stable and/or heat-labile enterotoxins and at least 25 different colonization factors that target the intestinal mucosa. The genes encoding the enterotoxins and most of the colonization factors are located on plasmids found across diverse E. coli serogroups. Whole-genome sequencing of a representative collection of ETEC isolated between 1980 and 2011 identified globally distributed lineages characterized by distinct colonization factor and enterotoxin profiles. Contrary to current notions, these relatively recently emerged lineages might harbor chromosome and plasmid combinations that optimize fitness and transmissibility. These data have implications for understanding, tracking and possibly preventing ETEC disease.
Helicobacter pylori colonizes the gastric and duodenal mucosa. The infection normally persists for life and causes peptic ulcers and gastric cancer in a subset of infected individuals. We hypothesized that the inability to clear the infection may be a consequence of H. pylori-specific regulatory T cells that actively suppress T-cell responses. Therefore, we characterized the T-cell responses to H. pylori in H. pylori-infected individuals without any subjective symptoms and in uninfected control subjects and investigated the role of regulatory CD4
A cohort of 321 children was followed from birth up to 2 years of age to determine the incidence of enterotoxigenic Escherichia coli (ETEC) in Bangladesh. The average number of diarrheal days and incidence rates were 6.6 and 2.3/child/year, respectively. ETEC was the most common pathogen and was isolated in 19.5% cases, with an incidence of 0.5 episode/child/year. The prevalence of rotavirus diarrhea was lower (10%). ETEC expressing the heat-stable enterotoxin (ST) was predominant. Strains isolated from diarrheal cases were positive for colonization factors (CFs) in higher frequency (66%) than from healthy children (33%) (P < 0.001). The heat-labile toxin (LT)-positive strains from healthy children were more often CF negative (92%) than those isolated from children with diarrhea (73%) (P < 0.001). In children with symptomatic or asymptomatic infections by CFA/I, CS1 plus CS3, CS2 plus CS3, or CS5 plus CS6 strains, a repeat episode of diarrhea or infection by the homologous CF type was uncommon. Repeat symptomatic infections were noted mostly for LTand ST-expressing ETEC. ETEC diarrhea was more prevalent in children in the A and AB groups than in those in the O blood group (P ؍ 0.032 to 0.023). Children with ETEC diarrhea were underweight and growth stunted at the 2-year follow-up period, showing the importance of strategies to prevent and decrease ETEC diarrheal morbidity in children.Enterotoxigenic Escherichia coli (ETEC) is a common cause of acute watery diarrhea in children in developing countries (25). ETEC is a multivalent pathogen producing the heatstable (ST) and/or heat-labile toxin (LT) as well as over 25 colonization factors (CFs). The ST phenotype of ETEC has been shown to be predominant (23,25), while the most common of the CFs are CFA/I and CS1 to CS6 (14,23,25,37). Studies in animals and in humans suggest that immunity against both LT and CFs may be important for protection against ETEC. However, results from different studies are conflicting regarding the relative importance of different toxin types and/or CFs on protection from further disease and infection (11,18,27,32), and data from different settings are needed to elucidate whether ETEC strains expressing these different virulence factors may prevent against repeated episodes of diarrhea. The first longitudinal study to determine the relationship between ETEC and other enteric pathogens and the incidence of diarrhea of children in a birth cohort was carried out in Mexico (10). In the present study, we have evaluated the natural history of ETEC infections, with emphasis on the different phenotypes, during the first 2 years of life in a birth cohort of 321 children in an urban slum area in Dhaka, Bangladesh. This included evaluation of the incidence, seasonality, and occurrence of symptomatic and asymptomatic ETEC infections. We have also evaluated whether blood group and nutritional factors may predispose to ETEC diarrhea. For comparison, we have also studied the incidence of other common enteric infections.
MATERIALS AND METHODS
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