Jose Flores

Enteroaggregative Escherichia coli infection

Purpose of review To review studies that improve the current knowledge on the epidemiology, virulence factors, detection, and chronic complications of enteroaggregative Escherichia coli (EAEC) infection. Recent findings EAEC infection is an important cause of diarrhea in outbreak and non-outbreak settings in developing and developed countries. In the USA, EAEC is one of the most common bacterial pathogens identified in cases of diarrhea not associated with immunodeficiency or foreign travel. Important advances have been made in the understanding of the pathogenesis of this enteropathogen. The extracellular matrix proteins fibronectin, laminin, and collagen IV have been shown to function as receptors for adherence frimbriae. A distinct aggregative adherence pilin hdaA has been identrified. The diagnosis of EAEC depends on the observation of the characteristic ‘stacked-brick’ like adhesion pattern when co-cultured with HEp-2 cells. At the molecular level, strains demonstrating the aggregative phenotype are heterogeneous; however, several virulence factors can be detected by polymerase chain reaction. Several EAEC proteins have shown antigenicity and could become vaccine candidates. Recently, infection with EAEC has been implicated in the development of irritable bowel syndrome, but this remains to be confirmed. Summary There has been significant progress in understanding the pathogenesis and clinical profile of EAEC infection.

Influence of Host Interleukin-10 Polymorphisms on Development of Traveler's Diarrhea Due to Heat-Labile Enterotoxin-Producing Escherichia coli in Travelers from the United States Who Are Visiting Mexico

ABSTRACT Up to 60% of U.S. visitors to Mexico develop travelers diarrhea (TD), mostly due to enterotoxigenic Escherichia coli (ETEC) strains that produce heat-labile (LT) and/or heat-stable (ST) enterotoxins. Distinct single-nucleotide polymorphisms (SNPs) within the interleukin-10 (IL-10) promoter have been associated with high, intermediate, or low production of IL-10. We conducted a prospective study to investigate the association of SNPs in the IL-10 promoter and the occurrence of TD in ETEC LT-exposed travelers. Sera from U.S. travelers to Mexico collected on arrival and departure were studied for ETEC LT seroconversion by using cholera toxin as the antigen. Pyrosequencing was performed to genotype IL-10 SNPs. Stools from subjects who developed diarrhea were also studied for other enteropathogens. One hundred twenty-one of 569 (21.3%) travelers seroconverted to ETEC LT, and among them 75 (62%) developed diarrhea. Symptomatic seroconversion was more commonly seen in subjects who carried a genotype producing high levels of IL-10; it was seen in 83% of subjects with the GG genotype versus 54% of subjects with the AA genotype at IL-10 gene position −1082 (P, 0.02), in 71% of those with the CC genotype versus 33% of those with the TT genotype at position −819 (P, 0.005), and in 71% of those with the CC genotype versus 38% of those with the AA genotype at position −592 (P, 0.02). Travelers with the GCC haplotype were more likely to have symptomatic seroconversion than those with the ATA haplotype (71% versus 38%; P, 0.002). Travelers genetically predisposed to produce high levels of IL-10 were more likely to experience symptomatic ETEC TD.

Characterization of Norovirus-Associated Traveler's Diarrhea

BACKGROUND Travelers diarrhea is the most common medical complaint of international visitors to developing regions. Previous findings suggested that noroviruses (NoVs) are an underappreciated cause of travelers diarrhea. METHODS. In the present study, we sought to define the presence of NoVs in 320 acute diarrheic stool samples collected from 299 US students who traveled to Guadalajara, Cuernavaca, or Puerto Vallarta, Mexico, during the period from 2007 through 2008. Conventional and quantitative real-time polymerase chain reaction assays were used to detect and determine NoV loads in stool samples. NoV strains were characterized by purification of viral RNA followed by sequencing of the viral capsid protein 1 gene. Sequences were compared using multiple sequence alignment, and phylogenetic trees were generated to evaluate the evolutionary relatedness of the viral strains associated with cases of travelers diarrhea. RESULTS NoV RNA was detected in 30 (9.4%) of 320 samples. Twelve strains belonged to genogroup I, and 18 strains belonged to genogroup II. NoV prevalence was higher in the winter season than in the summer season (23% vs 7%, respectively; P = .001). The cDNA viral loads of genogroup I viruses were found to be 500-fold higher than those of genogroup II strains. Phylogenetic analysis revealed a diverse population of NoV strains over different locations and years. CONCLUSIONS NoV strains are important causes of travelers diarrhea in Mexico, especially during the wintertime, and US students in Mexico may represent a suitable group for future NoV vaccine efficacy trials.

Genetics of Susceptibility to Infection with Enteric Pathogens

Purpose of review This review examines recent developments in human genetic susceptibility to enteropathogens that cause infectious diarrhea. Recent findings The affinity of specific norovirus genogroups to different histoblood group antigens (HBGAs) on secretor cells has been studied in different epidemiologic studies. HBGAs are also used as receptors by Vibrio cholerae with different degrees of affinity between biotypes. Polymorphisms in the CD14, lactoferrin and osteoprotegerin promoter genes were associated to diarrhea in travelers. Single nucleotide polymorphisms in the IL-8 genes are also associated to increased risk for enteroaggregative Escherichia coli and Clostridium difficile infection. IL-10 haplotypes were associated to enterotoxigenic E. coli associated diarrhea in exposed individuals. A family-based study showed a significant association of the LPLUNC1 gene and cholera. The major histocompatibility complex class II antigens are associated to different degrees of susceptibility and resistance to Salmonella, Cryptosporidium and Entamoeba infection. Summary Variants in genes that encode molecules that mediate attachment, pathogen recognition, inflammatory cytokine response, innate and acquired immunity are being identified as determinants of host genetic susceptibility to infectious diarrhea.

Single Nucleotide Polymorphisms in the Promoter of the Gene Encoding the Lipopolysaccharide Receptor CD14 Are Associated With Bacterial Diarrhea in US and Canadian Travelers to Mexico

BACKGROUND Under normal conditions, the expression of CD14, which is the principal receptor for bacterial lipopolysaccharide, is down-regulated in the intestinal mucosa but increases in response to inflammatory stimuli. The aim of the present study was to investigate whether fecal CD14 levels increased in response to infection with diarrheagenic Escherichia coli and whether single nucleotide polymorphisms (SNPs) in the CD14 gene were associated with an increased susceptibility to travelers diarrhea (TD) in US visitors to Mexico. METHODS Six SNPs located at the promoter, exon, and untranslated regions of CD14 were typed in a prospective cohort study of 1360 visitors to Mexico at risk for TD. Stools from visitors with TD were studied for enteric pathogens by culture, colony hybridization, and polymerase chain reaction. Fecal soluble CD14 (sCD14) was measured in a subgroup of 203 adults with diarrhea and 66 healthy controls by enzyme-linked immunosorbent assay. RESULTS The minor allele frequencies for CD14 SNPs were significantly different among the various racial and ethnic groups studied. Two SNPs in the promoter region of CD14 (-159 C > T; rs2569190 and -4191 C > T; rs5744441) were found to be associated with TD in White visitors. The -159 TT genotype was associated with a higher risk for TD (Relative risk [RR], 1.21; 95% confidence interval [CI], 1.05-1.38; P = .008), whereas individuals with the -4191 TT genotype were protected from infection (RR, 0.82; 95% CI, 0.71-0.92; P = .006). Subjects with TD excreted higher levels of fecal CD14 than did healthy controls (33,480 pg/mL vs 6178 pg/mL; P < .02). Fecal sCD14 levels were higher in stool samples from visitors with TD and the -159 TT genotype than they were in visitors with the CC/CT genotypes (P = .02), and stool samples from subjects with the -4191 CC genotype had higher fecal sCD14 levels than did stool samples from visitors with the CT/TT (P = .005) genotype. In a multivariate analysis with haplotypes constructed with the 6 SNPs studied, subjects with the haplotype containing the -159 C and the -4191 T allele were less likely to acquire TD (P = .015). CONCLUSIONS Our study suggests that CD14 levels increase in response to bacterial diarrhea and that polymorphisms in the CD14 gene influence susceptibility to TD. Intestinal CD14 plays an important role in the innate immune response to enteric pathogens.

A single-nucleotide polymorphism in the gene encoding osteoprotegerin, an anti-inflammatory protein produced in response to infection with diarrheagenic Escherichia coli, is associated with an increased risk of nonsecretory bacterial diarrhea in North American travelers to Mexico

BACKGROUND Osteoprotegerin (OPG), an immunoregulatory member of the TNF receptor superfamily, is expressed in inflamed intestinal mucosa. We investigated whether OPG is produced by intestinal epithelial cells and tested the hypothesis that single-nucleotide polymorphisms (SNPs) in the gene encoding OPG (TNFRSF11B) are associated with travelers diarrhea (TD) among North American travelers to Mexico. METHODS OPG concentration was measured in the supernatants of T84 cells infected with various diarrheagenic Escherichia coli pathotypes. Genotyping was performed for 4 SNPs in the OPG gene for 968 North American travelers with or without TD. Stool samples from travelers with TD were evaluated for the presence of enteric pathogens. RESULTS T84 cells produced higher OPG levels in response to infection with various diarrheagenic E. coli pathotypes than with E. coli controls (P<.05). A SNP in the exon 1 region of the OPG gene (OPG+1181G>C) was associated with TD in white travelers who stayed in Mexico for >1 week during the summer (P=.009) and for TD due to nonsecretory pathogens (P=.001). CONCLUSIONS Our study suggests that OPG is secreted by intestinal epithelial cells in response to enteropathogens and that a polymorphism in the OPG gene is associated with an increased susceptibility to TD.

Seroprevalence of the enteroaggregative Escherichia coli virulence factor dispersin among USA travellers to Cuernavaca, Mexico: A pilot study

This pilot study examined the change in the seroprevalence of the enteroaggregative Escherichia coli (EAEC) virulence factor dispersin in USA students during a short stay in Cuernavaca, Mexico, between June and August 2004. One hundred and ninety-five students provided paired serum samples - one on arrival to Mexico (pre-serum) and a second on departure from Mexico (post-serum) after a mean stay of 19 days. Serum samples were tested for IgG antibody to a recombinant purified dispersin protein by ELISA. For all travellers, with and without diarrhoea, the mean+/-sd pre-serum absorbance value (read at 450 and 570 nm) was 0.340+/-0.212 and the mean post-serum value was 0.513+/-0.316 (P<0.00001). Both travellers who developed diarrhoea and those who did not develop diarrhoea had an increase in IgG antibody to dispersin from the time of arrival to the time of departure from Cuernavaca (diarrhoea group 0.323+/-0.197 to 0.501+/-0.311, P<0.00001, and the asymptomatic group 0.354+/-0.224 to 0.525+/-0.321, P<0.00001). The pre-serum absorbance value (read at 450 and 570 nm) for IgG antibody to dispersin was not associated with protection against the development of diarrhoeal illness. These results indicate that USA travellers to Mexico show seroconversion for the EAEC virulence factor dispersin. Further studies are needed to characterize in more detail the host clinical and immunological responses to the dispersin protein.