Enteropathogens associated with acute diarrheal disease in urban infants in São Paulo, Brazil

Diarrheogenic Escherichia coli

The diarrheogenic E coli are currently difficult to diagnose and treat. For physicians in the United States, they are primarily a concern in children returning from international travel. The exception to this generalization is STEC, which, because of the low inoculum, ease of transmission, and serious consequences, are important pathogens in the United States.

Acute diarrhea and malnutrition: lethality risk in hospitalized infants

OBJECTIVES

Acute diarrhea is a very frequent disease in developing countries and is the first cause of death in infants under two years of age. This study was designed to evaluate the clinical and epidemiological factors associated to the death of 17 out of 511 infants hospitalized due to severe acute diarrhea between January 1989 and December 1995.

PATIENTS AND METHODS

The patients were divided into two groups according to their clinical evolution: Group I--Death and Group II--Survival. The following parameters were evaluated: birth weight, gender, age, duration of diarrhea (days) prior to admission, nutritional status, hydration, presence of an enteropathogenic agent in the stools, food intolerance and duration of hospitalization.

RESULTS

The analyzed factors have shown a significant association with death for the following variables: age, relative factor of death (RFD)=4.0 for infants less than six months of age, identification of an enteropathogenic Escherichia coli (EPEC) strain in the stools (RFD=3.3), severe malnutrition at admission to the hospital (RFD=4.5), occurrence of food intolerance during hospitalization (RFD=2.7). Some enteropathogenic agent was identified in the stools of 253 infants (54.9%), among the 461 (90.2%) studied. Group I revealed the presence of an enteropathogenic agent in 75% of the cases. The most frequent agents identified in Group I were: EPEC (56.3%) and Shigella (12.5%), while in Group II EPEC was identified in 26.5% of the patients.

CONCLUSIONS

The association of some factors, such as age less than six months, severe malnutrition, food intolerance and the identification of EPEC strains in the stool culture, indicate a high risk of death in infants hospitalized due to severe acute diarrhea.

A localized adherence-like pattern as a second pattern of adherence of classic enteropathogenic Escherichia coli to HEp-2 cells that is associated with infantile diarrhea

Escherichia coli strains that cause nonbloody diarrhea in infants are known to present three distinct patterns of adherence to epithelial cells, namely, localized (LA), diffuse (DA), and aggregative (AA) adherence. Strains with LA (typical Enteropathogenic Escherichia coli [EPEC]) are well recognized as a cause of secretory diarrhea, but the role of strains with DA (DAEC) is controversial, and strains with AA (EAEC) have been more frequently related to persistent diarrhea whereas its relationship with acute diarrhea is not well defined. To determine the relationship of the different types of E. coli adherence patterns with acute diarrhea (lasting less than 14 days) and persistent diarrhea (lasting more than 14 days) in São Paulo, Brazil, we studied stool specimens from 40 infants under 1 year of age with diarrhea and 40 age-matched control infants without any gastrointestinal symptoms. Twenty-eight (35.0%) of eighty cases yielded adherent E. coli (HEp-2 cells). Strains with localized and aggregative adherence were associated with acute and persistent diarrhea. A total of 11.2% of the adherent strains were typical EPEC serotypes and hybridized with the enteroadherence factor probe; 5.0% were EAEC and hybridized with the EAEC probe. DAEC strains were isolated from 10.0% of patients and 7.5% of controls and did not hybridize with the two probes used (daaC and AIDA-I). Strains with a localized adherence-like pattern (atypical EPEC) were found significantly more frequently (P = 0.028) in cultures from children with diarrhea (17.5%) than in controls (2.5%).

Expression of a pilin subunit BfpA of the bundle-forming pilus of enteropathogenic Escherichia coli in an aroA live salmonella vaccine strain

Enteropathogenic Escherichia coli (EPEC) is a major cause of childhood diarrhea in developing countries and is a leading cause of severe diarrheal illness among Brazilian infants. As one approach to constructing a vaccine candidate against diarrhea caused by EPEC, we evaluated whether the pilin subunit (BfpA) of the bundle-forming pilus (BFP) could be expressed by a live Salmonella vaccine strain. Several copies of the coding region of BfpA (bfpA) were amplified by PCR from a preparation of the EAF plasmid of EPEC strain B171 and cloned into plasmid vectors. An intact copy of bfpA was subcloned into the heat inducible prokaryotic expression vector pCYTEXP1, and the resulting pBfpA was used to transform the aroA S. typhimurium strain SL3261, generating SL3261(pBfpA). The recombinant vaccine strain was able to express, but not to process, rBfpA as evidenced by a prominent 21 kDa protein that crossreacted with anti-BFP antiserum found only in extracts of heat-treated SL3261(pBfpA), but not in strains of untreated SL3261(pBfpA) or SL3261 not carrying the plasmid. Furthermore, rBfpA accumulation was not toxic to the Salmonella host, as evidenced by similar plating efficiencies between induced and uninduced strains of SL3261(pBfpA). Finally, SL3261(pBfpA) orally administered to BALB/c mice was capable of eliciting a sustained and vigorous humoral immune response to BfpA, achievable even with a single oral dose of approximately 10(9) organisms. Therefore, this pilin product may serve as a potential immunogen as part of a live combined vaccine strategy to prevent two of the major public health problems in Brazil--salmonellosis and EPEC childhood diahrrea.

Adherence patterns and adherence-related DNA sequences in Escherichia coli isolates from children with and without diarrhea in São Paulo city, Brazil

The correlation between various adherence patterns and adherence-related DNA sequences in Escherichia coli isolates from 1- to 4-year-old children with and without diarrhea in São Paulo, Brazil, was evaluated. A total of 1,801 isolates obtained from 200 patients and 200 age-matched controls were studied. The adherence patterns found were classified as diffuse, aggregative, aggregative in a 6-h assay, aggregative predominantly in coverslips, localized, localized-like, and noncharacteristic. In general, the DNA sequences used as probes showed excellent specificities (>93%), but their sensitivities varied. Thus, the results of bioassays and assays with DNA probes normally used to search for adherent E. coli did not correlate well, and the best method for the identification of these organisms in the clinical research setting remains controversial. Isolates presenting diffuse adherence or hybridizing with the related daaC probe, or both, were by far the most frequent in patients (31.5, 26.0, and 23.0%, respectively), followed by isolates presenting aggregative adherence or hybridizing with the related EAEC probe, or both (21.5, 13.0, and 10.5%, respectively). None of the different combinations of adherence patterns and adherence-related DNA sequences found were associated with acute diarrhea.

Etiological study of diarrheal patients in Vientiane, Lao People's Democratic Republic

The etiological agents of diarrhea in Vientiane, Lao People's Democratic Republic (Lao PDR), were studied in the period from October 1996 to August 1997. A total of 880 patients with diarrhea visiting medical facilities were examined for Shigella, Salmonella, diarrheagenic Escherichia coli, vibrio, Aeromonas, Campylobacter, and rotavirus. Shigella spp., heat-stable enterotoxin (ST)-producing E. coli, and serogroup-based enteropathogenic E. coli were found to be the main organisms causing diarrhea in Vientiane, with frequencies of 16.8% (148 of 880), 17.2% (111 of 645), and 11.0% (97 of 880), respectively. Relatively low incidences were observed in the cases of Salmonella spp., (0.6%; 5 of 880), Campylobacter spp. (4.4%; 39 of 880), and rotavirus (6.1%; 9 of 148), and no isolates of V. cholerae O1 or O139 or Aeromonas were recovered. An analysis of the incidences of enteropathogens with respect to age and seasonal variations demonstrated that the frequencies of isolation of Shigella spp. and heat-labile enterotoxin-producing E. coli were significantly higher in those aged 1 to 5 years than in those younger than 1 year of age and those older than 5 years of age (P < 0.0001 and P < 0.05, respectively) and that the frequencies of isolation of Shigella spp. and ST-producing E. coli were significantly higher in the rainy season than in the dry season (P < 0.005 and P < 0.001, respectively). Almost all strains of Shigella spp. tested were resistant to ampicillin, tetracycline, and erythromycin and were susceptible to cefdinir and ofloxacin. This is the first intensive and longitudinal study to define the etiologic agents of diarrheal diseases in Lao PDR.

Placental transfer of IgG and IgG subclass antibodies anti-purified Escherichia coli LPS O16, O6 and O111

We evaluated 22 paired maternal and cord sera regarding the presence of IgG and IgG subclasses against purified Escherichia coli LPS O6, O16 and O111 employing ELISA for titre and avidity analysis, isoelectric focusing associated with affinity-blotting for spectrotypic analysis, and the Western-blotting technique for recognition of the various bands in lipopolysaccharide (LPS). Levels of anti-LPS IgG antibodies in cord sera were equivalent to their respective maternal sera, showing a significant correlation (P < 0.0001). IgG1 antibody levels were higher in cord sera than in maternal sera (P < 0.005 for anti-O111, P < 0.05 for anti-O16 and P < 0.02 for anti-O6). Cord IgG2 antibody levels were not different from the maternal levels (P > 0.1). The levels of IgG3 and IgG4 were undetectable. The avidity of anti-O6 and anti-O111 IgG in 10 cord sera showed an extremely significant correlation with maternal antibody avidity (P < 0.0001). Identical patterns of recognition were found in the paired samples analysed by Western blotting. Most of the serum samples recognized the O-repetitive chains and also the region corresponding to core and lipid A. Although the antibody spectrotypes varied among individuals, paired cord and maternal serum samples showed identical patterns. Our findings suggest the occurrence of placental transfer of IgG antibodies against LPS O6, O16 and O111, mainly involving the IgG1 or IgG2 subclasses.

Association of Providencia alcalifaciens with diarrhea in children

It has been demonstrated in previous studies that Providencia alcalifaciens can produce diarrhea by an invasive mechanism. In the present study, P. alcalifaciens was isolated from the stool specimens of 17 of 814 diarrheal children younger than 5 years of age (2.1%) and from those of 4 of 814 matched controls (0.49%) (P = 0.004), indicating that the organism is significantly associated with diarrhea. However, 71% of P. alcalifaciens-positive diarrheal children had simultaneous infections with other recognized enteric pathogens.

Effect of prior experimental human enteropathogenic Escherichia coli infection on illness following homologous and heterologous rechallenge

Two studies of adult volunteers were performed to determine whether prior enteropathogenic Escherichia coli (EPEC) infection confers protective immunity against rechallenge. In the first study, a naive control group and volunteers who had previously ingested an O55:H6 strain were fed an O127:H6 strain. In the second study, a control group and volunteers who had previously ingested either the O127:H6 strain or an isogenic eae deletion mutant of that strain were challenged with the homologous wild-type strain. There was no significant effect of prior infection on the incidence of diarrhea in either study. However, in the homologous-rechallenge study, disease was significantly milder in the group previously challenged with the wild-type strain. Disease severity was inversely correlated with the level of prechallenge serum immunoglobulin G against the O127 lipopolysaccharide. These studies indicate that prior EPEC infection can reduce disease severity upon homologous challenge. Further studies may require the development of new model systems.

Diarrheagenic Escherichia coli

Escherichia coli is the predominant nonpathogenic facultative flora of the human intestine. Some E. coli strains, however, have developed the ability to cause disease of the gastrointestinal, urinary, or central nervous system in even the most robust human hosts. Diarrheagenic strains of E. coli can be divided into at least six different categories with corresponding distinct pathogenic schemes. Taken together, these organisms probably represent the most common cause of pediatric diarrhea worldwide. Several distinct clinical syndromes accompany infection with diarrheagenic E. coli categories, including traveler's diarrhea (enterotoxigenic E. coli), hemorrhagic colitis and hemolytic-uremic syndrome (enterohemorrhagic E. coli), persistent diarrhea (enteroaggregative E. coli), and watery diarrhea of infants (entero-pathogenic E. coli). This review discusses the current level of understanding of the pathogenesis of the diarrheagenic E. coli strains and describes how their pathogenic schemes underlie the clinical manifestations, diagnostic approach, and epidemiologic investigation of these important pathogens.

Culture supernatant of Shiga toxin-producing Escherichia coli strains provoke fluid accumulation in rabbit ileal loops

Production of Shiga toxin (Stx) in Escherichia coli strains belonging to serogroups O26, O111, and O157 was evaluated in the rabbit ileal loop assay and results were compared to those using tissue culture assays and DNA hybridization with specific probes for Stx1 and Stx2. All 14 Shiga toxin-producing E. coli strains tested provoked fluid accumulation in the rabbit intestinal loop. Eleven strains hybridized with Stx1 probe, one strain with Stx2 and two strains with both probes. Filtered culture supernatants of all E. coli strains presented cytotoxic effects in both HeLa and Vero cells. In this study, we found a strong association between the production of Stx and its effect in an animal model. This is the first description of high-level Stx-producing E. coli O111ac isolated in Brazil.

Occurrence, distribution, and associations of O and H serogroups, colonization factor antigens, and toxins of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of infectious diarrhea worldwide. Four categories of antigens have been commonly studied: O serogroup, H serogroup, colonization factor antigens (CFA), and toxins. A database has been complied from published reports of nearly 1,000 ETEC isolates from 18 locations and analyzed to determine the occurrence, distribution, and associations of O serogroup, H serogroup, CFA, and toxin type. Tables listing the associations of antigens are presented. This analysis documents the widespread nature and variety of ETEC. Even the most common combination of antigens, O6:H16 CFA/II LTST, accounted for only 11% of the ETEC isolates in the database. It was isolated from 12 locations. Many phenotypes occurred only once. CFA detection based on enzyme-linked antibodies with polyclonal sera is suggested as the preferred assay. A combination of CFA and toxin-based antigens is suggested as the most practical vaccine.

Random amplification of polymorphic DNA reveals serotype-specific clonal clusters among enterotoxigenic Escherichia coli strains isolated from humans

The genetic diversity of 47 enterotoxigenic Escherichia coli (ETEC) strains of serotypes O6:H16, O27:H7, O29:H21, O128ac:H12, and O153:H45, previously isolated from diarrheic patients in Brazil over a period of 15 years, was investigated by random amplification of polymorphic DNA (RAPD). Informative band arrays were obtained with three 10-mer primers with G+C contents of 50, 60, and 70%. Based on the combination of the band profiles generated by the three primers 22 RAPD types were detected, and 5 major clonal clusters, each one with at least 80% identical bands, were established. The clonal clusters corresponded to strains having the same serotype which, in most cases, also had the same virulence factors (colonization factors and toxin types) and outer membrane protein and lipopolysaccharide sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles. The results suggested a correlation between phenotypic properties and genetic relatedness of ETEC isolates of human origin and indicated that a reduced number of clonally related strains are found in areas of ETEC endemicity in Brazil. Moreover, the RAPD technique revealed intraserotype-specific variations, undetectable by the combination of several phenotypic typing methods, among the ETEC strains analyzed. These results show that RAPD typing represents a useful tool for population genetics as well as for epidemiological studies of ETEC.

Age-specific prevalence of Escherichia coli with localized and aggregative adherence in Venezuelan infants with acute diarrhea

To evaluate the epidemiological significance of HEp-2 cell-adherent Escherichia coli isolates in diarrheal disease, we performed a study with 513 Venezuelan infants with diarrhea and 241 age-matched controls to determine the prevalence of enteropathogenic E. coli (enteroadherent E. coli, enterotoxigenic E. coli, enteroinvasive E. coli, and enterohemorrhagic E. coli) and their correlation with O:H serotypes. E. coli isolates exhibiting localized and aggregative adherence in the HEp-2 cell assay were significantly more frequently isolated from the patients (8.5 and 26.9%, respectively) than from the controls (1.7 and 15%, respectively). This difference was significant for the group 0 to 2 months of age but for older infants. Regardless of age, E. coli isolates with diffuse adherence were found at similar frequencies in both the patients and the controls. A striking correlation between classic O serogroups and localized adherence was also observed. These findings confirm the pathogenic role of E. coli with localized and aggregative adherence in diarrheal disease, as well as the epidemiological importance of O:H serotyping for characterizing localized-adhering E. coli.

Evaluation of a rapid screening assay for bacterial identification (Dot-ELISA) in fecal samples from children

With the objective of standardizing a Dot Enzyme-Linked Immunosorbent Assay (Dot-ELISA) to detect antigens of fecal bacterial enteropathogens, 250 children, aged under 36 months and of both sexes, were studied; of which 162 had acute gastroenteritis. The efficacy of a rapid screening assay for bacterial enteropathogens (enteropathogenic Escherichia coli "EPEC", enteroinvasive Escherichia coli "EIEC", Salmonella spp. and Shigella spp.) was evaluated. The fecal samples were also submitted to a traditional method of stool culture for comparison. The concordance index between the two techniques, calculated using the Kappa (k) index for the above mentioned bacterial strains was 0.8859, 0.9055, 0.7932 and 0.7829 respectively. These values express an almost perfect degree of concordance for the first two and substantial concordance for the latter two, thus enabling this technique to be applied in the early diagnosis of diarrhea in infants. With a view to increasing the sensitivity and specificity of this immunological test, a study was made of the antigenic preparations obtained from two types of treatment: 1) deproteinization by heating; 2) precipitation and concentration of the lipopolysaccharide antigen (LPS) using an ethanol-acetone solution, which was then heated in the presence of sodium EDTA.

Bacteroides fragilis toxin rapidly intoxicates human intestinal epithelial cells (HT29/C1) in vitro

Enterotoxigenic Bacteroides fragilis strains associated with childhood diarrhea produce a 20-kDa protein toxin (BFT). Purified BFT causes striking morphologic changes in subconfluent human colonic epithelial cells (HT29/C1). In a 3-h HT29/C1 cell assay, the estimated half-maximal effective concentration of BFT was 12.5 pM, and morphologic effects were detectable as early as 30 min and nearly complete by 1.5 h. Concentrations as low as 0.5 pM could also cause intoxication, but morphologic changes were detectable only when the assay was extended to 18 h. The onset of this intoxication was concentration dependent and rapid, occurring within minutes (<7 min at 0.25 nM, <2 min at 2.5 nM). Notably, the onset of intoxication at 37 degrees C became irreversible to washing within 2 min after exposure to BFT. Morphologic changes were completely inhibited by treatment of HT29/C1 cells with BFT at 4 degrees C but could be demonstrated by subsequent warming to temperatures of 15 degrees C or higher after washing. The time required for the association of BFT with HT29/C1 cells at 4 degrees C was inversely correlated with concentration. Inhibitors of endosomal and Golgi trafficking (NH4Cl and brefeldin A) prevented the intoxication of HT29/C1 cells by Clostridium difficile toxin A and cholera toxin, respectively, but not by BFT. Agents altering microtubule structure did not affect the cellular activity of BFT. These data indicate that a purified toxin from B. fragilis strains associated with diarrhea rapidly and irreversibly intoxicates human intestinal epithelial cells (HT29/C1) in a concentration- and temperature-dependent manner and that the process of intoxication may not involve internalization mechanisms utilizing microtubules or sensitive to pH or brefeldin A.

Prospective study of enteropathogens in two communities of Misiones, Argentina

Children under five years of age, from two communities of different socio-economic strata (97 from Zaiman and 55 from Las Dolores) were examined epidemiologically during 2 years, by means of quarterly visits of the working team, who carried out the collection of faecal samples. During the study, one or more enteropathogens were identified in 73.9% of samples in children from Zaiman and in 58.3% of the samples from Las Dolores, being associated to diarrhoea in 70.5% and to asymptomatic infections in 65.7%. The number of diarrheic episodes was higher in Zaiman (15.45%) than in Las Dolores (12.35%), being more frequent in the spring-summer seasons. In Zaiman, the bacterial enteropathogen proportion was relevantly higher (p < 0.005) in children with diarrhoea, whereas the presence of parasites was more frequent in asymptomatic children (p < 0.01). Rotavirus had an even distribution within diarrheic and asymptomatic children. In Las Dolores, no relevant differences were found in the detection of enteroparasites between diarrheic and asymptomatic children. Mixed infections were detected; enterotoxigenic Escherichia coli (ETEC)-rotavirus and ETEC-parasites being the most frequent ones. ETEC was involved in 85% of these infections. These data, together with the high enteropathogen carriage, suggest an elevated level of environmental contamination. The latter plays an important role in diarrheic diseases, and added to the most extreme poverty, it affects children's lives.

Nutritional impact and ultrastructural intestinal alterations in severe infections due to enteropathogenic Escherichia coli strains in infants

OBJECTIVE

Enteropathogenic Escherichia coli (EPEC) strains are able to adhere to human intestinal tissue inducing a typical lesion causing dissolution of the brush border membrane and loss of microvillus structure at sites of bacterial attachment. The presence of these lesions can provoke perpetuation of diarrhea associated with malabsorption of the nutrients and nutritional aggravation. In this paper we report the nutritional impact of severe EPEC gastroenteritis in infants in a small bowel ultrastructural study.

METHODS AND RESULTS

Two infants aged 3 months and one 4 month old infant with profuse watery diarrhea lasting less than 6 days were studied. After rehydration therapy, the patients were fed a cow's milk formula and since food intolerance was diagnosed, a protein-hydrolisate, lactose-free formula was introduced. This dietary modification was successful, diarrhea ceased, the patients were discharged and followed up for 30 days. The following EPEC strains were identified in the stools and in the jejunal secretion: O111ab:H2, O119:H6 and O18ab:H14. A small bowel biopsy was performed and the electron microscopic study revealed bacteria tightly adhered to the apical portion of the enterocyte and effacement of the microvilli. These lesions were more prominent in the areas where bacteria were present.

CONCLUSION

The patients underwent an acute nutritional aggravation due to food intolerance, but the introduction of a protein-hydrolisate, lactose-free formula, allowed prompt cessation of diarrhea and nutritional recovery.

Species and serovars of enteropathogenic agents associated with acute diarrheal disease in Rosario, Argentina

We report the most frequent species and serovars of enteropathogenic organisms in Rosario from 1985 to 1993. Enteropathogenic Escherichia coli was the most prevalent agent affecting 144/570 (25.2%) children; 0111 represented 41.8%, 055: 13.6%, 0119: 12.7%. Among enterotoxigenic E. coli (ETEC) the most frequent were ETEC-ST 0128:H21 and 0153:H45. Shigella spp were isolated in 8.8%; S. flexneri: 7%, principally type 2 (59.5%); S. sonnei: 1.6%, and S. dysenteriae type 2: 0.2%. Campylobacter spp were found in 6.1% of patients; C. jejuni: 4.6%; C. coli: 1.4% and C. lari: 0.2%; except groups 0 13.50 and 0 4 (2 cases each), no predominant serogroups were found. Salmonella was isolated in 2.8% of cases, being the predominant serovar S. typhimurium until 1986, but a dramatically increase of cases due to S. enteritidis was observed since 1987. There was 1.9% of Aeromonas spp and 2 cases due to Vibrio cholerae non 0-1. No Yersinia was found. In patients with gastroenteritis due to Shigella, Campylobacter, Salmonella, or EPEC as the unique pathogen, leukocytes were observed in the faeces in 70%, 50%, 20%, and 10% of cases respectively.

Multiple drug resistant non typhoidal Salmonella spp associated with acute diarrheal disease

Rectal swabs/stool specimens from 115 children (0-5 years) suffering with acute diarrhea were screened for non typhoidal salmonella species. 7 (6%) patients were found to be positive for non typhoidal salmonella. 4 (3.47%) were positive for S. paratyphi B and 3 (2.6%) were positive for S. typhimurium. Multidrug resistance was seen in 57 percent of the strains. All strains were sensitive to Ciprofloxacin. All strains were resistant to Ampicillin followed by Ciprofloxacin. All strains were resistant to Ampicillin followed by Gentamycin (43%), Kanamycin (43%), Tetracycline (43%), Streptomycin (28.5%) and Chloramphenicol (28.5%).

Major enteropathogenic bacteria isolated from diarrheal patients in Bolivia: A hospital-based study

A total of 1,234 fecal samples from diarrhea cases were examined for etiological bacterial agents at medical facilities in La Paz and Sucre, Bolivia. Eighty strains of Shigella spp., 39 strains of Salmonella spp., 29 strains of Vibrio cholerae, and 222 strains of enteropathogenic Escherichia coli (139 EPEC, 55 ETEC, 29 EIEC, and 1 EHEC) were isolated. With regard to the serovars of Shigella, S. flexneri 2a, 3a, and 1b were predominant. In the case of Salmonella, S. enteritidis was the most common, followed by S. typhi, S. poona, and S. paratyphi B. Out of 29 cholera strains, 25 belonged to biovar El Tor, serovar Ogawa while the remaining 4 were serovar Inaba. Among 55 strains of ETEC serotypes, 5 showed ST producers but none showed LT producers. Likewise, among 55 strains of enterohemorrhagic serotypes, only one strain (O157:H7) produced verocytotoxin (VT 2). The results of drug sensitivity tests revealed the predominance of Shigella, EPEC, and ETEC strains resistant to aminobenzil-penicillin (ABPC) and trimethoprim. Since diarrheal patients in Bolivia are treated mainly with ABPC or sulfamethoxazole/trimethoprim (SXT) and rarely with gentamicin, kanamycin, or other drugs, it is possible that ABPC- and SXT-resistant strains will increase and persist in the near future.

Colorimetric detection of heat-labile toxin-encoding gene of enterotoxigenic Escherichia coli by PCR

In the developing world, enterotoxigenic Escherichia coli (ETEC) strains which produce enterotoxins are a significant cause of morbidity and mortality. Heat-labile (LT) toxin PCR detection methods have been described, but they have limited applications in a routine laboratory setting. A colorimetric DNA method for the rapid amplification and detection of the LT toxin gene in ETEC strains is described. Target amplification together with colorimetric detection would overcome many of the limitations of conventional PCR. This paper describes a colorimetric PCR detection method specific for LT-gene-encoding ETEC strains. DNA was extracted from two representative colonies from each bacterial isolate and amplified by PCR. Digoxigenin was incorporated into the amplification product, permitting a one-step direct detection using anti-digoxigenin alkaline phosphatase-conjugated antibody. This technique was applied to the investigation of 70 E. coli isolates derived from clinical fecal samples obtained from an Irish population. Eleven percent of the samples were LT positive, confirming the applicability of this method. All LT-positive ETEC strains (controls and clinical isolates) were detected, and no false-positive results occurred.

Identification of enteropathogenic Escherichia coli by PCR-based detection of the bundle-forming pilus gene

A rapid and simple method of detecting enteropathogenic Escherichia coli (EPEC) was developed. The procedure is based on amplifying by the PCR method a 326-bp region of the bundle-forming pilus gene of EPEC. The oligonucleotide DNA primers used in this procedure did not amplify DNA of any other bacterial enteropathogens tested. The procedure was 100% specific for EPEC strains that exhibit a characteristic pattern of attachment (localized adherence) to HeLa cells.

Differentiation of pathogenic Escherichia coli strains in Brazilian children by PCR

A PCR technique to differentiate pathogenic enteric Escherichia coli strains in a field setting was evaluated. Among 76 children with acute diarrhea, this technique identified 12 children (16%) with enterotoxigenic E. coli, 6 (8%) with enteropathogenic E. coli, and 1 (1%) with enteroinvasive E. coli infection. Compared with the conventional assays, the PCR method proved to be simpler, more rapid, and inexpensive and therefore suitable for application in a developing-country field setting.

Controlled study of Escherichia coli diarrheal infections in Bangladeshi children

Diarrheal diseases are highly prevalent in Bangladesh. However, the relative contribution of diarrheagenic Escherichia coli organisms--those that are enterotoxigenic (ETEC), enteropathogenic (EPEC), enteroinvasive, enterohemorrhagic, enteroaggregative, and diffuse adherent--to diarrhea in Bangladeshi populations is not known. With DNA probes specific for these diarrheagenic E. coli strains, we analyzed fecal E. coli from 451 children up to 5 years of age with acute diarrhea seeking treatment at a Dhaka hospital and from 602 matched control children without diarrhea from July 1991 to May 1992. Enteroinvasive E. coli was not isolated from any children; enterohemorrhagic E. coli was not isolated from any diarrheal children but was isolated from five control children; enteroaggregative and diffuse adherent E. coli strains were isolated with similar frequencies from children with and without diarrhea, thereby showing no association with diarrhea; ETEC was significantly associated with diarrhea in the diarrheal children as a whole and especially in the age groups of 0 to 24 months and 37 to 48 months (further analysis suggests an association with diarrhea for the heat-stable toxin only and for both heat-labile- and heat-stable-toxin-producing ETEC only); and EPEC was significantly associated with diarrhea in the diarrhea group as a whole and particularly in infants up to 1 year of age. Further analysis suggested that EPEC strains of only the traditional serogroups were significantly associated with diarrhea. ETEC and EPEC infections peaked during warm months. Our data thus suggest that EPEC and ETEC are important causes of acute diarrhea in children in this setting.

Is protection against shigellosis induced by natural infection with Plesiomonas shigelloides?

Shigellosis due to Shigella sonnei is rare among people growing up and living in developing countries; however, infections due to S sonnei becomes more common than those due to S flexneri as societies develop economically. The relation between risk of S sonnei infection and economic development may be explained by the exposure of developing-country populations to Plesiomonas shigelloides. P shigelloides is often found in surface water, and one serotype (serotype 17) possesses a cell-wall lipopolysaccharide identical to that of S sonnei. Thus, exposure to P shigelloides by drinking contaminated water may immunise populations to S sonnei. As economic development occurs, water quality improves and populations become susceptible to S sonnei. Although drinking water has many advantages, immunisation against S sonnei may be one benefit of traditional water sources.

Adhesion and its role in the virulence of enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) organisms are an important cause of diarrheal disease in young children. The virulence of EPEC is a multifactorial process and involves a number of distinct stages. Initial adherence to intestinal mucosa is mediated by fimbriae which bring about a distinct form of adhesion, localized adhesion. Intimate adhesion of the bacterium to the eukaryotic membrane occurs, resulting in the activation of signal transduction pathways. Microvilli are disrupted and effaced from the apical membrane which then cups around the organism to form pedestal structures, the attaching and effacing lesion. Diarrhea may be produced by alteration of the permeability of the apical membrane and also through a malabsorption mechanism. The pathways involved in the production of the attaching and effacing lesion are described. EPEC organisms were originally thought to belong to a number of distinct serogroups; it is now apparent that many isolates belonging to these serogroups are not pathogenic or belong to other pathogenic groups of E. coli. In addition, isolates falling outside of these serogroups are considered to be true EPEC. The definition of EPEC based on serotyping is inaccurate and should be replaced by methods that specifically detect the virulence properties of EPEC.

Transient, asymptomatic colonisation of newborn, Ethiopian infants by Salmonella

We performed faecal cultures from 71 Addis Ababa infants. Salmonella spp. were found in 12 of 61 hospitalised infants. None had diarrhoea. Colonisation was most common (8/21) during the second week of life. There was no correlation to mode of delivery, breast feeding, type of ward or antibiotic treatment in this small sample.

Epidemiology of diarrhoeal disease: implications for control by vaccines

Vaccines present perhaps the most attractive solution to the worldwide problem of diarrhoeal disease. Epidemiological evidence has important implications for the development and use of such vaccines, and results of studies on diarrhoeal diseases in developing and developed countries, in particular among children, and travellers' diarrhoea are reviewed. The virulence and pathogenicity of various enteropathogens are discussed, and the extent to which immunity may be acquired. It is concluded that the development of appropriate vaccines may be a complex task.

Enteropathogenic Escherichia coli

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Virulence factors of enteric Escherichia coli in young Aboriginal children in north-west Australia

Enterotoxigenic Escherichia coli (ETEC) were the most frequently identified enteric pathogens associated with diarrhoea in 0-5 year old Aboriginal children in tropical north-west Australia with an incidence similar to those from other tropical regions. Heat-stable toxin-producing (ST+) strains were associated with diarrhoea throughout the year but heat-labile toxin-producing (LT+) strains were more important in the monsoonal summer season. ST+ strains were commonest in children with diarrhoea between 6 and 18 months of age while LT+ strains were associated with diarrhoea in children aged 18-24 months. Vero-toxigenic E. coli (VTEC) which produced VT1, but not VT2, and enteroadherent (EAF+) E. coli were significant causes of diarrhoea, mainly in children below 18 months but without a seasonal pattern.