The significance of enteroaggregative Escherichia coli in the etiology of hospitalized diarrhoea in Calcutta, India and the demonstration of a new honey-combed pattern of aggregative adherence

Previous studies have identified enteroadherent Escherichia coli that exhibit localized adherence, diffuse adherence and atypical diffuse adherence as diarrhoeagenic agents associated with infantile diarrhoea in Calcutta, India. In this study, a DNA probe specific for enteroaggregative adherence was used to determine the etiological significance of enteroaggregative E. coli in the causation of diarrhoea. From a total of 330 strains of E. coli recovered from 159 cases of acute secretory diarrhoea and 174 cases of invasive diarrhoea, 20 strains hybridized with the probe, whereas of the 25 E. coli strains recovered from 25 healthy controls only 1 strain hybridized with the probe. Of the 21 probe positive strains, 19 adhered to HeLa cells in the typical stacked-brick pattern while 2 strains recovered from 2 cases of secretory diarrhoea adhered to the glass surface in a hitherto undescribed formation which we have termed, based on the appearance, as the honey-comb pattern. The enteroaggregative E. coli strains identified in this study did not produce any conventional enterotoxins and were significantly associated with patients with secretory diarrhoea (10.7%) than with invasive diarrhoea (1.7%). The results of this study indicate that enteroaggregative E. coli play a causal role in acute secretory diarrhoea in this part of the world which lends credence to the involvement of a potent toxin in the pathogenesis of EAggEC mediated infections.     

A case-control study of diarrhoea in children caused by Escherichia coli producing heat-stable enterotoxin (EAST-1)

Escherichia coli strains associated with diarrhoeal disease have been classified into several types according to the pathogenic mechanism. Among these, enteroaggregative E. coli strains (EAggEC) have been associated with persistent childhood diarrhoea. Some strains of EAggEC produce a heat-stable toxin (EAST-1) that differs from others described previously. The main goal of this case-control study was to determine the prevalence of EAggEC and EAST-1-producing E. coli strains as a cause of diarrhoea in children in Spain and to study their in-vitro susceptibility to 21 antimicrobial agents. In the case group (115 children) 22 (19%) isolates and four (3.5%) isolates were EAST-1-producing E. coli and EAggEC, respectively, whereas in the control group (79 children) four (5%) isolates produced EAST-1 (p = 0.005) and three (3.8%) isolates were EAggEC. The present study suggests that EAST-1-producing E. coli strains are associated with diarrhoeal diseases in Spanish children, whereas EAggEC strains are not. Moreover, EAST-1-producing E. coli strains showed a high susceptibility to all the antimicrobial agents tested except for ampicillin.     

Escherichia coli strains involved in diarrhea in France: high prevalence and heterogeneity of diffusely adhering strains

Two hundred sixty-two strains of Escherichia coli isolated from diarrheal stool specimens from infants, children, and adults hospitalized in Clermont-Ferrand, France, were studied to classify them in the previously described pathogenic groups of E. coli involved in diarrheal diseases. A total of 1.5% of them belonged to the enterotoxigenic E. coli pathotype, but none belonged to the enteroinvasive E. coli, enterohemorrhagic E. coli, or enteropathogenic E. coli pathotypes. Seventeen strains (6.5%) exhibited an aggregative pattern of adhesion to HEp-2 cells (EAggEC pathotype), but of these, three (17.6%) did not hybridize with the EAggEC DNA probe. Most of the strains involved in diarrhea belonged to the diffusely adhering E. coli group; 100 strains (38.2%) exhibited a diffuse adhesion (DA) to HEp-2 cells. Only eight strains (8.9%) from controls diffusely adhered to HEp-2 cells. The highly significant difference (P < 0.0001) between DA strains from patients and from controls suggests that the diffusely adhering E. coli strains should be considered pathogens. Only 33 of them (33%) hybridized with the previously described DA DNA probe, and only 2 (2%) hybridized with the AIDA DNA probe. Four different major proteins were observed in the bacterial surface extracts of the 33 strains positive with the DA DNA probe. In addition, 16 strains that diffusely adhered to HEp-2 cells induced a cytotoxic effect on HEp-2 cells that was characterized by pyknosis and lysis of the cytoplasmic membrane. This cytotoxic effect was correlated with the synthesis of a hemolysin. The genes involved in diffuse adhesion to HEp-2 cells were located on conjugative R plasmids in strains that did not hybridize with the DA or AIDA DNA probes.     

Enteropathogenicity markers in Escherichia coli isolated from infants with acute diarrhoea and healthy controls in Rio de Janeiro, Brazil

Faeces from urban children < 2 years old with acute diarrhoeal illness and from non-diarrhoeal infants (controls) were examined for Escherichia coli and other enteropathogens. A total of 990 E. coli isolates from 100 patients and 50 controls was tested for enteropathogenic E. coli (EPEC) serotype (O:H), adherence to HEp-2 cells after incubation for 3 and 6 h, fluorescent actin staining (FAS), DNA hybridisation with EAF, eaeA, STh, STp and EAggEC probes and production of heat-labile enterotoxin (LT) and verocytotoxin (VT) with Y1 and Vero cells. EPEC were the most prevalent enteropathogens in patients (32.7%; and 14% in controls). Enteroinvasive E. coli (EIEC) and Vero cytotoxin-producing E. coli (VTEC) were not detected. The rate of isolation of enterotoxigenic E. coli (ETEC) was identical in both groups. Among the EPEC isolates the prevalent serotypes were O111:H2, O55:NM and O119:H6. Localised adherence (LA) was found significantly more frequently in isolates from patients (19.6%) than controls (2.1%). All LA-positive EPEC isolates were FAS+ and eaeA+, but only 75.2% of them hybridised with the EAF probe. Diffusely adhering E. coli (DAEC) and enteroaggregative E. coli (EAggEC) were found with equal frequency in patients and controls. Twenty-seven E. coli isolates were negative for EAF but positive for eaeA and FAS and produced LA in 6-h adherence tests. These EAF-/eaeA+ strains were the only putative enteropathogen identified in seven patients and were not found in controls. The ability of these strains to elicit ultrastructural cell alterations and cell-signalling events was evaluated in Caco-2 cells (human colon carcinoma cell line) by the gentamicin invasion assay and by transmission electron microscopy. The numbers of intracellular bacteria in cell invasion tests varied from 0.4% to 1.6% of the cell-associated bacteria after a 6-h incubation period. Tyrosine phosphorylation of host cell proteins was assessed in HEp-2 cells by immunofluorescence microscopy and all strains gave positive results. EAF-/eaeA+ E. coli strains express most of the virulence properties found among true EPEC strains and can be a relevant cause of infant diarrhoea in developing countries.     

Hemolysin-positive enteroaggregative and cell-detaching Escherichia coli strains cause oncosis of human monocyte-derived macrophages and apoptosis of murine J774 cells

Infection of human monocyte-derived macrophages (HMDM) and J774 cells (murine macrophage cell line) with several enteroaggregative and cytodetaching Escherichia coli (EAggEC and CDEC, respectively) strains demonstrated that some strains could induce macrophage cell death accompanied by release of lactate dehydrogenase activity and interleukin 1beta (IL-1beta) into culture supernatants. The mode of cell death differed in the two types of macrophages. Damage to macrophage plasma membrane integrity without changes in nuclear morphology resulted in cytolysis of HMDM. This mechanism of cell death has been previously described for virulent Shigella infection of HMDM and is termed oncosis. In contrast, infection of J774 cells by EAggEC and CDEC strains resulted in apoptosis. The presence of alpha-hemolysin (Hly) in EAggEC and CDEC strains appears to be critical for both oncosis in HMDM and apoptosis in J774 cells. Bacteria lacking Hly, including Hly- EAggEC strains as well as enterotoxigenic, enteropathogenic, and enterohemorrhagic E. coli strains, behaved like avirulent Shigella flexneri in that the macrophage monolayers were intact, with no release of lactate dehydrogenase activity or IL-1beta into the culture supernatants.     

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.     

Adhesion of enteroaggregative Escherichia coli to formalin-fixed intestinal and ureteric epithelia from children

The adhesion characteristics of enteroaggregative Escherichia coli (EAggEC) to the mucosal surfaces of formalin-fixed paediatric intestinal and ureteral tissue were studied. The technique offers a means of overcoming the problem of limited tissue access in childhood and a way of examining the initial steps of bacterial adhesion. Five EAggEC strains isolated from children with diarrhoea in the UK and a well characterised, prototype EAggEC strain (221) were examined. Five of the six EAggEC strains showed preferential adhesion to jejunal mucosa with limited adhesion to ileum and colon. Five of the six also adhered to ureteric tissue. EAggEC can adhere to proximal, as well as distal, regions of the gastrointestinal tract in children, a previously unrecognised characteristic.     

An outbreak of foodborne illness caused by Escherichia coli O39:NM, an agent not fitting into the existing scheme for classifying diarrheogenic E. coli

An outbreak of gastrointestinal illness with clinical and epidemiologic features of enterotoxigenic Escherichia coli (ETEC) occurred among patrons of a restaurant during April 1991. Illnesses among several groups of patrons were characterized by diarrhea (100%) and cramps (79%-88%) lasting a median of 3-5 days. Median incubation periods ranged from 50 to 56 h. A nonmotile strain of E. coli (E. coli O39), which was negative for heat-labile (LT) and heat-stable (STa, STb) ETEC toxins, was isolated only from ill patrons. This organism produced enteroaggregative E. coli heat-stable enterotoxin 1 and contained the enteropathogenic E. coli gene locus for enterocyte effacement; it did not display mannose-resistant adherence, but produced attaching and effacing lesions in the absence of mannose on cultured HEp-2 cells. E. coli that are not part of highly characterized but narrowly defined groups may be important causes of foodborne illness.     

The effects of phospholipid molecular species on cholesterol crystallization in model biles: the influence of phospholipid head groups

A study of the etiologies of diarrhea in adults in relation to their human immunodeficiency virus (HIV) serostatus and number of CD4+ cells was carried out in the Central African Republic. In cases and controls, multi-parasitism was observed. Salmonella spp. were identified mainly during acute diarrhea, with 50% of the S. enteritidis isolated during the study being responsible for septicemia and/or urinary tract infection in immunodeficient patients. Enteroaggregative Escherichia coli (EAggEC) were the most frequently identified agent in HIV+ patients with persistent diarrhea; 42.8% of the patients with EAggEC as sole pathogens had bloody diarrhea, and these strains were negative for the presence of a virulence plasmid. Coccidia were found in those with acute and persistent diarrhea. Blood was observed in 53.3% of infections involving coccidia as the sole pathogen. Microsporidium spp. and Blastocystis hominis were found only in HIV+ patients with persistent diarrhea. Shigella spp., Campylobacter spp., and Entamoeba histolytica were found in HIV+ and HIV- dysenteric patients; bacteria resembling spirochetes that could not be cultivated were identified only in HIV+ cases with dysentery. Shiga-like toxin-producing E. coli O157:H- was isolated from two cases with hemolytic-uremic syndrome. Fungi were identified as the sole pathogen in 6.4% of the HIV+ patients with persistent diarrhea. Most of enteropathogenic bacteria identified were resistant to ampicillin and trimethoprim-sulfamethoxazole, remained susceptible to ampicillin plus clavulanic acid, and were susceptible to amikacin, gentamicin, and ciprofloxacin.     

Successful treatment of diarrheal disease associated with enteroaggregative Escherichia coli in adults infected with human immunodeficiency virus

The presence of enteroaggregative Escherichia coli (EAggEC) in stool has been strongly associated with persistent diarrhea. No treatment trials have been done to demonstrate that clearance of EAggEc results in an improvement of diarrheal symptoms. Twenty-four adults infected with the human immunodeficiency virus (HIV) with diarrhea and EAggEC were randomized to a double-blind placebo-control cross-over treatment trial (ciprofloxacin 500 mg orally twice daily for 7 days vs. placebo). After treatment with ciprofloxacin, the subjects had significantly fewer (50%) stools per day (from 5.0+/-2. 9 to 2.4+/-1.9). Intestinal symptoms decreased by 42% after active treatment. EAggEc were eradicated from stool of all participants after active treatment. These data strengthen the link between the presence of the EAggEc in stool and their role in the pathogenesis of diarrheal disease. It is likely that EAggEc are a treatable cause of diarrheal disease in some persons with HIV and no other apparent enteric pathogen.     

HEp-2 cell-adherent Escherichia coli in patients with human immunodeficiency virus-associated diarrhea

Diarrhea occurs commonly in African human immunodeficiency virus (HIV) infections. A case-control (HIV-positive vs. -negative) study of adults with diarrhea was done in Lusaka, Zambia, to determine the prevalence of intestinal infection by HEp-2 cell-adherent Escherichia coli. Adherent E. coli were more common in HIV-positive patients with acute diarrhea than among HIV-negative controls (60% vs. 33%) and were found significantly more often in HIV-positive patients with chronic diarrhea than among HIV-negative controls with chronic diarrhea (79% vs. 17%, P < .002). Adherent strains were found significantly more often among HIV-positive patients (69%) than in 22 asymptomatic subjects (36%, P < .02). The HEp-2 cell adherence of the E. coli strains did not show a common pattern. Adherent bacteria were also observed in colonic biopsies from 32% of Zambians with chronic diarrhea who underwent endoscopy. Adherent E. coli may be an important cause of HIV-associated diarrhea in Zambia.     

Evaluation of three different STb assays and comparison of enterotoxin pattern over a five-year period in Swedish porcine Escherichia coli

The pig intestinal loop (PIL) assay, inhibition enzyme-linked immunosorbent assay (ELISA), and DNA hybridization assay were compared for analysis of Escherichia coli heat-stable enterotoxin b (STb) on 201 porcine E. coli strains. The DNA hybridization had a 95% correlation with the STb ELISA and was therefore chosen as the method for subsequent screening of enterotoxin genes: heat labile (LT), heat-stable a (STa), and/or STb. In contrast to the PIL assay, both the STb ELISA and DNA hybridization assays were more sensitive, reliable, reproducible, and showed good correlation with each other. Consequently, the STb ELISA is preferable for analysis of toxin preparations and screening of E. coli, whereas the DNA hybridization is better for large-scale epidemiologic screening. Escherichia coli strains (n = 437) associated with porcine diarrhea isolated in Sweden during 1989 were investigated. Of the strains, 135 (31%) were positive for at least one of these toxins and, therefore, designated enterotoxigenic E. coli (ETEC). Our results were compared with the enterotoxin pattern found in earlier studies of Swedish porcine strains. The only change in occurrence of toxins was found in strains isolated from piglets less than 1 week of age. LT- and STb-producing ETEC had decreased, and STa-producing ETEC had increased in prevalence. The occurrence of STb among ETEC of weaned pigs was 93%. This toxin was also found to be more common than STa when strains from all age groups were considered.     

Enteropathogenic, enterotoxigenic and enteroinvasive Escherichia coli isolated from acute gastroenteritis patients in Lagos, Nigeria

Enteropathogenic, enterotoxigenic and enteroinvasive Escherichia coli were isolated from 52 (4.8%) of 1,082 patients with acute gastroenteritis reporting at the Lagos University Teaching Hospital, Lagos, Nigeria between October 1979 and March, 1981. Of the 52 strains of E. coli isolated, 35 (67.3%) were enteropathogenic, 12 (23.1%) were enterotoxigenic and five (9.6%) were enteroinvasive. E. coli 0111 (25.7%) was the most predominant among the serotypes of the "classical" enteropathogenic strains found in this study. Diarrhoea associated with enteropathogenic E. coli occurred only in children aged less than five years, whereas enterotoxigenic and enteroinvasive E. coli were found primarily in adults. The study has highlighted for the first time the important role that enterotoxigenic and enteroinvasive E. coli strains could play in acute diarrhoeal diseases in Lagos, Nigeria.     

Clinical features of infections due to Escherichia coli producing heat-stable toxin during an outbreak in Wisconsin: a rarely suspected cause of diarrhea in the United States

In September 1994, a foodborne outbreak of enterotoxigenic Escherichia coli (ETEC) infection occurred in attendees of a banquet in Milwaukee. E. coli was isolated from stool specimens from 13 patients that were comprehensively tested; isolates from five patients were positive for E. coli producing heat-stable toxin, were biochemically identified and serotyped as E. coli O153:H45, and were all resistant to tetracycline, ampicillin, sulfisoxazole, and streptomycin. Diarrhea (100%) and abdominal cramps (83%) were the most prevalent symptoms in 205 cases; vomiting (13%) and fever (19%) were less common. The median duration of diarrhea and abdominal cramps was 6 days and 5 days, respectively. In the United States, health care providers rarely consider ETEC as a possible cause of diarrhea in their patients, and few laboratories offer testing to identify ETEC. Hence, outbreaks of ETEC infection may be underdiagnosed and underreported. As in this outbreak, the relatively high prevalence of diarrhea and cramps lasting > or = 4 days and the low prevalence of vomiting and fever can help distinguish ETEC infection from Norwalk-like virus infection and gastroenteritis due to other causes with incubation times of > or = 15 hours and can provide direction for confirmatory laboratory testing.     

Psyllium improves fecal consistency and prevents enhanced secretory responses in jejunal tissues of piglets infected with ETEC

Infection with enterotoxigenic E. coli (ETEC) induces secretory diarrhea by stimulating net secretion of fluid and electrolytes. We tested the hypothesis that ETEC potentiates jejunal ion secretion induced by other agonists and also examined whether the soluble fiber psyllium ameliorates effects of ETEC-induced pathophysiology. Noninfected or ETEC-infected piglets were given oral electrolyte solution twice daily or electrolyte solution supplemented with psyllium for 48 hr. Jejunal tissues were mounted in flux chambers and basal and stimulated ion transport responses, as reflected by short-circuit current (I(SC)) were measured. The severity of ETEC-induced diarrhea was reduced by psyllium. I(SC) responses to carbachol and 5-hydroxytryptamine were greater in tissues from infected piglets compared with noninfected controls or infected piglets given psyllium. These results suggest that psyllium ameliorates ETEC-induced diarrhea and prevents the enhanced secretory responses to calcium-mediated agonists that occur in ETEC-infected piglet jejunum.     

Prevalence of the "high-pathogenicity island" of Yersinia species among Escherichia coli strains that are pathogenic to humans

The fyuA-irp gene cluster contributes to the virulence of highly pathogenic Yersinia (Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica 1B). The cluster encodes an iron uptake system mediated by the siderophore yersiniabactin and reveals features of a pathogenicity island. Two evolutionary lineages of this "high pathogenicity island" (HPI) can be distinguished on the basis of DNA sequence comparison: a Y. pestis group and a Y. enterocolitica group. In this study we demonstrate that the HPI of the Y. pestis evolutionary group is disseminated among species of the family Enterobacteriaceae which are pathogenic to humans. It prevails in enteroaggregative Escherichia coli and in E. coli blood culture isolates (93 and 80%, respectively), but is rarely found in enteropathogenic E. coli, enteroinvasive E. coli, and enterotoxigenic E. coli isolates. In contrast, the HPI was absent from enterohemorrhagic E. coli, Shigella, and Salmonella enterica strains investigated. Polypeptides encoded by the fyuA, irp1, and irp2 genes located on the HPI could be detected in E. coli strains pathogenic to humans. However, these E. coli strains showed a reduced sensitivity to the bacteriocin pesticin, whose uptake is mediated by the FyuA receptor. Escherichia strains do not possess the hms gene locus thought to be a part of the HPI of Y. pestis. Deletions of the juA-irp gene cluster affecting solely the fyuA part of the HPI were identified in 3% of the E. coli strains tested. These results suggest horizontal transfer of the HPI between Y. pestis and some pathogenic E. coli strains.     

eaeA genes in Escherichia coli derived from Japanese patients with sporadic diarrhea

To investigate the prevalence of attaching and effacing Escherichia coli, we examined 364 strains isolated from the feces of 9,684 patients with diarrhea at the Anjo Kosei Hospital in Japan for the presence of eaeA. Twenty-nine (8%) of the strains were eaeA positive. Of enteropathogenic E. coli (EPEC), 11 of the 87 (13%) strains were for the positive eaeA gene. The serotypes and the numbers of eaeA-positive strains among the strains tested were as follows: O26:H-(2/3), O55:H7 (4/4), O55:H-(2/ 2) and O128:H2(3/3). Two enterohemorrhagic E. coli (EHEC) strains (Verotoxin positive O157:H7) were also eaeA positive. Among 260 non-EPEC strains that were not categorized as diarrheagenic E. coli, 16 (6%) were eaeA positive. Those serotypes were as follows: O15:H2, O20:H6, O28:H28, O63:H6. O153:H7, O28:H6, O153:H19 and O157:H45. EPEC strains including O18:H7 and six other serotypes, enteroinvasive E. coli (EIEC), and enterotoxigenic E. coli (ETEC) were all eaeA negative.     

Both 987P and F41 fimbriae produced by the same enterotoxigenic Escherichia coli strain isolated from a piglet with diarrhea

An enterotoxigenic Escherichia coli strain isolated from a piglet with diarrhea was examined for the presence of fimbriea 987P and F41 by a direct agglutination (with MAbs), an indirect immunofluorescence technique (MAbs as first antibodies), SDS-PAGE and Western blots (antisera IgG as probes). Results of these techniques revealed that both 987P and F41 fimbrial adhesins were produced by the same strain, not by separate ones.     

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.     

Relative importance of enterotoxigenic and invasive enteropathogenic bacteria in infantile diarrhoea

Swedish children and adults (648 patients) with acute diarrhoea were investigated for enterotoxigenic strains in stool cultures. A total number 74 strains were isolated from 28 patients and assayed in the rabbit intestinal loop test and the adrenal cell test. Only three of the enterotoxigenic E. coli (ETEC) isolates belonged to classical enteropathogenic serotypes of E. coli (EPEC). Two enterotoxigenic strains of Proteus morganii, two of Enterobacter hafniae and one of Citrobacter freundii were isolated. None of 67 EPEC strains were found to produce a heat-labile enterotoxin (LT) in either of the two test systems. A number of Yersinia enterocolitica and Pseudomonas aeruginosa strains from stool cultures often produced toxic effects in the cell test but no enterotoxin activity was detected for any of the strains investigated either in the adrenal cell test for heat-labile enterotoxin (LT) or the suckling mouse test for heat-stable enterotoxin (ST). All EPEC isolates were also tested for ST and for invasive properties in the Sereny test; each isolate was negative in both test systems. It is concluded that production of LT and ST enterotoxin were common in stool isolates from Ethiopian children but a rare phenomenon among Swedish children with acute infantile diarrhoea. Isolation of aerobic stool bacteria with invasive properties seems to be uncommon both in Ethiopian and Swedish children. However, since both LT and ST as well as invasive properties seem to be very unstable genetic properties in many of these stool isolates improved sensitive methods for the last two properties will probably change this picture in the future.