Enteroinvasive Escherichia Coli Research Articles

Survey of clinical isolates of diarrhoeogenic Escherichia coli: diffusely adhering E. coli strains with multiple adhesive factors.

A total of 335 Escherichia coli strains were isolated from sporadic cases of aqueous diarrhoea in patients hospitalized in Clermont-Ferrand, France, during 1991 and 1992. Many of these strains belonged to the diffusely adhering E. coli (DAEC) group, since 51 of them (15.2%) hybridized with the daaC probe corresponding to the accessory gene of the F1845 adhesin and 13 (3.9%) with the AIDA-I (adhesin involved in diffuse adhesion-I) structural gene. The other pathogenic E. coli groups were weakly represented: 0.6% (2 strains) of enterotoxigenic E. coli (ETEC), 0.6% (2 strains) of enterohaemorrhagic E. coli (EHEC) and 3.9% (13 strains) of enteroaggregative E. coli (EAggEC). Neither enteropathogenic E. coli (EPEC) nor enteroinvasive E. coli (EIEC) were isolated in our study period. Among the DAEC strains studied, we described two major surface proteins of 16 and 29 kDa. We showed that the 16-kDa protein (CF16K) was involved in adhesion in vitro to Caco-2 and HEp-2 cells. Pretreatment of bacteria with anti-CF16K serum or of Caco-2 cells with purified CF16K greatly decreased the adhesion of the E. coli CF1085 strain producing the CF16K protein to both cell types. The CF16K adhesive factor was found in 9.5% (33 strains) of the 335 E. coli strains studied by colony immunoblot assays with anti-CF16K serum. Twelve strains producing CF16K hybridized with the daaC probe, indicating that the CF16K is not related to the Dr family adhesins which recognized the Dr blood group antigen as receptor. The 29-kDa protein, isolated from 9 strains out of the 335 studied (5.1%), was identified as the CS31A antigen by Western blot assay using anti-CS31A serum and by hybridization experiments with a CS31A DNA probe. This antigen is routinely observed in septicaemic or enterotoxigenic bovine E. coli strains. We showed that a single diarrhoeogenic E. coli strain could harbour at least two adhesive factors, since 36% of CF16K E. coli strain producers and 68.4% of CS31A E. coli strain producers hybridized with the daaC DNA probe.

Pathogenic or potentially pathogenic bacteria as contaminants of fresh water from different sources in Araraquara, Brazil

The microbiological quality of various fresh waters in the Araraquara region, state of São Paulo, Brazil was investigated. Ninety-nine water samples were taken from rivers, reservoirs, artesian and non-artesian wells, springs and tap waters, and these waters were analysed using: plate counts of heterotrophic microorganisms (per 1 ml); Most Probable Number (MPN) of fecal coliforms and E. coli (per 100 ml); tests for presence of Salmonella, Shigella, Yersinia, the E. coli pathogens of classes EPEC, ETEC and EIEC and Mycobacterium, Shigella, Yersinia and enteroinvasive E. coli (EIEC) were not isolated. The other types of microorganisms were isolated in varying proportions. We conclude that the waters investigated represent a potential microbiological health risk.

Hyper-invasive mutants define a novel Pho-regulated invasion pathway in Escherichia coli.

We have isolated two transposon insertion mutations of the pst-phoU operon which result in the constitutive expression of the phoA gene product, alkaline phosphatase. The two mutations also render Escherichia coli invasive towards cultured HEp-2 cells and define a novel Pho-regulated invasion pathway. The presence of the large 'invasion' plasmid derived from an entero-invasive E. coli (EIEC) clinical isolate in these mutants leads to enhanced invasiveness toward cultured HEp-2 cells, a phenomenon referred to as the 'hyper-invasive' phenotype. Transduction of a pst-phoU insertion mutation into clinical isolates of EIEC and Shigella flexneri results in constitutive PhoA expression and coupled hyper-invasiveness in the former but not the latter. We speculate that the Pho-regulated invasion pathway described here, while silent in bacteria grown in standard laboratory rich media, may become functional in the host when invasive bacteria encounter nutrient starvation and/or other related stress conditions.

Evaluation of alkaline phosphatase-labelled ipaH probe for diagnosis of Shigella infections.

The presence of many enteropathogens which are not easily detectable by routine stool culture has led to the development of alternative diagnostic methods. One of these techniques, nucleic acid probe hybridization, has been used to identify Shigella spp. and enteroinvasive Escherichia coli (EIEC) in stool specimens through the detection of genetic material encoded by a specific large approximately 200-kbp virulence-related plasmid. In the present study, an alkaline phosphatase-labelled oligonucleotide probe developed to detect the gene for ipaH, a repetitive genetic sequence thought to be present on both the virulence-related plasmid and the chromosomes of all strains of Shigella and EIEC, was tested in a developing-country setting through a prospective clinical trial. In a group of 219 Peruvian adults and children with acute gastroenteritis, the ipaH probe detected 85% of cases of shigellosis and demonstrated a specificity of 95% when compared with simultaneous detection by several stool culture techniques. Additionally, three cases of EIEC infection which could not be diagnosed by culture methods alone were detected with the ipaH probe and were confirmed by plasmid analysis and Sereny testing. These preliminary results suggest that, with further research, the ipaH probe should prove to be a useful and rapid adjunct in the diagnosis of acute gastroenteritis in developing countries.

Detection of Shigellae and EnteroinvasiveEscherichia coliby Amplification of the Invasion Plasmid Antigen H DNA Sequence in Patients with Dysentery

Detection of Shigella organisms and enteroinvasive Escherichia coli (EIEC) by polymerase chain reaction (PCR) was evaluated in 20 patients with dysentery before and in 17 of the 20 after treatment with ciprofloxacin. DNA sequences coding for IpaH antigen, a multiple copy sequence found on the chromosome, and the invasion plasmid locus (ial) was detected after DNA amplification in 13 stools from patients from whom shigellae or EIEC were isolated but not in 21 nondysenteric stools containing other enteric bacteria. Although shigellae or EIEC were not isolated from any patient with dysentery after ciprofloxacin treatment, IpaH and ial sequences were found after PCR amplification in 7 patients after treatment with ciprofloxacin. IpaH sequences alone were detected in 4 patients; DNA augmentation of IpaH in stools in a specific way to identify Shigella or EIEC infection in persons from whom cultures cannot be obtained promptly after the onset of diarrhea or who have received antibiotics.

Microbiological quality of recreational waters in Araraquara, SP, Brazil

The microbiological flora of 108 water samples was explored to evaluate the role of recreational waters as a possible source of human diseases in Araraquara, S.P., Brazil. These waters included six swimming pools and three lakes with beaches. The number of total and fecal coliforms, Escherichia coli, fecal streptococci, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, and heterotrophic organisms was determined. As was the occurrence of Salmonella, Shigella, yersinia, enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), Mycobacteria, yeasts in general and dermatophytes. Shigella, Yersinia, EIEC and dermatophytes were not isolated. Other organisms or groups of microorganisms were found in variable proportions. From this study it is concluded that recreational waters used by the population of Araraquara, may be contaminated with potentially pathogenic microorganism and this may serve as a source of human diseases.

Diarrhoea caused byEscherichia coli

Since the mid-1940s, Escherichia coli has been recognized as a cause of diarrhoea. Subsequently it has been shown that at least five different pathogenic mechanisms are used to cause disease. Enterotoxigenic E. coli (ETEC) and enteropathogenic E. coli (EPEC) produce a noninflammatory diarrhoea, whereas enteroinvasive E. coli (EIEC), enterohaemorrhagic E. coli (EHEC) and enteroaggregative E. coli (EAggEC) produce an inflammatory diarrhoea. ETEC are a major cause of diarrhoea in infants (up to three episodes per year) and travellers. They produce diarrhoea by attaching to the small intestinal mucosa and elaborate one or both of heat labile and heat stable toxins. EPEC attach firmly to the intestinal mucosa leading to dissolution of the brush border by inducing vesiculation of the microvilli. This process is known as attaching-effacement, and in the jejunum and ileum results in a loss of brush border disaccharidase enzymes and a large area of absorptive surface. EPEC are a major cause of summer diarrhoea in infants and neonatal diarrhoea. EIEC attach to colonic enterocytes, penetrate by an endocytotic mechanism and replicate therein. This results in necrosis and stripping of large areas of colonic mucosa and a dysentery similar to but usually less severe than Shigella dysentery. EHEC produce attaching-effacement to the terminal ileal and colonic mucosa and release the toxins, verocytotoxin (VT) 1 or 2. These kill colonic enterocytes and produce haemorrhagic colitis. In addition, VT can damage vascular endothelial cells, leading to haemolytic uraemic syndrome. The role of EHEC in diarrhoea in children in the tropics is not known. The most recently described group are the EAggEC. They damage and blunt colonic villi by haemorrhagic necrosis, although the precise pathogenic mechanisms are unclear. EAggEC are a major cause of chronic diarrhoea in children. Although certain O-serotypes are associated with the different enteropathic E. coli, serotyping is not sufficiently specific or sensitive for use as a diagnostic tool. Specific diagnosis is expensive and time consuming and depends upon demonstration of the pathogenicity trait, and the pathogenicity gene(s) or their gene product(s). At present, to undertake such testing is not recommended for routine diagnosis but is most useful when surveys of the aetiology of acute and chronic diarrhoea are undertaken.

VacB, a novel chromosomal gene required for expression of virulence genes on the large plasmid of Shigella flexneri.

Shigellae, the causative agents of bacillary dysentery, are capable of adhering to and invading epithelial cells and spreading into adjacent cells. A chromosomal mutant of Shigella flexneri 2a YSH6000 with reduced invasive capacity was isolated by Tn5 insertion mutagenesis. The linkage of the mutant phenotype to the Tn5 insertion was determined by P1 phage transduction. The site of the Tn5 insertion was assigned to a NotI chromosomal restriction map, confirming that the virulence-associated locus, designated vacB, is a new locus on the chromosome. In the vacB mutant, production of the four plasmid-encoded virulence antigens, IpaB, -C, and -D and VirG, decreased to a low level compared with that in the wild type. In contrast, levels of transcription of the operons for virG, ipa, region-3.4, region-5, virF, and virB on the large plasmid, as determined by Northern dot blotting, were unaffected in the vacB mutant. Furthermore, transcriptional activation of the ipa operon by exploiting a tac promoter could not restore the vacB mutant to production of the same levels of the IpaB, -C, and -D proteins as those in the wild type, indicating that the vacB locus is involved in expression of the vir genes on the large plasmid at the posttranscriptional level. Cloning followed by nucleotide sequencing of the vacB region showed it to contain a 2,280-bp open reading frame encoding an 86.9-kDa protein located 669 bp downstream from the 3' end of the open reading frame for the purA gene. Disruption of the vacB gene of other serotypes of Shigella spp. and enteroinvasive Escherichia coli (EIEC) resulted in reduced expression of virulence phenotypes, indicating that the vacB gene encodes a novel type of virulence-associated gene required for the full expression of the virulence phenotype of Shigella spp. and EIEC.

Polymerase Chain Reaction Identification of Enteroinvasive Escherichia coli Seeded into Raw Milk

Molecular biological techniques for identifying pathogenic foodborne bacteria use small amounts of bacterial nucleic acids that must be purified and concentrated from complex food matrices. The polymerase chain reaction (PCR) amplifies specific segments of DNA and speeds the identification of bacterial strains. Methods for preparing DNA for PCR analysis were tested by seeding enteroinvasive Escherichia coli (EIEC) cells into raw milk. Test samples of milk were heated at 35°C and were treated with proteinase and detergent. As few as 102 cells of EIEC per ml of seeded milk were identified after amplification of a plasmid-borne gene required for invasion.

Molecular characterization of strains of enteroinvasive Escherichia coli O143, including isolates from a large outbreak in Houston, Texas.

A large diarrhea outbreak due to enteroinvasive Escherichia coli (EIEC) serogroup O143 occurring in Houston, Tex., provided the opportunity to investigate aspects of the molecular epidemiology of this and related organisms. This was done by comparing the plasmid patterns and the chromosomal restriction endonuclease digestion patterns by pulsed-field gel electrophoresis (PFGE) of EIEC from the outbreak, other E. coli from the same serogoup (O143), and EIEC isolated from other patients with diarrhea. Among the isolates studied, there was marked restriction fragment length polymorphism. All 3 non-O143 EIEC isolates had very different restriction endonuclease digestion patterns, as did 5 of 5 O143 non-EIEC isolates and 6 of 15 O143 EIEC isolates. Four Houston outbreak O143 EIEC isolates had the same restriction pattern as an O143 EIEC strain isolated 2 months before in Mexico and was nearly identical to another two O143 EIEC Mexican isolates. These related strains also had the same plasmid pattern; however, the presence of only a few plasmid bands, versus the 21 to 30 chromosomal bands seen with PFGE, suggests that plasmid patterns could be a less specific way to distinguish different strains. These results demonstrate that PFGE can distinguish between different E. coli strains of the same serogroup and phenotype. This technique can also identify relatedness within O143 EIEC, and our data suggest the spread of a strain of EIEC from Mexico to Houston, where it caused a large outbreak. PFGE may be useful to study the epidemiology of EIEC.

Shigella and Enteroinvasive Escherichia coli Infections in Households of Children with Dysentery in Bangkok

Shigellae and enteroinvasive Escherichia coli (EIEC) were identified in children with dysentery and their household contacts in Bangkok. Shigellae were isolated from 49% and EIEC from 6% of 306 children with dysentery seen at the outpatient department of Children's Hospital on weekdays during January through June 1989 and October 1989 through October 1990. The same serotype infecting the index child was isolated from 21 (4%) of 522 household contacts of 151 index children with Shigella infections and from none of 60 household contacts of 19 index children with EIEC infections. Amplification of DNA sequences coding for the invasion-associated locus (ial) by polymerase chain reaction increased the identification of Shigella and EIEC infections from 57% (111/193) to 68% (132/193). ial sequences were identified in 3 of 20 drinking water specimens from which shigellae or EIEC were not isolated. Amplification of ial sequences identified more shigellae and EIEC than did bacteriologic and colony hybridization methods in children with dysentery and in drinking water in Bangkok.

Food poisoning caused by enteroinvasive Escherichia coli (O164:H-)--a case in which the causative agent was identified

Food poisoning due to "Godofu (Sasayuki tofu)" as a main causative foodstuff which broke out on July 14, 1988. There were 670 out of 918 persons who ingested this food who became ill (incidence 73.0%). The main symptoms were diarrhea (93.4%), fever (77.5%), abdominal pain (64.5%), and vomiting (19.9%). A high degree of fever and watery diarrhea were characteristic of this poisoning. The average latent period was 35 hours with a range of one to 156. The O164:H- strains of enteroinvasive Escherichia coli (EIEC) were detected from 22 of the 32 fecal samples collected from the patients, five of ten samples collected from workers engaged in tofu making, and one sample of left-over Godofu. The virulence of EIEC strains isolated from the patients, workers, and left-over food was confirmed by invasion into HeLa and HEp-2 cells, Sereny test, and ELISA test to detect invasive plasmid-derived protein of the organism (conducted at Tokyo Metropolitan Research Laboratory of Public Health). These EIEC strains were sensitive (less than or equal to 0.19 to 6.25 micrograms/ml) to GM, ABPC, CBPC, CER, CET, NA, PB, MINO, TC and CP as well as KM and OFLX which were used for treatment. However, their susceptibility to FOM varied to some extent (6.25 to 25.0 micrograms/ml) and one strain isolated from a tofu worker was resistant to MINO, TC, FOM and CP (25 to greater than or equal to 100 micrograms/ml). Since investigation revealed that Godofu was left at room temperature about 29 degrees C until ingested, we did a experiment to check the bacterial growth in Godofu under similar conditions at the time of outbreak.(ABSTRACT TRUNCATED AT 250 WORDS)

Contact-haemolysin production by entero-invasive Escherichia coli and shigellae

Entero-invasive Escherichia coli (EIEC) and shigellae were tested for contact-haemolysin (CH) with red blood cells (RBCs) of guinea-pig, rabbit, rat, mouse, monkey, man, sheep and chicken; all bacteria showed the best lysis with guinea-pig RBCs. The best culture medium for CH activity of shigellae was tryptic soy broth, and for EIEC it was casamino acid-yeast extract broth with 1 mM CaCl2. CH production by all species was best at the slightly alkaline pH which is optimal for growth; it was also dependent on the presence of a large (140-Mda) plasmid. Pre-treatment of bacteria with homologous antisera inhibited CH activity. Various treatments of bacterial cells and RBCs suggested that CH may be a protein molecule, and that a chitotriose-like moiety may serve as CH receptor. RBCs that were incubated with bacteria at 4 degrees C, or with heat-killed bacteria at 37 degrees C, were not lysed; also, isolated cell-surface components (lipopolysaccharide and outer-membrane protein) did not lyse RBCs. This suggests that metabolically active cells are required for CH activity. Production of CH by both EIEC and shigellae is consistent with a common mechanism for the virulence of these organisms.

Diarrhoeal disease in children less than one year of age at a children's hospital in Guangzhou, People's Republic of China

We performed a case-control study of diarrhoea to determine its causes in children <1 year old in Guangzhou, People's Republic of China, in April to September 1989. Stools were cultured for Salmonella, Shigella, Campylobacter and vibrios by standard techniques; rotavirus (RV) was identified by polyacrylamide gel electrophoresis; and specific deoxyribonucleic acid probes were used to identify Escherichia coli containing genes coding for Shiga-like toxin I and II, enteropathogenic E. coli adherence factor, and enteroinvasive E. coli (EIEC). E. coli isolates were tested for heat-labile toxin (LT) and heat-stable toxin (ST) production and mannose-resistant adherence to HeLa cells. Rotavirus was identified in 13 of 174 children with diarrhoea (cases) and in 2% of 174 age-matched children without diarrhoea (controls), P < 0·001. C. jejuni was identified in 10% of cases and 2% of controls, P = 0·003. Giardia lamblia was identified in 4 cases, LT and ST enterotoxigenic E. coli (ETEC) in 2, and S. flexneri in 1 case; they were not found in controls. ETEC that produced LT only was isolated from 5 cases and 3 controls, P = 0·721; E. coli that adhered to HeLa cells in a diffuse pattern was isolated from 30 cases and 40 controls, P = 0·229; and E. coli that adhered in an aggregative pattern was isolated from 20 cases and 18 controls, P = 0·863. EIEC was not isolated from cases or controls. Nine cases (5%) developed persistent diarrhoea (>14 d duration). C. jejuni and aggregative E. coli were isolated from different children with persistent diarrhoea. E. coli (serogroup 0119), adherence factor positive, which adhered to HeLa cells in a localized pattern, was isolated from 1 control. Rotavirus and C. jejuni were the most common causes of diarrhoea in children <1 year of age in Guangzhou in the summer of 1989.

Microbiology and Diagnosis of Infections with Shigella and Enteroinvasive Escherichia coli

The etiology of dysentery in Thailand and the existing methods of diagnosing infections with Shigella and enteroinvasive Escherichia coli (EIEC) are reviewed. The four Shigella species (S. dysenteriae, S. flexneri, S. boydii, and S. sonnei) are classically identified by culture of fecal specimens on selective media and testing of isolates for agglutination in species-specific antisera. DNA probes have been used to identify both lactose-fermenting and non-lactose-fermenting EIEC as well as Shigella isolates that do not agglutinate in antisera. These DNA probes are not necessary for the identification of Shigella if a competent bacteriology laboratory with shigella antisera is available. In Thailand Shigella and EIEC are isolated more often from children greater than 2 years of age than from younger children. The clinical illness associated with EIEC infections is similar to shigellosis. Fewer children with EIEC infections than with shigellosis, however, have occult blood in stool (36% vs. 82%) and more than 10 fecal leukocytes per high-power field (36% vs. 67%). Standard bacteriologic methods and testing of E. coli isolates for hybridization with the shigella/EIEC probe are currently the most sensitive means of diagnosing infections caused by these enteric pathogens. A more rapid method of identifying Shigella and EIEC infections in a situation where a bacteriology laboratory is not available will probably involve immunologic assays.

140-MDa plasmids of Escherichia coli and Shigella flexneri 5 do not influence phagocytosis

Enteroinvasive Escherichia coli (EIEC) and Shigella flexneri possessing a 140-megadalton (MDa) plasmid are capable of invading intestinal epithelial cells and causing dysentery. To determine if this plasmid affected phagocytosis of the organisms by leukocytes, we studied the in vitro phagocytosis of isogenic pairs of EIEC and S. flexneri 5 which differed only in the presence or absence of the 140-MDa plasmid. In addition five EIEC strains containing 140-MDa plasmids as well as one non-enteroinvasive E. coli strain possessing a 120-MDa plasmid were studied. The 140-MDa plasmid did not affect phagocytosis of these bacteria by normal human blood neutrophils or monocytes.

Etiology of childhood diarrhea in Beijing, China

To determine the role of recently recognized enteropathogens in childhood diarrhea in China, 221 children with diarrhea and 108 controls seen at the Beijing Children's Hospital were studied during April and May 1989. Stools were examined for ova, parasites, and rotavirus, cultured for bacterial pathogens, and probed for enterotoxigenic Escherichia coli (ETEC), enteroinvasive E. coli (EIEC), enterohemorrhagic E. coli (EHEC), and enteropathogenic adherence factor-positive (EAF+) E. coli. Pathogens were identified in 56.5% of children with diarrhea and 43.5% of controls (P = 0.04). Detection of enteropathogens was significantly greater in patients examined within 1 week of symptom onset (65%) than in patients examined later (39%; P = 0.01). ETEC was the most frequently detected pathogen in children with diarrhea, accounting for 20% of the cases. Other agents identified in patients included the following: salmonellae, 12%; rotavirus, 7%; EIEC, 7%; EHEC, 7%; members of the Aeromonas hydrophila group, 6%; EAF+ E. coli, 5%; Ascaris lumbricoides, 3%; shigellae, 3%; campylobacters, 2%; and Vibrio spp., 0.5%. The isolation rates of salmonellae (P = 0.02), EAF+ E. coli (P = 0.04), and mixed pathogens (P = 0.05) were significantly greater for diarrhea patients than for controls. Resistance to multiple antimicrobial agents occurred in 39% of the Salmonella isolates, 22% of the Aeromonas isolates, and 17% of the Shigella isolates. Multiresistant salmonellae (P = 0.05) and shigellae were recovered from diarrheal stools only. Ciprofloxacin, cefotaxime, and imipenem were the only agents tested to which all bacterial isolates were susceptible in vitro. These results suggest that both traditional and newly recognized agents are important causes of childhood diarrhea in Beijing and that therapy may be complicated by indigenous antimicrobial resistance.

Two new Escherichia coli O groups: O172 from »Shiga‐like» toxin II‐producing strains (EHEC) and O173 from enteroinvasive E. coli (EIEC)

Two Escherichia coli strains were established as antigenic test strains for two new O groups, O172 and O173. The O172 strain (EHEC) which produces "Shiga-like" toxin II (verocytotoxin 2) was isolated from a case of haemorrhagic colitis while the enteroinvasive O173 strain (EIEC) originated from a child with diarrhoea.

Pathogenic Escherichia coli found in food

The bacteria constituting the species Escherichia coli are commonly found in the intestinal flora of man and animals, and were until late 1950s recognized as non-pathogenic normal cohabitants. However, certain strains might induce disease, and E. coli should therefore be regarded as a potential pathogenic organism. The pathogenic strains can cause distinct disease syndrome as different diarrheal diseases, wound infectionsm meningitis, septicemia, artherosclerosis, hemolytic uremic syndrome and immunological diseases such as reactive and rheumatoid arthritis. Several different groups of diarrhea-inducing strains are known. The enterotoxigenic E. coli (ETEC) strains produce one or more of toxins from the heat-labile and the heat-stable enterotoxin families. These strains possess specific adhesion fimbria for intestinal attachment and colonization. Some enteropathogenic E. coli strains (EPEC) produce one or more of the cytotoxins, but adhere also to intestinal cells interfering with the electrolyte transport system. The group of strains possessing invasive properties are designated enteroinvasive E. coli (EIEC). Recently, the enterohemorrhagic E. coli (EHEC) strains have been identified and shown to produce one or more of the cytotoxins (vero-cytotoxins, shiga-like toxins). Food originating from warm-blooded animals may be contaminated with E. coli, but contamination from human sources are more common for food involved in outbreak of disease. In general, strains causing disease in animals do possess other colonization factors than those found on human pathogenic strains. EIEC strains are, like Shigella, only known to induce disease in man. However, both healthy and sick cattle are suspected to be a major reservoir for EHEC strains, and several outbreaks have been associated with consumtion of meat or meat products. Cheeses have been the source of outbreaks of both ETEC and EIEC in Europe and the USA, while water seems to be a major source for the different diarrheic E. coli strains affecting children and tourists in the 3rd world. Strains causing non-enteric disease are less known as being transmitted to humans with food as a vector, but the importance of some of these diseases, should implicate further research on what role food plays in spreading these organisms. The recipient of the potential pathogenic E. coli through food, the humans, are also of different risk of contracting diseases. The factors of most importance seems to be the immunological and nutritional status of the host, and recently E. coli strains previously regarded as non-pathogenic, have been implicated in cases of disease in persons with AIDS. Because the species E. coli consists of both pathogenic and non-pathogenic strains, and due to the fact that the latter constitute a part of normal intestinal flora, differentiation between pathogenic and non-pathogenic strains becomes very important. Traditional cultivation from food samples, using selective enrichment broths, has been shown to give growth preference to strains of environmental origin compared to strains of human origin. Isolated strains have a tendency to loose extrachromosomal genes encoding important pathogenicity factors during such selective enrichment. It is of the greatest importance to be able to identify the pathogenicity markers such as toxins and adhesins, and differentiate these strains from non-pathogenic strains originating from animals or the environment. This is a difficult task, but genetic probing and PCR technologies can be useful tools in making this type of diagnosis efficient, and provide information of epidemiological importance, specially with respect to routes for spreading pathogenic E. coli strains with food as a vector.

Diarrheagenic Escherichia coli and Virulence Determinants.

Escherichia coli is normally the most common facultative anaerobe in the large bowel and usually nonpathogenic for man. However, some E. coli strains which cause distinct syndromes of diarrhea diseases have been proved to be pathogenic. These organisms are one of the most common causes of food poisoning in Japan. In developing countries, these pathogens are known to be main causative agents of diarrhea which is the major cause of infantile morbidity and mortality. These E. coli strains are divided into four groups : enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), enterotoxigenic E. coli (ETEC), and enterohemorrhagic E. coli (EHEC). The four groups are distinguished on the basis of pathogenic, clinical, and epidemiologic features. Moreover, the fifth group of diarrheagenic E. coli, termed enteroaggregative E. coli (EAggEC), has been recently proposed. The strains of EAggEC exhibit characteristic patterns of adherence when bound to cultured epithelial cells. But the epidemiologic significance of EAggEC as diarrheal pathogens has not been yet determined. Although the features of the four groups are different, they have certain underlying commonalities with respect to pathogenesis as follows. (1) Critically virulent properties are encoded in plasmids. (2) Characteristic interactions with intestinal mucosa occurred. (3) Enterotoxins or cytotoxins are produced. In this review, microbiological features and etiological significances of these strains, are described.