Conjugal acquisition and stable maintenance of Ent plasmids in nontoxigenic wild-type strains of Escherichia coli

In spite of the ability of the genetic determinants for enterotoxin production to be conjugally transferred, mobilized or transposed, enterotoxigenic Escherichia coli (ETEC) isolated from diarrheal patients is restricted to certain serotypes. Four conjugative enterotoxigenic plasmids (Ent plasmids) encoding either a heat-labile enterotoxin or a heat-stable enterotoxin or both and belonging to one of three incompatibility groups IncFI, IncHl, or IncX, were examined for their transferability to and stability in 157 nonenterotoxigenic Escherichia coli strains belonging to various serotypes and 89 clinical isolates nonenterotoxigenic but belonging to those serotypes in which ETEC from diarrheal patients are usually found. The serotypes of the strains to which Ent plasmids were efficiently transferred and in which they were maintained stably were not always the serotypes in which ETEC had usually been found and vice versa. The frequencies of transfer of four Ent and two R plasmids to each of the 157 recipients were correlated with each other, indicating that the frequency of transfer of the plasmid is not determined by a resident plasmid, if there is one, but by a recipient factor which commonly affects transferability to all donors. These results have led to the conclusion that the reason why only certain serotypes are found among ETEC isolated from diarrheal patients is not the ability of these strains specifically and preferentially to acquire and maintain the Ent plasmids.     

Molecular Comparison of Plasmids Encoding Heat-Labile Enterotoxin Isolated from Escherichia coli Strains of Human Origin

The molecular properties of enterotoxin (Ent) plasmids from 12 Escherichia coli strains of human origin were examined. Ten strains belonged to the O78 serogroup, and the remainder were of serogroup O7 or O159. Eleven plasmids coded for heat-labile enterotoxin (LT), and one coded for heat-stable enterotoxin (ST) and LT. The results of restriction enzyme digests and deoxyribonucleic acid reassociation experiments showed that all of the Ent plasmids were related, and supported the subdivision of the LT plasmids into three groups based on their genetic properties (M. M. McConnell et al., J. Bacteriol. 143: 158–167, 1980). Within group 1, two plasmids from South African strains were indistinguishable but differed in EcoRI and HindIII digests from the LT plasmid that originated from an Ethiopian strain. The three plasmids had >70% homology. The two non-autotransferring group 2 plasmids identified in O78.H11 strains from Bangladesh were indistinguishable. The group 3 plasmids were from strains belonging to serogroups O7 and O78 isolated in Bangladesh, India, and Thailand. They shared >95% homology but showed slight differences in fragment patterns when treated with EcoRI and HindIII. There was 60 to 70% homology between the plasmids of groups 1 and 3, and the group 2 plasmid had 40 to 50% homology with members of these two groups. The autotransferring Ent plasmids had up to 40% homology with R factors of incompatibility groups FI, FII, and FIV.     

Detection of heat-stable and heat-labile enterotoxin genes of Escherichia coli in diarrhoeic faecal samples of mithun (Bos frontalis) calves by polymerase chain reaction

Aims:  To find out the prevalence of different serogroups of Escherichia coli ( E. coli ) and to detect heat-stable (ST) and heat-labile (LT) enterotoxin genes of enterotoxigenic E. coli (ETEC) from the faeces of mithun calves with diarrhoea.
Methods and Results:  Faecal samples obtained from 65 diarrhoeic mithun calves of under 2 months of age were examined for E. coli using polymerase chain reaction (PCR). Fifty-four E. coli isolates were obtained from those samples, which belonged to 38 different serogroups. Out of 54 isolates tested by PCR, two isolates (3·70%) belonging to serogroups O26 and O55 were found to possess gene that code for ST enterotoxin and one isolate (1·85%) belonging to serogroup O125 was found to carry LT enterotoxin gene.
Conclusions:  Escherichia coli isolates from diarrhoeic mithun calves were found to possess ST and LT enterotoxin genes, which are designated as ETEC, and these isolates can be detected through PCR using specific primers.
Significance and Impact of the Study:  This study reports the isolation of ETEC possessing ST and LT enterotoxin genes for the first time and ETEC could be a cause of diarrhoea in mithun calves leading to calf mortality.     

Production of enterotoxins by strains of Escherichia coli isolated from pigs

The production of enterotoxins by 237 hemolytic strains of Escherichia coli isolated from pigs was determined with the use of CTE in CHO. Vero and Hela cells and ILT. More frequent (p less than 0.01) production of enterotoxins, determined by ILT, was found for the serotypes being pathogenic for the animals (63.8% of the strains). No correlation between intensity of ILT and particular serotype was observed. Both the serotypes pathogenic for pigs and other serotypes produced LT enterotoxins and ST toxin. The frequency of LT enterotoxin production was statistically insignificant compared to the frequency of ST enterotoxin production by strains with serotypes pathogenic for the pigs. Strains of E. coli producing only enterotoxin ST belonged both to the pathogenic serotypes as well as to other hemolytic serotypes. The cytotoxic activity of supernatants of E. coli strains with different serotypes isolated from pigs in Vero and Hela cells and simultaneous CTE in CHO cells was observed. This suggests the production by the strains of enterotoxin LT and cytotoxin VT. Seven out of the 96 isolates showing CTE in CHO cells gave no reaction in the ILT in pigs. This suggests the production by these isolates of a toxin (toxins) differing from the E. coli enterotoxins.     

Expression of plasmids coding for colonization factor antigen II (CFA/II) and enterotoxin production in Escherichia coli

Two plasmids transferred from enterotoxigenic Escherichia coli (ETEC) of serotype O6. H16 and biotypes A and C coded for mannose-resistant haemagglutination (MRHA) and production of heat-stable enterotoxin (ST) and heat-labile enterotoxin (LT). Both plasmids were nonautotransferring being mobilized most efficiently by the R plasmid R100-1. They were similar in their genetic properties being incompatible with each other and plasmids of the Inc group FI. The wild-type strains produced the colonization factor antigen II (CFA/II) which was made up of different coli surface antigens (CS). The biotype A strains produced CS1 and CS3 while the biotype C strains produced CS2 and CS3. These three antigens have the ability to cause MRHA. When plasmids coding for MRHA were transferred to K12 strains, the degree of haemagglutination was markedly reduced and only CS3 was produced. When both plasmids were transferred back into biotype A strains, good MRHA was restored and the strains produced CS1 and CS3. In a biotype C strain CS2 and CS3 were formed. The production of the antigens was compared by enzyme-linked immunosorbent assay (ELISA). The strains were also examined by electron microscopy where it was found that CS1 and CS2 were fimbrial antigens while CS3 was not.     

人毒素原性大肠杆菌肠毒素ST、LT-B基因的融合

将毒素原性大肠杆菌(ETEC)编码耐热肠毒素(ST)的基因片段与编码热敏肠毒素B亚基(LT—B)的基因进行融合,并在此基础上进行不同数目ST基因的串联。ELISA检测融合基因表达蛋白产物,观察到ST与LT-B之间存在着相互影响。ST的检测滴度随基因串联个数增加而逐渐升高,而LT的ELISA滴度则减弱。本研究说明ST可以通过基因串联提高表达产物抗原活性。这为毒素原性大肠杆菌多价疫苗的研制提供了重要的研究基础。     

Phenotypic and molecular characteristics of Escherichia coli isolated from aquatic environment of Bangladesh

Pathogenic Escherichia coli remains important etiological agent of infantile diarrhea in Bangladesh. Previous studies have focused mostly on clinical strains, but very little is known about their presence in aquatic environments. The present study was designed to characterize potentially pathogenic E. coli isolated between November 2001 and December 2003 from aquatic environments of 13 districts of Bangladesh. Serotyping of 96 randomly selected strains revealed O161 to be the predominant serotype (19%), followed by O55 and O44 (12% each), and 11% untypable. Serotype-based pathotyping of the E. coli strains revealed 47%, 30%, and 6% to belong to EPEC, ETEC, and EHEC pathotypes, respectively. The majority of the 160 strains tested were resistant to commonly used antimicrobial agents. Plasmid pro-filing showed a total of 17 different bands ranging from 1.3 to 40 kb. However, 35% of the strains did not contain any detectable plasmid, implying no correlation between plasmid and drug resistance. Although virulence gene profiling revealed 97 (61%) of the strains to harbor the gene encoding heat-stable enterotoxin (ST), 2 for the gene encoding Shiga toxin (Stx), and none for the gene for heat-labile enterotoxin (LT), serotype-based pathotyping of E. coli was not fully supported by this gene profiling. A dendrogram derived from the PFGE patterns of 22 strains of three predominant serogroups indicated two major clusters, one containing mainly serogroup O55 and the other O8. Three strains of identical PFGE profiles belonging to serogroup O55 were isolated from three distinct areas, which may be of epidemiological significance. Finally, it may be concluded that serotype-based pathotyping may be useful for E. coli strains of clinical origin; however, it is not precise enough for reliably identifying environmental strains as diarrheagenic.     

Production of thermolabile enterotoxins of Escherichia coli by Yersinia enterocolitica and Yersinia pseudotuberculosis

The plasmids pCG86 and RP4elt coding for thermolabile enterotoxins of Escherichia coli (LT) were transferred in conjugation to Yersinia enterocolitica and Yersinia pseudotuberculosis cells. Both plasmids were stably inherited by the recipient cells. The elt genes of the toxins were expressed in Yersinia cells at the level comparable to the one registered in Escherichia coli cells. In the broth cultures of transconjugant cells the major part of LT toxin is bound with cells (74-97%). The obtained data may serve an experimental basis in favour of possibility of Ent+ strains of Yersinia enterocolitica and Yersinia pseudotuberculosis formation in nature and expediency of search and diagnosing of such strains.     

Genetic diversity of heat-labile toxin expressed by enterotoxigenic Escherichia coli strains isolated from humans

The natural diversity of the elt operons, encoding the heat-labile toxin LT-I (LT), carried by enterotoxigenic Escherichia coli (ETEC) strains isolated from humans was investigated. For many years, LT was supposed to be represented by a rather conserved toxin, and one derivative, produced by the reference H10407 strain, was intensively studied either as a virulence factor or as a vaccine adjuvant. Amplicons encompassing the two LT-encoding genes (eltA and eltB) of 51 human-derived ETEC strains, either LT(+) (25 strains) only or LT(+)/ST(+) (26 strains), isolated from asymptomatic (24 strains) or diarrheic (27 strains) subjects, were subjected to restriction fragment length polymorphism (RFLP) analysis and DNA sequencing. Seven polymorphic RFLP types of the H10407 strain were detected with six (BsaI, DdeI, HhaI, HincII, HphI, and MspI) restriction enzymes. Additionally, the single-nucleotide polymorphic analysis revealed 50 base changes in the elt operon, including 21 polymorphic sites at eltA and 9 at eltB. Based on the deduced amino acid sequences, 16 LT types were identified, including LT1, expressed by the H10407 strain and 23 other strains belonging to seven different serotypes, and LT2, expressed by 11 strains of six different serotypes. In vitro experiments carried out with purified toxins indicated that no significant differences in GM1-binding affinity could be detected among LT1, LT2, and LT4. However, LT4, but not other toxin types, showed reduced toxic activities measured either in vitro with cultured cells (Y-1 cells) or in vivo in rabbit ligated ileal loops. Collectively, these results indicate that the natural diversity of LTs produced by wild-type ETEC strains isolated from human hosts is considerably larger than previously assumed and may impact the pathogeneses of the strains and the epidemiology of the disease.     

Role of heat-stable enterotoxins in the induction of early immune responses in piglets after infection with enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) strains that produce heat-stable (ST) and/or heat-labile (LT) enterotoxins are cause of post-weaning diarrhea in piglets. However, the relative importance of the different enterotoxins in host immune responses against ETEC infection has been poorly defined. In the present study, several isogenic mutant strains of an O149:F4ac(+), LT(+) STa(+) STb(+) ETEC strain were constructed that lack the expression of LT in combination with one or both types of ST enterotoxins (STa and/or STb). The small intestinal segment perfusion (SISP) technique and microarray analysis were used to study host early immune responses induced by these mutant strains 4 h after infection in comparison to the wild type strain and a PBS control. Simultaneously, net fluid absorption of pig small intestinal mucosa was measured 4 h after infection, allowing us to correlate enterotoxin secretion with gene regulation. Microarray analysis showed on the one hand a non-toxin related general antibacterial response comprising genes such as PAP, MMP1 and IL8. On the other hand, results suggest a dominant role for STb in small intestinal secretion early after post-weaning infection, as well as in the induced innate immune response through differential regulation of immune mediators like interleukin 1 and interleukin 17.     

Characterization of a putative colonization factor (PCFO166) of enterotoxigenic Escherichia coli of serogroup O166

Enterotoxigenic Escherichia coli (ETEC) of serogroup O166 gave mannose-resistant haemagglutination (MRHA) with bovine and human erythrocytes. The strains did not react with antisera prepared against the known colonization factors CFA/I, CFA/II, CFA/III, CFA/IV and PCFO159:H4. Strain E7476 of serotype O166:H27, which produced heat-stable enterotoxin (ST), was examined initially. It produced fimbriae about 7 nm in diameter. On SDS-PAGE two possible fimbrial polypeptides of molecular mass 15.5 and 17.0 kDa were seen. When variants of strain E7476 were isolated, loss of ST and MRHA together was associated with loss of a 98 MDa plasmid, while loss of ST alone correlated with plasmid deletion. An absorbed anti-strain E7476 antiserum reacted specifically with the 15.5 and 17.0 kDa polypeptides in Western immunoblotting and bound to the intact fimbriae by immuno-electron microscopy. When this antiserum was used in an ELISA to examine other strains of serogroup O166, a positive reaction was obtained with all the ST- and MRHA-positive strains. One strain of serotype O71:H27 and two strains of serotype O98:H- also reacted with the absorbed anti-strain E7476 antiserum. The antiserum did not react with ETEC carrying known colonization factors. E. coli K12 and a number of E. coli of different serotypes carrying a plasmid coding for ST transferred from strain E7476, all gave MRHA and reacted with the absorbed anti-strain E7476 antiserum. The term putative colonization factor O166 (PCFO166) is proposed to describe the adhesive factor(s) on ETEC of serogroup O166 because of the similarity of properties with those of known colonization factors.     

Positive regulation of colonization factor antigen I (CFA/I) production by enterotoxigenic Escherichia coli producing the colonization factors CS5, CS6, CS7, CS17, PCFO9, PCFO159:H4 and PCFO166

Entertoxigenic Escherichia coli (ETEC) strains of nineteen serogroups which produced colonization factors (coli-surface-associated antigens CS5, CS6, CS7 and CS17, colonization factor antigen CFA/III and putative colonization factors PCFO159:H4, PCFO166 and PCFO9) were tested for hybridization with a DNA probe containing the cfaD sequence that regulates expression of CFA/I. Strong colony hybridization, similar to that with the CFA/I-positive control strain H10407, occurred with ETEC strains of serogroups O27, O159 and O169 which produced CS6 antigen, and with all the strains which produced PCFO166 fimbriae. Weak colony hybridization, compared to the control strain, was found with ETEC producing CS5 fimbriae with CS6 antigen, CFA/III fimbriae with CS6 antigen, CS7 fimbriae or PCFO159:H4 fimbriae. CS6-antigen-positive strains of serogroups O79, O89 and O148 and all the CS17-antigen-positive and PCFO9-fimbriae-positive strains were negative in colony hybridization tests with the cfaD probe. Plasmid DNA of nine ETEC strains and their colonization-factor-negative derivatives was tested for hybridization with the cfaD probe and with ST and LT oligonucleotide probes. The sequences that hybridized with the cfaD probe were on the plasmids which coded for enterotoxin production. Fifteen strains were transformed with NTP513, a recombinant plasmid which contains the CFA/I region 1 fimbrial subunit operon but lacks a functional cfaD sequence, in order to determine whether DNA in any of these strains could substitute for the cfaD sequence in the regulation of production of CFA/I fimbriae.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biological properties of enterotoxigenic Escherichia isolated from patients with acute intestinal diseases of unknown etiology

As the result of the comparative examination of adult patients with acute enteric diseases and normal adults, 173 E. coli enterotoxigenic strains were isolated (161 strains from the patients and 12 strains from normal persons). 83% of the isolated enterotoxigenic E. coli (ETEC) produced two enterotoxins: thermolabile (LT) and thermostable (ST). Enterotoxigenicity was most pronounced in the strains of ETEC belonging to the prevaling variant ST + LT +. The enterotoxigenic properties of ETEC were highly stable: the production of ST and LT in the strains remained unchanged after their storage for up to 4 years. The isolated ETEC comprised 48 serogroups and 61 strains. The strains belonging to the same seroval had a similar degree of toxigenicity. The strains belonging to different serovars considerably differed in the activity of their enterotoxins. The production of two kinds of enterotoxins in the isolated E. coli strains was inter-related: the strains with a high activity of ST were, as a rule, good producers of LT.     

In vivo expression of the heat stable (estA) and heat labile (eltB) toxin genes of enterotoxigenic Escherichia coli (ETEC)

Enterotoxigenic Escherichia coli (ETEC) colonize the intestine and adhere to the epithelium by means of different host specific colonization factors (CFs). Colonizing ETEC produce one or both of two enterotoxins; the heat stable (ST) and heat labile (LT) toxins which are both able to cause diarrhoea. The regulation of virulence genes in ETEC during infection of the human intestine is mainly unknown. In this study we analysed the level of mRNA expression of estA, coding for ST, and eltB, coding for the B subunit of LT, during human infection. The expressions of the toxins in ETEC strains expressing both ST and LT were investigated in bacteria isolated directly from patient stool without sub-culturing, (in vivo) and compared to the expression pattern of the corresponding ST/LT strains grown in liquid broth (in vitro) by quantitative competitive RT-PCR using fluorescent primers. We found that estA and eltB are expressed in the in vivo samples but no significant up-or down regulation of the expression levels of either estA or eltB could be determined in vivo as compared to in vitro.     

Transposition of ampicillin resistance to an enterotoxin plasmid in an Escherichia coli strain of human origin.

We examined a strain of Escherichia coli, serotype O159.H34, of human origin which produced heat-stable and heat-labile enterotoxins, was resistant to ampicillin, and produced colicin. By conjugation and transformation experiments plasmids coding for enterotoxin production (Ent), enterotoxin production and ampicillin resistance (Ap-Ent), ampicillin resistance (Ap), and colicin production were isolated. Both the Ent and Ap-Ent plasmids were autotransferring and belonged to the F-incompatibility complex. However, the Apr Ent+ transconjugants showed differences in their levels of resistance and in their abilities to propagate F-specific phages and to transfer resistance. The results suggested there was transposition from the small Ap plasmid to the Ent plasmid. The Ap-Ent plasmids were larger than the enterotoxin factor and when treated with restriction endonuclease BamHI showed an additional fragment not present in the enterotoxin plasmid. The insertion of ampicillin resistance probably occurred at different sites on the enterotoxin plasmid, resulting in the observed variation in phenotype.     

表达大肠杆菌K88ac-ST1-LTB融合蛋白基因工程菌株的构建

利用PCR技术,从大肠杆菌C83902质粒中扩增出K88ac基因、ST1突变基因和LTB基因,通过分离、纯化、内切酶酶切、连接和转化,构建了含K88ac-ST1-LTB融合基因表达载体的重组菌株BL21（DE3）（pXKST3LT5)。经酶切鉴定和DNA序列分析证实,构建的重组质粒pXKST3LT5中含有K88ac-ST1-LTB融合基因,且基因序列和阅读框架均正确。经ELISA检测,重组菌株表达的K88ac-ST1-LTB融合蛋白能够被ST1单抗、LTB和K88ac抗体识别。经乳鼠灌胃试验证实,表达的融合蛋白已丧失天然ST1肠毒素的活性。免疫实验结果表明,K88ac-ST1-LTB融合蛋白能够诱发小白鼠产生抗体,该抗体具有中和天然ST1肠毒素的毒性作用,表明构建的重组菌株可以作为预防仔猪黄、白痢基因工程菌苗的候选菌株。     

Genotypic and Phenotypic Profiles of Enterotoxigenic <Emphasis Type="Italic">Escherichia coli</Emphasis> Associated with Acute Diarrhea in Tunis,Tunisia

No past studies of acute diarrhea in Tunisia have examined the phenotypic and genotypic profiles of enterotoxigenic Escherichia coli (ETEC) isolates. We determined 65 ETEC isolates derived from a total of 327 E. coli isolates collected from a previous study (acute diarrheal and healthy persons, children and adults n = 214) and 32 E. coli isolates derived from an acute diarrheal outbreak in Kabaria-Ennour city, Tunis. All E. coli isolates were screened by polymerase chain reaction (PCR) for ETEC virulence genes: sta (heat-stable toxin gene) and elt (heat-labile toxin gene). Seventy-two percent (47 of 65) of ETEC strains expressed the sta gene only, 21.5% (14 of 65) expressed the elt gene and 6.1% (4 of 65) expressed both genes. For the outbreak isolates, the elt gene was predominant (10 isolates out of 14). Ganylioside GM1 enzyme-linked immunosorbent assay (GM1-ELISA) was used to validate the PCR results and this was confirmed by dot blot assay. The same results were obtained. The most common colonization factors (CFs) were CFA/I (44.6%) and coli surface antigen 6 (CS6) (11%), and 44.6% of the isolates showed no association with either CFAs. Resistance of ETEC isolates to tetracycline (38.5%), streptomycin (26%), and beta-lactam agents (ticarcillin 26%, amoxicillin 24.6%, cephalotin 21.5%) was common. Regarding serotypes, the majority of ETEC isolates serotyped as O86:H(-) (n = 16), O128:H2 (n = 11), and O127:H21 (n = 10). Other serotypes found were O111:H(-) (n = 6) and O126: H(-) (n = 5). DNA macrorestriction fragment analysis by pulsed-field gel electrophoresis (PFGE) using the XbaI enzyme was conducted to investigate the epidemiological clonal relationship among ETEC isolates. Major patterns were identified among which some of outbreak ETEC isolates belonged. These data suggest that a proportion of acute diarrhea in Tunis represents the confluence of small epidemics by clonality-related ETEC isolates that are transiently introduced or that persist in our community.     

产肠毒素大肠杆菌的热敏肠毒素B亚基(LT-B)和耐热肠毒素(ST)基因融合及其表达

采用基因重组技术构建了表达产肠毒素大肠杆菌(ETEC)的耐热肠毒素(ST)基因和热敏肠毒素B亚基(LT-B)基因融合抗原的疫苗候选株。将ST基因的5’端与LT-B基因的3’端连接,并置于同一阅读框。编码ST的基因是通过PCR从pSLM004质粒中扩增得到的,含有ST的pro序列(其编码ST前体的pro区域),并应用寡核苷酸定点突变技术将编码ST的第14位氨基酸残基发生突变,使ST的第14位氨基酸残基Ala突变为Leu。在所构建的结构中,于LT-B和proST之间分别插入了不同长度的氨基酸Linkers。表达的融合多肽同时具有ST和LT-B的抗原性,并保留结合GM-1神经节苷脂的能力,且无LT和ST的生物毒性。表达的融合蛋白免疫动物,能诱导产生相应的特异性抗体。     

Production of cytotoxin VT in enteropathogenic and non-enteropathogenic Eschericha coli strains of porcine origin

Abstract We have investigated the production of verotoxin (VT) in 55 enteropathogenic and 48 non-enteropathogenic Escherichia coli strains of porcine origin, belonging to 48 serotypes. VT cytotoxin was only produced by seven out of the eight enteropathogenic strains with serotypes O138:K81, O139:K82, O141:K85ab and O141:K85ac. Five haemolytic non-enteropathogenic E. coli , four with serotypes O75:K-, O75:K95 and O2:K2, and one not typable, synthesized a new thermolabile product not related with enterotoxin (LT) or VT, and which induced the formation of multinucleate cells in Vero monolayers.     

The prevalence and molecular typing of enterotoxigenic Escherichia coli strains isolated from diarrheic stools in Malatya, Turkey

This study was performed from June 2002 to November 2003 year in Malatya, eastern Turkey. Stools of 172 diarrheic patients and 90 healthy controls were analysed for enterotoxigenic Escherichia coli (ETEC). Heat-labile (LT) and heat-stable (ST) toxins were investigated by passive latex agglutination and enzyme immunoassay, respectively. Nine ETEC strains were isolated from 172 diarrheic stools (5.2%). Seven of the ETEC strains (10.1%) were isolated from 69 children in the 0-5 year age group. Two of these pediatric isolates were ST positive (2.9%) and five were LT positive (7.2%). ETEC was not isolated in the 6-18 year age group. Two ST producing E. coli strains were detected in diarrheic adult patients (> 18 years). In the 90 controls, two ETEC strains were detected (2.2%). One of them was a LT producer (1.1%) and the other was a ST producer (1.1%). E. coli strains producing both toxins simultaneously were not observed. ETEC positivity was higher in the diarrheic group than in the control group but statistically not significant (p > 0.05). The rate of resistance among ETEC strains to cefuroxime axetil, ampicillin, piperacillin, and trimethoprim-sulfamethoxazole was 72.7%, 54.5%, 45.5%, and 36.4%, respectively whereas the resistance rate to the same antibiotics in non-ETEC strains was 14%, 62%, 54%, and 66%, respectively. All ETEC isolates were intermediately resistant to cephalothin and fully susceptible to other antibiotics tested. Typing of the ETEC strains was done by arbitrary primed polymerase chain reaction (AP-PCR). Only two LT strains of the 11 typed strains had a unique profile. The remaining nine were mixed LT and ST strains and divided into two groups. The first group had three strains having a similarity coefficient ranging from 70-90%. The other one had six strains, five of them were similar and one was subtype isolate. It can be concluded that ETEC strains might be considerably important enteropathogens especially in pediatric patients in the 0-5 year age group. High clonal relation indicated that ETEC strains were epidemiologically related.