Journal of Applied Sciences Research, 6(6): 756-776, 2010 © 2010, INSInet Publication Toxin of Enterotoxigenic E. coli Causing Gastroenteritis in Children Hesham M. Mahdy, Mohamed A. Fareid and Moustafa E. Negm Botany & Microbiology Department, Faculty of Science, Al-Azhar University, Cairo, Egypt Abstract: Out of 135 bacterial isolates; 63 E. coli isolates were identified. Five strains of enterotoxigenic E. coli (ETEC) were determined by agglutination test. ETEC strains were subjected for protein fractionation to get toxin subunits in pure form. Each fraction was tested for toxicity to mice. Fractions 2, 3 and 4 of ETEC strain N 27 were toxic to mice after 24 hours. Fraction 3 (ETEC strain N 4), o. o. fraction 3 (ETEC strain N 45) and fractions 5 and 6 of ETEC strain N 66 were also toxic to mice after o. o. 24 hours and mortality ratio recorded 100%. The protein content of all toxic fractions ranged from 59 to 95 mg/ml, while non toxic fractions ranged from 8 to 159 mg/ml. The most common amino acids detected in all fractions were glutamic acid, aspartic acid (except ETEC strain N 27, fraction 4), serine (except o. strain N 66, fraction 5) and glycine (except strain N 17, fraction 3). Histidine and citrulline were o. o. detected only in fractions 3 and 5 of ETEC strains N 17 and 66 respectively. o. Key words: Children, gastroenteritis, Toxin, Enterotoxigenic E. coli. INTRODUCTION Bacterial toxins are cell-associated or secreted proteins that damage the eukaryotic target cell. Bacterial toxins harm host cells by a variety of mechanisms, and a number of excellent reviews have been published that define these categories . [1,2,3} Schlessinger and Schaechter grouped bacterial toxins [3] by mode of action into those that (i) help bacteria spread in tissues (e.g., hyaluronidase, collagenase, elastase); (ii) lyse host cells (alpha-toxin of Staphylococcus aureus, Escherichia coli alpha [a] hemolysin, streptolysin O); (iii) block protein synthesis (e.g., diphtheria toxin, Pseudomonas aeruginosa exotoxin A, Shiga toxins from Shigella dysenteriae and E. coli); and (iv) act pharmacologically by elevating or depressing normal cell functions. Examples of the latter toxins include those that elevate cyclic AMP, such as cholera toxin and E. coli labile toxins, and those that inhibit the release of neurotransmitters, such as tetanus toxin and botulinum toxin. In 1987, Levine described several categories of E. coli that cause gastroenteritis and subsequently two additional categories have been added. These six types of diarrheagenic E. coli include enterotoxigenic E. coli (ETEC), enterohemorrhagic E. coli (EHEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAggEC), enteropathogenic E. coli (EPEC), and diffusely adherent E. coli (DAEC). ETEC strains produce two types of enterotoxin a choleralike toxin called heat-labile toxin (LT) and a second diarrheal toxin called heat-stable toxin (ST). A number of different O serogroups and H serotypes are represented among ETEC strains . The diarrhea [4] produced by adherent ETEC strains is caused by the action of two different toxins: heat-labile toxin (LT) and heat-stable toxin (ST). ("Heat stable" is defined as retention of toxin activity after incubation at 100°C for 30 min and "heat labile" means that toxin activity is lost under these conditions . [5] MATERIALS AND METHODS Samples Collection: This study was carried out in the period between December 2004 and April 2006. The stool samples collected from children symptomatically affected diarrhea. Children ages were 3 months to 5 years. All samples collected before antibiotics therapy began. The diarrhea samples were collected from Abu- Elrish hospital for children, Cairo University, Giza. The samples were transferred within one hour to the laboratory to be cultured immediately. Isolation of Bacteria: A diarrhea samples were suspended in peptone water before inoculation, then a loopfull was directly seeded on MacConkey`s agar, Eosin-methylene blue agar and Endo-agar media (Readymade, Difco, USA). The best growing colonies were selected for identification and further studies. Identification of E. coli: - Morphological, Biochemical and Physiological Tests: Identification of E. coli bacteria was carried out Corresponding Author: Hesham M. Mahdy, Botany & Microbiology Department, Faculty of Science, Al-Azhar University, Cairo, Egypt. 756