Introduction: Shiga toxin- producing Escherichia coli (STEC) is an emerging bacterial pathogen in developing countries that causes several diseases such as diarrhea, hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS), particularly in children. Aim of the research was detection of STEC in diarrheal specimens from under 5 year olds and study of the patterns of antibiotic resistance of these strains. Methods: In the study,300 fecal samples were collected from children with diarrhea referring to Ali Asghar Hospital. E.coli species were isolated by standard bacteriological and biochemical tests. Presence of shiga toxin genes (stx1/2) was investigated by PCR technique (Qiagen). Antibiogram test for strains containing the toxin gene was performed using 16 different antibiotic discs (MAST) by disc diffusion agar (Kirby-Bauer) method. Results: From 39 E.coli isolates, 9(23.1%) strains were detected by PCR to contain stx1/2 gene. One strain was resistant to all 16 antibiotics. All the STEC strains were sensitive to meropenem (MRP), imipenem (IMI), gentamycin (GEN) and nitrofurantoin (NI). 4(44.44%) strains showed multi-drug resistant pattern. All these 4strains were resistant to cotrimoxazole(SxT). Also, 6(66.66%) strains were resistant to at least one antibiotic. Conclusion: In Iran, shiga toxin- producing Escherichia coli (STEC) may be a commonly bacterial pathogen causing diarrhea, particularly in children. Therefore, we should use new techniques for investigation of these strains. Increase in number of emerging and new strains that could be resistant to classic antibiotics such as cotrimoxazole may be foreseen. It is suggested that antibiotics prescription programs in treatment of diarrhea causing E.coli strains be updated.

Keywords: Shiga toxin- producing Escherichia coli (STEC), Diarrhea, Children, Antibiotic resistance

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