| Enterhemorrhgic Escherichia coli (EHEC) were recognized as important human pathogens. EHEC strains infection can cause diversity clinical symptoms, e.g. watery diarrhea, hemorrhagic colitis(HC), even may led to more severe complications, such as hemolytic uremic syndrome(HUS) and thrombotic thrombocytopenic purpura(TTP). EHEC infections are mainly caused by E.coli belonging to the O157:H7 serotype which has been implicated in large food-borne outbreaks all over the world. Other EHEC serotype (026, 0111, 0103 ect.)have also been associated with small to large outbreaks of HC or with human sporadic infectionsEHEC strains resulted in diseases by stx gene which they possess coding for the Shiga-toxins Stxl and/or Stx2, also called these strains Shiga-toxin producing E.coli(STEC). Additionally the second is that most EHEC have eae gene coding for intimin, located in the LEE locus associated to the attaching and effacing phenotype and hlyA gene located on a large plasmid (90kb) coding for the synthesis of entero-hemolysin. The natural population of STEC found in the intestine of domestic animals is considered as the natural reservoir of EHEC, and cattle have been implicated as the source of EHEC pathogens in a number of food borne outbreaks associated with the consumption of undercooked ground beef or raw milk products. Antibiotic resistant strains emerged in the process of infectious diseases treatment and the mechanism were variety, e.g. permeation of bacterial cell membrane; producing hydrolysis enzymes; efflux pump ect. However. Recent advances in the molecular characterization of antibiotic resistance mechanisms have highlighted the existence of genetic structures, calledintegrons.Integrons are genetic elements able to capture foreign genes and make them to functional genes, it is mobile DNA. It is more frequently existed in gram-negative bacteria, e.g. enterobacteria and P.aeruginosa. it is the important reason of rapid development about multiple resistance in gram negative bacteria. It is composed of two conserved segments, separated by a segment of variable length and sequence which includes inserted antibiotic resistance genes, called insertion cassette, also called gene cassette. Nowadays gene cassette-integrons system in STEC are not clear. So this subject is beginning with the molecular identification of STEC and EHEC, further more to study on the action of resistance and integrons in STEC or EHEC emerge and transfermation.First of all is to isolate the E.coli from all kinds of samples by general method and biochemistry characteristic. Then PCR amplified 4 kinds of virulent genes which STEC possess using specific primers of stxl, stx2, eaeA and hlyA. 76 E.coli were isolated from 112 samples (human; cattle, food, water), further to identify 18 isolates STEC, they were serotyped into O157:H7 and non O157:H7 two groups using diagnostic serum. So total 48 isolates STEC(2 non-STEC)were following tested, recovered from U.S 20 isolates; China epidemic diseases study institute 10 isolates and 18 from this study.All isolates were examined to better understand the prevalence of antibiotic resistance using K-B method suggested by WHO. Based on the NCCLS results, all isolates almost were susceptible to chloramphenial and nitrofurantoin, all isolates, however, were resistant to sulfamethoxazole, 95%( 19/20), 70%( 14/20), 30%(6/20), 30%(6/20)isolates from U.S. and 60.7%(17/28), 78.6%(22/28), 60.7%(17/28), 14.3%(4/28) isolates STEC from China were resistant toerythromycin, streptomycin, ampicillin and gentamycin respectively; Both of the U.S. and China isolates also were resistant to tetracycline, the rate was 25%(5/20) and 17.9%(5/28) respectively. Others basically were identical. The date suggested that selection pressure imposed by the use of sulfa drugs, erythromycin, ampicillin, gentamycin, whether therapeutically in human and veterinary medicine or as prophylaxis in the animal production environment, is a key driving force in the selection of antimicrobial resistance in STEC and EHEC.11...
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