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Escherichia coli and Klebsiella pneumoniae, especially the resistant ones, are the most prevalent gram-negative bacteria to induce nosocomial infections. Because of the third generation Cepholosporins’ worldwide using, many gram-negative bacteria have become resistant to the Cepholosporins, and the main resistant mechanism is producing β-lactamase. Since 1983, the frist ESBLs (TEM-3) has been reported in Germany, ESBLs-producing E coli and K. pneumoniae were becoming prevalence in the world. ESBLs are a kind of plasmid-mediated enzymes, these plasmids often carry two or more resistant genes. Furthermore, the plasmids are easily transmitted among different members of Enterobacteriaceae, and lead to multiple-drug-resistant. The prevalent ESBLs are derivative from TEM-1、 2 and SHV-1. They have mainly been found in strains of Escherichia coli and Klebsiella pneumoniae. Most of them are Ceftazidimases, and a few of them are Cefotaximases. There are many other ESBLs acting as Ceftazidimases, for example PER, VEB, TLA-1, GES/IBC, and Cefotaximases: CTX-M (Toho ), SFO-1 and BES-1 et. al. In China, the most prevalent genotypes of ESBLs TEM、CTX-M and SHV, these have been reported in many areas. In order to study the resistant phenotype, genotype and hydrolyzation of ESBLs, we detected the most prevalent genotype TEM、CTX-M and SHV in Escherichia coli and Klebsiella pneumoniae, and detected the stability hydrolysis of four cephalosporins.In the part one, 295 strains of Escherichia coli and Klebsiella pneumoniae from hospitals in Beijing were studied in our research. We detected their resistant phenotype, genotype and Isoelectric point, then sequencing. 18.6% of strains of the family Enterobactericeae were considered ESBLs producers by double disk synergy test. The prevalences of ESBLs in isolates of Escherichia coli and Klebsiella pneumoniae were 27.7% and 8.57%, respectively. TEM type (81.8%,45/55) β-lactamase was the main type among those ESBL-producing strains, followed by CTX-M type(74.5%, 41/55) and SHV type (20%, 11/55). In the Escherichia coli, the incidence of TEM, CTX-M, SHV were 88.4%(38/43), 69.76% (30/43) and
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