| The production of extended-spectrum β-lactamases (ESBLs) is the most common mechanism of resistance to the third generation cephalosporins in Enterobacteriaceae bacteria especially Escherichia coli and klebsiella pneumoniae. Most ESBLs are derived from TEM-1, 2 or SHV-1 enzymes and are capable of hydrolyzing oximino-cephalosporins. ESBLs are plasmid-mediated and can be inhibited by β-lactamase inhibitors. The number of non-TEM and non-SHV enzymes such as CTX-M group and OXA type ESBLs have been increasing. The ESBL-producing organisms mainly cause nosocomial infections and have become common pathogens in hospital all over the world. The ESBL-producing strains are usually multi-resistant, and become big challenge to treatment of infections. The prevalence of ESBL-producing strains differs from country to country and from institute to institute. Only a few studies regarding this topic have been reported in China. We investigated the prevalence, resistance of ESBL producers, gene type of ESBLs, and clinical features of infections caused by ESBL producers in E. coli and k. pneumoniae in Huashan Hospital from 1 January to 31 December 1999. The results are presented as follows.Part 1 Detection and study of extended-spectrumβ-lactamase in Klebsiellae pneumoniae and Escherichia coli isolatesTo investigate the prevalence, resistance of ESBL producers, and probable gene type of ESBLs in Escherichia coli and Klebsiellae pneumoniae isolates, 427 strains of Escherichia coli and 559 strains of Klebsiellae pneumoniae were collected from patients in Huashan Hospital from 1 January to 31 December 1999. ESBL-producing isolates were detected by the agar dilution test (NCCLS Confirmatory Test). MICs of ESBL producers were tested by agar dilution test. The partial blagene of ESBL producer was amplified by PCR using universal primers for TEM, SHV, CTX-M-1group, and TOHO-1group repectively. The molecular typing of ESBL producers isolated from intensive care unit (ICU) was determined by PFGE. ESBL-producing strains were 23.6% detected in strains of Escherichia coli (101/427) and 51% of Klebsiellae pneumoniae (285/559), most strains of which wereisolated from patients in intensive care unit and neurosurgical ward. ESBL-producing strains were highly resistant to most β-lactams (including the third-generation cephalosporins and monobactams) and non-β-lactams (such as fluoroquinolones, aminoglycosides, tetracycline, and chloramphenicol), however all were susceptible to imipenem and most were susceptible to cefmetazole andβ-lactam/clavulanic acid. More than half of ESBL producers were still susceptible to cefepime. Resistance rates of ESBL-producing E. coli to ceftazidime, amikacin, and levofloxacin were different significantly from that of K. pneumoniae, being 15.8%, 48.5%, 86.1% and 79.6%, 87.7%, 45.6% respectively. TEM type was the most common β-lactamases found and SHVβ-lactamases, CTX-M type the next. No TOHO-1β-lactamases were found. Some strains of ESBL-producing E. coli and most strains of ESBL-producing K. pneumoniae produced more than one type of β-lactamases. There were a few ESBL producers produced non-TEM, non-SHV, non-CTX-M-1, non-TOHO-1groupβ-lactamases. 10 PFGE patterns in 23 ESBL-producing E. coli strains and 16 patterns in 73 ESBL-producing K. pneumoniae strains were found by PFGE. There were five isolates in one of the PFGE patterns in ESBL-producing E. coli, while most of the ESBL-producing K. pneumoniae strains were in Kpn-A (22 isolates), Kpn-B (14 isolates), or Kpn-C (12 isolates) PFGE type. These data show that ESBL producers are common in nosocomial strains of E. coli and K. pneumoniae, being usually multi-resistant. Some epidemic ESBL-producing strains exist in ICU patients. TEM type β-lactamase is the most common enzyme, and CTX-M-1group type the next. Therefore, It is important to detect ESBL producers in clinical isolates for control of their spread in hospital. Part 2 Conjugation experiments and detection of ESBL producers, resistance, plasmids, blagene, pI of β-lactamases in... |
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