Study of clinical isolates of Enterobacteriaceae producing extended spectrum β-lactamases
Objective To investigate the prevalence, phenotypical and genotypical characteristics of extended spectrum β lactamases producing Enterobacteriaceae strains from Peking Union Medical College Hospital in China. Methods 162 strains of nosocomial Enterobacteriaceae from February to April, 1999 were investigated for the production for extended spectrum β lactamases (ESBLs) by phenotypic screening and confirmatory test provided by the National Committee for Clinical Laboratory Standards. Isoelectric focusing, inhibition assay, conjugation were used to determine the phenotype of the enzyme; Plasmid DNA preparation, pulsed field gel electrophoresis (PFGE), TEM or SHV or CTX M3 specific PCR and DNA sequencing were used to determine the genotype of the enzymes. Results 11.4% (5/44) of E.coli , 39.5% (17/43) of K.pneumoniae , 6.0% (3/50) of E.cloacae and 8.0% (2/25) of C.freundii produced ESBLs. Cefotaxime MICs was much higher than ceftazidime in the ESBL producing strains, and all of the strains were susceptible to imipenem except 1 strain of E.cloacae . Most isolates produced two to six enzymes. 19 of 27 ESBL producing strains (70.3%) expressed CTX M 3 β lactamase (pI 8.6), which can be inhibited by clavulanate. This ESBL properties can be transferred into E.coli C600 and conferred higher resistance to cefotaxime than ceftazidime. A subset of clinical isolates tested by PFGE of chromosomal DNA revealed multiple clones. Conclusion ESBL producing strains were very common in this hospital and CTX M 3 β lactamase was the most prevalent. [