Dissemination of CTX-M-Type β-Lactamases among Clinical Isolates of Enterobacteriaceae in Paris, France

We analyzed 19 clinical isolates of the family Enterobacteriaceae (16 Escherichia coli isolates and 3 Klebsiella pneumoniae isolates) collected from four different hospitals in Paris, France, from 2000 to 2002. These strains had a particular extended-spectrum cephalosporin resistance profile characterized by a higher level of resistance to cefotaxime and aztreonam than to ceftazidime. The blaCTX-M genes encoding these β-lactamases were involved in this resistance, with a predominance of blaCTX-M-15. Ten of the 19 isolates produced both TEM-1- and CTX-M-type enzymes. One strain (E. coli TN13) expressed CMY-2, TEM-1, and CTX-M-14. blaCTX-M genes were found on large plasmids. In 15 cases the same insertion sequence, ISEcp1, was located upstream of the 5′ end of the blaCTX-M gene. In one case we identified an insertion sequence designated IS26. Examination of the other three blaCTX-M genes by cloning, sequencing, and PCR analysis revealed the presence of a complex sul1-type integron that includes open reading frame ORF513, which carries the bla gene and the surrounding DNA. Five isolates had the same plasmid DNA fingerprint, suggesting clonal dissemination of CTX-M-15-producing strains in the Paris area.