Diversity of CTX-M β-lactamases and their promoter regions fromEnterobacteriaceaeisolated in three Parisian hospitals

Abstract

Nine clinical isolates of Enterobacteriaceae (six Escherichia coli and three Proteus mirabilis) isolated in three Parisian hospitals between 1989 and 2000 showed a particular extended-spectrum cephalosporin-resistance profile characterized by resistance to cefotaxime and aztreonam but not to ceftazidime. CTX-M-1, CTX-M-2, CTX-M-9, CTX-M-14 and two novel plasmid-mediated CTX-M β-lactamases (CTX-M-20, and CTX-M-21) were identified by polymerase chain reaction and isoelectric focusing (pI>8) and were associated in eight cases with TEM-1 (pI=5.4) or TEM-2 (pI=5.6) β-lactamases. We used internal ISEcp1 and IS26 forward primers and the CTX-M consensus reverse primer to characterize the CTX-M β-lactamase promoter regions and showed their high degree of structure diversity. We found upstream of some bla_CTX-M genes, a 266-bp sequence 100% identical to the sequence upstream of the Kluyvera ascorbataβ-lactamase gene, suggesting that this chromosomal enzyme is the progenitor of the CTX-M-2/5 cluster.