G E NE TIC S U PPO RT OF bla C TX-M GEN E SThe dissemination of genes encoding CTX-M-like ESBLs is extremely worrisome, and the problem has appeared recently, as compared with the dissemination of blaTEM and blaSHV ESBL genes. The blaCTX-M genes originate from the chromo- somes of Kluyvera species, Kluyvera georgiana probably being the progenitor of the blaCTX-M-8- like and blaCTX-M-9-like genes, and Kluyvera ascor-and Kluyvera cryocrescens the progenitors of batathe blaCTX-M-1-like and blaCTX-M-2-like genes [10]. Different genetic elements have been found to be involved in the acquisition of blaCTX-M genes, including insertion sequences ISEcp1 and ISCR1 (formerly CR1 element), and also phage-related elements.ISEcp1-like insertion sequence elements have been identified in association with genes encod-ing enzymes of the CTX-M-1, CTX-M-2 and CTX- M-9 clusters. ISEcp1 belongs to the IS1380 family and is able to mobilise blaCTX-M genes by a peculiar transposition process [11]. It mobilises adjacent sequences by transposition, after recog- nition of a variety of DNA sequences as right inverted repeats (IRRs). Thus, a single copy of ISEcp1 located upstream of a blaCTX-M gene is sufficient to mobilise the gene from the chromo-
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