Characterization of the highly variable region surrounding the blaCTX-M-9 gene in non-related Escherichia coli from Barcelona

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Abstract
Objectives: The dispersion of a clone, a plasmid or a mobile element carrying the blaCTX-M-9 gene was evaluated in 30 Escherichia coli strains isolated in Barcelona between 1996 and 1999. The presence of the previously described orf513-bearing class 1 integron, In60, carrying the blaCTX-M-9 gene, was also studied. Methods: The clonality was analysed by pulsed-field gel electrophoresis. Plasmid analysis was performed by S1 digestion and hybridization with the CTX-M-9 probe. PCR mapping using specific designed primers was used to study the presence of In60 and In60-like structures. Results: The clonality between the 30 strains was minor. The size of blaCTX-M-9 carrying plasmids ranged between ∼80 and 430 kb. One strain produced only a chromosome-encoded CTX-M-9 β-lactamase. Thirty-six per cent of the strains showed differences with respect to the In60 structure due to an insertion or deletion events. Conclusions: These findings suggest that the blaCTX-M-9 gene may be carried by a mobile element that disperses it between plasmids. The fast dispersion of the CTX-M-9 enzyme could therefore be due to both diffusion of plasmids and mobile elements.