Mechanisms of resistance to expanded-spectrum cephalosporins in Escherichia coli isolates recovered in a Spanish hospital

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Abstract
Objectives: To characterize the β-lactamase genes of the expanded-spectrum cephalosporin-resistant Escherichia coli isolates recovered in a Spanish hospital during the March 2002–March 2003 period. Methods: Thirty-four of the 1700 E. coli isolates recovered from unrelated patients in a Spanish hospital showed expanded-spectrum cephalosporin resistance. The presence of genes encoding TEM, SHV, CTX-M, CMY-2-type or FOX β-lactamases as well as the existence of mutations in the regulatory region of the chromosomal ampC gene were studied by PCR and sequencing in these 34 E. coli isolates. Results: The following extended-spectrum β-lactamases (ESBLs) or plasmidic class C β-lactamase genes were detected (number of isolates): blaCTX-M-14 (14), blaCTX-M-9 (4), blaCTX-M-32 (1), blaTEM-52 (2), blaSHV-12 (3) and blaCMY-2 (2). The remaining eight isolates showed a mutation in the promoter/attenuator region of the ampC chromosomal gene at position −42, in combination with mutations at positions −18, −1 and +58. The blaTEM-1 gene was also detected in 12 of the ESBL-producing isolates, in both CMY-2-producing isolates and in four of the eight isolates that showed a mutation at position −42 of the ampC promoter. Other mutations in the promoter/attenuator region were detected in association with ESBL or CMY-2 genes, such as the combination −18, −1 and +58, −28 and +58, or +22, +26, +27 and +32. No clonal relationship was found among the CTX-M-producing E. coli isolates by PFGE with XbaI enzyme. Conclusions: Approximately 1.5% of the E. coli isolates of our hospital harboured ESBL genes, those of the CTX-M-9 group being the most common ones.

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