Plasmid-encoded and class 3 integron-associated extended-spectrum b-lactamase gene blaGES-1 from Escherichia coli in Switzerland

Abstract number: P1211

Poirel L., Bruderer T., Frei R., Bernabeu S., Nordmann P.

Objectives:Escherichia coli isolate TB7 showing an extended-spectrum b-lactamase (ESBL) phenotype was isolated in 1998 from urine of a Swiss patient who had no recent travel history. That strain was resistant to most b-lactams, except piperacillin-tazobactam, cephamycins and carbapenems, with a synergy image between clavulanic acid and extended-spectrum cephalosporins. In addition, a peculiar synergy between cefoxitin and cefuroxime was noticed. The aim of the present study was to identify the ESBL gene and the genetic structures at the origin of its acquisition.

Methods: Genomic DNA E. coli TB7 was extracted and used for PCR screening of known ESBL genes. Plasmids were extracted using the Kieser technique. Mating-out assays were performed using E. coli J53 as recipient strain and a selection with ceftazidime (30 mg/L)- and azide (100 mg/L)-containing media. Class 1 and class 3 integron features were mapped by PCR using specific primers.

Results: PCR and sequencing showed that E. coli TB7 expressed the ESBL GES-1. Mating-out assays remained unsuccessful but electro-transformation allowed to obtain transformant E. coli (pTB7) harbouring the blaGES-1 gene on a 12-kb plasmid. E. coli (pTB7) expressed an ESBL phenotype consistent with GES-1 expression, and was resistant in addition to amikacin and kanamycin, but susceptible to all other compounds, including sulfonamides. PCR mapping did not allow identification of class 1 integron features whereas blaGES-1 is usually associated to those structures. Further screening evidenced class 3 integron features, with the Int3 integrase encoding gene located upstream of blaGES-1. Downstream of blaGES-1, a repC gene encoding a putative replicase related to those of broad-host range IncQ plasmids was found.

Conclusion: This study identified ESBL GES-1 in Switzerland for the first time. This is one of the very few reports of acquisition of antibiotic resistance gene mediated by a class 3 integron. Noteworthy, the same blaGES-1-class 3 integron structure association had been evidenced onto a plasmid from a Klebsiella pneumoniae isolate recovered in 1999 in Portugal. This finding strengthens the dissemination of GES-1 enzyme worldwide, after its identification in France, Portugal, Argentina and Brazil.