A novel type of IncQ plasmid harbouring a class 3 integron from Escherichia coli
Abstract number: P693
Objectives: The genes encoding the extended-spectrum b-lactamases (ESBLs) of the GES type are usually part of class 1 integron structures. Those integrons are themselves usually identified onto Tn21/Tn402 transposon structures. Our study was initiated by the identification of a blaGES-1 gene inside a peculiar class 3 integron structure.
Methods:Escherichia coli isolate TB7 had been isolated in 1998 in Switzerland from an hospitalized patient. Genomic DNA E. coli TB7 was extracted and used for PCR screening of known ESBL genes. Plasmids were extracted using the Kieser technique. Whole sequencing of the natural plasmid harbouring the blaGES-1 gene was achieved by a primer-walking approach.
Results:E. coli TB7 harboured a blaGES-1 gene that was not bracketed by class 1 integron features. Whole sequence analysis of plasmid pTB7 identified a gene encoding the class 3 integrase Int3 upstream of the blaGES-1 gene cassette, sharing 60% amino acid identity with the class 1 integrase Int1. Downstream of blaGES-1, the blaOXA-10/aac(6')-Ib fused gene cassette was identified. The extremities of the class 3 integron were not clearly defined, but suggested that a deletion of those extremities had occurred during evolution. The backbone of plasmid pQ7 contained five open reading frames; RepC, RepA, a fused relaxase-primase protein, MobC, and an hypothetical protein, showing a replication machinery similar to that of other IncQ-type plasmids, including the oriV and the iteron-based incompatibility determinant. However, plasmid pTB7 exhibited replicase genes and iteron sequences that significantly differed from those of all the previously reported IncQ plasmid. The comparative analysis of the replication proteins of pQ7 showed it was homologous to two other plasmids; pGNB2 recovered from a wastewater treatment plant from an unknown host strain and harbouring the quinolone resistance gene qnrS2, and pWES-1 identified from Salmonella enterica Westhampton in France and carrying the ESBL gene blaCTX-M-53.
Conclusion: We propose here that pQ7 and its two related plasmids may be classified into a novel sub-family of IncQ plasmids, defined as IncQ-2 type, that correspond to non-conjugative and broad-host range resistance plasmids.
|Session name:||Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases|
|Location:||Vienna, Austria, 10 - 13 April 2010|
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