Description of an original integron encompassing blaVIM-2, qnrVC1 and genes encoding bacterial group II intron...

A burn unit of a hospital in Tunis underwent an endemic situation caused by imipenem-resistant Pseudomonas aeruginosa. For nine non-repetitive isolates of a clonal VIM-2-producing strain, the blaVIM-2 genetic background was characterized and the associated qnrVC1 gene molecularly analysed.

The imipenem resistance mechanism was investigated by phenotypic and molecular tests, and resistance transfer was studied by conjugation and transformation experiments. The integron's structure was characterized by sequencing, and qnrVC1 expression was explored after cloning experiments.

The nine VIM-2-producing strains were collected from eight patients and one environmental sample. All transfer assays failed, suggesting a chromosomal location of blaVIM-2. This latter was found to be part of a class 1 integron of ∼7500 bp, which also contains blaOXA-2, aadA1 and two copies of the aadB, arr-6 and qnrVC1 genes. qnrVC1 exhibited higher homology with the chromosomally encoded qnr genes of Vibrionaceae than with plasmid-mediated qnr genes of Enterobacteriaceae. The qnrVC1 gene cassette possesses a promoter allowing its expression, and it conferred decreased fluoroquinolone susceptibility to Escherichia coli. Additionally, on the same integron, genes encoding an uncommon group IIC-attC intron were detected.

A VIM-2-producing P. aeruginosa outbreak led us to characterize an integron harbouring a qnrVC1 cassette and a new group IIC-attC intron. This is the first known description of a qnr determinant in a P. aeruginosa strain. Its presence conferred a low level of resistance to quinolones in E. coli, which might favour the emergence of highly resistant mutants.