In70 of plasmid pAX22, a bla(VIM-1)-containing integron carrying a new aminoglycoside phosphotransferase gene cassette.

Maria Letizia Riccio,Lucia Pallecchi,Gian Maria Rossolini,Roberta Fontana

doi:10.1128/aac.45.4.1249-1253.2001

Maria Letizia Riccio, Lucia Pallecchi + Show 2 more

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https://doi.org/10.1128/aac.45.4.1249-1253.2001

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Abstract

An Achromobacter xylosoxydans strain showing broad-spectrum resistance to beta-lactams (including carbapenems) and aminoglycosides was isolated at the University Hospital of Verona (Verona, Italy). This strain was found to produce metallo-beta-lactamase activity and to harbor a 30-kb nonconjugative plasmid, named pAX22, carrying a bla(VIM-1) determinant inserted into a class 1 integron. Characterization of this integron, named In70, revealed an original array of four gene cassettes containing, respectively, the bla(VIM-1) gene and three different aminoglycoside resistance determinants, including an aacA4 allele, a new aph-like gene named aphA15, and an aadA1 allele. The aphA15 gene is the first example of an aph-like gene carried on a mobile gene cassette, and its product exhibits close similarity to the APH(3')-IIa aminoglycoside phosphotransferase encoded by Tn5 (36% amino acid identity) and to an APH(3')-IIb enzyme from Pseudomonas aeruginosa (38% amino acid identity). Expression of the cloned aphA15 gene in Escherichia coli reduced the susceptibility to kanamycin and neomycin as well as (slightly) to amikacin, netilmicin, and streptomycin. Characterization of the 5' and 3' conserved segments of In70 and of their flanking regions showed that In70 belongs to the group of class 1 integrons associated with defective transposon derivatives originating from Tn402-like elements. The structure of the 3' conserved segment indicates the closest ancestry with members of the In0-In2 lineage. In70, with its array of cassette-borne resistance genes, can mediate broad-spectrum resistance to most beta-lactams and aminoglycosides.

Highlights

VIM-1 and VIM-2 are new metallo-␤-lactamases, 90% identical to each other at the sequence level, that have recently been identified in carbapenem-resistant Pseudomonas aeruginosa nosocomial isolates from the Mediterranean area [12, 17, 21, 27]
The aphA15 gene is the first example of an aph-like gene carried on a mobile gene cassette, and its product exhibits close similarity to the APH(3؅)-IIa aminoglycoside phosphotransferase encoded by Tn5 (36% amino acid identity) and to an APH(3؅)-IIb enzyme from Pseudomonas aeruginosa (38% amino acid identity)
The blaVIM-1 gene was originally cloned from a P. aeruginosa strain that was isolated at the University Hospital of Verona (Verona, Italy), having caused an outbreak in the Intensive Care Unit of that hospital [14]

Summary

Introduction

VIM-1 and VIM-2 are new metallo-␤-lactamases, 90% identical to each other at the sequence level, that have recently been identified in carbapenem-resistant Pseudomonas aeruginosa nosocomial isolates from the Mediterranean area [12, 17, 21, 27]. These enzymes exhibit a very broad substrate specificity (including carbapenems and most other ␤-lactams) and were found to be encoded by determinants carried on mobile gene cassettes inserted into integrons [12, 17]. We report on the finding of a plasmid-borne blaVIM-1 determinant in an Achromobacter xylosoxydans isolate from the same hospital and on the characterization of the blaVIM-1containing integron carried by that plasmid

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