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

An Achromobacter xylosoxydans strain showing broad-spectrum resistance to b eta -lactams (including carbapenems) and aminoglycosides was isolated at th e University Hospital of Verona (Verona, Italy), This strain was found to p roduce metallo-beta -lactamase activity and to harbor a 30-kb nonconjugativ e plasmid, named pAX22, carrying a bla(VIM-1) determinant inserted into a c lass 1 integron, Characterization of this integron, named In70, revealed an original array of four gene cassettes containing, respectively, the bla(vi m-1) gene and three different aminoglycoside resistance determinants, inclu ding 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 mob ile gene cassette, and its product exhibits close similarity to the APH(3') -IIa aminoglycoside phosphotransferase encoded by Tn5 (36% amino acid ident ity) and to an APH(3')-IIb enzyme from Pseudomonas aeruginosa (38% amino ac id identity). Expression of the cloned aphA15 gene in Escherichia coli redu ced the susceptibility to kanamycin and neomycin as well as (slightly) to a mikacin, netilmicin, and streptomycin, Characterization of the 5' and 3' co nserved segments of In70 and of their flanking regions showed that In70 bel ongs 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-In 2 lineage. In70, with its array of cassette-borne resistance genes, can med iate broad-spectrum resistance to most beta -lactams and aminoglycosides.