New trimethoprim-resistant dihydrofolate reductase cassette, dfrXV, inserted in a class 1 integron

Abstract

The nucleotide sequence of a plasmid-borne trimethoprim resistance gene from a commensal fecal Escherichia coli isolate revealed a new dihydrofolate reductase gene, dfrXV, which occurred as a gene cassette integrated in a site-specific manner in a class 1 integron. The new gene shows 84% nucleotide identity and the predicted protein shows 90% amino acid identity with dfrI and DHFR type I, respectively. Genes for spectinomycin resistance, aadA1 [ant (3")-Ia], and sulfonamide resistance, sulI, were located downstream of dfrXV in a manner identical to that in pLMO229.

FIG. 1

Restriction map, gene map, cassette boundaries, and direction of sequencing (→) of pUK2412.

FIG. 2

Nucleotide sequence and translated polypeptide of dfrXV. The sequence used as a gene probe is printed in boldface type. The gene cassette boundaries are marked (↑), and the imperfect inverted repeat (59-base element) is underlined (interrupted lines); gaps indicate mismatched bases, asterisks denote extra bases in the left half of the element which interrupt the inverted repeat, and arrows (---›) denote the direction of symmetry. The putative promoter sequences of the conserved element are underlined, and the start codon of intI1 is in italics.