Novel streptomycin and spectinomycin resistance gene as a gene cassette within a class 1 integron isolated from Escherichia coli

Abstract

The aadA genes, encoding resistance to streptomycin and spectinomycin, have been found as gene cassettes in different gram-negative and gram-positive bacterial species. The present study has revealed the sequence of a new gene, aadA5, integrated as a gene cassette together with the trimethoprim resistance gene dfr7 in a class 1 integron. The integron was located on a plasmid and was identified in a pathogenic porcine Escherichia coli isolate.

FIG. 1

Positions of gene cassettes and integron CSs of E. coli 9516014-1. Designations are as follows: intI1, integrase; attI, recombination site; dfr7, dihydrofolate reductase (trimethoprim resistance) gene; aadA5, streptomycin and spectinomycin resistance gene; qacEΔ1, quaternary ammonium compound resistance gene; sulI, sulfonamide resistance gene. Horizontal arrows indicate putative promoters (P) and direction of translation, and vertical arrows show recombination hot spots where the gene cassettes integrate. Black circles indicate the 59-bp elements, and the line beneath the integron structure indicates the sequenced area.