Molecular cloning and analysis of Staphylococcus aureus chromosomal aminoglycoside resistance genes

Abstract

Most of the aminoglycoside resistant Staphylococcus aureus strains isolated in France are resistant to all the antibiotics belonging to this family. Two aminoglycoside-modifying enzymes were detected in the wild-type strains studied: an APH3'III and an AAC6'-APH2". These strains also carry two types of streptomycin resistance: high-level resistance due to chromosomal mutation(s) affecting ribosome affinity and low-level resistance, the mechanism of which was not characterized. All the aminoglycoside resistance genes were located on the chromosome. DNA fragments of 1.5 and 1.95 kb carrying the aphA and aacA genes, respectively, were isolated, by cloning, from the cellular DNA of a clinical isolate. When these genes were introduced into Escherichia coli and Bacillus subtilis strains, the enzymes synthesized were indistinguishable from those produced by the S. aureus strains. When the cellular DNAs of wild-type and resistant strains were hybridized with the cloned fragments, sequences homologous to the fragment carrying the aphA gene were found to be located at the same chromosomal site, while those hybridizing with the fragment carrying the aacA gene were at different chromosomal sites.