Summary
Three aminoglycoside-modifying enzymes (AMEs) were produced by a clinical isolate of Shigella flexneri which was resistant to gentamicin, tobramycin, netilmicin, kanamycin, sisomicin and streptomycin: acetyltransferase (AAC) (3)-II-type, and phosphotransferase (APH) (3″)- and (6)-type enzymes. The aminoglycoside-resistance genes were located on a 75-Kb plasmid. Two genes, strA-HK and strB-HK, in a transcriptional unit were found to code for streptomycin-resistance. The genetic organization and sequence of this transcriptional unit were identical to those of strA and strB in plasmid RSF1010. strA-HK and strB-HK when expressed separately produced functional enzymes. Our substrate profile study on the crude extracts of StrA-HK and StrB-HK proteins confirmed that StrA-HK was an APH(3″)-type and showed that StrB-HK was a member of the APH(6) family.