PRESENCE OF STRA-STRB GENE WITHIN A STREPTOMYCIN-RESISTANCE OPERON INA CLINICAL ISOLATE OF SHIGELLA-FLEXNERI

Three aminoglycoside-modifying enzymes (AMEs) were produced by a clini cal isolate of Shigella flexneri which was resistant to gentamicin, to bramycin, netilmicin, kanamycin, sisomicin and streptomycin: acetyltra nsferase (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 u nit were found to code for streptomycin-resistance. The genetic organi zation and sequence of this transcriptional unit were identical to tho se of strA and strB in plasmid RSF1010. strA-HK and strB-HK when expre ssed separately produced functional enzymes. Our substrate profile stu dy on the crude extracts of StrA-HK and StrB-HK proteins confirmed tha t StrA-HK was an APH(3 '')-type and showed that StrB-HK was a member o f the APH(6) family.