Resistance to Apramycin in Escherichia coli Isolated from Animals: Detection of a Novel Aminoglycoside-modifying Enzyme

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Abstract
The mechanisms of resistance to apramycin of 5 isolates of E. coli from animals were investigated. Three isolates, which were resistant to all the aminoglycosides tested, did not transfer their resistance and did not produce aminoglycoside-modifying enzymes. The 4th isolate, which was resistant to apramycin, tobramycin, gentamicin, kanamycin and neomycin, but not to amikacin, owed its resistance to production of the acetyltransferase AAC(3)IV. The gene specifying this enzyme was carried on a transposon, Tn800, on a plasmid designated R1535. The 5th isolate was resistant to apramycin, neomycin and kanamycin but not to gentamicin, tobramycin or amikacin. It produced an acetyltransferase that readily acetylated only apramycin, neomycin and paromomycin, a compound closely related to neomycin. Synthesis of this enzyme was specified by a chromosomal gene located near pyrD at .apprx. 20 min on the map of the E. coli K12 chromosome.