Characterization of Acinetobacter haemolyticus aac(6')-Ig gene encoding an aminoglycoside 6'-N-acetyltransferase which modifies amikacin.

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The amikacin resistance gene acc(6')-Ig of Acinetobacter haemolyticus BM2685 encoding an aminoglycoside 6'-N-acetyltransferase was characterized. The gene was identified as a coding sequence of 438 bp corresponding to a protein with a calculated mass of 16,522 Da. Analysis of the deduced amino acid sequence suggested that it was the fourth member of a subfamily of aminoglycoside 6'-N-acetyltransferases. The resistance gene was not transferable either by conjugation to Escherichia coli or to Acinetobacter baumannii or by transformation into Acinetobacter calcoaceticus. Plasmid DNA from strain BM2685 did not hybridize with an intragenic aac(6')-Ig probe. These results suggest a chromosomal location for this gene. The gene was detected by DNA hybridization in all 20 strains of A. haemolyticus tested but not in 179 other Acinetobacter strains, including A. baumannii, A. lwoffii, A. junii, and A. johnsonii and genospecies 3, 6, 11, 13, 14, 15, 16, and 17, of which 162 were amikacin resistant. The probe did not hybridize in dot blot assays with DNAs purified from members of the families Enterobacteriaceae and Pseudomonadaceae that encode 6'-N-acetyltransferases. These data suggest that the aac(6')-Ig gene is species specific and may be used to identify A. haemolyticus.

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