CHARACTERIZATION OF THE CHROMOSOMAL AAC(6')-IJ GENE OF ACINETOBACTER SP-13 AND THE AAC(6')-IH PLASMID GENE OF ACINETOBACTER-BAUMANNII

The amikacin resistance genes aac(6')-Ih of Acinetobacter baumannii BM 2686 and aac(6')-Ij of Acinetobacter sp. 13 BM2689 encoding aminoglyco side 6'-N-acetyltransferases were characterized. The 441-bp coding seq uences predict proteins with calculated masses' of 16,698 and 16,677 D a, respectively. Analysis of the deduced amino acid sequences indicate d that the proteins belonged to a subfamily of 6'-aminoglycoside acety ltransferase type I enzymes from gram-negative bacteria, The aac(6')-I h gene of BM2686 was located on a 13.7-kb nonconjugative plasmid. The aac(6')-Ij gene from BM2689 was not transferable either by conjugation to Escherichia coli or A. baumannii or by transformation to Acinetoba cter calcoaceticus. Plasmid DNA from BM2689 did not hybridize with an intragenic aac(6')-Ij probe. These results suggest a chromosomal locat ion for this gene. The aac(6')-Ij gene was detected by DNA hybridizati on in all 28 strains of Acinetobacter sp. 13 tested but not in other A cinetobacter strains, including A. baumannii, proteolytic genospecies 4, 6, 14, 15, 16, and 17, and ungrouped strains. The aac(6')-Ih and :I j probes did not hybridize in dot blot assays with DNA from members of the families Enterobacteriaceae and Pseudomonadaceae that produced 6' -N-acetyltransferases. These data suggest that the genes are confined to the Acinetobacter genus and that the aac(6')-Ij gene is species spe cific and may be used to identify Acinetobacter sp. 13.