MOLECULAR CHARACTERIZATION OF TRANSFERABLE AMIKACIN RESISTANCE IN ENTEROBACTERIACEAE STRAINS ISOLATED FROM INTRAHOSPITALARY INFECTIONS

Sixty three amikacin resistant strains of Enterobacteriaceae isolated in three hospitals from Santiago, between 1988 and 1990 were included in this study. The strains were multiresistant and harbored 1-5 plasmids. Fifty six isolates (88.9%) transferred amikacin resistance to E coli C600 receptor strain by conjugation. The transconjugants acquired a 11 kilobase-pair or a larger plasmid. The plasmids also encoded resistance to kanamycin, tobramycin, streptomycin and ampicillin. A DNA probe from the gene AAC (6')-I encoding an aminoglycoside 6'-N-acetyltransferase, AAC (6')-I hybridized in Southern blot with plasmid DNA of the 10 Enterobacteriaceae strains tested, but not with the plasmid DNA of 8 amikacin resistant clinical strains of A baumannii. The results indicate that amikacin resistance in Enterobacteriaceae is due mainly to conjugative plasmids encoding an AAC (6)-I.