MOLECULAR CHARACTERIZATION OF TRANSFERABL E 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 plasmi ds. Fifty six isolates (88.9%) transferred amikacin resistance to E co li C600 receptor strain by conjugation. The transconjugants acquired a 11 kilobase-pair or a larger plasmid. The plasmids also encoded resis tance to kanamycin, tobramycin, streptomycin and ampicillin. A DNA pro be from the gene AAC (6')-I encoding an aminoglycoside 6'-N-acetyltran sferase, AAC (6')-I hybridized in Southern blot with plasmid DNA of th e 10 Enterobacteriaceae strains tested, but not with the plasmid DNA o f 8 amikacin resistant clinical strains of A baumannii. The results in dicate that amikacin resistance in Enterobacteriaceae is due mainly to conjugative plasmids encoding an AAC (6)-I.