Human isolates of apramycin-resistant Escherichia coli which contain the genes for the AAC(3)IV enzyme.

Gentamicin-resistant Escherichia coli isolated at different periods from patients in two hospitals were tested for resistance to the aminoglycoside antibiotic apramycin. Twenty-four of 93 (26%) gentamicin-resistant isolates collected from the Royal Liverpool Hospital between 1981 and 1990 were resistant to apramycin. Thirteen isolates were highly resistant to apramycin (minimal inhibitory concentration (MIC) > or = 1024 micrograms/ml), were also resistant to gentamicin, netilmicin and tobramycin, and hybridized with a DNA probe derived from the aminoglycoside acetyltransferase (3)IV (AAC(3)IV) gene. The proportion of gentamicin-resistant isolates which had high level resistance to apramycin increased from 7% in 1981-5 to 24% in 1986-90. Twelve gentamicin-resistant E. coli from Guy''s and St Thomas''s Hospital isolated between 1977 and 1980 were also tested for resistance to apramycin. For five of these isolates the MICs of apramycin was 32-256 micrograms/ml. None was shown to have a conjugative plasmid carrying resistance to apramycin and only one hybridized with the DNA probe for the AAC(3)IV enzyme.