GENTAMICIN RESISTANCE IN CLINICAL ISOLATES OF ESCHERICHIA-COLI ENCODED BY GENES OF VETERINARY ORIGIN

Seven (27 %) of 26 gentamicin-resistant human clinical isolates of Esc herichia coli were resistant to the veterinary aminoglycoside antibiot ic apramycin. A gentamicin-resistant Klebsiella pneumoniae isolate fro m a patient infected with gentamicin/apramycin-resistant E. coli was a lso resistant to apramycin. DNA hybridisation studies showed that all gentamicin/apramycin-resistant isolates contained a gene encoding the enzyme 3-N-aminoglycoside acetyltransferase type IV (AAC[3]IV) that me diates resistance to gentamicin and apramycin in bacteria isolated fro m animals. Seven of the eight gentamicin/apramycin-resistant isolates were also resistant to the veterinary antihelminthic agent hygromycin B, a phenomenon observed previously in gentamicin/apramycin-resistant Enterobacteriaceae isolated from animals. Resistance to gentamicin/apr amycin and hygromycin B was cotransferable in six of the isolates. Res triction enzyme analysis of plasmids in apramycin-resistant transconju gants derived from E. coli and K. pneumoniae isolates from the same pa tient were virtually identical, suggesting that inter-generic transfer of plasmids encoding apramycin resistance had occurred in vivo. These findings support the view that resistance to gentamicin and apramycin in clinical isolates of E. coli results from the spread of resistant organisms from animals to man, with subsequent inter-strain or inter-s pecies spread, or both, of resistance genes on transferable plasmids.