A NOVEL GENTAMICIN RESISTANCE GENE IN ENTEROCOCCUS

Enterococcus gallinarum SF9117 is a veterinary isolate for which the M IC of gentamicin is 256 mu g/ml. Time-kill studies with a combination of ampicillin plus gentamicin failed to show synergism against SF9117. A probe representing aac(6')-aph(2 '') did not hybridize to DNA from SF9117, A 3,2-kb fragment from plasmid pYN134 of SF9117 was cloned and conferred resistance to gentamicin in Escherichia coli DH5 alpha. Nuc leotide sequence analysis revealed the presence of a 918-bp open readi ng frame whose deduced amino acid sequence had a region with homology to the C-terminal domain of the bifunctional enzyme AAC(6')-APH(2 ''). The gene is designated aph(2 '')-Ic, and its observed phosphotransfer ase activity is provisionally designated APH(2 '')-Ic. An intragenic p robe hybridized to the genomic DNA from an Enterococcus faecium isolat e from the peritoneal fluid of one patient and to the plasmid DNA of a n Enterococcus faecalis isolate from the blood of another patient, An enterococcal isolate containing this novel resistance gene might not b e readily detected in clinical laboratories that use gentamicin at 500 or 2,000 mu g/ml for screening for high-level resistance.