ABSTRACT
Genes encoding streptomycin/spectinomycin adenylyltransferases [ANT(3")(9)] have been reported to exist in gram-negative organisms and Staphylococcus aureus. During a study of high-level aminoglycoside resistance in enterococci, we encountered an isolate ofEnterococcus faecalis that was streptomycin resistant but did not appear to contain the 6′-adenylyltransferase gene (aadE) when examined by PCR with specific primers. Phosphocellulose paper binding assays indicated the presence of an ANT(3")(9) enzyme. Streptomycin and spectinomycin MICs of 4,000 and 8,000 μg/ml, respectively, were observed for the isolate. PCR primers corresponding to a highly conserved region of the aadA gene were used to amplify a specific 284-bp product. The product hybridized with a digoxigenin-labeled PCR product from E. coliC600(pHP45Ω) known to contain the aadA gene. TheaadA gene was transferred via filter matings from theE. faecalis donor to E. faecalisJH2-2. PCR primers designed for analysis of integrons were used to amplify a 1-kb product containing the aadA gene, which was cloned into the vector pCRII and transformed into Escherichia coli DH5-α competent cells. d-Rhodamine dye terminator cycle sequencing was used to determine the gene sequence, which was compared to previously reported sequences of aadAgenes. We found the aadA gene in E. faecalis to be identical to the aadA genes reported by Sundström et al. for E. coli plasmid R6-5 (L. Sundström, P. Rådström, G. Swedberg, and O. Sköld, Mol. Gen. Genet. 213:191–201, 1988), by Fling et al. for theaadA within transposon Tn7 (M. E. Fling, J. Kopf, and C. Richards, Nucleic Acids Res. 13:7095–7106, 1985), and by Hollingshead and Vapnek for E. coliR538-1 (S. Hollingshead and D. Vapnek, Plasmid 13:17–30, 1985). Previous reports of the presence of the aadA gene in enterococci appear to be erroneous and probably describe anaadE gene, since the isolates were reported to be susceptible to spectinomycin.
- Copyright © 1999 American Society for Microbiology
