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Antimicrobial Agents and Chemotherapy, January 1999, p. 157-160, Vol. 43, No. 1
Hospital Infections Program, National Center
for Infectious Diseases, Centers for Disease Control and Prevention,
Atlanta, Georgia 303331;
Department of
Medical Microbiology, School of Medicine, University of Tromsø,
Tromsø, Norway2; and
Department of
Pathology and Laboratory Medicine, University of Wisconsin Hospital
and Clinics, Madison, Wisconsin 537923
Received 16 April 1998/Returned for modification 15 July
1998/Accepted 27 October 1998
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 of
Enterococcus 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. coli
C600(pHP45
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Detection of a Streptomycin/Spectinomycin
Adenylyltransferase Gene (aadA) in Enterococcus
faecalis
) known to contain the aadA gene. The
aadA gene was transferred via filter matings from the E. faecalis donor to E. faecalis
JH2-2. 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-
competent cells. D-Rhodamine dye
terminator cycle sequencing was used to determine the gene sequence,
which was compared to previously reported sequences of aadA
genes. 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 the
aadA 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. coli
R538-1 (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 an
aadE gene, since the isolates were reported to be
susceptible to spectinomycin.
*
Corresponding author. Mailing address: Nosocomial
Pathogens Laboratory Branch, Centers for Disease Control and
Prevention, 1600 Clifton Rd., N.E., Mailstop G08, Atlanta,
GA 30333. Phone: (404) 639-0195. Fax: (404) 639-1381. E-mail:
ncc1{at}cdc.gov.
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