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Antimicrobial Agents and Chemotherapy, July 2005, p. 2949-2953, Vol. 49, No. 7
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.7.2949-2953.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Worldwide Disseminated armA Aminoglycoside Resistance Methylase Gene Is Borne by Composite Transposon Tn1548

M. Galimand,1* S. Sabtcheva,1,{dagger} P. Courvalin,1 and T. Lambert1,2

Unité des Agents Antibactériens, Institut Pasteur, 75724 Paris Cedex 15,1 Centre d'Etudes Pharmaceutiques, 92296 Châtenay-Malabry, France2

Received 13 January 2005/ Returned for modification 25 February 2005/ Accepted 23 March 2005

The armA (aminoglycoside resistance methylase) gene, which confers resistance to 4,6-disubstituted deoxystreptamines and fortimicin, was initially found in Klebsiella pneumoniae BM4536 on IncL/M plasmid pIP1204 of ca. 90 kb which also encodes the extended-spectrum ß-lactamase CTX-M-3. Thirty-four enterobacteria from various countries that were likely to produce a CTX-M enzyme since they were more resistant to cefotaxime than to ceftazidime were studied. The armA gene was detected in 12 clinical isolates of Citrobacter freundii, Enterobacter cloacae, Escherichia coli, K. pneumoniae, Salmonella enterica, and Shigella flexneri, in which it was always associated with blaCTX-M-3 on an IncL/M plasmid. Conjugation, analysis of DNA sequences, PCR mapping, and plasmid conduction experiments indicated that the armA gene was part of composite transposon Tn1548 together with genes ant3"9, sul1, and dfrXII, which are responsible for resistance to streptomycin-spectinomycin, sulfonamides, and trimethoprim, respectively. The 16.6-kb genetic element was flanked by two copies of IS6 and migrated by replicative transposition. This observation accounts for the presence of armA on self-transferable plasmids of various incompatibility groups and its worldwide dissemination. It thus appears that posttranscriptional modification of 16S rRNA confers high-level resistance to all the clinically available aminoglycosides except streptomycin in gram-negative human and animal pathogens.

* Corresponding author. Mailing address: Unité des Agents Antibactériens, Institut Pasteur, 25, rue du Docteur Roux, 75724 Paris Cedex 15, France. Phone: (33) 1 45 68 83 18. Fax: (33) 1 45 68 83 19. E-mail: galimand{at}pasteur.fr.

{dagger} Present address: Laboratory for Clinical Microbiology, National Oncology Center, 1756 Sofia, Bulgaria.

Antimicrobial Agents and Chemotherapy, July 2005, p. 2949-2953, Vol. 49, No. 7
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.7.2949-2953.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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