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Antimicrobial Agents and Chemotherapy, September 2006, p. 2903-2911, Vol. 50, No. 9
0066-4804/06/$08.00+0     doi:10.1128/AAC.00325-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Evolution and Global Dissemination of Macrolide-Resistant Group A Streptococci{dagger}

D. Ashley Robinson,1 Joyce A. Sutcliffe,2 Wezenet Tewodros,1,{ddagger} Anand Manoharan,1,§ and Debra E. Bessen1*

Department of Microbiology and Immunology, New York Medical College, Valhalla, New York,1 Rib-X Pharmaceuticals, Inc., New Haven, Connecticut2

Received 16 March 2006/ Returned for modification 5 June 2006/ Accepted 18 June 2006

Macrolide-resistant group A streptococci (MRGAS) have been recovered from many countries worldwide. However, the strain typing information that is available has been insufficient for estimating the total number of macrolide-resistant clones, their geographic distributions, and their evolutionary relationships. In this study, sequence-based strain typing was used to characterize 212 MRGAS isolates from 34 countries. Evaluation of clonal complexes, emm type, and resistance gene content [erm(A), erm(B), mef(A), and undefined] indicate that macrolide resistance was acquired by GAS organisms via ≥49 independent genetic events. In contrast to other collections of mostly susceptible GAS, genetic diversification of MRGAS clones has occurred primarily by mutation rather than by recombination. Twenty-two MRGAS clonal complexes were recovered from more than one continent; intercontinental strains represent nearly 80% of the MRGAS isolates under study. The findings suggest that horizontal transfer of macrolide resistance genes to numerous genetic backgrounds and global dissemination of resistant clones and their descendants are both major components of the present-day macrolide resistance problem found within this species.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, New York Medical College, Valhalla, NY 10595. Phone: (914) 594-4193. Fax: (914) 594-4176. E-mail: debra_bessen{at}nymc.edu.

{dagger} Supplemental material for this article may be found at http://aac.asm.org/.

{ddagger} Present address: Spartan Health Science University School of Medicine, Vieux Fort, St. Lucia, West Indies.

§ Present address: Department of Medicine Unit I and Infectious Diseases, Christian Medical College, Vellore, India.

Antimicrobial Agents and Chemotherapy, September 2006, p. 2903-2911, Vol. 50, No. 9
0066-4804/06/$08.00+0     doi:10.1128/AAC.00325-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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