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Antimicrobial Agents and Chemotherapy, February 2008, p. 619-625, Vol. 52, No. 2
0066-4804/08/$08.00+0     doi:10.1128/AAC.01081-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

New Genetic Element Carrying the Erythromycin Resistance Determinant erm(TR) in Streptococcus pneumoniae

Department of Infectious, Parasitic and Immunemediated Diseases, Istituto Superiore di Sanità, Rome,¹ Laboratorio di Microbiologia Molecolare e Biotecnologia, Dipartimento di Biologia Molecolare, Università di Siena, Siena, Italy²

Received 17 August 2007/ Returned for modification 17 October 2007/ Accepted 20 November 2007

erm(A) subclass erm(TR), a common macrolide resistance determinant in Streptococcus pyogenes but quite rare in Streptococcus pneumoniae, was found in a clinical S. pneumoniae isolate (AP200) from Italy. In this isolate, erm(TR) was found included in a genetic element approximately 56 kb in size that did not appear to be conjugative but could be transferred by transformation. An erm(TR)-containing DNA fragment of approximately 10 kb was sequenced and 12 open reading frames (ORFs) were identified. Upstream of erm(TR), a regulatory protein of the TetR family and the two components of an efflux pump of the ABC type were found. Downstream of erm(TR), there were ORFs homologous to a spectinomycin phosphotransferase, transposases, and a relaxase. Since the genomic sequence of S. pyogenes MGAS10750 carrying erm(TR) became available, comparison between the erm(TR)-containing genetic elements in AP200 and in MGAS10750 was performed. The region flanking erm(TR) in MGAS10750 showed identity with AP200 for 10 ORFs out of 12. PCR mapping using primers designed on the sequence of MGAS10750 confirmed that AP200 carries a genetic element similar to that of MGAS10750. In AP200 the genetic element was inserted inside an ORF homologous to spr0790 of S. pneumoniae R6, coding for a type I restriction modification system. Homologies between the insertion sites in AP200 and MGAS10750 consisted of eight conserved nucleotides, of which three were duplicated, likely representing target site duplication. The structure of the erm(TR)-carrying genetic element shows characteristics of a transposon/prophage remnant chimera. In AP200 this genetic element was designated Tn1806.

Published ahead of print on 10 December 2007.