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Antimicrob. Agents Chemother. doi:10.1128/AAC.00782-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A DNA methylase activity as a marker for the presence of a family of phage-like elements conferring efflux-mediated macrolide resistance in streptococci

Instituto de Microbiologia, Instituto de Medicina Molecular, Faculdade de Medicina de Lisboa, Lisboa, Portugal

^* To whom correspondence should be addressed. Email: ramirez{at}fm.ul.pt.

	Abstract

Recently two related chimeric genetic elements (Tn1207.3 and 10394.4) were shown to carry the macrolide efflux gene mef in Streptococcus pyogenes (GAS). The dissemination of elements belonging to the Tn1207.3/10394.4 family in recent isolates of GAS, Streptococcus dysgalactiae subsp. equisimilis, Streptococcus pneumoniae and Streptococcus agalactiae recovered in Portugal was surveyed. In total, 149 GAS, 18 S. pneumoniae, 4 S. dysgalactiae subsp. equisimilis and 5 S. agalactiae isolates from infections, presenting the M phenotype of macrolide resistance and containing the mef gene, were screened for the presence of Tn1207.3/10394.4 by PCR targeting ORFs specific for these related elements. All the GAS isolates tested and one of the S. dysgalactiae subsp. equisimilis isolates carried Tn1207.3. However, neither of these elements was found in the isolates of the other streptococcal species. It was also noted that the DNA of the isolates carrying Tn1207.3 was resistant to cleavage by the endonuclease SmaI. Cloning and expression of ORF12 of Tn1207.3, in Escherichia coli, showed that it encoded a methyltransferase that rendered DNA refractory to cleavage by SmaI (M.Spy10394I). Using this characteristic as a marker for the presence of the Tn1207.3/10394.4 family, we reviewed the literature and concluded that these genetic elements are widely distributed among tetracycline susceptible GAS presenting the M phenotype from diverse geographic origins and may have played an important role in the dissemination of macrolide resistance in this species.

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