title: Distribution and molecular analysis of mef(A)-containing elements in tetracycline-susceptible and -resistant Streptococcus pyogenes clinical isolates with efflux-mediated erythromycin resistance.
abstract: OBJECTIVE
  To analyse the distribution and molecular features of mef(A)-containing elements in a large collection of different Streptococcus pyogenes clinical isolates with efflux-mediated erythromycin resistance. To further characterize a tet(O)-mef(A) element.
  
  
  METHODS
  Gene detection was carried out by PCR using primers designed from established sequences or from sequences in this study. From a tet(O)-mef(A) element (approximately 60 kb), an 11 972 bp region including the tet(O) and mef(A) genes was sequenced.
  
  
  RESULTS
  In the tetracycline-susceptible isolates (n =28), the mef(A) gene was contained in a regular Tn1207.1 transposon (7.2 kb), which was inserted into one of two previously described elements, Tn1207.3 (approximately 52 kb) or a 58.8 kb chimeric element, both flanked by the comEC gene. In the tetracycline-resistant isolates (n =61), all of which carried the tet(O) gene, the mef(A) gene was part of a variable Tn1207.1-related transposon inserted into unique elements which contained the tet(O) gene approximately 2.3 to 5.5 kb upstream of the mef(A) gene and were not flanked by the comEC gene. In the Tn1207.1-like transposon of these tet(O)-mef(A) elements, only msr(D) (orf5) and a modified orf6, in addition to mef(A), were detected by PCR in all isolates tested; while orf1 and orf2 were always undetectable, orf3, orf7 and orf8 were found in variable percentages. In an orf3-positive element, sequencing identified four new open reading frames downstream of the tet(O) gene, followed by three short sequences with homology to sequences of the pneumococcal mega element.
  
  
  CONCLUSIONS
  The mef(A) gene is carried on different chromosomal genetic elements depending on whether the isolates are susceptible or resistant to tetracycline.
authors.affiliation: Institute of Microbiology and Biomedical Sciences, Marche Polytechnic University, 60131 Ancona, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Brenciani
authors.forename: Kayode K
authors.initials: KK
authors.lastname: Ojo
authors.forename: Alessia
authors.initials: A
authors.lastname: Monachetti
authors.forename: Stefano
authors.initials: S
authors.lastname: Menzo
authors.forename: Marilyn C
authors.initials: MC
authors.lastname: Roberts
authors.forename: Pietro E
authors.initials: PE
authors.lastname: Varaldo
authors.forename: Eleonora
authors.initials: E
authors.lastname: Giovanetti
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D002352:Carrier Proteins / Q000235:genetics; D004251:DNA Transposable Elements; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004917:Erythromycin / Q000494:pharmacology; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D013297:Streptococcus pyogenes / Q000187:drug effects* / Q000235:genetics; D013752:Tetracycline / Q000494:pharmacology*; D013753:Tetracycline Resistance
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004251:DNA Transposable Elements; C117866:MefA protein, Streptococcus; D008565:Membrane Proteins; C083139:Tet O resistance protein, Bacteria; D004917:Erythromycin; D013752:Tetracycline