title: Genetic determinants and elements associated with antibiotic resistance in viridans group streptococci.
abstract: OBJECTIVE
  To investigate the distribution of erythromycin, tetracycline and chloramphenicol resistance mechanisms and determinants and the relevant genetic environments and elements in viridans group streptococci (VGS).
  
  
  METHODS
  A total of 263 VGS collected from routine throat swabs in 2010-12 and identified to the species level were studied. Antibiotic resistance determinants and the relevant genetic contexts and elements were determined using amplification and sequencing assays and restriction analysis.
  
  
  RESULTS
  The investigation provided original information on the distribution of resistance mechanisms, determinants and genetic elements in VGS. Erythromycin-resistant isolates totalled 148 (56.3%; 37 belonging to the cMLS phenotype and 111 belonging to the M phenotype); there were 72 (27.4%) and 7 (2.7%) tetracycline- and chloramphenicol-resistant isolates, respectively. A number of variants of known genetic contexts and elements carrying determinants of resistance to these antibiotics were detected, including the mega element, Φ10394.4, Tn2009, Tn2010, the IQ element, Tn917, Tn3872, Tn6002, Tn916, Tn5801, a tet(O) fragment from ICE2096-RD.2 and ICESp23FST81.
  
  
  CONCLUSIONS
  These findings shed new light on the distribution of antibiotic resistance mechanisms and determinants and their genetic environments in VGS, for which very few such data are currently available. The high frequency and broad variety of such elements supports the notion that VGS may be important reservoirs of resistance genes for the more pathogenic streptococci. The high rates of macrolide resistance confirm the persistence of a marked prevalence of resistant VGS in Europe, where macrolide resistance is, conversely, declining among the major streptococcal pathogens.
authors.affiliation: Unit of Microbiology, Department of Biomedical Sciences and Public Health, Polytechnic University of Marche Medical School, 60126 Ancona, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Brenciani
authors.forename: Erika
authors.initials: E
authors.lastname: Tiberi
authors.forename: Emily
authors.initials: E
authors.lastname: Tili
authors.forename: Marina
authors.initials: M
authors.lastname: Mingoia
authors.forename: Claudio
authors.initials: C
authors.lastname: Palmieri
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*; D002701:Chloramphenicol / Q000494:pharmacology; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D004917:Erythromycin / Q000494:pharmacology; D006801:Humans; D007558:Italy; D008969:Molecular Sequence Data; D010614:Pharynx / Q000382:microbiology; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013290:Streptococcal Infections / Q000382:microbiology; D013752:Tetracycline / Q000494:pharmacology; D034363:Viridans Streptococci / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D004917:Erythromycin; D002701:Chloramphenicol; D013752:Tetracycline
keywords: Tn916 family transposons; genetic elements; genetic environments; oral streptococci; resistance determinants