title: Macrolide resistance mechanisms and in vitro susceptibility patterns of viridans group streptococci isolated from blood cultures.
abstract: OBJECTIVE
  Our aim was to study the macrolide resistance mechanisms and antimicrobial susceptibilities of viridans group streptococci (VGS) isolated from blood cultures.
  
  
  METHODS
  In vitro susceptibilities to nine antimicrobials were studied for 85 VGS isolated from blood cultures by agar dilution. Pheno- and genotyping of erythromycin-resistant isolates were studied by the double disc test and PCR.
  
  
  RESULTS
  Resistance to erythromycin was found in 27% (n = 23) of the isolates. Erythromycin-resistant Streptococcus oralis (n = 13) predominated among the other erythromycin-resistant species isolated. The phenotypes among 23 erythromycin-resistant isolates were as follows: 12 constitutive macrolide-lincosamide-streptogramin (cMLS(B)) resistance phenotype and 11 macrolide (M) resistance phenotype. Of the cMLS(B) isolates 11 had erm(B) genes and 11 of the M phenotype isolates had mef(A) genes. Four of the cMLS(B) isolates had both erm(B) and mef(A) genes. None of the isolates had erm(TR) genes. Combined resistance to erythromycin with penicillin, clindamycin, chloramphenicol, tetracycline and quinupristin/dalfopristin was found in 100, 61, 74, 100 and 100% of the isolates, respectively. No resistance was found for vancomycin, linezolid and levofloxacin.
  
  
  CONCLUSIONS
  The macrolide resistance mechanisms of our VGS isolates revealed that the cMLS(B) phenotype associated with erm(B) and the M phenotype associated with mef(A) genes are found with similar frequencies.
authors.affiliation: School of Health Services, Hacettepe University, 06100, Ankara, Turkey. aergin@hacettepe.edu.tr
authors.forename: Alper
authors.initials: A
authors.lastname: Ergin
authors.forename: Serpil
authors.initials: S
authors.lastname: Ercis
authors.forename: Gülsen
authors.initials: G
authors.lastname: Hasçelik
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004917:Erythromycin / Q000494:pharmacology; D005838:Genotype; D006801:Humans; D018942:Macrolides / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D013290:Streptococcal Infections / Q000097:blood / Q000382:microbiology*; D034363:Viridans Streptococci / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D004917:Erythromycin