title: PCR ribotype prevalence and molecular basis of macrolide-lincosamide-streptogramin B (MLSB) and fluoroquinolone resistance in Irish clinical Clostridium difficile isolates.
abstract: BACKGROUND
  Antimicrobial use is recognized as a risk factor for Clostridium difficile infection (CDI) and outbreaks. We studied the relationship between PCR ribotype, antimicrobial susceptibility and the genetic basis of resistance in response to exposure to antimicrobial agents.
  
  
  METHODS
  C. difficile isolates were cultured from 133 CDI patients for whom recent antimicrobial drug exposure had been recorded. Isolates were ribotyped by PCR and assessed for their susceptibility to the macrolide-lincosamide-streptogramin B (MLS(B)) group of compounds (erythromycin and clindamycin) and fluoroquinolone antimicrobials (ciprofloxacin, levofloxacin and moxifloxacin). Where relevant, the genetic basis of resistance was determined.
  
  
  RESULTS
  Prevalent ribotypes (including 027, 001 and 106) exhibited significantly greater antimicrobial resistance compared with ribotypes 078 and 014, among others. Clindamycin-resistant ribotype 078 was detected for the first time. Ribotypes 027 and 001 were more likely to exhibit MLS(B) resistance, a feature that was associated with the erm(B) gene. Exposure to MLS(B) or fluoroquinolone antimicrobial compounds in the 8 weeks prior to the onset of infection was not associated with specific genetic markers of resistance. Single amino acid substitutions in the A and B subunits of DNA gyrase were noted and were ribotype specific and linked to resistance to moxifloxacin.
  
  
  CONCLUSIONS
  Resistance to MLS(B) and fluoroquinolone antimicrobial compounds is common among prevalent ribotypes of C. difficile. The genetic basis for antimicrobial resistance appears to be ribotype specific and conserved in the absence of recent antimicrobial selection pressure.
authors.affiliation: School of Public Health, Physiotherapy & Population Science, UCD Veterinary Sciences Centre, University College Dublin, Belfield, Dublin 4, Ireland. katie.solomon@ucd.ie
authors.forename: Katie
authors.initials: K
authors.lastname: Solomon
authors.forename: Seamus
authors.initials: S
authors.lastname: Fanning
authors.forename: Sinead
authors.initials: S
authors.lastname: McDermott
authors.forename: Sean
authors.initials: S
authors.lastname: Murray
authors.forename: Louise
authors.initials: L
authors.lastname: Scott
authors.forename: Alan
authors.initials: A
authors.lastname: Martin
authors.forename: Mairead
authors.initials: M
authors.lastname: Skally
authors.forename: Karen
authors.initials: K
authors.lastname: Burns
authors.forename: Ed
authors.initials: E
authors.lastname: Kuijper
authors.forename: Fidelma
authors.initials: F
authors.lastname: Fitzpatrick
authors.forename: Lynda
authors.initials: L
authors.lastname: Fenelon
authors.forename: Lorraine
authors.initials: L
authors.lastname: Kyne
mesh_terms: D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001424:Bacterial Infections / Q000453:epidemiology / Q000382:microbiology; D016360:Clostridioides difficile / Q000187:drug effects*; D027081:DNA Gyrase / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004761:Enterocolitis, Pseudomembranous / Q000453:epidemiology / Q000382:microbiology; D024841:Fluoroquinolones / Q000494:pharmacology*; D006801:Humans; D007494:Ireland / Q000453:epidemiology; D055231:Lincosamides / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology*; D008780:Methyltransferases / Q000235:genetics; D008826:Microbial Sensitivity Tests; D020133:Reverse Transcriptase Polymerase Chain Reaction; D021521:Ribotyping; D025381:Streptogramin B / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D024841:Fluoroquinolones; D055231:Lincosamides; D018942:Macrolides; D025381:Streptogramin B; D008780:Methyltransferases; C035181:rRNA (adenosine-O-2'-)methyltransferase; D027081:DNA Gyrase