title: Emergence of reduced susceptibility to metronidazole in Clostridium difficile.
abstract: OBJECTIVE
  Antimicrobial treatment for Clostridium difficile infection (CDI) has typically been metronidazole, although reports have questioned the efficacy of this option. We screened recently isolated C. difficile (2005-06) for susceptibility to metronidazole and compared results for historic isolates (1995-2001).
  
  
  METHODS
  C. difficile ribotypes 001 (n = 86), 106 (n = 81) and 027 (n = 48) and isolates from the 10 other most prevalent ribotypes in Leeds (n = 57) were screened using spiral gradient endpoint analysis (SGE). C. difficile with metronidazole SGE MICs > or = 6 mg/L were analysed further by agar incorporation and Etest. Multiple-locus variable-number tandem-repeat analysis (MLVA) typing was performed for 28 C. difficile isolates.
  
  
  RESULTS
  No reduced metronidazole susceptibility was observed in C. difficile ribotypes 106 and 027 (geometric mean SGE MICs 1.11 and 0.90 mg/L, respectively). In contrast, 21 (24.4%) C. difficile ribotype 001 demonstrated reduced susceptibility to metronidazole (geometric mean SGE MICs 3.51 mg/L, P < 0.001). Variations in susceptibility were observed relating to the method and media, but increased metronidazole MICs were confirmed by an agar incorporation method. Geometric mean agar incorporation MICs for historic C. difficile ribotype 001 (n = 72) were 1.03 (range 0.25-2) mg/L compared with 5.94 (4-8) mg/L (P < 0.001) for recent isolates displaying reduced metronidazole susceptibility. MLVA typing revealed two clonal complexes of C. difficile with reduced susceptibility to metronidazole.
  
  
  CONCLUSIONS
  We have demonstrated the emergence of reduced susceptibility to metronidazole in 24.4% of the recent C. difficile ribotype 001 isolates from our institution. Our observations could have implications in the clinical setting due to the poor penetration of metronidazole into the colon.
authors.affiliation: Department of Microbiology, Institute of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Simon D
authors.initials: SD
authors.lastname: Baines
authors.forename: Rachael
authors.initials: R
authors.lastname: O'Connor
authors.forename: Jane
authors.initials: J
authors.lastname: Freeman
authors.forename: Warren N
authors.initials: WN
authors.lastname: Fawley
authors.forename: Celine
authors.initials: C
authors.lastname: Harmanus
authors.forename: Paola
authors.initials: P
authors.lastname: Mastrantonio
authors.forename: Ed J
authors.initials: EJ
authors.lastname: Kuijper
authors.forename: Mark H
authors.initials: MH
authors.lastname: Wilcox
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D015373:Bacterial Typing Techniques; D016360:Clostridioides difficile / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D004761:Enterocolitis, Pseudomembranous / Q000382:microbiology; D005838:Genotype; D006801:Humans; D008795:Metronidazole / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D018598:Minisatellite Repeats; D021521:Ribotyping
chemical_list: D000890:Anti-Infective Agents; D004269:DNA, Bacterial; D008795:Metronidazole