title: Comparison of supplemented Brucella agar and modified Clostridium difficile agar for antimicrobial susceptibility testing of Clostridium difficile.
abstract: BACKGROUND
  Antimicrobial susceptibility testing (AST) of Clostridium difficile is increasingly important because of the rise in resistant strains. The standard medium for the AST of C. difficile is supplemented Brucella agar (sBA), but we found that the growth of C. difficile on sBA was not optimal. Because active growth is critical for reliable AST, we developed a new, modified C. difficile (mCD) agar. C. difficile grew better on mCD agar than on sBA.
  
  
  METHODS
  C. difficile isolates were collected from patients with healthcare-associated diarrhea. sBA medium was prepared according to the CLSI guidelines. Homemade mCD agar containing taurocholate, L-cysteine hydrochloride, and 7% horse blood was used. For 171 C. difficile isolates, we compared the agar dilution AST results from mCD agar with those from sBA.
  
  
  RESULTS
  No significant differences were observed in the 50% minimal inhibitory concentration (MIC50) and 90% minimal inhibitory concentration (MIC90) of clindamycin (CLI), metronidazole (MTZ), moxifloxacin (MXF), piperacillin-tazobactam (PTZ), and rifaximin (RIX), but the values for vancomycin (VAN) were two-fold higher on mCD agar than on sBA. The MICs of CLI, MXF, and RIX were in 100% agreement within two-fold dilutions, but for MTZ, VAN, and PTZ, 13.7%, 0.6%, and 3.1% of the isolates, respectively, were outside the acceptable range.
  
  
  CONCLUSIONS
  The MIC ranges, MIC50 and MIC90, were acceptable when AST was performed on mCD agar. Thus, mCD agar could be used as a substitute medium for the AST of C. difficile.
authors.affiliation: Department of Laboratory Medicine, Hanyang University College of Medicine, Seoul, Korea.
authors.forename: Gye Hyeong
authors.initials: GH
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Korea.
authors.forename: Jieun
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Korea.
authors.forename: Hyunjoo
authors.initials: H
authors.lastname: Pai
authors.affiliation: Department of Laboratory Medicine, Hanyang University College of Medicine, Seoul, Korea.
authors.forename: Jung Oak
authors.initials: JO
authors.lastname: Kang
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D016360:Clostridioides difficile / Q000187:drug effects* / Q000302:isolation & purification; D003015:Clostridium Infections / Q000382:microbiology; D003967:Diarrhea / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*
chemical_list: D000890:Anti-Infective Agents
keywords: Antimicrobial susceptibility test; Clostridium difficile; Minimum inhibitory concentration; Susceptibility testing media