title: tcdA As a diagnostic target in a loop-mediated amplification assay for detecting toxigenic Clostridium difficile.
abstract: BACKGROUND
  The illumigene® (Meridian Bioscience, Inc., Cincinnati, OH) and GeneOhm® (BD Diagnostics, La Jolla, CA) Clostridium difficile assays target the tcdA gene and tcdB gene, respectively. We assessed the use of tcdA as the molecular target in the illumigene® C. difficile loop-mediated amplification assay in detecting a wide variety of C. difficile strains including those with tcdA deletions.
  
  
  METHODS
  We tested 38 C. difficile strains and 108 patient stool specimens using the illumigene® assay. The GeneOhm® real-time polymerase chain reaction (PCR) assay served as the reference method. Discordant results were resolved by repeat testing, anaerobic culture, and a laboratory-developed real-time PCR targeting tcdA and tcdB.
  
  
  RESULTS
  Both illumigene® and GeneOhm® assays detected all 37 C. difficile toxin B(+) strains representing seven toxinotypes and including four toxin A(-) B(+) isolates. No cross-reactivity with 20 other Clostridium species or toxin-negative C. difficile was observed in either assay. Among patient stool specimens, agreement was 94.4% (102/108). After discordant result resolution, agreement was 96.3% (104/108). Specimens with initially discordant results had target concentrations approaching the limit of detection for the two commercial assays. Discordance appeared unrelated to whether tcdA or tcdB was the amplification target.
  
  
  CONCLUSIONS
  The tcdA 5' region used by the illumigene® assay is a practical target for toxigenic C. difficile detection.
authors.affiliation: Associated Regional and University Pathologists (ARUP) Laboratories, Institute for Clinical and Experimental Pathology, Salt Lake City, Utah, USA.
authors.forename: Brianne
authors.initials: B
authors.lastname: Couturier
authors.forename: Robert
authors.initials: R
authors.lastname: Schlaberg
authors.forename: Chris
authors.initials: C
authors.lastname: Konzak
authors.forename: Jeff
authors.initials: J
authors.lastname: Nicholes
authors.forename: Christian
authors.initials: C
authors.lastname: Law
authors.forename: Rosemary C
authors.initials: RC
authors.lastname: She
mesh_terms: D001427:Bacterial Toxins / Q000235:genetics*; D016360:Clostridioides difficile / Q000235:genetics* / Q000302:isolation & purification; D004761:Enterocolitis, Pseudomembranous / Q000175:diagnosis / Q000382:microbiology*; D004768:Enterotoxins / Q000235:genetics*; D005243:Feces / Q000382:microbiology; D006801:Humans; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; C041348:tcdA protein, Clostridium difficile