JCM Accepts, published online ahead of print on 21 October 2009

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J. Clin. Microbiol. doi:10.1128/JCM.01490-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Evaluation of a New Commercial Taqman PCR Assay for Direct Detection of the Clostridium difficile Toxin B Gene from Clinical Stool Specimens

Paul D. Stamper, Wisal Babiker, Romina Alcabasa, Deborah Aird, Jennifer Wehrlin, Ijeoma Ikpeama, Linda Gluck, and Karen C. Carroll^*

Division of Medical Microbiology, Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and The Johns Hopkins Hospital Microbiology Laboratory, Baltimore, Maryland

^* To whom correspondence should be addressed. Email: kcarrol7{at}jhmi.edu.

The Prodesse ProGastro^TM Cd Assay (Prodesse, Inc., Waukesha, WI) is a new commercial Taqman PCR assay that detects tcdB. The ProGastro Cd^TM Assay was compared to the Wampole® C. difficile Toxin B Test (TOX-B) (TechLab®, Blacksburg, VA), a cell culture cytotoxicity neutralization assay (CCCNA), and to anaerobic toxigenic bacterial culture as the "gold standard" on 285 clinical stool specimens. Assays were independently performed according to manufacturers' directions. A 1.0 ml sample was removed from the stool specimen from which 20 μl was used for the extraction on the NucliSENS® easyMAG^TM (bioMérieux, Inc., Durham, NC) for the Prodesse ProGastro^TM Cd Assay and 200 μl of the stool filtrate for the TOX-B CCCNA. Anaerobic toxigenic culture was done by heating an additional 1.0 ml of the stool sample to 80° C for 10 min before inoculation onto modified cycloserine, cefoxitin, fructose agar with horse blood (CCFA-HB) (Remel, Lenexa, KS) and into a pre-reduced chopped meat glucose (CMG) broth (BBL, BD Diagnostics, Sparks, MD). The prevalence of toxin producing strains of C. difficile was 15.7% (n=44) as determined by anaerobic toxigenic culture. The sensitivity, specificity, positive and negative predictive values of the Prodesse ProGastro^TM Cd Assay compared to the TOX B Test was 83.3%, 95.6%, 69.4%, and 98%, respectively. Compared to toxigenic culture, the sensitivity, specificity, positive and negative predictive values of the Prodesse ProGastro^TM Cd Assay were 77.3%, 99.2%, 94.4% and 95.9% and the TOX B Test were 63.6%, 99.2%; 93.3%, and 93.6%, respectively. Although no statistical difference (Fisher's exact) was detected (p=0.242) between the sensitivity of the Prodesse ProGastro^TM Cd Assay and a standard CCCNA when compared to anaerobic culture for the detection of toxigenic C. difficile, the Prodesse ProGastro^TM Cd Assay did detect more toxigenic C. difficile than CCCNA.