Quantitative real time PCR detection of Clostridium difficile growth inhibition by probiotic organisms

BACKGROUND: Probiotic microorganisms are potential treatments for Clostridium difficile diarrheal disease (CDD) but better methods are needed to determine the relative potency of probiotic microorganisms against pathogenic organisms in mixed cultures. AIM: Quantify C. difficile in the presence of putative probiotic organisms using molecular methods to determine relative probiotic potency. MATERIALS AND METHODS: C. difficile strains were cultivated anaerobically. Serial dilutions of Lactobacillus cultures or microbial mixtures from kefir were co-cultured with C. difficile for 48 hours. Bacterial DNA was extracted and qPCR was used to measure C. difficile toxin A gene, on the basis of cycle threshold (Ct) number. RESULTS: Strains of Lactobacillus (human and ATCC derived), and mixed cultures from commercial kefir were co-cultured with C. difficile. Lactobacillus and the microbial mixture from kefir were ranked in order of their potency in C. difficile growth inhibition. CONCLUSIONS: PCR allows facile quantification of C. difficle in the presence of other. The technique measures relative potency of over-the-counter probiotics and may predict human strains meriting probiotic status.