How to detect Clostridium difficile variant strains in a routine laboratory.

Toxin A-negative, toxin B-positive strains (A-/B+) are the best studied examples of Clostridium difficile variant strains. In addition, there are some other groups of variant C. difficile strains that produce both toxins (A+/B+) or are non-cytotoxic (A-/B-) but differ from the reference strain VPI 10463 in their toxin genes. Here we describe two simple methods (amplification of the tcdA gene and amplification of the binary toxin gene cdtA) which can be used in rapid screening for variant C. difficile strains in collections or in routine laboratories.