Clostridium difficile Toxinotypes

Toxinotyping is a RFLP-PCR based method for differentiating Clostridium difficile strains according to changes in their toxin genes when compared to the reference strain VPI 10463.

Definition of toxinotype
Unlike C. perfringens, where toxinotypes are defined  according to the combination of different toxins produced by a given strain, the definition of a toxinotype in C. difficile is based on variability of the PaLoc region coding for two toxins, TcdA and TcdB.

Toxinotype is a group of strains with identical changes in PaLoc region. At the time 31 toxinotypes are known. Strains with toxin genes similar to reference strain VPI 10463 belong to toxinotype 0. Strains with changes in toxin genes are grouped in variant toxinotypes I to XXXI (Table 1).

Toxin production in toxinotypes
Despite changes in PaLoc can variant toxinotypes produce both toxins, only toxin A, only toxin B or none of both.
Some variant toxins display different cytopathic effect and differ from the toxins produced by the strain VPI 10463 also GTPases used as substrate.
The majority of variant strains produce also third toxin, binary toxin CDT (Table 1).

Correlation with other typing methods
Toxinotyping correlates good but not entirely with serotyping.
Correlation with other molecular typing methods as ribotyping or REA is very good (Table 2).