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
24 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 XXIV (Table 1).
Toxin production in toxinotypes
Despite changes in PaLoc can variant toxinotypes produce
both toxins, only toxin A 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) |