GENOME MAPPING OF CLOSTRIDIUM-PERFRINGENS STRAINS WITH I-CEUI SHOWS MANY VIRULENCE GENES TO BE PLASMID-BORNE

The intron-encoded endonuclease I-CeuI from Chlamydomonas eugametos wa s shown to cleave the circular chromosomes of all Clostridium perfring ens strains examined at single sites in the rRNA operons, thereby gene rating ten fragments suitable for the rapid mapping of virulence genes by pulsed-field gel electrophoresis (PFGE). This method easily distin guishes between plasmid and chromosomal localisations, as I-CeuI only cuts chromosomal DNA. Using this approach, the genes for three of the four typing toxins, beta, epsilon, and iota, in addition to the entero toxin and lambda-toxin genes, were shown to be plasmid-borne. In a min ority of strains, associated with food poisoning, where the enterotoxi n toxin gene was located on the chromosome, genes for two of the minor toxins, theta and mu, were missing.