Survey of the extrachromosomal gene pool of Clostridium difficile.

Pseudomembranous colitis, a severe diarrheal disease, has been linked to the administration of antibiotics and to two toxins produced by Clostridium difficile. Eighty-two strains of C. difficile isolated from humans and hamsters were assayed for the presence of plasmid DNA. Agarose gel electrophoresis of Sarkosyl-lysed cells indicated that 18% of the strains contained from one to four plasmids. The plasmid DNA in these strains ranged in molecular weight from 2.7 X 10(6) to 60 X 10(6). Strains with and without plasmids were examined for the cytopathogenic effect of the toxins on MRC-5 cells. No correlation was observed between plasmid content and cytopathogenic effect. The results of in vitro antibiotic susceptibility testing with plasmid-containing strains revealed that 33% of the strains tested exhibited growth with four or more of the antimicrobial agents used.