Six different agglutinating antisera were obtained by immunizing rabbits with Formol-treated strains of Clostridium difficile. After appropriate absorption, these antisera were used to define six serogroups designated by the letters A, B, C, D, F, and G. Altogether, 315 strains of C. difficile from various origins were tested for slide agglutination by these antisera; 312 (99%) of them were agg...