New strains of Clostridium botulinum subtype Af.

Two new strains of Clostridium botulinum subtype Af have been isolated from soil samples of Mendoza Province, Argentina. Some serological and other biological properties of these new isolates have been studied in comparison with the prototype 84-SC2 strain. No differences in morphology and biochemical activities were found among these three so far known strains of this subtype. Neither serologic differences have been recorded, suggesting that the bispecificity and the type A to type F serologic ratio (A:F) is a stable genetic trait of subtype Af. The three strains were found in well separated areas. None of the type A strains isolated either from soil samples or from human botulism outbreaks in Mendoza have shown such a high degree of toxigenicity as that shown by Af strains. All these facts suggest that this peculiar type is not the product of a recent genetic relationship between types A and F. Rather, it represents a stable type in nature.