Abstract
A serotyping scheme for Clostridium welchii (C. perfringens) type A employing 57 antisera has been used to investigate the epidemiology of 153 food-poisoning outbreaks and 32 cases of gas gangrene and other clinical infections. Respectively 65% and 59% of the isolates were typable, and in 55% of the food-poisoning outbreaks the causative serotypes were established. Isolation and reporting methods that would render the typing scheme of even greater epidemiological value are described. The type-specific antigen was shown to reside in the capsule and to be lost from strains that had become rough. Development of roughness and its prevention are described. A great range of antisera and an internationally acceptable serotyping scheme is expected after integration of this set with those developed independently in America and Japan.