Differences in the pathogenicity of various bacterial isolates used in an induction model for gangrenous dermatitis in broiler chickens.

A gangrenous dermatitis model was developed in broiler chickens, in which birds previously vaccinated at 14 days of age with a bursal disease virus vaccine were challenged at 4 wk of age with various bacterial combinations with the combination of subcutaneous and intramuscular injection. Gangrenous dermatitis lesions were not produced in birds injected with one of the Staphylococcus aureus isolates, either alone or in combination with various Clostridium septicum isolates. Other S. aureus isolates produced significant levels of gangrenous dermatitis either alone or in combination with the same C. septicum isolates. These same C. septicum isolates when given alone did not produce gangrenous lesions. Data from this experiment show the highest level of mortality occurred in birds challenged with a mixture of C. septicum and S. aureus isolates, whereas lower or no mortality was associated with the same isolates given separately. The data clearly demonstrate that the pathogenicity of isolates responsible for gangrenous dermatitis varies widely, indicating that the frequency and severity of lesion production, as well as the occurrence of mortality, are largely dependent upon the specific isolate or isolates with which the birds are challenged.