Type C avian botulism with reference to the role of bacteriophages

Highly toxigenic as well as hypotoxigenic strains of Clostridium botulinum type C were isolated from 8 of 73 soil samples obtained from an avian botulism endemic area in Ontario. Amongst wild birds a high proportion of healthy pheasants carried the organism in their digestive tracts. One-third of the birds from an outbreak had C. botulinum type C in the liver. All isolates from dead birds were highly toxigenic. These strains produced cultures containing 37 500 to 425 000 mouse LD50 units of toxin/ml and were capable of causing death in pheasants in oral doses of 0.3 ml or less. The phages played a major role in producing botulism toxin of varying potency. All strains were infected with one or two types of phages. Three types of phages - large, small and intermediate - were observed. The role of phages in toxigenicity of 14 of 20 strains was proved. In highly toxigenic strains, phage-bacterium relationship was characterized by a stable lysogeny. Several toxigenic phages were antigenically similar. The loss of phages through spore-state was not as frequent as suggested by some workers..