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Twenty strains of Clostridium botulinum type C, including 12 isolates from avian sources with varying toxigenic properties, were examined by electron microscope for the presence of bacteriophages. All toxigenic strains were infected with one or two types of phages. Three types of phages designated large, small, and intermediate were observed. Most of the strains carried the large and small phage, with the large phage being present in much greater numbers. Since there is evidence that highly toxigenic strains of C. botulinum type C are responsible for large outbreaks of botulism in wild birds, the phenomenon of toxigenic variation among the type C strains was investigated. Experiments were carried out employing a broth medium on a phagefree nontoxigenic strain for elucidating the role of bacteriophages in toxigenicity. All phage suspensions contained large phages, with the exception of one that caused conversion. The exception was a preparation containing an intermediate type of phage. Phages from different strains produced cultures of varying toxigenic characteristics. By employing a tube-lytic test and an agar-overlay-phage assay technique, it was determined that whenever the phage-bacterium relationship resulted in an initial high degree of lysis, the potency of toxin in the culture was weak. It appeared that in highly toxigenic strains, the phage-bacterium relationship is characterized by a stable lysogenic type of association. It was also found that in a highly toxigenic converted culture the percentage of toxigenic cells was 100, whereas in hypotoxigenic culture the percentage was only 20.

Observations on bacteriophages of Clostridium botulinum type C isolates from different sources and the role of certain phages in toxigenicity