The Stability of Toxigenicity in Clostridium botulinum Types C and D

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Abstract
Several type C and D strains of C. botulinum, which were converted to the toxigenic state by phages [C-st, c-n 71, d-1873 and c-203], were serially transferred through cooked meat medium with and without specific anti-phage serum. Most of the converted strains lost their toxigenicity even during transfer without antiserum, and the nontoxigenic variants that appeared were resistant to lysis and conversion by the original phage. In some combinations of phage and host bacteria, toxigenicity was stable after 10 transfers, though it showed a transient decrease, and the non-toxigenic variants that arose remained sensitive to lysis and conversion. When converted strains were transferred in medium containing anti-phage serum, toxigenicity was lost more rapidly than in the absence of serum and the nontoxigenic variants that appeared remained sensitive to lysis and conversion by the parent phage. Filtrates of the supernatants of culture fluids of strains transferred without anti-phage serum converted non-toxigenic strains to toxigenicity at varying rates. A non-converting phage was demonstrated in 1 of these filtrates. This phage was identical to the original converting phage in its morphology, host range and antigenicity. Indicator strains treated with this phage acquired resistance to lysis by the parent phage. Re-infection and conversion to toxigenicity apparently occurred in combinations showing stable toxigenicity after 10 transfers. In those combinations that lost toxigenicity, re-infection with a non-coverting mutant of the original phage may have occurred with non-toxigenic variants becoming resistant to the converting phage. This may be 1 cause of the toxigenicity loss which is common in some type C and D strains of C. botulinum.

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