Radiation Survival Curves of Clostridium Botulinum Spores

Abstract

SUMMARYSurvival curves were obtained for massive concentrations of spores of Clostridium botulinum strain 12885A, when subjected to a wide range of gamma radiation doses under various conditions. The spore concentrations ranged from 37,000 to 64,800,000,000 per ampoule, with no recovery at 5 Mrad or more. Only at lower doses were observed survival counts compatible with classical hit theory. More than one hit is apparently required to inactivate the Cl. botulinurn spore by gamma radiation. The number of hits required for inactivation is estimated at somewhere near 13. Freeze‐dried spores exhibited less radioresistance in the dry state than when resuspended in neutral phosphate buffer. Spore suspensions in neutral phosphate buffer exhibited less radioresistance when irradiated under air than when irradiated under nitrogen. Spores exhibited less radioresistance suspended in phosphate buffer than in a nutrient medium (pork‐pea infusion). Changes in concentration of spores over a range of 37 × 103 to 53 × 109 did not significantly affect the percent survival for a given dose except in the tail area. Regardless of spore concentration, a so‐called “tailing off” of surviving spores was observed at the higher dose levels employed for varying spore concentrations. The “tailing off” phenomenon did not appear to follow the classical hit theory.