The effect of oxygen and redox potential on growth of Clostridium botulinum type E from a spore inoculum

Abstract

Small volumes of oxygen introduced into vials of medium at pH 7 prepared under anaerobic conditions reacted with the medium during sterilization by heating, and also raised the redox potential. The partial pressure of oxygen ( pO 2) in the medium, and the redox potential ( E h ) were measured and their effect on the number of spores of Clostridium botulinum type E required to produce growth, and hence on the probability of growth from single spore inocula, was determined. In the presence of a pO 2 of up to 4·5 × 10 −3 atm resulting in an E h of c. + 217 mV, the probability of growth from single spores within 5 days at 20°C was equal to that in strictly anaerobic conditions at an E h of − 400 mV. At pO 2 values of between 5·3 × 10 −3 atm and 8·4 × 10 −3 atm corresponding to E h values of between + 226 mV and + 254 mV an inoculum of between 10 and 1000 spores was required to produce growth and at pO 2 values of between 1·12 × 10 −2 atm,and 1·6 × 10 −2 atm, corresponding to redox potentials of between + 271 mV and + 294 mV, the number of spores required to produce growth was between 2 × 10 4 and > 2 × 10 5. The relationship between pO 2 and E h depends on the chemical nature of a culture medium or food, and in order to assess the probable influence of these parameters on growth of C. botulinum in a medium or a food it is necessary to determine both the redox potential and the partial pressure of oxygen.