Growth and heat resistance of clostridium sporogenes PA 3679 spores heated and recovered in acidified media

Abstract

The effect of subculture medium composition (pH, type of acidulant, presence of EDTA) on the germination of spores of Clostridium sporogenes PA 3679, both with and without heat treatment in phosphate buffer (30 s at 125°C), was studied. Additionally, the effect of the heating medium substrate and pH and subculture medium pH and composition on the heat resistance of the spores was evaluated. The results indicate that the pH of the recovery medium and the type of acidulant have significant effects (P ≤ 0.05) on counts of PA 3679. Adding EDTA only increases inhibition of this microorganism when the pH is near neutral. For a given pH level, citric acid provided greater inhibiting power than glucono-δ-lactone, although the percentage of undissociated acid was less for citric acid. No growth was observed at pH 5.7, although in the case of glucono5-lactone sporadic colony development was seen in some plates. The pH of the heating medium acidified with glucono-δ- lactone did not affect the heat-resistance parameters (D and z) of spores heated to temperatures between 121 and 140°C in relation to the unacidified extract. Nor did we see any significant influence of the composition and pH of the recovery medium on these heatresistance parameters when comparing the results with those obtained using the usual recovery medium. Copyright © International Association of Milk, Food and Environmental Sanitarians.