Defined conditions for synthesis of Bacillus cereus enterotoxin by fermenter grown cultures

Abstract

B. cereus has been recognized as the causative agent of a relatively mild form of intestinal illness, involving diarrhea and abdominal pain, and also of a more severe illness with vomiting as the primary symptom. There is some evidence that the strains responsible for the milder, 'classic' food poisoning syndrome can be separated from those causing the more severe symptoms by serotyping flagellar antigens. In recent years B. cereus has been shown to produce an extracellular factor that induces fluid accumulation in the ligated ileal loop assay in rabbits, evokes a dermal necrotic reaction in guinea pigs, and increases vascular permeability in rabbits. This factor has been shown to meet two of the three experimental criteria established by Bonventre et al. to determine that a toxin acts directly on the gastrointestinal tract and is therefore referred to as an enterotoxin. A strain of B. cereus produced high levels of enterotoxin when grown in a semidefined medium in a laboratory scale fermenter. The optimum conditions for enterotoxin synthesis by cultures grown in this medium, which contained Casamino Acids and yeast extract, were found to be: inoculation of vigorously growing culture at the 1% level, addition of glucose at a concentration of 1%, control of culture pH at 8.0,incubation at 32°C, use of a moderate stirring rate, and addition of air at low flow rates to minimize foaming. The enterotoxin yield in fermenter grown cultures was approximately 20 to 50 times higher than the yield obtained in shake flask cultures.