Consumption by healthy adults of pasteurized milk with a high concentration of Bacillus cereus: A double-blind study

Abstract

A double-blind experiment with 34 healthy human volunteers, aged between 20 and 60 years, was conducted to obtain information about the allowable concentration of B. cereus in pasteurized milk. During a period of 3 weeks the subjects were exposed to B. cereus naturally present in pasteurized milk following storage for 3 to 14 days at 7.5°C. Of 259 milk exposures, gastrointestinal complaints were observed in 18 cases. According to total numbers of B. cereus ingested per exposure the complaints per number of exposures were distributed as follows: < 106; 5 in 132; 106 to 107:2 in 32; 107 to 108: 2 in 26; and > 108: 9 in 69. Symptoms, however, were not typical of those caused by B. cereus. There was a weak significance (P ≤ 0.1) for symptoms when >108 B. cereus cells were ingested. Milk with 106 to 107 B. cereus cells per ml showed a very low diarrheal enterotoxin titer. Pure cultures of B. cereus strains isolated from samples with high B. cereus concentrations also showed a low production of enterotoxin. It can be concluded that for healthy adults the probability of become diseased from cold-stored pasteurized milk is small. From the results no evidence is obtained that B. cereus concentrations less than 105/ml will cause intoxication.