Intestinal carriage ofBacillus cereus: faecal isolation studies in three population groups

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Abstract
SUMMARY: The results of examinations of stools forBacillus cereusamong three unrelated groups of individuals are presented. The groups consisted of (1) healthy schoolchildren aged 6–11 years in a rural region of South Africa examined during each of the four seasons of the year; (2) 15 healthy volunteers comprising staff of a London microbiology laboratory and their families examined on each of 3 consecutive weeks; (3) 75 unrelated young children, 2 months to 5 years of age, in a second rural region of South Africa examined during a pilot study of 1 week's duration on the aetiology of rural gastroenteritis. The stools of the last group were submitted as being related to present or recent diarrhoea in the respective children.In group 1,B. cereusisolation rates ranged from 24·3% at the autumn visit to 43% at the summer visit with a significantly higher rate of isolation in the summer than at other seasons of the year(P <0·05).B. cereuswas isolated from 40% of group 2 volunteers on week 1, none on week 2 and 20% on week 3. The organism was detected in the 12 positive specimens at levels of approximately 102/g and constituted 2·5–30% of the total aerobic spore-forming bacillus population in the stools. In group 3,B. cereuswas recovered from 18·7% of the stool samples and was isolated consecutively with other pathogens (entcropathogenicEscherichia coliand rotavirus) on only five occasions. In groups 1 and 3, < 5% of the stools had ‘3+ ‘levels ofB. cereus(> 10 colonies per direct plate culture).B. cereuswas readily isolated from all of 10 food samples, representative of the typical diet of the group 1 individuals, and was present in substantial numbers (104to 5·5 × 106/g) in half of them.The isolation results, supported by serotyping, indicated that carriage ofB. cereusin stools is transient and its presence at any one time reflects solely its intake with foods.