A carcinogenicity study of instant coffee in Swiss mice.

Commercially available regular instant coffee was given in the diet to barrier-maintained, specified pathogen-free Swiss mice for 2 yr. Groups of 150 males and 150 females were fed diets containing 10, 25 or 50 g instant coffee powder/kg. The animals had already been exposed to coffee in utero. Coffee increased the energy expenditure of the animals as shown by increased daily calorific intake and depressed growth. The overall tumour incidence was inversely correlated to the coffee intake, and no unusual tumour or site of origin was found. The most frequent neoplasms were lymphosarcomas, bronchiolo-alveolar adenomas and adenocarcinomas, as well as hepatocellular adenomas. The incidence of total neoplasms (benign and malignant) decreased from 70.6 and 56.8% in control males and females, respectively, to 34.8 and 36.2%, respectively, in the high-dose group. This decrease, which was essentially due to a reduction in the number of lymphosarcomas and hepatocellular adenomas, was associated with a slower growth rate. The number of leiomyomas in the uterus was slightly increased due to coffee intake as shown by the analysis of positive trend (P less than or equal to 0.05). However, the incidence of this benign tumour was very low; 2.72% of mice affected in the high-dose group, 1.37% in the low-dose group and 0% in the control and medium-dose groups. From this study it is concluded that instant coffee did not increase the incidence of malignant neoplasms in mice when fed at dietary levels of up to 5% for 2 yr.

Barrier effect of Bifidobacterium longum on a pathogenic Escherichia coli strain by gut colonization in the germ-free rat.

The predominance of Bifidobacteria in normal breast-fed babies is well established. Even under unfavourable hygienic conditions of delivery and during the breast-feeding period Bifidobacteria develop and colonize the intestinal tract at high concentrations. In the present study we investigated the interaction between Bifidobacterium longum and a pathogenic E. coli strain in the germ-free rat. Sequential counts of the two bacterial strains allowed their proliferation to be followed. Electron microscopic as well as light microscopic examinations of selected intestinal mucosa segments revealed minor morphological changes. Bifidobacterium completely protected the rats against mortality from a consecutive infection with E. coli. Repeated inoculation of Bifidobacteria even decreased and kept down the initial E. coli population. Thus it appears that the germ-free rat is an appropriate model to study the development and interaction of both bacterial species and that the sequence of inoculation is most important.