Immunological response of mice to members of the autochthonous intestinal microflora

Based on agglutination, complement fixation, bactericidal, and opsonization tests, it is evident that suspensions of a Bacteroides sp. isolated from the mouse intestine and given by parenteral routes do not initiate antibody formation in mice. Rats also respond poorly to the antigenic stimulus. In contrast, suspensions of other bacterial species isolated from the rodent intestine are highly immunogenic. Furthermore, high titers of antibody are produced in rabbits, guinea pigs, and sheep after parenteral injection of the Bacteroides suspensions. Marked differences in the absolute and relative numbers of Bacteroides in the intestinal contents of rodents and the latter three animal species have been demonstrated. It is proposed that the immunological unresponsiveness of rodents to this organism is related to its existence as a member of the autochthonous microflora in these animals.

Changes in the mouse intestinal microflora during weaning: role of volatile fatty acids

The influence of volatile fatty acids on the ecology of the bacterial flora of the mouse intestinal tract has been studied in three situations where large fluctuations in the composition of the microflora have been observed. Young mice were shown to ingest solid food particles when 11 days old; this correlated with the appearance of strictly anaerobic fusiform bacilli in the intestinal lumen and a 10,000-fold decrease in numbers of coliform bacilli. Over the same period, volatile fatty acids were shown by gas-liquid chromatography to appear in the intestinal content. It is suggested that the fusiform bacilli are responsible for the presence of the volatile acids (especially butyric acid) which exert an inhibitory effect on the coliform bacteria, resulting in the decline in numbers. When germ-free mice are placed in a specific pathogen-free mouse colony, changes in the intestinal flora occurred which were similar to those observed in the young mice approaching weaning. Once again, the decline in the coliform population correlated with the appearance of significant levels of butyric acid in the large intestine. In a further series of experiments, mice were fed penicillin and levels of the intestinal fatty acids were measured. The antibiotic eliminated the anaerobic fusiforms from the intestine, resulting in the disappearance of significant levels of butyric acid and a million-fold increase in the numbers of coliform bacilli.

Preweaning growth of inbred, F 1 hybrid, and random-bred mice as a measure of mother's lactation

A cross-fostering experiment was performed in which inbred and random-bred mothers suckled three groups of young: inbred (the SWR strain), F1hybrid (SWR × C3H), and random-bred (originally synthesized from SWR, C3H, CBA and C57BL). Two inbred mothers and one random-bred mother were placed in each of 43 cross-fostering sets, and each mother suckled two of her own young and two from each of the other two mothers. Body weights of young were recorded individually at birth and at 12 days.In 12-day weight and gain from birth to 12 days, differences among the three groups of young and differences between inbred and random-bred mothers were significant (P < 0.01). Although the ratios of the between-dam to within-dam mean squares in log scale varied among nine mother-young subgroups, the differences between any pair of these ratios were statistically insignificant. It was therefore concluded that in detecting lactation differences among mothers the value of a given type of young was not different between inbred and random-bred mothers and that as a means of detecting lactation differences among random-bred mothers, inbred and F1hybrid young did not appear to offer any substantial advantage over random-bred young.

The mouse intestinal microflora with emphasis on the strict anaerobes

The various components of the intestinal microflora in the mouse become established according to a definite time sequence; the strict anaerobes are the last groups of bacteria to reach their maximum population levels, 14-16 days after birth. The multiplication of these strict anaerobes in the mouse intestine seems to depend upon the prior multiplication of other bacterial species, and coincides with the ingestion of food other than maternal milk. These two conditioning factors may correspond to the establishment of a suitably reduced Eh potential and to the provision of certain metabolites. Once established, the strict anaerobes constitute by far the largest percentage of the total intestinal microflora; most of them are associated in a viable form with the mucosa. In normal animals they persist at very high levels throughout the life span. However, their populations can be drastically reduced by dietary manipulation of the animal, by administration of vancomycin, or by certain disease processes of the intestine. The strict anaerobic bacteria seem to play an important, and perhaps essential role in the maintenance of the anatomic structures and physiological functions of the intestine. They also seem to hold in check several species of intestinal bacteria, in particular the coliform bacilli.