The findings to be reported in this and the following papers reveal that mice and other mammals normally harbor an extensive bacterial flora not only in the large intestine, b u t also in the stomach and small intestine. Although this flora plays an essential role in the development and well being of its host, its exact composition is not known. In fact, several of its most important and numerous components are usually overlooked in bacteriological studies because they have exacting g r o w t h requirements, and because their susceptibility to the antagouistic activity of other microbial species makes it difficult to cultivate them in vitro.We shall describe in the present paper: (a) the methods used in our laboratory for quantitative bacteriological studies of the gastrointestinal tract; and (b) the development of the gastrointestinal flora as observed in newborn mice until the time of weaning. Materials and MethodsExperimental Animals.--Extensive studies of the gastrointestinal flora have been carried out during the past 6 years with socalled Swiss mice of the NCS colony, maintained in our laboratory under the conditions described earlier (1-3); mice from other colonies, raised under conventional conditions, were also used for comparative studies.The animals were housed, and allowed to mate, in stainless steel cages, with autoclaved wood shavings as litter. The drinking water, given ad lib., was acidified with HC1 to control bacterial contamination as described earlier.In certain experiments, the same end was achieved by adding an organic silver compound in a dilution of 1 part of silver per million. The food also given ad lib. consisted either of pasteurized pellets (supplied by Dietrich and Gambrill, Frederick, Maryland) or of a semisynthetic complete diet containing 15 per cent casein (described in reference 4). It is worth emphasizing that both the pellets and the casein diets had been so treated as to eliminate all bacterial contaminants except a few spores.Preparation of Specimer~ for Bacteriological Examination.--Stool specimens were collected from mice on sterile paper between 9:00 a.m. and 10:30 a.m. Approximately 0.1 gm of stool was emulsified in 5 ml of sterile diluent (charcoal water) by 4 minutes agitation on a mechanl-
Several species of animals have been raised and made to reproduce under germfree conditions. While the animals so produced seem to have a normal fife span, they exhibit histological, anatomical, and physiological characteristics , . J
Comparative studies of albino mice obtained from various colonies have revealed that the so called indigenous (or normal) microbiota of these animals exerts a profound influence on their rate of growth, their efficiency in the utilization of food, and their resistance to infection, toxic substances, and other stressful agencies (1-4). Indeed, many attributes of mice which are characteristic of the colonies from which the animals were derived are in reality determined not by genetic endowment, but by the microbiota prevailing in the colony. The very statement of this fact illustrates the ambiguity of the phrase "normal microbiota". This phrase merely denotes a multiplicity of microbial types which happen to be associated with a given animal population, but it does not imply that such organisms are necessarily present in other populations of the same animal species. As we shall see later, the same kind of ambiguity applies to the phrase normal microbiota when applied to man.The study of the intestinal bacterial flora has necessitated the development of special bacteriological techniques, designed for the quantitative enumeration of bacterial types which are extremely abundant in vivo, but which commonly fail to grow on the usual culture media under aerobic conditions. These techniques, which are described in the preceding paper, have enabled us to follow the trend of the bacterial population in the gastrointestinal tract of mice from the time of birth (5).In the present paper, we shall focus attention on some unexpected findings concerning the composition and distribution of the indigenous flora in adult animals. We shall show in particular that (a) the whole gastrointestinal tract harbors throughout life an abundant bacterial flora, the composition of which is characteristic for each section of the tract; and (b) some bacterial species are intimately associated with the wall of the various organs.
As commonly used, the phrase "early influences" denotes the conditioning of behavior by the experiences of early life. Early experiences, however, do more than condition behavioral patterns; they also affect, profoundly and lastingly, other biological characteristics such as initial growth rate, efficiency in the utilization of food, anatomic structures, physiologic attributes, maximum adult size, resistance to infection, response to various forms of stimuli, in brief almost every phenotypic expression of the adult.Epidemiologic evidence strongly suggests that some of the most important medical problems in underprivileged countries (and in prosperous ones as well) have their origin in environmental influences that affect human beings during the formative phases of their prenatal and neonatal development. Many effects of such early influences appear irreversible.Among early influences, the most extensively studied so far are those assodated with the nutritional state. Reviews of the literature on this topic will be found in references 1-8.The lasting character of the biological effects of early nutritional influences is strikingly illustrated in the results of investigations carried out in England during the 1960's by . These investigators compared the growth rate of rats suckled in small litters (3 young per lactating female) with that of comparable animals suckled in large litters (18 young per lactating female). They found that the rats of the latter group (large litters) became much smaller adults than those of the former group, even though the animals of both groups were given the same diet after weaning. An obvious reason for this finding is that the animals raised in small litters enjoyed a nutritional advantage during the lactation period. As McCance and Widdowson pointed out, however, other factors may have played a role in the difference between
The oral administration to mice of certain antibacterial drugs brings about profound and lasting changes in their fecal flora; the duration of these changes is conditioned by the composition of the diet fed the animals (1). It will be shown in the present paper that the growth rates of mice and some at least of their nutritional requirements are also affected by the administration of antibacterial drugs. Materials and MethodsThe two colonies of Swiss mice, NCS and Ha/ICR, used in the present study, as well as the experimental diets, were described in preceding papers (1, 2).All experiments to be reported here were carried out with mice housed individually in stainless steel cages, with wire grids. All NCS mice were of the same age at the beginning of each experiment (30 to 33 days old); within this age group, they were selected for uniformity in weight (within 18 to 22 gin). These requirements for age and initial weight could not be fulfilled for mice of the Ha/ICR colony because their exact date of birth was not known, and also because they were less uniform than NCS mice at the time of receipt from the producer.All animals were weighed individually between 9 a.m. and 10 a.m. This detail is of importance since most mice progressively lose weight during the daylight hours as a result of the fact that they do not consume any significant amount of food or water between 8 a.m. and 8 p.m. (2). The results presented in the figures correspond to arithmetic averages for 5 to 10 mice. RESULTS Effect of Antibacterial Drugs on the Weight Gain of NCS Mice Fed a DietDeficient in Lysine and Threonine.--Purified wheat gluten is deficient in several amino acids, particularly in lysine and threonine; in consequence, diets made from this protein usually do not permit good growth unless adequately supplemented. This is true for ordinary Swiss mice as well as for other types of experimental animals. However, we have consistently observed in many different experiments carried out over the past four years that NCS mice gain weight
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