Germfree animals in surgical research

Gut Microbial Influences on the Mammalian Intestinal Stem Cell Niche

The mammalian intestinal epithelial stem cell (IESC) niche is comprised of diverse epithelial, immune, and stromal cells, which together respond to environmental changes within the lumen and exert coordinated regulation of IESC behavior. There is growing appreciation for the role of the gut microbiota in modulating intestinal proliferation and differentiation, as well as other aspects of intestinal physiology. In this review, we evaluate the diverse roles of known niche cells in responding to gut microbiota and supporting IESCs. Furthermore, we discuss the potential mechanisms by which microbiota may exert their influence on niche cells and possibly on IESCs directly. Finally, we present an overview of the benefits and limitations of available tools to study niche-microbe interactions and provide our recommendations regarding their use and standardization. The study of host-microbe interactions in the gut is a rapidly growing field, and the IESC niche is at the forefront of host-microbe activity to control nutrient absorption, endocrine signaling, energy homeostasis, immune response, and systemic health.

The piglet as a model for B cell and immune system development

The ability to identify factors responsible for disease in all species depends on the ability to separate those factors which are environmental from those that are intrinsic. This is particularly important for studies on the development of the adaptive immune response of neonates. Studies on laboratory rodents or primates have been ambiguous because neither the effect of environmental nor maternal factors on the newborn can be controlled in mammals that: (i) transmit potential maternal immunoregulatory factors in utero and (ii) are altricial and cannot be reared after birth without their mothers. Employing the newborn piglet model can address each of these concerns. However, it comes at the price of having first to characterize the immune system of swine and its development. This review focuses on the porcine B cell system, especially on the methods used for its characterization in fetal studies and neonatal piglets. Understanding these procedures is important in the interpretation of the data obtained. Studies on neonatal piglets have (a) provided valuable information on the development of the adaptive immune system, (b) lead to important advances in evolutionary biology, (c) aided our understanding of passive immunity and (d) provided opportunities to use swine to address specific issues in veterinary and biomedical research and immunotherapy. This review summarizes the history of the development of the piglet as a model for antibody repertoire development, thus providing a framework to guide future investigators.

Isolator and other neonatal piglet models in developmental immunology and identification of virulence factors

The postnatal period is a ‘critical window’, a time when innate and passive immunity protect the newborn mammal while its own adaptive immune system is developing. Neonatal piglets, especially those reared in isolators, provide valuable tools for studying immunological development during this period, since environmental factors that cause ambiguity in studies with conventional animals are controlled by the experimenter. However, these models have limited value unless the swine immune system is first characterized and the necessary immunological reagents developed. Characterization has revealed numerous features of the swine immune system that did not fit mouse paradigms but may be more generally true for most mammals. These include fetal class switch recombination that is uncoupled from somatic hypermutation, the relative importance of the molecular mechanisms used to develop the antibody repertoire, the role of gut lymphoid tissue in that process, and the limited heavy chain repertoire but diverse IgG subclass repertoire. Knowledge gained from studies of adaptive immunity in isolator-reared neonatal pigs suggests that isolator piglets can be valuable in identification of virulence factors that are often masked in studies using conventional animals.

Experimental Shigella infections. V. Studies in germ-free guinea pigs

Formal, Samuel B., (Walter Reed Army Institute of Research, Washington, D. C.), Gustave Dammin, Helmuth Sprinz, Donald Kundel, Herman Schneider, Richard E. Horowitz, and Martin Forbes. Experimental shigella infections. V. Studies in germ-free guinea pigs. J. Bacteriol. 82:284-287. 1961.-Germ-free guinea pigs succumb after oral infection with Shigella flexneri serotype 2a; they survive a similar challenge with either a strain of Escherichia coli or a culture of lactobacillus. Animals monocontaminated with E. coli survive, whereas those monocontaminated with lactobacilli succumb to subsequent challenge with dysentery bacilli. Prior subcutaneous inoculation of heat-killed S. flexneri 2a does not render germ-free guinea pigs resistant to the fatal infection with viable dysentery bacilli.

Results of experimental intestinal strangulation obstruction in germfree rats

Experimental low ileal strangulation obstruction has been produced in germfree and conventional rats. The mean survival time was 240 hours in the germfree rats and 44 hours in the conventional controls. 4 of the 10 germfree rats survived 15 or more days, whereas the 10 conventional animals were all dead within 2½ days. The strangulation obstruction fluid from the germfree animals was sterile and non-toxic when injected into mice even after a fourfold concentration. The same fluid from the conventional animals contained a great number of microorganisms and caused death within 24 hours when injected intraperitoneally into mice.

Rearing of germfree and monocontaminated chicks in rigid plastic isolators

A Plexiglas isolator for rearing germfree vertebrates is described. Plastic components were precut and finished by a Plexiglas supplier. This equipment is relatively inexpensive; moreover, neither special facilities nor skills are required in their construction. Advantages of this type of isolator are: readily dismantled for cleaning, durable, excellent visibility of the interior, and minimal maintenance. In 30 separate groups of animals, 27 of these yielded germfree chicks. Many of these chicks were reared germfree for 4 weeks; and several were maintained for about 2 months, without microbial contamination. Pure cultures of Candida albicans, Streptococcus faecalis, and Clostridium perfringens were established as monocontaminations in the intestinal tracts of chickens. In contrast, Alcaligenes faecalis ATCC 9220 failed to grow in the gut of chicks, following peroral administration of this organism. All chicks described were employed on other experiments, and were killed for various assays at times specified.

Germfree animals and technics in surgical research

Germfree animals have been reared to a size, weight, and age permitting the performance of major surgical procedures and the pursuit of a variety of surgical research problems. Germfree dogs have been maintained in the isolator system through three generations, indicating that life, reproduction, and growth are all possible in the absence of microbial contamination. The value of the germfree approach to surgical problems has been utilized in studies of a variety of gastrointestinal problems, shock, cancer, immunology, burns, wound healing, and in direct patient application. Patients have been maintained in isolator environments for prevention of infection, for operative procedures, for treatment of extensive burns, and for management of immune-suppressed individuals. We conclude that germfree animals and germfree technics provide a valuable addition to the armamentarium of the surgeon in both research and clinical applications.

The role of the microbial flora in uremia. I. Survival times of germfree, limited-flora, and conventionalized rats after bilateral nephrectomy and fasting

Germfree rats were used in 3 experiments to study the effects of the microbial flora on survival time after acute uremia produced by a one-stage bilateral nephrectomy. Germfree rats, limited-flora rats, and conventionalized rats (all maintained continuously in isolators) were subjected to nephrectomy or to sham nephrectomy, deprived of food and water until they died, respectively, of uremia or of starvation, and their survival times compared. To establish a limited defined flora in advance of nephrectomy, germfree rats were either monocontaminated (Staphylococcus albus), dicontaminated (S. albus and Proteus mirabilis) or tetracontaminated (S. albus, S. faecalis, P. mirabilis, and E. coli); to conventionalize germfree rats, they were exposed to the mixed microbial flora contained in the cecal contents of ordinary rats, which was the source of the aforementioned bacteria and which included other uncharacterized microorganisms as well. The intestine of all rats with a limited flora persisted in a morphologic state that was virtually no different from that of the germfree rat, including the presence of an enlarged, thin-walled cecum; by contrast, the intestine of the conventionalized rats permanently assumed the morphological characteristics of ordinary, open-laboratory rats with the cecum reduced to normal size. After nephrectomy and food and water deprivation (death from anuria): (a) All germfree rats but one outlived their conventionalized counterparts in each of the 3 experiments; the 21 germfree rats (127 hr) lived, on the average, 2 days longer than did the 24 conventionalized rats (75 hr). No sex difference was demonstrated. (b) The rats with a limited flora died correspondingly sooner as the complexity of their flora increased; survival time of the tetracontaminated rats was significantly shorter than that of the germfree rats, and statistically no different from that of the conventionalized rats. After sham nephrectomy and food and water deprivation (delayed death from starvation): (a) All rats, irrespective of microbial status or sex, outlived their fasting nephrectomized partners. The conventionalized rats endured starvation approximately 2.5 wk longer than they did anuria and the germfree rats 1 wk longer. (b) All conventionalized rats, both male and female, outlived their respective germfree counterparts by about 1 wk. (c) All males, irrespective of microbial status, survived longer than did the females; the average difference was 4 days. The differences in tolerance to anuria or starvation did not correlate with initial body weight or rate of weight loss.

The response of the lymphatic tissue to the microbial flora. Studies on germfree mice

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Vitamin A deficiency in the germ-free rat

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The hormonal induction of a vaginal leukocytic exudate in the germ-free mouse

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