THE EFFECT OF ANTIBACTERIAL DRUGS ON THE WEIGHT OF MICE

Effects of Bifidobacterium animalis subsp. lactis BB-12 and yogurt on mice during oral antibiotic administration

Probiotics have the potential to prevent disruptions to normal gastrointestinal function caused by oral antibiotic use. In this study, we examined the capacity of Bifidobacterium animalis subspecies lactis BB-12 (BB-12) and yogurt, separately and combined, to mitigate the effects of the antibiotic amoxicillin-clavulanate (AMC) on the gut microbiota and metabolomes of C57BL/6 J mice. Male and female mice were administered either BB-12, yogurt, BB-12 in yogurt, or saline for 10 days concurrent with the inclusion of AMC in the drinking water. Male mice exposed to AMC exhibited significant reductions (p<0.05) in body weight over the course of the study compared to sham (no AMC) controls whereas no such effects were observed for female mice. AMC administration resulted in rapid alterations to the intestinal microbiota in both sexes irrespective of BB-12 or yogurt treatment, including significant (p<0.05) losses in bacterial cell numbers and changes in microbial alpha-diversity and beta-diversity in the feces and cecal contents. The effects of AMC on the gut microbiota were observed within one day of administration and the bacterial contents continued to change over time, showing a succession marked by rapid reductions in Muribaculaceae and Lachnospiraceae and temporal increases in proportions of Acholeplasmataceae (day 1) and Streptococcaceae and Leuconostocaceae (day 5). By day 10 of AMC intake, high proportions of Gammaproteobacteria assigned as Erwiniaceae or Enterobacteriaceae (average of 63 %), were contained in the stools and were similarly enriched in the cecum. The cecal contents of mice given AMC harbored significantly reduced concentrations of (branched) short-chain fatty acids (SCFA), aspartate, and other compounds, whereas numerous metabolites, including formate, lactate, and several amino acids and amino acid derivatives were significantly enriched. Despite the extensive impact of AMC, starting at day 7 of the study, the body weights of male mice given yogurt or BB-12 (in saline) with AMC were similar to the healthy controls. BB-12 (in saline) and yogurt intake was associated with increased Streptococcaceae and both yogurt and BB-12 resulted in lower proportions of Erwiniaceae in the fecal and cecal contents. The cecal contents of mice fed BB-12 in yogurt contained levels of formate, glycine, and glutamine that were equivalent to the sham controls. These findings highlight the potential of BB-12 and yogurt to mitigate antibiotic-induced gut dysbiosis.

Maternal-Fetal Exposure to Antibiotics: Levels, Mother-to-Child Transmission, and Potential Health Risks

Due to its widespread applications in various fields, antibiotics are continuously released into the environment and ultimately enter the human body through diverse routes. Meanwhile, the unreasonable use of antibiotics can also lead to a series of adverse outcomes. Pregnant women and developing fetuses are more susceptible to the influence of external chemicals than adults. The evaluation of antibiotic exposure levels through questionnaire surveys or prescriptions in medical records and biomonitoring-based data shows that antibiotics are frequently prescribed and used by pregnant women around the world. Antibiotics may be transmitted from mothers to their offspring through different pathways, which then adversely affect the health of offspring. However, there has been no comprehensive review on antibiotic exposure and mother-to-child transmission in pregnant women so far. Herein, we summarized the exposure levels of antibiotics in pregnant women and fetuses, the exposure routes of antibiotics to pregnant women, and related influencing factors. In addition, we scrutinized the potential mechanisms and factors influencing the transfer of antibiotics from mother to fetus through placental transmission, and explored the adverse effects of maternal antibiotic exposure on fetal growth and development, neonatal gut microbiota, and subsequent childhood health. Given the widespread use of antibiotics and the health threats posed by their exposure, it is necessary to comprehensively track antibiotics in pregnant women and fetuses in the future, and more in-depth biological studies are needed to reveal and verify the mechanisms of mother-to-child transmission, which is crucial for accurately quantifying and evaluating fetal health status.

Intrauterine antibiotic exposure affected neonatal gut bacteria and infant growth speed

Although abundant evidence has suggested that early-life antibiotic exposure was associated with adipogenesis later in life, limited data were available on the effect of intrauterine antibiotic exposure on infant growth and growth speed. Additionally, few studies have investigated the role of the neonatal gut microbiota in the above association. In this study, we examined the association between intrauterine cumulative antibiotic exposure and infant growth and explored the potential role of the neonatal gut microbiota in the association. 295 mother-child pairs from the Shanghai Maternal-Child Pairs Cohort (MCPC) study were included, and meconium samples and infant growth measurements were assessed. Z-scores of length-for-age, weight-for-age (weight-for-age), and body mass index (BMI)-for-age (BMI-for-age) were calculated. Eighteen common antibiotics were measured in meconium. Multivariable linear regression models were applied to test the interrelationships between antibiotic exposure, diversity indicators, and the relative abundance of selected bacterial taxa from phylum to genus levels from least absolute shrinkage and selection operator (LASSO) and infant growth indicators. The detection rates of the 18 antibiotics, except for chlortetracycline, penicillin, and chloramphenicol, were below 10 %. Penicillin was found to be positively associated with infant growth at birth and with growth speed from 2 to 6 months. The Pielou and Simpson indexes were negatively associated with meconium penicillin. Nominally significant associations between penicillin and the relative abundances of several bacterial taxa from the phyla Proteobacteria, Bacteroidetes, and Firmicutes were found. The Pielou and Simpson indexes were also found to be negatively associated with infant growth. Among taxa selected from LASSO regression, the relative abundances of the phyla Actinobacteria and Firmicutes and order Bifidobacteriales were found to be significantly associated with weight and BMI growth speeds from 2 to 6 months. In conclusion, intrauterine antibiotic exposure can affect infant growth. The neonatal gut microbiota might play a role in the abovementioned association.

Testosterone disruptor effect and gut microbiome perturbation in mice: Early life exposure to doxycycline

Veterinary tetracyclines drugs are emerging organic pollutants detected at high concentrations in the urine of school children and a potential public health risk. However, the implications of early-life exposure to tetracyclines on testosterone production, being new endocrine disruptors, remain unknown. We investigated whether the early-life exposure to low-doxycycline, a widely used tetracycline, on mitochondria dysfunction and testosterone disruption in Leydig cells in vitro and in vivo. Next, we determined the mRNA levels of testis cells markers for early-life exposure to low-doxycycline outcomes of testis health in later-life. Finally, we compared the weight gain performance exposed to low- and therapeutic-doses through 15 weeks and examined the role of the microbiota during development. Our results showed doxycycline disturbed steroidogenesis process by mitochondrial dysfunction in mouse Leydig tumor cell line (MLTC-1) cells in vitro. Leydig cells mitochondrial function was disrupted by early-life exposure to low-doxycycline from birth to 49 days, causing testosterone deficiency and decreased quality of the sperm in mice. Early-life exposure to low-doxycycline significantly altered the mRNA levels of key genes in Leydig cells (Cyp11a1, Cyp17a1 and 17β-HSD) and spermatogenic cells (Grfal, Plzf, and Stra8) in later-life in mice. Subchronic low- and therapeutic-doses doxycycline changed gut microbiota differences in diversity reduction and compositional alteration. Moreover, the weight gain effects of doxycycline were only observed in low-dose in male mice. Overall, these results provide insight into the effects of doxycycline on both testis and gut microbiota health. The results provide insight that environmental antibiotics are needed additional research to classify as ECDs.

The Microbiological Memory, an Epigenetic Regulator Governing the Balance Between Good Health and Metabolic Disorders

If the transmission of biological information from one generation to the next is based on DNA, most heritable phenotypic traits such as chronic metabolic diseases, are not linked to genetic variation in DNA sequences. Non-genetic heritability might have several causes including epigenetic, parental effect, adaptive social learning, and influence of the ecological environment. Distinguishing among these causes is crucial to resolve major phenotypic enigmas. Strong evidence indicates that changes in DNA expression through various epigenetic mechanisms can be linked to parent-offspring resemblance in terms of sensitivity to metabolic diseases. Among non-genetic heritable traits, early nutrition could account for a long term deviant programming of genes expression responsible for metabolic diseases in adulthood. Nutrition could shape an inadequate gut microbiota (dysbiosis), triggering epigenetic deregulation of transcription which can be observed in chronic metabolic diseases. We review herein the evidence that dysbiosis might be a major cause of heritable epigenetic patterns found to be associated with metabolic diseases. By taking into account the recent advances on the gut microbiome, we have aggregated together different observations supporting the hypothesis that the gut microbiota could promote the molecular crosstalk between bacteria and surrounding host cells which controls the pathological epigenetic signature. We introduce for the first time the concept of "microbiological memory" as the main regulator of the epigenetic signatures, thereby indicating that different causes of non-genetic heritability can interact in complex pathways to produce inheritance.

Gut Microbiome and Antibiotics

Despite that the human gastrointestinal tract is the most populated ecological niche by bacteria in the human body, much is still unknown about its characteristics. This site is highly susceptible to the effects of many external factors that may affect in the quality and the quantity of the microbiome. Specific factors such as diet, personal hygiene, pharmacological drugs and the use of antibiotics can produce a significant impact on the gut microbiota. The effect of these factors is more relevant early in life, when the gut microbiota has not yet fully established. In this review, we discussed the effect of type and doses of the antibiotics on the gut microbiota and what the major consequences in the use and abuse of these antimicrobial agents.

Regulation of energy balance by a gut-brain axis and involvement of the gut microbiota

Despite significant progress in understanding the homeostatic regulation of energy balance, successful therapeutic options for curbing obesity remain elusive. One potential target for the treatment of obesity is via manipulation of the gut-brain axis, a complex bidirectional communication system that is crucial in maintaining energy homeostasis. Indeed, ingested nutrients induce secretion of gut peptides that act either via paracrine signaling through vagal and non-vagal neuronal relays, or in an endocrine fashion via entry into circulation, to ultimately signal to the central nervous system where appropriate responses are generated. We review here the current hypotheses of nutrient sensing mechanisms of enteroendocrine cells, including the release of gut peptides, mainly cholecystokinin, glucagon-like peptide-1, and peptide YY, and subsequent gut-to-brain signaling pathways promoting a reduction of food intake and an increase in energy expenditure. Furthermore, this review highlights recent research suggesting this energy regulating gut-brain axis can be influenced by gut microbiota, potentially contributing to the development of obesity.

Heterogeneity of the gut microbiome in mice: guidelines for optimizing experimental design

Targeted manipulation of the gut flora is increasingly being recognized as a means to improve human health. Yet, the temporal dynamics and intra- and interindividual heterogeneity of the microbiome represent experimental limitations, especially in human cross-sectional studies. Therefore, rodent models represent an invaluable tool to study the host–microbiota interface. Progress in technical and computational tools to investigate the composition and function of the microbiome has opened a new era of research and we gradually begin to understand the parameters that influence variation of host-associated microbial communities. To isolate true effects from confounding factors, it is essential to include such parameters in model intervention studies. Also, explicit journal instructions to include essential information on animal experiments are mandatory. The purpose of this review is to summarize the factors that influence microbiota composition in mice and to provide guidelines to improve the reproducibility of animal experiments.

Given the unmet need for standardizing the experimental work flow related to gut microbial research in animals, guidelines are required to isolate true effects from confounding factors.

Metabolic and metagenomic outcomes from early-life pulsed antibiotic treatment

Mammalian species have co-evolved with intestinal microbial communities that can shape development and adapt to environmental changes, including antibiotic perturbation or nutrient flux. In humans, especially children, microbiota disruption is common, yet the dynamic microbiome recovery from early-life antibiotics is still uncharacterized. Here we use a mouse model mimicking paediatric antibiotic use and find that therapeutic-dose pulsed antibiotic treatment (PAT) with a beta-lactam or macrolide alters both host and microbiota development. Early-life PAT accelerates total mass and bone growth, and causes progressive changes in gut microbiome diversity, population structure and metagenomic content, with microbiome effects dependent on the number of courses and class of antibiotic. Whereas control microbiota rapidly adapts to a change in diet, PAT slows the ecological progression, with delays lasting several months with previous macrolide exposure. This study identifies key markers of disturbance and recovery, which may help provide therapeutic targets for microbiota restoration following antibiotic treatment.

The potential recovery of the human gut microbiota after an antibiotic treatment, and its effects on our health, are poorly understood. Here, the authors use a mouse model mimicking paediatric antibiotic use to shed new light into these processes.

Antibiotics in early life and obesity

The intestinal microbiota can influence host metabolism. When given early in life, agents that disrupt microbiota composition, and consequently the metabolic activity of the microbiota, can affect the body mass of the host by either promoting weight gain or stunting growth. These effects are consistent with the role of the microbiota during development. In this Perspective, we posit that microbiota disruptions in early life can have long-lasting effects on body weight in adulthood. Furthermore, we examine the dichotomy between antibiotic-induced repression and promotion of growth and review the experimental and epidemiological evidence that supports these phenotypes. Considering the characteristics of the gut microbiota in early life as a distinct dimension of human growth and development, as well as comprehending the susceptibility of the microbiota to perturbation, will allow for increased understanding of human physiology and could lead to development of interventions to stem current epidemic diseases such as obesity, type 1 diabetes mellitus and type 2 diabetes mellitus.

Altering the intestinal microbiota during a critical developmental window has lasting metabolic consequences

Acquisition of the intestinal microbiota begins at birth, and a stable microbial community develops from a succession of key organisms. Disruption of the microbiota during maturation by low-dose antibiotic exposure can alter host metabolism and adiposity. We now show that low-dose penicillin (LDP), delivered from birth, induces metabolic alterations and affects ileal expression of genes involved in immunity. LDP that is limited to early life transiently perturbs the microbiota, which is sufficient to induce sustained effects on body composition, indicating that microbiota interactions in infancy may be critical determinants of long-term host metabolic effects. In addition, LDP enhances the effect of high-fat diet induced obesity. The growth promotion phenotype is transferrable to germ-free hosts by LDP-selected microbiota, showing that the altered microbiota, not antibiotics per se, play a causal role. These studies characterize important variables in early-life microbe-host metabolic interaction and identify several taxa consistently linked with metabolic alterations. PAPERCLIP:

Effects of medicated diet to eradicate Helicobacter spp. on growth, pathology, and infection status in Rag1-/- and nude mice

The use of a commercial 4-drug diet has been shown to eradicate Helicobacter spp. from immunocompetent mice and those with innate immunodeficiencies. However the efficacy of this diet has not been confirmed in mice with altered adaptive immunity. We hypothesized that an 8-wk treatment with medicated diet would eradicate H. hepaticus and H. typhlonius from young naturally infected nude and Rag1 mice lacking functional T cells (Foxn1(nu)) or T and B cells (B6.129S7-Rag1(tm1Mom)/J), respectively. We evaluated helicobacter status, body weight, and gross and histologic changes between medicated and control diet in groups of infected and uninfected mice throughout treatment and at 8 wk after treatment completion. Initial infection status was confirmed by fecal PCR at weaning and 3 wk later, with study initiation in 7-wk-old mice. PCR testing demonstrated that independent of strain and sex, all treated mice tested negative for Helicobacter spp. after 4 wk of treatment and remained negative for the duration of the study. Irrespective of infection status, nude and Rag1 mice fed 8 wk of medicated diet gained less weight than did their untreated controls. Both strains normalized body weight while on control diet for the 8 wk after treatment. Mice fed medicated diet developed severe gastroesophageal hyperkeratosis, suggestive of reduced feed consumption, and enlarged ceca. These conditions improved or resolved after the return to control diet. This report is the first to demonstrate the efficacy and physical effects of providing medicated diet for the eradication of Helicobacter spp. from mice with adaptive immune deficiencies.

Lactobacillus reuteri and Escherichia coli in the human gut microbiota may predict weight gain associated with vancomycin treatment

BACKGROUND

Antibiotics, used for 60 years to promote weight gain in animals, have been linked to obesity in adults and in children when administered during early infancy. Lactobacillus reuteri has been linked to obesity and weight gain in children affected with Kwashiorkor using ready-to-use therapeutic food. In contrast, Escherichia coli has been linked with the absence of obesity. Both of these bacteria are resistant to vancomycin.

OBJECTIVES AND METHODS

We assessed vancomycin-associated weight and gut microbiota changes, and tested whether bacterial species previously linked with body mass index (BMI) predict weight gain at 1 year. All endocarditis patients treated with vancomycin or amoxicillin in our center were included from January 2008 to December 2010. Bacteroidetes, Firmicutes, Lactobacillus and Methanobrevibacter smithii were quantified using real-time PCR on samples obtained during the 4-6 weeks antibiotic regimen. L. reuteri, L. plantarum, L. rhamnosus, Bifidobacterium animalis and E. coli were quantified on stool samples obtained during the first week of antibiotics.

RESULTS

Of the193 patients included in the study, 102 were treated with vancomycin and 91 with amoxicillin. Vancomycin was associated with a 10% BMI increase (odds ratio (OR) 14.1; 95% confidence interval (CI; 1.03-194); P=0.047) and acquired obesity (4/41 versus 0/56, P=0.01). In patients treated with vancomycin, Firmicutes, Bacteroidetes and Lactobacillus increased, whereas M. smithii decreased (P<0.05). The absence of E. coli was an independent predictor of weight gain (OR=10.7; 95% CI (1.4-82.0); P=0.02). Strikingly, a patient with an 18% BMI increase showed a dramatic increase of L. reuteri but no increase of E. coli.

CONCLUSION

The acquired obesity observed in patients treated with vancomycin may be related to a modulation of the gut microbiota rather than a direct antibiotic effect. L. reuteri, which is resistant to vancomycin and produces broad bacteriocins, may have an instrumental role in this effect.

Lactobacillus reuteri and Escherichia coli in the human gut microbiota may predict weight gain associated with vancomycin treatment

Background:

Antibiotics, used for 60 years to promote weight gain in animals, have been linked to obesity in adults and in children when administered during early infancy. Lactobacillus reuteri has been linked to obesity and weight gain in children affected with Kwashiorkor using ready-to-use therapeutic food. In contrast, Escherichia coli has been linked with the absence of obesity. Both of these bacteria are resistant to vancomycin.

Objectives and methods:

We assessed vancomycin-associated weight and gut microbiota changes, and tested whether bacterial species previously linked with body mass index (BMI) predict weight gain at 1 year. All endocarditis patients treated with vancomycin or amoxicillin in our center were included from January 2008 to December 2010. Bacteroidetes, Firmicutes, Lactobacillus and Methanobrevibacter smithii were quantified using real-time PCR on samples obtained during the 4–6 weeks antibiotic regimen. L. reuteri, L. plantarum, L. rhamnosus, Bifidobacterium animalis and E. coli were quantified on stool samples obtained during the first week of antibiotics.

Results:

Of the193 patients included in the study, 102 were treated with vancomycin and 91 with amoxicillin. Vancomycin was associated with a 10% BMI increase (odds ratio (OR) 14.1; 95% confidence interval (CI; 1.03–194); P=0.047) and acquired obesity (4/41 versus 0/56, P=0.01). In patients treated with vancomycin, Firmicutes, Bacteroidetes and Lactobacillus increased, whereas M. smithii decreased (P<0.05). The absence of E. coli was an independent predictor of weight gain (OR=10.7; 95% CI (1.4–82.0); P=0.02). Strikingly, a patient with an 18% BMI increase showed a dramatic increase of L. reuteri but no increase of E. coli.

Conclusion:

The acquired obesity observed in patients treated with vancomycin may be related to a modulation of the gut microbiota rather than a direct antibiotic effect. L. reuteri, which is resistant to vancomycin and produces broad bacteriocins, may have an instrumental role in this effect.

Cecal Enlargement and Microbial Flora in Suckling Mice Given Antibacterial Drugs

Enlargement and microbial colonization of the cecum were examined in neonatal mice suckling mothers drinking either water or an aqueous solution of penicillin. The full ceca increased in weight at the same rate in both drug-treated and control mice during the first 15 to 17 days after birth. Thereafter, cecal weight increased at a greater rate in the drug-treated animals than in the untreated controls. At weaning, the ceca in treated mice were two to three times the size of control organs and remained enlarged as long as penicillin was given. The enlarged ceca did not differ histologically from those in controls. From birth, the cecal microflora in the drug-treated mice differed qualitatively and quantitatively and in colonization pattern from the flora of control mice. The ceca of untreated animals were colonized primarily by large populations of lactobacilli during the first week after birth, small populations of coliforms and enterococci during the second week, and enormous populations of bacteroides and certain gram-negative fusiform-shaped anaerobic bacteria during the third week. In contrast, the organs of the treated mice were populated by large populations of coliforms and enterococci during the first week and enormous populations of clostridia and unusual gram-negative nonsporeforming bacteria during the third week. These large abnormal populations were present in the ceca as they enlarged during the third week after birth in the drug-treated animals. These findings confirm that only certain populations of anaerobic bacteria can act to maintain cecal size in normal animals.

Effect of antibiotics on intestinal absorption in mice

1. The effects of dietary antibiotics (penicillin, neomycin or terramycin) on the absorption of D-glucose, D-galactose, L-arginine or L-histidine by the mouse were investigated by using sacs of entire everted ileum.

2. Compared with the controls, there was generally an increased absorption of all these solutes. Tissue uptake of the solutes remained unaltered. The inward movement of water into the sacs was increased but was generally independent of solute transport.

3. The body-weight decreased slightly and caecal weight increased with penicillin only. The weight of the small intestine decreased with the different antibiotics, and the gut wall became thinner. Faecal fat increased slightly, but not significantly, with neomycin only. Water intake decreased with the different antibiotics.

Effects of neomycin and penicillin administration on mucosal proliferation of the mouse small intestine. With morphological and functional correlations

The effects of an oral neomycin and penicillin regimen on intestinal bacteriology and on morphology and function of the small intestine of mice were investigated. Quantitative and qualitative stool cultures on selective media of the treated animals revealed only growth of yeast organisms. The treated animals developed enlargement of the ceca with fluid contents and watery stools, resembling characteristics of germfree animals. Radioautography with tritiated thymidine revealed an increased epithelial cell migration rate in the mice treated with the antibiotics for 3 to 5 wk. A slight increase in villus height was also noted. The treated male mice showed greater variance than the treated females in epithelial cell migration rates. Histochemical staining reactions showed a decrease in nonspecific esterase and in NADH dehydrogenase activity in the proximal gut of the antibiotic animals. Stains of distal gut and those for acid and alkaline phosphatase, NADPH dehydrogenase, lactic dehydrogenase, and succinic dehydrogenase were similar to the controls. A slight increase in sucrase activity and a slight decrease in lactase activity in the antibiotic animals was observed in contrast to control animals. Germfree mice, however, had greater sucrase and lactase activity. Transport of L-methionine was slightly reduced in the distal segment of the treated animals. Since the direction of these changes is away from the intestinal state observed in germfree animals, they are probably the result of the direct action of the antibiotics on the gut.

Alterations in the mouse cecum and its flora produced by antibacterial drugs

Addition of penicillin, Terramycin, or kanamycin to the drinking water of adult mice rapidly induced in them an enlargement of the cecum. In all animals, this occurred within 12 hr after the beginning of drug administration-the effect being most pronounced with penicillin. The cecums remained enlarged and generally continued to increase in size as long as the antibacterial drugs were administered. The increase in wet weight of the cecums was due primarily to an accumulation of water in the lumens during the first 24-48 hr of drug administration. At that time, there were no detectable histological changes in any case, but the bacteriological picture differed from drug to drug. The cecums were free of bacteria in animals receiving penicillin, fusiform-shaped bacteria and bacteroides were present in those receiving Terramycin, and lactobacilli and bacteroides in those receiving kanamycin. After the initial 48 hr, an abundant and complex secondary microflora developed in all treated animals, its composition being characteristic for each type of antibacterial drug. When penicillin was administered for 2 wk, the cecal weights and microbial populations did not return to normal levels for over 14 days after discontinuance of the drug. This recovery period could be shortened to 10 days by giving the mice food contaminated with cecal homogenates prepared from normal animals. A period of 7 or 8 days was required for the cecal weights and microflora to reach normal levels when the administration of penicillin lasted only 24 hr; this period could not be shortened by giving the animals contaminated food. The effects of drugs on the size and bacterial contents of the cecum have been discussed in the light of earlier findings concerning the characteristics of the huge cecums uniformly found in germfree mice. Taken together, these observations support the hypothesis that certain elements of the intestinal microflora-not yet completely identified-play an essential role in maintaining the integrity of the water-transport mechanism in the intestinal epithelium.

Coliform bacteria in the intestine of mice

Mice of the NCS and NCS-D colonies, bred at the Rockefeller University, harbored in their intestine an endemic strain of slow lactose-fermenting Escherichia coli 081+/-: :H21 serotype. In addition, NCS mice have recently acquired E. coli 0109+/-:K48:H14. Both strains persisted during the period of observation, whereas they were not encountered in the feces of mice from two other colonies. Other coliform strains encountered were more transient in their occurrence. Since strains of E. coli 081+/-: :H21 and 0109+/-:K48:H14 are extremely uncommon in human beings, it seems probable that they possess specificity for the mouse host.

The influence of endotoxin administration on the nutritional requirements of mice

Albino mice lose weight within 24 hours following administration of bacterial endotoxin. The initial weight loss is proportional to the dose of endotoxin injected only when this dose is very small. The loss during the 1st day reaches a maximum with 10 to 30 microg of endotoxin; larger doses increase the duration of the overall effect. The rate at which mice regain weight after administration of endotoxin is markedly influenced by the composition of the diet. Recovery was rapid and complete within a few days when the animals were fed commercial pellets or a semisynthetic diet containing casein. In contrast, recovery was slow and incomplete when wheat gluten was used instead of casein in the diet. The deleterious effect of the gluten diet was less marked in older than in younger animals, probably because the latter have less exacting nutritional requirements. It was postulated that the failure of endotoxin-treated mice to regain weight when fed the gluten diet was due to the fact that this protein is low in certain amino acids. In fact, rapid and complete recovery from the weight loss uniformly occurred when the gluten diet was supplemented with proper amounts of lysine and threonine. The composition of the diet did not influence the extent of the initial loss of weight caused by endotoxin, nor did it prevent the animals from developing tolerance to this substance.

Colonization of the mouse intestine with Escherichia coli

Young albino Swiss mice, of the NCS and NCS-D colonies, proved highly susceptible to the establishment of intestinal infection with an enteropathogenic strain of E. coli administered per os or by stomach tube. The period of highest susceptibility was rather short, extending from the day of birth to approximately 2 weeks of age. Adult NCS and NCS-D mice failed to become experimentally colonized with E. coli, even when large doses were administered per os on 3 consecutive days. The extent of colonization of the various parts of the gastrointestinal tract was related to the size of the infective dose. Many of the young mice died within 2 to 3 days following per os infection with large doses of enteropathogenic E. coli. However, practically all the animals which survived cleared their intestinal infection at approximately the same age. For example, in mice infected with 23 x 10(6) bacteria, colonization of the intestinal tract usually came to an abrupt end when the animals were 24 to 28 days old, irrespective of the age at which they had been infected. There is suggestive evidence that the acquisition of resistance with age, and the ability of adult animals to control the intestinal infection, are related to the development in the gastrointestinal tract of a microbiota which is antagonistic to E. coli.