Occurrence of necrotizing enterocolitis may be dependent on patterns of bacterial adherence and intestinal colonization: studies in Caco-2 tissue culture and weanling rabbit models

Gram-Negative Colonization and Bacterial Translocation Drive Neonatal Sepsis in the Indian Setting

BACKGROUND

The gut microbiota, comprising billions of microorganisms, plays a pivotal role in health and disease. This study aims to investigate the effect of sepsis on gut microbiome of neonates admitted to the Neonatal Intensive Care Unit.

METHODS

A prospective cohort study was carried out in the NICU of tertiary care hospital in Karnataka, India, from January 2021 to September 2023. Preterm neonates with birth weight < 1500 g and gestational age < 37 weeks were recruited, excluding those with congenital gastrointestinal anomalies, necrotizing enterocolitis, or blood culture-negative infections. The study population was divided into three groups: healthy neonates (Group A), neonates with drug-sensitive GNB sepsis (Group B), and neonates with pan drug-resistant GNB sepsis (Group C). Stool samples were collected aseptically, snapped in liquid nitrogen, and stored at -80⁰C for extraction of DNA and microbiome analysis.

RESULTS

The gut microbiota of healthy neonates (Group A) was dominated by Proteobacteria (24.04%), Actinobacteria (27.13%), Firmicutes (12.74%), and Bacteroidetes (3%). Predominant genera included Bifidobacterium (55.17%), Enterobacter (12.55%), Enterococcus (50.69%), Streptococcus (7.92%), and Bacteroides (3.58%).Groups B and C, the microbiota exhibited higher Proteobacteria abundance (57.16% and 66.58%, respectively) and reduced diversity of beneficial bacteria. Notably, the presence of sepsis was associated with an increase in pathogenic bacteria and a decrease in beneficial commensal bacteria.

CONCLUSION

Neonates with sepsis exhibited significant gut microbiome dysbiosis, characterized by increased Proteobacteria and reduced beneficial bacteria diversity. These findings highlight the potential of microbiome profiling as a diagnostic tool and underscore the importance of gut microbiota modulation in managing neonatal sepsis.

The neonatal gut microbiome and global health

The role of gut microbiome in health, a century-old concept, has been on the center stage of medical research recently. While different body sites, disease conditions, and populations have been targeted, neonatal and early infancy appear to be the most suitable period for such interventions. It is intriguing to note that, unlike traditional use in diarrhea and maintenance of gastrointestinal health, microbiome-mediating therapies have now addressed the most serious medical conditions in young infants such as necrotizing enterocolitis and neonatal sepsis. Unfortunately, almost all new endeavors in this space have been carried out in the Western world leaving behind millions of neonates that can benefit from such manipulations while serving as a large resource for further learning. In this review, an attempt has been made to quantify the global burden of neonatal morbidity and mortality, examples presented on interventions that have failed as a result of drawing from studies conducted in the West, and a case made for manipulating the neonatal gut microbiome to address the biggest killers in early life. A brief comparative analysis has been made to demonstrate the differences in the gut microbiota of North and South and a large clinical trial of synbiotics conducted by our group in a South Asian setting has been presented. Although challenging, the value of conducting such global health research is introduced with an intent to invite medical scientists to engage in well-planned, scientifically robust research endeavors. This can bring about innovation while saving and serving the most vulnerable citizens now and protecting them from the negative health consequences in the later part of their lives, ultimately shaping a resilient and equitable world as pledged by 193 United Nations member countries in 2015.

Animal models of necrotizing enterocolitis

Background

Necrotizing enterocolitis (NEC) is one of the leading causes of death in premature infants. To determine the factors present in the disease that lead to increased morbidity and mortality, manipulation of variables that are shown to have a positive response has been tested using various animal models. Testing and manipulation of these variables are unwarranted in humans due to regulatory health standards.

Methods

The purpose of this review is to provide an update to previous summaries that determine the significance of animal models in studying the mechanisms of NEC. A large variety of animal models including rats, mice, rabbits, piglets, nonhuman primates, and quails have been described in literature. We reviewed the reported animal models of NEC and examined the pros and cons of the various models as well as the scientific question addressed.

Results

The animals used in these experiments were subject to gavage feeding, hypoxia, hypothermia, oxygen perfusion, and other methods to induce the disease state. Each of these models has been utilized to show the effects of NEC on the premature, undeveloped gut in animals to find a correlation to the disease state present in humans. We found specific advantages and disadvantages for each model.

Conclusions

Recent advances in our understanding of NEC and the ongoing therapeutic strategy developments underscore the importance of animal models for this disease.

Therapeutic Microbiology: The Role of Bifidobacterium breve as Food Supplement for the Prevention/Treatment of Paediatric Diseases

The human intestinal microbiota, establishing a symbiotic relationship with the host, plays a significant role for human health. It is also well known that a disease status is frequently characterized by a dysbiotic condition of the gut microbiota. A probiotic treatment can represent an alternative therapy for enteric disorders and human pathologies not apparently linked to the gastrointestinal tract. Among bifidobacteria, strains of the species Bifidobacterium breve are widely used in paediatrics. B. breve is the dominant species in the gut of breast-fed infants and it has also been isolated from human milk. It has antimicrobial activity against human pathogens, it does not possess transmissible antibiotic resistance traits, it is not cytotoxic and it has immuno-stimulating abilities. This review describes the applications of B. breve strains mainly for the prevention/treatment of paediatric pathologies. The target pathologies range from widespread gut diseases, including diarrhoea and infant colics, to celiac disease, obesity, allergic and neurological disorders. Moreover, B. breve strains are used for the prevention of side infections in preterm newborns and during antibiotic treatments or chemotherapy. With this documentation, we hope to increase knowledge on this species to boost the interest in the emerging discipline known as "therapeutic microbiology".

A randomized synbiotic trial to prevent sepsis among infants in rural India

Sepsis in early infancy results in one million annual deaths worldwide, most of them in developing countries. No efficient means of prevention is currently available. Here we report on a randomized, double-blind, placebo-controlled trial of an oral synbiotic preparation (Lactobacillus plantarum plus fructooligosaccharide) in rural Indian newborns. We enrolled 4,556 infants that were at least 2,000 g at birth, at least 35 weeks of gestation, and with no signs of sepsis or other morbidity, and monitored them for 60 days. We show a significant reduction in the primary outcome (combination of sepsis and death) in the treatment arm (risk ratio 0.60, 95% confidence interval 0.48-0.74), with few deaths (4 placebo, 6 synbiotic). Significant reductions were also observed for culture-positive and culture-negative sepsis and lower respiratory tract infections. These findings suggest that a large proportion of neonatal sepsis in developing countries could be effectively prevented using a synbiotic containing L. plantarum ATCC-202195.

Probiotics and prebiotics in neonatal necrotizing enterocolitis: New opportunities for translational research

Neonatal necrotizing enterocolitis (NEC) in premature infants has been recognized as a defined disease entity for at least four decades. Although survival has increased due to the advent of more sophisticated intensive care, incidence and long term health impacts due to NEC remain unchanged and no preventive therapy is currently available. Different probiotic strains of bacteria have been examined in their ability to prevent NEC with varied but encouraging results. Undigestable prebiotic sugars known to promote the growth of probiotic bacteria in the colon have been used in neonates with no clear benefit. The literature on NEC and probiotics is now cluttered with more reviews and meta-analyses than number of clinical trials. On the other hand, significant new information is available on microbiota and their impact on gut immunity. This review attempts to reiterate the risk factors of NEC and the pathogenesis of NEC with special reference to gut permeability. The reader is then introduced to gut microbiota, uniqueness and differences among probiotic strains, and how multiple resident flora talk to each other in the community setting in the human gut. After presenting a concise review of available clinical research results, the reader is challenged to question as to why no precise answer is available at present. Some modalities to examine the complex microflora and changes in the neonatal gut are then proposed including non-invasive methods and mathematical modeling. The review concludes by attracting the reader's attention to known immunomodulators of inflammation and injury. Justice to this review will be done only if the readers, clinical, and basic science investigators from multiple fields gather courage for a paradigm shift and embark on understanding the pathophysiology of the disease and attempt to discern the difference from equally preterm, equally vulnerable neonates that do not develop NEC. Learning about the developing microbiota in neonatal gut and its immunological impacts on the host in the face of many variables will provide a leap in our pursuit to select better, if not the best candidate probiotics, and put them to work against this stubborn disease that continues to take a toll on our precious neonates and the society.

Bacterial invasion of HT29-MTX-E12 monolayers: effects of human breast milk

AIM

The supramucosal gel, crucial for gut barrier function, might be compromised in necrotizing enterocolitis (NEC). Breast milk is associated with a reduced incidence of NEC. We compared the effects of human breast milk (BM) versus a neonatal formula, Nutriprem 1 (FF), on adherence, internalisation, and penetration of NEC-associated Escherichia coli through monolayers of mucus producing intestinal cells, HT29-MTX-E12 (E12).

METHODS

E12 cells were grown to confluence on membranes permeable to bacteria. E. coli, reference strain and isolated from a NEC-affected intestine, were cultured in LB broth, labelled with fluorescein and biotinylated. Bacteria were suspended in tissue culture medium (TC) or mixtures of TC with BM or FF and applied to the E12 cultures. Bacterial numbers were assessed by fluorescence. DyLight 650-labelled neutravidin, which cannot cross cell membrane, evaluated extracellular bacteria. Fluorescence of basolateral medium was measured to quantify translocation. Bacterial concentrations were compared using the Mann Whitney U test.

RESULTS

After 1h exposure, E12 cultures adhered or internalised more NEC-derived bacteria than standard strain E. coli and more suspended in FF than BM (P<0.001). A greater proportion of NEC-derived bacteria internalised when suspended in TC or BM. In FF, the NEC-derived strain internalised least. More translocation occurred in BM incubations compared to FF in the first 1-4h: NEC-E. coli less than the reference strain. After 24h translocated bacterial populations were equal.

CONCLUSION

In this pilot study, breast milk was associated with relatively less adhesion and internalisation of NEC-associated E. coli to mucus covered E12s compared to formula milk.

Gut mucosal injury in neonates is marked by macrophage infiltration in contrast to pleomorphic infiltrates in adult: evidence from an animal model

Necrotizing enterocolitis (NEC) is an inflammatory bowel necrosis of premature infants. In tissue samples of NEC, we identified numerous macrophages and a few neutrophils but not many lymphocytes. We hypothesized that these pathoanatomic characteristics of NEC represent a common tissue injury response of the gastrointestinal tract to a variety of insults at a specific stage of gut development. To evaluate developmental changes in mucosal inflammatory response, we used trinitrobenzene sulfonic acid (TNBS)-induced inflammation as a nonspecific insult and compared mucosal injury in newborn vs. adult mice. Enterocolitis was induced in 10-day-old pups and adult mice (n = 25 animals per group) by administering TNBS by gavage and enema. Leukocyte populations were enumerated in human NEC and in murine TNBS-enterocolitis using quantitative immunofluorescence. Chemokine expression was measured using quantitative polymerase chain reaction, immunoblots, and immunohistochemistry. Macrophage recruitment was investigated ex vivo using intestinal tissue-conditioned media and bone marrow-derived macrophages in a microchemotaxis assay. Similar to human NEC, TNBS enterocolitis in pups was marked by a macrophage-rich leukocyte infiltrate in affected tissue. In contrast, TNBS-enterocolitis in adult mice was associated with pleomorphic leukocyte infiltrates. Macrophage precursors were recruited to murine neonatal gastrointestinal tract by the chemokine CXCL5, a known chemoattractant for myeloid cells. We also demonstrated increased expression of CXCL5 in surgically resected tissue samples of human NEC, indicating that a similar pathway was active in NEC. We concluded that gut mucosal injury in the murine neonate is marked by a macrophage-rich leukocyte infiltrate, which contrasts with the pleomorphic leukocyte infiltrates in adult mice. In murine neonatal enterocolitis, macrophages were recruited to the inflamed gut mucosa by the chemokine CXCL5, indicating that CXCL5 and its cognate receptor CXCR2 merit further investigation as potential therapeutic targets in NEC.

Probiotics-supplemented feeding in extremely low-birth-weight infants

OBJECTIVE

The objective of this trial was to test whether probiotic-supplemented feeding to extremely low-birth-weight (ELBW) infants will improve growth as determined by decreasing the percentage of infants with weight below the 10th percentile at 34 weeks postmenstrual age (PMA). Other important outcome measures, such as improving feeding tolerance determined by tolerating larger volume of feeding per day and reducing antimicrobial treatment days during the first 28 days from the initiation of feeding supplementation were also evaluated.

STUDY DESIGN

We conducted a multicenter randomized controlled double-blinded clinical study. The probiotics-supplementation (PS) group received Lactobacillus rhamnosus GG and Bifidobacterium infantis added to the first enteral feeding and continued once daily with feedings thereafter until discharge or until 34 weeks (PMA). The control (C) group received unsupplemented feedings. Infant weight and feeding volumes were recorded daily during the first 28 days of study period. Weights were also recorded at 34 weeks PMA.

RESULT

A total of 101 infants were enrolled (PS 50 versus C 51). There was no difference between the two groups in the percentage of infants with weight below the 10th percentile at 34 weeks PMA (PS group 58% versus C group 60%, (P value 0.83)) or in the average volume of feeding during 28 days after study entry (PS group 59  ml  kg(-1) versus C group 71  ml  kg(-1), (P value 0.11)). Calculated growth velocity was higher in the PS group compared with the C group (14.9 versus 12.6  g per day, (P value 0.05)). Incidences of necrotizing enterocolitis (NEC), as well as mortality were similar between the two groups.

CONCLUSION

Although probiotic-supplemented feedings improve growth velocity in ELBW infants, there was no improvement in the percentage of infants with growth delay at 34 weeks PMA. There were no probiotic-related adverse events reported.

Comparative effects of probiotics, prebiotics, and synbiotics on growth factors in the large bowel in a rat model of formula-induced bowel inflammation

OBJECTIVES

Supplementation with probiotics has been shown to prevent gastrointestinal damage possibly through preservation of growth factors. We tested the hypothesis that probiotics, prebiotics, or synbiotics supplementation preserves intestinal insulin-like growth factors (IGFs) and epidermal growth factors (EGFs) in formula-fed neonatal rats.

MATERIALS AND METHODS

At birth (postnatal day 0 [P0]), neonatal rat pups (n = 18 pups/group) were either maternally fed or hand-gavaged with formula supplemented with probiotics (Pro-Fed), prebiotics, or synbiotics from P0 to P3. A formula-fed control group received formula without supplementation. At P4, large bowel samples were assessed histologically and assayed for vascular endothelial growth factor (VEGF), soluble VEGF receptor-1, IGF-I, IGF-II, and EGF.

RESULTS

All formula-fed groups were severely growth suppressed with comparable mortalities. Moderate preservation of bowel integrity was noted in the Pro-Fed group. In contrast, severe inflammation was seen in all of the other formula groups. This was associated with significant increases in VEGF levels in all of the formula groups (P < 0.05) except the Pre-Fed group. Similar elevations in soluble VEGF receptor-1 (P < 0.05), IGF-I (P < 0.05), and EGF (P < 0.05) were noted, but statistical significance was achieved only in the Pro-Fed group.

CONCLUSIONS

Induction of IGF-I and EGF with moderate bowel integrity may represent a protective effect of probiotics against formula-induced inflammation. These data, taken collectively, suggest that probiotics may provide more beneficial effects on the developing large bowel than prebiotics and synbiotics.

Diet-dependent mucosal colonization and interleukin-1beta responses in preterm pigs susceptible to necrotizing enterocolitis

OBJECTIVES

Intestinal colonization challenges the neonatal innate immune system, especially in newborns with an immature immune response lacking the supportive bioactive components from mother's milk. Accordingly, formula-fed preterm pigs frequently show bacterial overgrowth, mucosal atrophy, and gut lesions reflecting necrotizing enterocolitis (NEC) within the first days after birth. We hypothesized that NEC development is related to a diet-dependent bacterial adherence and a subsequent proinflammatory cytokine response in the gut mucosa immediately after introduction of enteral food.

MATERIALS AND METHODS

Premature piglets (92% gestation) received 2 to 3 days of total parenteral nutrition followed by 0, 8, or 17 hours of enteral formula or sow's colostrum feeding.

RESULTS

Following 8 hours, but not 17 hours, of colostrum feeding, a reduced number of intestinal samples with adherent bacteria (both Gram-negative and Gram-positive bacteria) was counted compared with 0 or 8 hours of formula feeding. Besides a more dense colonization, formula feeding leads to higher intestinal interleukin-1beta (IL-1beta) levels and more NEC-like lesions from 8 hours onward. The load of adherent bacteria was especially high in NEC lesions. Toll-like receptor 4 was detected in enteroendocrine, neuronal, and smooth muscle cells, potentially mediating the increase in IL-1beta levels by Gram-negative bacteria.

CONCLUSIONS

Formula feeding facilitates bacterial adherence and the development of a proinflammatory state of the intestine, which may be among the key factors that predispose formula-fed preterm neonates to NEC.

16S rRNA gene-based analysis of fecal microbiota from preterm infants with and without necrotizing enterocolitis

Neonatal necrotizing enterocolitis (NEC) is an inflammatory intestinal disorder affecting preterm infants. Intestinal bacteria play a key role; however no causative pathogen has been identified. The purpose of this study was to determine if there are differences in microbial patterns which may be critical to the development of this disease. Fecal samples from twenty preterm infants, ten with NEC and ten matched controls (including four twin pairs) were obtained from patients in a single site Level III neonatal intensive care unit. Bacterial DNA from individual fecal samples were PCR amplified and subjected to terminal restriction fragment length polymorphism analysis and library sequencing of the 16S rRNA gene to characterize diversity and structure of the enteric microbiota. The distribution of samples from NEC patients distinctly clustered separately from controls. Intestinal bacterial colonization in all preterm infants was notable for low diversity. Patients with NEC had even less diversity, an increase in abundance of Gammaproteobacteria, a decrease in other bacteria species, and had received a higher mean number of previous days of antibiotics. Our results suggest that NEC is associated with severe lack of microbiota diversity which may accentuate the impact of single dominant microorganisms favored by empiric and wide-spread use of antibiotics.

Long-term colonization of a Lactobacillus plantarum synbiotic preparation in the neonatal gut

BACKGROUND

Probiotic, prebiotic, and synbiotic (a combination of pro- and prebiotic) supplements increasingly are being used to prevent and treat a variety of health conditions. Although colonization is considered a key element in the success of such treatments, few clinical studies have addressed colonizing ability. Studies are even more limited in neonates and infants, who may benefit most from such treatment. The present study was conducted to determine the colonizing ability, tolerance, and impact on the stool flora of 7 days of administration of a synbiotic supplement to a neonatal cohort, in preparation for a larger hospital-based trial.

PATIENTS AND METHODS

In this randomized, double-masked, controlled trial, healthy inborn newborns >35 weeks of gestational age and >1800 g birth weight were randomized between 1 and 3 days after birth to receive an oral synbiotic preparation (Lactobacillus plantarum and fructooligosaccharides) or a dextrose saline placebo. Two babies were treated with the synbiotic preparation for every 1 baby treated with the placebo. Duration of therapy was 7 days. Comprehensive stool cultures were done at baseline and on days 3, 7, 14, 21, and 28.

RESULTS

Nineteen infants received the active study supplement and 12 infants received the placebo for 7 days. L plantarum was cultured from the stools of 84% of the treated infants after 3 days of treatment, and from 95% of infants on day 28 after birth. Of the infants, 100%, 94%, 88%, 56%, and 32% remained colonized at months 2, 3, 4, 5, and 6, respectively. In both groups, the total mean number of species and the mean log colony counts increased over time. The number of bacterial species was significantly higher on days 21 and 28 in the synbiotic preparation group compared with placebo (P = 0.002 and 0.03, respectively). There was a linear increase in the mean log gram-negative colony counts in the placebo group during the 4-week period that was significantly higher than that in the Lactobacillus group on days 14, 21, and 28 (P < 0.001 for each). In contrast, the supplement group had significantly higher gram-positive colony counts on days 14 (P = 0.002) and 28 (P = 0.04). Only 1 infant in the placebo group was colonized with L fermentum during the first 28 days of life. No difference was found in the percent increase in weight between baseline and day 7, but on day 28 and months 2, 3, and 6, the percent increase from baseline was higher in the probiotic-treated group (P </= 0.05). The supplement was tolerated well.

CONCLUSIONS

The synbiotic preparation colonized quickly after 3 days of administration and the infants stayed colonized for several months after therapy was stopped. There was an increase in bacterial diversity and gram-positive organisms and a reduction of gram-negative bacterial load in the treatment group. Because a combination preparation was used, it is difficult to specifically attribute the colonization to either the probiotic or prebiotic component in this study. Larger efficacy trials are warranted to examine the mechanism of action and precise effects of these supplements.

Probiotics: role in pathophysiology and prevention in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an inflammatory bowel disease largely affecting low birth weight, premature infants. Once acquired, NEC is accompanied by significant mortality and morbid sequelae. Our understanding of the pathophysiology of NEC continues to evolve, and the development of NEC is likely multifactorial with resultant bowel injury mediated through a final, common inflammatory pathway. The predisposition for NEC appears to involve the interplay between intestinal integrity and function, enteral feeding and bacterial colonization, and regulation of the gastrointestinal and systemic inflammatory response. Commensal organisms or probiotics have been shown to be crucial in the development and modulation of each of these factors within the intestinal epithelium. As a result, probiotic supplementation has been proposed as a promising new intervention for the prevention of NEC. To understand the potential utility of probiotics in NEC, we will discuss: the components of gut defense; the role of the intestinal ecosystem in modulating immunity and inflammation; bacterial colonization patterns in the preterm infant compared with patterns seen in the healthy, full-term infant; the evidence for probiotic use in other populations and diseases; and finally, the evidence of probiotic use specific to the preterm infant and NEC.

Cytokines in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intra-abdominal emergency in the newborn period. The disease involves bowel wall inflammation, ischemic necrosis, eventual perforation, and the need for urgent surgical intervention. Unrecognized or left untreated, the neonate can decompensate quickly, often progressing to shock, multisystem organ failure, and eventual death. During the past several years, a number of basic science and clinical trials have been established in an attempt to understand the pathophysiology of NEC. As many researchers feel that NEC develops as an uncontrolled inflammatory response that leads to intestinal ischemia, a large number of studies have been focused on the inflammatory cascade and the role that cytokines play within that cascade. Although a large amount of data has been generated from these studies, the events leading to the ischemic injury of the intestine are still not fully understood. This article will therefore focus on the key cytokines involved with NEC, in an attempt to present the current literature and studies that support their involvement.

Probiotics and other preventative strategies for necrotising enterocolitis

Necrotising enterocolitis (NEC) remains one of the commonest causes of death and significant morbidity in preterm infants after the first few postnatal days. NEC affects approximately 5-10% of infants born at <or=28 weeks; about a third will die. Although there do not appear to be any 'simple fixes', it is clear that there are many clinical strategies that affect NEC. There is controlled trial evidence for breast milk, fluid regimes, enteral antibiotics, immunonutrients and probiotic supplements. This paper will review the evidence relevant to current populations of preterm infants and determine which, if any, can be safely and effectively introduced into current clinical practice.

Probiotic bacteria change Escherichia coli-induced gene expression in cultured colonocytes: Implications in intestinal pathophysiology

AIM: To investigate the change in eukaryotic gene expression profile in Caco-2 cells after infection with strains of Escherichia coli and commensal probiotic bacteria.

METHODS: A 19200 gene/expressed sequence tag gene chip was used to examine expression of genes after infection of Caco-2 cells with strains of normal flora E. coli, Lactobacillus plantarum, and a combination of the two.

RESULTS: The cDNA microarray revealed up-regulation of 155 and down-regulation of 177 genes by E. coli. L. plantarum up-regulated 45 and down-regulated 36 genes. During mixed infection, 27 genes were up-regulated and 59 were down-regulated, with nullification of stimulatory/inhibitory effects on most of the genes. Expression of several new genes was noted in this group.

CONCLUSION: The commensal bacterial strains used in this study induced the expression of a large number of genes in colonocyte-like cultured cells and changed the expression of several genes involved in important cellular processes such as regulation of transcription, protein biosynthesis, metabolism, cell adhesion, ubiquitination, and apoptosis. Such changes induced by the presence of probiotic bacteria may shape the physiologic and pathologic responses they trigger in the host.

Necrotizing enterocolitis: a practical guide to its prevention and management

Neonatal necrotizing enterocolitis is the second most common cause of morbidity in premature infants and requires intensive care over an extended period. Despite advances in medical and surgical techniques, the mortality and long-term morbidity due to necrotizing enterocolitis remain very high. Recent advances have shifted the attention of researchers from the classic triad (ischemia, bacteria, and the introduction of a metabolic substrate into the intestine) of necrotizing enterocolitis, to gut maturation, feeding practices, and inflammation. The focus on inflammation includes proinflammatory cytokines such as tumor necrosis factor-alpha, interleukin (IL)-6, IL-18, and platelet-activating factor. Research related to the etiology of necrotizing enterocolitis has moved quickly from clostridial toxin to bacterial and other infectious agents. More recently, the pattern of bacterial colonization has been given emphasis rather than the particular species or strain of bacteria or their virulence. Gram-negative bacteria that form part of the normal flora are now speculated as important factors in triggering the injury process in a setting where there is a severe paucity of bacterial species and possible lack of protective Gram-positive organisms. Although the incidence of necrotizing enterocolitis has increased because of the survival of low birthweight infants, clinicians are more vigilant in their detection of the early gastrointestinal symptoms of necrotizing enterocolitis; however, radiographic demonstration of pneumatosis intestinalis remains the hallmark of necrotizing enterocolitis. With prompt diagnosis, a large proportion of infants with necrotizing enterocolitis are now able to be managed medically with intravenous fluid and nutrition, nasogastric suction, antibacterials, and close monitoring of physiologic parameters. In the advanced cases that require surgery, clinicians tend to opt for either simple peritoneal drainage (for very small and sick infants) or laparotomy and resection of the affected part. Intestinal transplantation later in life is available as a viable option for those who undergo resection of large segments of the intestine. It is becoming more evident that treatment of this devastating disease is expensive and comes with the toll of significant long-term sequelae. This has resulted in renewed interest in designing alternative strategies to prevent this serious gastrointestinal disease. Simple trophic feeding and the use of L-glutamine and arginine are novel avenues that have been examined. The use of probiotics ('friendly' bacterial flora) has been introduced as a promising tool for establishing healthy bacterial flora in the newborn gut to block the injury process that may ultimately lead to necrotizing enterocolitis.

Intestinal trefoil factor in treatment of neonatal necrotizing enterocolitis in the rat model

AIM

Neonatal necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of premature infants. The role of cytokines and growth factors in the pathophysiology of NEC is not yet clearly defined. Among these factors, the intestinal trefoil factor (ITF) is known as cytoprotective to the gut. We studied the cytoprotective effect of trefoil factor in the 1-day-old Wistar rat pup model following hypoxic-ischemic cold stress.

MATERIALS AND METHODS

In the present study, thirty 1-day-old Wistar rat pups were randomly divided into three groups: Group 1, normal controls: Group 2, NEC; Group 3, NEC+ITF. Experimental NEC was induced by exposure to hypoxia for 60 s followed by cold stress at 4 degrees C for 10 min. The animals were euthanized at development of NEC, and at 96 h the intestinal tissue was processed and examined for histological changes of NEC.

RESULTS

The pathological lesions indicated severe separation of the submucosa and lamina propria and tissue necrosis in Group 2, and slight submucosal and lamina propria separation in Group 3. There were no histopathological changes in the controls. The mean of histological grade of group 2 was 2.8 (range 2-4), and 1.2 (range 0-2) in group 3. A difference was found when the two groups were compared (P<0.05).

CONCLUSION

ITF may provide a new way for the therapy of NEC in rats.

Potential prophylactic value of bovine colostrum in necrotizing enterocolitis in neonates: an in vitro study on bacterial attachment, antibody levels and cytokine production

Necrotizing enterocolitis (NEC) is an important disease of low birth-weight neonates. The immaturity of the gut mucosa may result in close contact between the host epithelium and microorganisms which are normally confined to the gut lumen. Damage of the mucosa due to endotoxin, cytokine production or other factors is believed to then occur. The aim of this study was to determine whether spray-dried bovine colostrum demonstrated potential in vitro as a prophylactic for NEC. Antiadherence was measured using a tissue culture assay and antibody levels against Enterobacteriaceae were determined by ELISA. The effect of bovine colostrum on the production of cytokines implicated in NEC was determined by a multiplex bead assay. Enterobacter cloacae, Klebsiella oxytoca, Escherichia coli, Serratia marcescens and Klebsiella pneumoniae ssp. pneumoniae were common in both NEC positive and NEC negative infants and IgA and IgG1 antibodies to these species were present in the bovine colostrum. Pretreatment with bovine colostrum produced a significant decrease (P<0.001) in attachment of bacteria to HT-29 cells. Bovine colostrum significantly increased the production of IL-8 in HT-29 cells and IL-8, IL-6 and TNF-alpha in THP-1 cells (P<0.001). The potential of bovine colostrum to increase the production of inflammatory mediators could limit its usefulness.

The subdiaphragmatic vagus nerves mediate activation of locus coeruleus neurons by peripherally administered microbial substances

Our earlier studies demonstrated that representative microbial substances--lipopolysaccharide, peptidoglycan, and poly-inosine: poly-cytosine (poly(I):(C))--increased the spontaneous discharge rates and sensory-evoked responses of isolated locus coeruleus (LC) neurons in a dose- and time-related manner after i.p. injection into rats. We then turned our attention to the mechanism by which microbial substances administered into the peritoneal cavity affect the LC neurons. The involvement of the subdiaphragmatic vagus nerves was examined in this regard since several brain responses to peripherally administered lipopolysaccharide have been found to depend upon the integrity of these nerves. The experiments reported here show that lipopolysaccharide, peptidoglycan, and poly(I):(C) all failed to excite LC neurons after i.p. injection into rats that had previously been subjected to complete transection of the subdiaphragmatic vagus nerves. Furthermore, selective transection of the subdiaphragmatic vagus nerve trunks indicated that the dorsal trunk, and not the ventral trunk, was necessary to excite LC neurons in response to i.p. lipopolysaccharide. The inability of LC neurons to respond to i.p. lipopolysaccharide in vagotomized rats is unlikely to be attributed to a desensitization of the neurons to lipopolysaccharide since i.c.v. injection of lipopolysaccharide excited LC neurons in vagotomized rats as it did in vagus-intact rats. These findings suggest that a variety of microbial substances excited LC neurons after administration into the peritoneal cavity in a manner involving the subdiaphragmatic vagus nerves.

The effects of endogenous interleukin-1 bioactivity on locus coeruleus neurons in response to bacterial and viral substances

In a previous study, we found that microinjection of the cytokine interleukin-1 (IL-1) into the locus coeruleus (LC) increased the electrophysiological activity of LC neurons. To determine if endogenous IL-1 similarly affects the LC, brain IL-1 was induced with lipopolysaccharide (LPS), a substance derived from Gram-negative bacteria. LPS microinjected directly into the LC increased the activity of LC neurons in anesthetized rats, and this effect was blocked by microinfusion of the IL-1 receptor antagonist (IL-1RA) protein into the LC indicating the involvement of IL-1 receptors. Similarly, intraperitoneal (i.p.) LPS injection increased the activity of LC neurons in a dose- and time-related manner that was sensitive to IL-1RA. The change in the activity of LC neurons caused by a single i.p. injection of LPS was surprisingly long-lasting, and evolved over a period of at least 3 weeks. Other microbial substances-namely, peptidoglycan from Gram-positive bacteria and poly-inosine/poly-cytosine (poly(I)/(C)), which resembles RNA viruses-were used to determine the generality of the findings with LPS. Both i.p. peptidoglycan and poly(I)/(C) increased LC activity but with lesser efficacy than LPS. IL-1RA reversed the increase in the activity of LC neurons caused by i.p. peptidoglycan treatment; however, that caused by i.p. Poly(I)/(C) was not diminished by IL-1RA. Thus, the increased activity of LC neurons caused by LPS and peptidoglycan requires IL-1 receptor binding, suggesting the involvement of endogenously-produced IL-1. In contrast, poly(I)/(C) increased the activity of LC neurons but this did not critically involve IL-1 receptors in the LC.

Epidermal growth factor and necrotizing enterocolitis

As the number of extremely low-birth-weight infants increases,necrotizing enterocolitis remains a critical eminent problem. Supplementation of enteral feeds with biologically active substances normally present in breast milk, such as epidermal growth factor, seems to be a logical and safe way to reduce the incidence of intestinal inflammation and necrotizing enterocolitis. Continuing basic research and clinical studies are essential before epidermal growth factor can be introduced as an efficient therapeutic approach in the treatment of neonatal necrotizing enterocolitis.

Probiotics for preterm infants?

Infants nursed in special care baby units develop an abnormal pattern of microbial colonisation, which may contribute to disease. Enteric feeding of live microbial supplements (probiotics) may provide benefit to such infants and help to prevent diseases such as neonatal necrotising enterocolitis.

Effects of oral Lactobacillus GG on enteric microflora in low-birth-weight neonates

BACKGROUND

Colonization patterns, especially by anaerobic flora, may play an important role in neonatal gut function. Probiotics could affect disease risk either directly through colonization or indirectly by promoting changes in gut microbial ecology.

METHODS

To study the ability of Lactobacillus GG(LGG) to colonize the neonatal gut and modify its microbial ecology, a prospective, randomized study was performed in 71 preterm infants of less than 2000 g birth weight. Infants less than 1500 g (24 treated, 15 control) received 10(9) LGG orally twice daily for 21 days. Those infants weighing 1500 to 1999 g (23 treated, 9 control) were treated for 8 days. Stools were collected before treatment and on day 7 to 8 (and day 14 and 21, in the infants weighing less than 1500 g) for quantitative aerobic and anaerobic cultures.

RESULTS

Colonization with LGG occurred in 5 of 24 (21%) infants who weighed less than 1500 g versus 11 of 23 (47%) in larger infants. Colonization was limited to infants who were not on antibiotics within 7 days of treatment with LGG. There was a paucity of bacterial species at baseline, although larger infants had more bacterial species (1.59 +/- 0.13 (SEM) vs 1.11 +/- 0.12; P < 0.03) and higher mean log colony forming units (CFU) (8.79 +/- 0.43 vs 7.22 +/- 0.63; P < 0.05) compared with infants weighing less than 1500 g LGG. Treatment in infants weighing less than 1500 g resulted in a significant increase in species number by day 7, with further increases by day 21. This increase was mainly the result of increased Gram (+) and anaerobic species. No difference in species number was noted in controls. Mean log CFU of Gram (-) bacteria did not change in treated infants weighing less than 1500 g. However, Gram (+) mean log CFU showed a significant increase on day 21 (6.1 +/- 0.9) compared with day 0 (3.5 +/- 0.9) (P < 0.05). No significant changes in species number or quantitative counts were noted after LGG treatment in the infants weighing 1500 to 1999 g LGG was well tolerated in all infants.

CONCLUSION

The neonatal response to a probiotic preparation is dependent on gestational and post-natal age and prior antibiotic exposure. Although LGG is a relatively poor colonizer in infants, especially those infants weighing less than 1500 g at birth, it does appear to affect neonatal intestinal colonization patterns.

Maternal milk reduces severity of necrotizing enterocolitis and increases intestinal IL-10 in a neonatal rat model

Necrotizing enterocolitis (NEC) is a devastating intestinal disease of premature infants. Maternal milk has been suggested to be partially protective against NEC; however, the mechanisms of this protection are not defined. The aim of this study was to examine the effect(s) of artificial feeding of rat milk (RM)-versus cow milk-based rat milk substitute (RMS) on the development of NEC in a neonatal rat model and elucidate the role of inflammatory cytokines in NEC pathogenesis. Newborn rats were artificially fed with either collected RM or RMS. Experimental NEC was induced by exposure to asphyxia and cold stress and evaluated by histologic scoring of damage in ileum. Intestinal cytokine mRNA expression was determined by real-time PCR. Cytokine histologic localization was performed by confocal microscopy. Similar to human NEC, artificial feeding of RM reduces the incidence and severity of NEC injury in neonatal rats. Freezing and thawing of collected RM did not eliminate the protective effect of maternal milk. Ileal IL-10 expression was significantly increased in the RM group compared with RMS. Increased IL-10 peptide production was detected in the RM group with signal localized predominantly in the cytoplasm of villus epithelial cells. These results suggest that the protective effect of maternal milk is associated with increased production of anti-inflammatory IL-10 in the site of injury. Better understanding of the mechanisms underlying these protective effects could be beneficial either in the prevention of NEC or in the development of future therapeutic strategies to cure NEC.

Host-dependent zonulin secretion causes the impairment of the small intestine barrier function after bacterial exposure

BACKGROUND & AIMS

Enteric infections have been implicated in the pathogenesis of both food intolerance and autoimmune diseases secondary to the impairment of the intestinal barrier. On the basis of our recent discovery of zonulin, a modulator of small-intestinal tight junctions, we asked whether microorganisms might induce zonulin secretion and increased small-intestinal permeability.

METHODS

Both ex vivo mammalian small intestines and intestinal cell monolayers were exposed to either pathogenic or nonpathogenic enterobacteria. Zonulin production and changes in paracellular permeability were monitored in Ussing chambers and micro-snapwells. Zonula occludens 1 protein redistribution after bacteria colonization was evaluated on cell monolayers.

RESULTS

Small intestines exposed to enteric bacteria secreted zonulin. This secretion was independent of either the species of the small intestines or the virulence of the microorganisms tested, occurred only on the luminal aspect of the bacteria-exposed small-intestinal mucosa, and was followed by a decrease in small-intestinal tissue resistance (transepithelial electrical resistance). The transepithelial electrical resistance decrement was secondary to the zonulin-induced tight junction disassembly, as also shown by the disengagement of the protein zonula occludens 1 protein from the tight junctional complex.

CONCLUSIONS

This zonulin-driven opening of the paracellular pathway may represent a defensive mechanism, which flushes out microorganisms and contributes to the host response against bacterial colonization of the small intestine.

A study of gut immunity to enteral endotoxin in rats of different ages: a possible cause for necrotizing enterocolitis

PURPOSE

Immature gut immunity can be a predisposing factor for necrotizing enterocolitis (NEC). The gut active immunity and innate defense to the Escherichia coli endotoxin lipopolysaccharide (LPS) in immature and mature rats were studied.

METHODS

LPS, started at a dose of 10 mg/kg, was instilled into the stomachs of fetal, newborn, 1-month and 3-month-old rats. Boost doses and normal saline control instillations were given on day 14. Rats that died after instillation had detailed postmortem examinations. For survivors, a group of 6 immunized and 6 controls were killed on day 7 for the collection of serum, spleens, mesenteric lymph nodes, and small intestines. Lymphocytes (10(6)) prepared from each tissue sample of individual group were cultured for 5 days. Serum and supernatant were analyzed for IgA and anti-E coli IgA levels.

RESULTS

All control rats survived. The doses of LPS given were 10, 5, 2.5, and 1.25 mg/kg. All fetal rats died after LPS instillation. Half-lethal dose for newborns was 2.5 mg/kg. One-month and 3-month-old rats survived all doses of LPS. The cause of death was endotoxemia. The serum IgA and total supernatant anti- E coli IgA levels of rats of all ages studied showed no significant difference.

CONCLUSION

The poor innate gut defense, not so much the active immunity, may provide an explanation for the susceptibility of the premature babies and newborn infants to the development of NEC.

Necrotizing enterocolitis, pathogenesis and the protector effect of prenatal corticosteroids

Necrotizing enterocolitis is the most frequently occurring gastrointestinal disorder in premature neonates. Animal models of necrotizing enterocolitis and prenatal administration of cortisone have demonstrated that cortisone may accelerate maturation of the mucosal barrier, therefore reducing the incidence of this gastrointestinal disorder. The authors present a review of the literature of the most important risk factors associated with necrotizing enterocolitis, such as inflammatory gastrointestinal mediators, enteral feeding and bacterial colonization, and immaturity of the gastrointestinal barrier, and we emphasize the necessity for additional studies to explore the prenatal administration of cortisone as a preventive strategy for necrotizing enterocolitis.

Hypothesis: inappropriate colonization of the premature intestine can cause neonatal necrotizing enterocolitis

Neonatal necrotizing enterocolitis (NEC) is a major cause of morbidity in preterm infants. We hypothesize that the intestinal injury in this disease is a consequence of synergy among three of the major risk factors for NEC: prematurity, enteral feeding, and bacterial colonization. Together these factors result in an exaggerated inflammatory response, leading to ischemic bowel necrosis. Human milk may decrease the incidence of NEC by decreasing pathogenic bacterial colonization, promoting growth of nonpathogenic flora, promoting maturation of the intestinal barrier, and ameliorating the proinflammatory response.

Duodenal microflora in very-low-birth-weight neonates and relation to necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in the neonatal period. Small-bowel overgrowth with aerobic gram-negative bacteria has previously been implicated in the development of NEC. This prospective study performed quantitative bacteriology on 422 duodenal aspirates collected from 122 very-low-birth-weight (<1,500-g) newborns, at the time of routine changing of nasogastric tubes. Isolates of Enterobacteriaceae were typed by repetitive extragenic, palindromic PCR and pulsed-field gel electrophoresis. One or more samples from 50% of these infants yielded gram-negative bacteria, predominantly Escherichia coli, Klebsiella spp., and Enterobacter spp., with counts up to 10(8) CFU/g. The proportion of samples with gram-negative bacteria increased with postnatal age, while the percentage of sterile samples declined. Molecular typing revealed marked temporal clustering of indistinguishable strains. All infants had been fed prior to isolation of gram-negative organisms. Antibiotic use had no obvious effect on colonization with Enterobacteriaceae. There were 15 episodes of suspected NEC (stage I) and 8 confirmed cases of NEC (2 stage II and 6 stage III) during the study period. Duodenal aspirates were collected prior to clinical onset in 13 episodes of NEC. Seven of these yielded Enterobacteriaceae, of which five strains were also isolated from infants without NEC. Very-low-birth-weight infants have high levels of duodenal colonization with Enterobacteriaceae, with evidence of considerable cross-colonization with indistinguishable strains. There was no association between duodenal colonization with particular strains of Enterobacteriaceae and development of NEC.

Carboxyl ester lipase activity in milk prevents fat-derived intestinal injury in neonatal mice

Carboxyl ester lipase (bile salt-stimulated lipase) is a pancreatic enzyme capable of hydrolyzing esters of cholesterol and fat-soluble vitamins. It also efficiently digests triglycerides (TG) into free fatty acids and glycerol and is abundant in the milk of humans and several other species. We used the mouse as a model to test the hypothesis that milk-derived carboxyl ester lipase (CEL) digests milk TG and that without its activity milk lipids and their digestion intermediates can disrupt the intestinal epithelium of neonates. CEL protein and enzymatic activity were shown to be abundant in mouse milk. After 24-h administration of the CEL-specific inhibitor, WAY-121,751-5, the small intestines of treated and control neonates were analyzed histologically for signs of fat malabsorption and injury to their villus epithelium. In vehicle-fed controls, TG were digested and absorbed in the duodenum and jejunum, whereas, in inhibitor-fed littermates, large intracellular neutral lipid droplets accumulated in enterocytes of the ileum, resulting in damage to the villus epithelium. Similar results were observed in neonates nursed by CEL knockout females compared with heterozygous controls. The results suggest that lack of CEL activity causes incomplete digestion of milk fat and lipid accumulation by enterocytes in the ileum of neonatal mice.

Bifidobacterial supplementation reduces the incidence of necrotizing enterocolitis in a neonatal rat model

BACKGROUND & AIMS

Neonatal necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease of premature infants partly caused by intestinal bacterial proliferation. Because bifidobacteria are thought to reduce the risk for intestinal disturbances associated with pathogenic bacterial colonization, we hypothesized that exogenous bifidobacterial supplementation to newborn rats would result in intestinal colonization and a reduction in the incidence of neonatal NEC.

METHODS

Newborn rat pups were given Bifidobacterium infantis (10(9) organisms per animal daily), Escherichia coli, or saline control and exposed to the NEC protocol consisting of formula feeding (Esbilac; 200 cal. kg(-1). day(-1)) and asphyxia (100% N(2) for 50 seconds followed by cold exposure for 10 minutes). Outcome measures included stool and intestinal microbiological evaluation, gross and histological evidence of NEC, plasma endotoxin concentration, intestinal phospholipase A(2) expression, and estimation of intestinal mucosal permeability.

RESULTS

Bifidobacterial supplementation resulted in intestinal colonization by 24 hours and appearance in stool samples by 48 hours. Bifidobacteria-supplemented animals had a significant reduction in the incidence of NEC compared with controls and E. coli-treated animals (NEC, 7/24 B. infantis vs. 19/27 control vs. 16/23 E. coli; P < 0.01). Plasma endotoxin and intestinal phospholipase A(2) expression were lower in bifidobacteria-treated pups than in controls, supporting the role of bacterial translocation and activation of the inflammatory cascade in the pathophysiology of NEC.

CONCLUSIONS

Intestinal bifidobacterial colonization reduces the risk of NEC in newborn rats.

Stool microflora in extremely low birthweight infants

AIM

To serially characterise aerobic and anaerobic stool microflora in extremely low birthweight infants and to correlate colonisation patterns with clinical risk factors.

METHODS

Stool specimens from 29 infants of birthweight <1000 g were collected on days 10, 20, and 30 after birth. Quantitative aerobic and anaerobic cultures were performed.

RESULTS

By day 30, predominant species were Enterococcus faecalis, Escherichia coli, Staphylococcus epidermidis, Enterbacter cloacae, Klebsiella pneumoniae, and Staphylococcus haemolyticus. Lactobacillus and Bifidobacteria spp were identified in only one infant. In breast milk fed (but not in formula fed) infants, the total number of bacterial species/stool specimen increased significantly with time (2.50 (SE 0.34) on day 10; 3.13 (0.38) on day 20; 4.27 (0.45) on day 30) as did quantitative bacterial counts; Gram negative species accounted for most of the increase. On day 30, significant inverse correlations were found between days of previous antibiotic treatment and number of bacterial species (r=0.491) and total organisms/g of stool (r=0.482). Gestational age, birthweight, maternal antibiotic or steroid treatment, prolonged rupture of the membranes, and mode of delivery did not seem to affect colonisation patterns.

CONCLUSIONS

The gut of extremely low birthweight infants is colonised by a paucity of bacterial species. Breast milking and reduction of antibiotic exposure are critical to increasing fecal microbial diversity.

Role of glutamine in bacterial transcytosis and epithelial cell injury

BACKGROUND

L-Glutamine is the principal energy source for small intestinal enterocytes. Diminution of intestinal function, mucosal atrophy, and increased bacterial translocation have been noted during total parenteral nutrition (TPN). In a rat model of glutamine starvation, we previously showed that luminal glutamine is essential for optimal intestinal function. In this study, we examined the effect of apical vs basolateral glutamine on bacterial translocation in a Caco-2 cell culture system and bacteria-induced tissue injury in a weanling rabbit ileal loop model.

METHODS

Caco-2 cells were grown in a transwell system. After confluence, apical and basolateral chambers received defined media, and glutamine deprivation was carried out over a 4- to 48-hour period. Escherichia coli transcytosis and structure/function studies were then performed. In a second series of experiments, the effect of intraluminal glutamine supplementation was evaluated in an E. coli-induced tissue injury model in weanling rabbit ileal loops.

RESULTS

Expression of disaccharidases, glucoamylase, and Na+/K(+)-adenosine 5'-triphosphatase (ATPase) were significantly reduced when cells were deprived of glutamine from the apical side, and there was increased bacterial translocation across the monolayer. Transepithelial epithelial resistance (TEER) across the monolayer was also reduced in the glutamine-free cultures. Glutamine replenishment over 24 to 48 hours restored the original functions. Basolateral deprivation had a smaller effect on the Caco-2 cells. Typical necrotic mucosal injury caused by E. coli in the ileal loops was blocked by co-infiltration of the loops with glutamine.

CONCLUSIONS

This study demonstrates for the first time that the supply of glutamine from the apical side is of critical importance for maintaining optimal structure and function of the enterocytes. The effects are not acute or energy related. These observations have important clinical implications in the management of patients under critical care, including premature infants and patients receiving TPN, for whom lack of glutamine from the luminal side could produce mucosal dysfunction, resulting ultimately in severe atrophic/necrotic complications.

Escherichia coli transcytosis in a Caco-2 cell model: implications in neonatal necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a serious gastrointestinal disorder of preterm infants. Other than an association with prematurity and gastrointestinal feeding, no single factor or mechanism has been consistently linked to this disease. We have previously demonstrated that Escherichia coli isolates obtained from the stool of infants with NEC caused NEC-like injury in a weanling rabbit ileal loop model; this injury, in turn, could be blocked by coinfection with selected Gram(+) bacteria (Enterococcus faecium) isolated from asymptomatic controls. Using Caco-2 cells in a trans-well system, we now demonstrate that the same E. coli isolates can cross epithelial cell monolayers in the absence of ultrastructural change or damage. These results with E. coli contrast with those seen with Salmonella typhimurium, which passed through the monolayer at a higher rate and were associated with striking ultrastructural damage. Transcytosis of E. coli was reduced 3-5-fold in the presence of E. faecium previously shown to block NEC-like injury in the loop model. There was a mild increase in the rate of E. coli transcytosis when studies were conducted with younger, undifferentiated cells; these immature cells had no brush border, had decreased production of brush border-specific enzymes, but retained well defined tight junctions, as demonstrated by transepithelial electrical resistance and electron microscopy. A further reduction/ complete blockage of E. coli transcytosis was observed when E. faecium was used as the coinfectant in studies with these undifferentiated cells. We hypothesize that the ability of E. coli to cross epithelial cell layer is a critical initial step in the cascade of events which lead ultimately to NEC; blockage or reduction in E. coli transcytosis in the presence of certain Gram(+) organisms may play a significant role in prevention of NEC.

Necrotizing enterocolitis: the search for a unifying pathogenic theory leading to prevention

During the past two decades, necrotizing enterocolitis has emerged as a major cause of mortality and morbidity in premature infants. The specific cause of the disease remains enigmatic, but several putative risk factors provide clues to a pathophysiology that seems to be multifactorial. With the use of newly developed scientific tools, an understanding of the basic pathophysiologic cascade that causes necrotizing enterocolitis is emerging, providing hope for improved treatment and prevention.