Enterobacter sakazakii enhances epithelial cell injury by inducing apoptosis in a rat model of necrotizing enterocolitis

Dysbiosis promotes recurrence of adenomatous polyps in the distal colorectum

BACKGROUND

Colorectal polyps, which are characterized by a high recurrence rate, represent preneoplastic conditions of the intestine. Due to unclear mechanisms of pathogenesis, first-line therapies for non-hereditary recurrent colorectal polyps are limited to endoscopic resection. Although recent studies suggest a mechanistic link between intestinal dysbiosis and polyps, the exact compositions and roles of bacteria in the mucosa around the lesions, rather than feces, remain unsettled.

AIM

To clarify the composition and diversity of bacteria in the mucosa surrounding or 10 cm distal to recurrent intestinal polyps.

METHODS

Mucosal samples were collected from four patients consistently with adenomatous polyps (Ade), seven consistently with non-Ade (Pol), ten with current Pol but previous Ade, and six healthy individuals, and bacterial patterns were evaluated by 16S rDNA sequencing. Linear discriminant analysis and Student's t-tests were used to identify the genus-level bacteria differences between groups with different colorectal polyp phenotypes. Pearson's correlation coefficients were used to evaluate the correlation between intestinal bacteria at the genus level and clinical indicators.

RESULTS

The results confirmed a decreased level of probiotics and an enrichment of pathogenic bacteria in patients with all types of polyps compared to healthy individuals. These changes were not restricted to the mucosa within 0.5 cm adjacent to the polyps, but also existed in histologically normal tissue 10 cm distal from the lesions. Significant differences in bacterial diversity were observed in the mucosa from individuals with normal conditions, Pol, and Ade. Increased abundance of Gram-negative bacteria, including Klebsiella, Plesiomonas, and Cronobacter, was observed in Pol group and Ade group, suggesting that resistance to antibiotics may be one risk factor for bacterium-related harmful environment. Meanwhile, age and gender were linked to bacteria changes, indicating the potential involvement of sex hormones.

CONCLUSION

These preliminary results support intestinal dysbiosis as an important risk factor for recurrent polyps, especially adenoma. Targeting specific pathogenic bacteria may attenuate the recurrence of polyps.

In Vitro Models for Investigating Intestinal Host-Pathogen Interactions

Infectious diseases are increasingly recognized as a major threat worldwide due to the rise of antimicrobial resistance and the emergence of novel pathogens. In vitro models that can adequately mimic in vivo gastrointestinal physiology are in high demand to elucidate mechanisms behind pathogen infectivity, and to aid the design of effective preventive and therapeutic interventions. There exists a trade-off between simple and high throughput models and those that are more complex and physiologically relevant. The complexity of the model used shall be guided by the biological question to be addressed. This review provides an overview of the structure and function of the intestine and the models that are developed to emulate this. Conventional models are discussed in addition to emerging models which employ engineering principles to equip them with necessary advanced monitoring capabilities for intestinal host-pathogen interrogation. Limitations of current models and future perspectives on the field are presented.

Development of the Neonatal Intestinal Barrier, Microbiome, and Susceptibility to NEC

The function of the intestinal barrier is partially dependent on host maturity and the colonization patterns of the microbiome to which it is exposed. Premature birth and stressors of neonatal intensive care unit (NICU)-related support (e.g., antibiotics, steroids, etc.) can alter the host internal environment resulting in changes in the intestinal barrier. Pathogenic microbial proliferation and breach of the immature intestinal barrier are proposed to be crucial steps in the development of neonatal diseases such as necrotizing enterocolitis. This article will review the current literature on the intestinal barrier in the neonatal gut, the consequences of microbiome development for this defense system, and how prematurity can influence neonatal susceptibility to gastrointestinal infection.

Development of a novel definitive scoring system for an enteral feed-only model of necrotizing enterocolitis in piglets

Introduction

Necrotizing enterocolitis (NEC) is a complex inflammatory disorder of the human intestine that most often occurs in premature newborns. Animal models of NEC typically use mice or rats; however, pigs have emerged as a viable alternative given their similar size, intestinal development, and physiology compared to humans. While most piglet NEC models initially administer total parenteral nutrition prior to enteral feeds, here we describe an enteral-feed only piglet model of NEC that recapitulates the microbiome abnormalities present in neonates that develop NEC and introduce a novel multifactorial definitive NEC (D-NEC) scoring system to assess disease severity.

Methods

Premature piglets were delivered via Caesarean section. Piglets in the colostrum-fed group received bovine colostrum feeds only throughout the experiment. Piglets in the formula-fed group received colostrum for the first 24 h of life, followed by Neocate Junior to induce intestinal injury. The presence of at least 3 of the following 4 criteria were required to diagnose D-NEC: (1) gross injury score ≥4 of 6; (2) histologic injury score ≥3 of 5; (3) a newly developed clinical sickness score ≥5 of 8 within the last 12 h of life; and (4) bacterial translocation to ≥2 internal organs. Quantitative reverse transcription polymerase chain reaction was performed to confirm intestinal inflammation in the small intestine and colon. 16S rRNA sequencing was performed to evaluate the intestinal microbiome.

Results

Compared to the colostrum-fed group, the formula-fed group had lower survival, higher clinical sickness scores, and more severe gross and histologic intestinal injury. There was significantly increased bacterial translocation, D-NEC, and expression of IL-1α and IL-10 in the colon of formula-fed compared to colostrum-fed piglets. Intestinal microbiome analysis of piglets with D-NEC demonstrated lower microbial diversity and increased Gammaproteobacteria and Enterobacteriaceae.

Conclusions

We have developed a clinical sickness score and a new multifactorial D-NEC scoring system to accurately evaluate an enteral feed-only piglet model of NEC. Piglets with D-NEC had microbiome changes consistent with those seen in preterm infants with NEC. This model can be used to test future novel therapies to treat and prevent this devastating disease.

State-of-the-art review and update of in vivo models of necrotizing enterocolitis

NEC remains one of the most common causes of mortality and morbidity in preterm infants. Animal models of necrotizing enterocolitis (NEC) have been crucial in improving our understanding of this devastating disease and identifying biochemical pathways with therapeutic potential. The pathogenesis of NEC remains incompletely understood, with no specific entity that unifies all infants that develop NEC. Therefore, investigators rely on animal models to manipulate variables and provide a means to test interventions, making them valuable tools to enhance our understanding and prevent and treat NEC. The advancements in molecular analytic tools, genetic manipulation, and imaging modalities and the emergence of scientific collaborations have given rise to unique perspectives and disease correlates, creating novel pathways of investigation. A critical review and understanding of the current phenotypic considerations of the highly relevant animal models of NEC are crucial to developing novel therapeutic and preventative strategies for NEC.

Apical-Out Enteroids as an Innovative Model for Necrotizing Enterocolitis

INTRODUCTION

Necrotizing enterocolitis (NEC) is a gastrointestinal disease of premature neonates. We previously validated a NEC enteroid model derived from human infant intestinal tissue. Typical enteroid configuration is basolateral-out (BO) without direct access to the luminal (apical) surface. Apical access is necessary to allow physiologic comparison of pathogen interaction with the intestinal epithelial barrier. We hypothesize that apical-out (AO) enteroids will provide a relevant NEC model to study this relationship.

METHODS

Following the institutional review board approval (#11610-11611), neonatal intestinal tissue was collected from surgical specimens. Stem cells were collected; enteroids were generated and grown to maturity in BO conformation then everted to AO. Enteroids were untreated or treated for 24 h with 100 μg/mL lipopolysaccharide and hypoxia. Protein and gene expression were analyzed for inflammatory markers, tight junction (TJ) proteins and permeability characteristic of NEC.

RESULTS

Apical TJ protein zonula occludens-1 and basolateral protein β-catenin immunofluorescence confirmed AO configuration. Treated AO enteroids had significantly increased messenger RNA (P = 0.001) and protein levels (P < 0.0001) of tumor necrosis factor-α compared to controls. Corrected total cell fluorescence of toll-like receptor 4 was significantly increased in treated AO enteroids compared to control (P = 0.002). Occludin was found to have significantly decreased messenger RNA in treated AO enteroids (P = 0.003). Expression of other TJ proteins claudins-1, -4 and zonula occludens-1 was significantly decreased in treated AO enteroids (P < 0.05).

CONCLUSIONS

AO enteroids present an innovative model for NEC with increased inflammation and gut barrier restructuring. This model allows for a biologically relevant investigation of the interaction between the pathogen and the intestinal epithelial barrier in NEC.

Models of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of death and disability from gastrointestinal disease in premature infants. The mortality of patients with NEC is approximately 30%, a figure that has not changed in many decades, reflecting the need for a greater understanding of its pathogenesis. Progress towards understanding the cellular and molecular mechanisms underlying NEC requires the study of highly translational animal models. Such animal models must mimic the biology and physiology of premature infants, while still allowing for safe experimental manipulation of environmental and microbial factors thought to be associated with the risk and severity of NEC. Findings from animal models have yielded insights into the interactions between the host, the colonizing microbes, and the innate immune receptor Toll-like Receptor 4 (TLR4) in driving disease development. This review discusses the relative strengths and weaknesses of available in vivo, in vitro, and NEC-in-a-dish models of this disease. We also highlight the unique contributions that each model has made to our understanding of the complex interactions between enterocytes, microbiota, and immune cells in the pathogenesis of NEC. The overall purpose of this review is to provide a menu of options regarding currently available animal models of NEC, while in parallel hopefully reducing the potential uncertainty and confusion regarding NEC models to assist those who wish to enter this field from other disciplines.

The Neonatal Innate Immune Response to Sepsis: Checkpoint Proteins as Novel Mediators of This Response and as Possible Therapeutic/Diagnostic Levers

Sepsis, a dysfunctional immune response to infection leading to life-threatening organ injury, represents a significant global health issue. Neonatal sepsis is disproportionately prevalent and has a cost burden of 2-3 times that of adult patients. Despite this, no widely accepted definition for neonatal sepsis or recommendations for management exist and those created for pediatric patients are significantly limited in their applicability to this unique population. This is in part due to neonates' reliance on an innate immune response (which is developmentally more prominent in the neonate than the immature adaptive immune response) carried out by dysfunctional immune cells, including neutrophils, antigen-presenting cells such as macrophages/monocytes, dendritic cells, etc., natural killer cells, and innate lymphoid regulatory cell sub-sets like iNKT cells, γδ T-cells, etc. Immune checkpoint inhibitors are a family of proteins with primarily suppressive/inhibitory effects on immune and tumor cells and allow for the maintenance of self-tolerance. During sepsis, these proteins are often upregulated and are thought to contribute to the long-term immunosuppression seen in adult patients. Several drugs targeting checkpoint inhibitors, including PD-1 and PD-L1, have been developed and approved for the treatment of various cancers, but no such therapeutics have been approved for the management of sepsis. In this review, we will comparatively discuss the role of several checkpoint inhibitor proteins, including PD-1, PD-L1, VISTA, and HVEM, in the immune response to sepsis in both adults and neonates, as well as posit how they may uniquely propagate their actions through the neonatal innate immune response. We will also consider the possibility of leveraging these proteins in the clinical setting as potential therapeutics/diagnostics that might aid in mitigating neonatal septic morbidity/mortality.

Necrotizing Enterocolitis: Overview on In Vitro Models

Necrotizing enterocolitis (NEC) is a gut inflammatory disorder which constitutes one of the leading causes of morbidity and mortality for preterm infants. The pathophysiology of NEC is yet to be fully understood; several observational studies have led to the identification of multiple factors involved in the pathophysiology of the disease, including gut immaturity and dysbiosis of the intestinal microbiome. Given the complex interactions between microbiota, enterocytes, and immune cells, and the limited access to fetal human tissues for experimental studies, animal models have long been essential to describe NEC mechanisms. However, at present there is no animal model perfectly mimicking human NEC; furthermore, the disease mechanisms appear too complex to be studied in single-cell cultures. Thus, researchers have developed new approaches in which intestinal epithelial cells are exposed to a combination of environmental and microbial factors which can potentially trigger NEC. In addition, organoids have gained increasing attention as promising models for studying NEC development. Currently, several in vitro models have been proposed and have contributed to describe the disease in deeper detail. In this paper, we will provide an updated review of available in vitro models of NEC and an overview of current knowledge regarding its molecular underpinnings.

Exploring Clinically-Relevant Experimental Models of Neonatal Shock and Necrotizing Enterocolitis

Neonatal shock and necrotizing enterocolitis (NEC) are leading causes of morbidity and mortality in premature infants. NEC is a life-threatening gastrointestinal illness, the precise etiology of which is not well understood, but is characterized by an immaturity of the intestinal barrier, altered function of the adaptive immune system, and intestinal dysbiosis. The complexities of NEC and shock in the neonatal population necessitate relevant clinical modeling using newborn animals that mimic the disease in human neonates to better elucidate the pathogenesis and provide an opportunity for the discovery of potential therapeutics. A wide variety of animal species-including rats, mice, piglets, and primates-have been used in developing experimental models of neonatal diseases such as NEC and shock. This review aims to highlight the immunologic differences in neonates compared with adults and provide an assessment of the advantages and drawbacks of established animal models of both NEC and shock using enteral or intraperitoneal induction of bacterial pathogens. The selection of a model has benefits unique to each type of animal species and provides individual opportunities for the development of targeted therapies. This review discusses the clinical and physiologic relevance of animal models and the insight they contribute to the complexities of the specific neonatal diseases: NEC and shock.

Molecular Characterization of Cronobacter sakazakii Strains Isolated from Powdered Milk

Cronobacter spp. are opportunistic pathogens of the Enterobacteriaceae family. The organism causes infections in all age groups, but the most serious cases occur in outbreaks related to neonates with meningitis and necrotizing enterocolitis. The objective was to determine the in silico and in vitro putative virulence factors of six Cronobacter sakazakii strains isolated from powdered milk (PM) in the Czech Republic. Strains were identified by MALDI-TOF MS and whole-genome sequencing (WGS). Virulence and resistance genes were detected with the Ridom SeqSphere+ software task template and the Comprehensive Antibiotic Resistance Database (CARD) platform. Adherence and invasion ability were performed using the mouse neuroblastoma (N1E-115 ATCCCRL-2263) cell line. The CRISPR-Cas system was searched with CRISPRCasFinder. Core genome MLST identified four different sequence types (ST1, ST145, ST245, and ST297) in six isolates. Strains 13755-1B and 1847 were able to adhere in 2.2 and 3.2 × 106 CFU/mL, while 0.00073% invasion frequency was detected only in strain 1847. Both strains 13755-1B and 1847 were positive for three (50.0%) and four virulence genes, respectively. The cpa gene was not detected. Twenty-eight genes were detected by WGS and grouped as flagellar or outer membrane proteins, chemotaxis, hemolysins, and invasion, plasminogen activator, colonization, transcriptional regulator, and survival in macrophages. The colistin-resistance-encoding mcr-9.1 and cephalothin-resis-encoding blaCSA genes and IncFII(pECLA) and IncFIB(pCTU3) plasmids were detected. All strains exhibited CRISPR matrices and four of them two type I-E and I-F matrices. Combined molecular methodologies improve Cronobacter spp. decision-making for health authorities to protect the population.

Nesfatin-1 ameliorates oxidative bowel injury in rats with necrotizing enterocolitis: The role of the microbiota composition and claudin-3 expression

BACKGROUND AND PURPOSE

Ongoing high mortality due to necrotizing enterocolitis (NEC) necessitates the investigation of novel treatments to improve the outcome of the affected newborns. The aim was to elucidate the potential therapeutic impact of the nesfatin-1, a peptide with anti-inflammatory and anti-apoptotic effects in several inflammatory processes, on NEC-induced newborn rats.

MATERIALS AND METHODS

Sprague-Dawley pups were separated from their mothers, fed with a hyperosmolar formula and exposed to hypoxia, while control pups had no intervention. NEC-induced pups received saline or nesfatin-1 (0.2 μg/kg/day) for 3 days, while some nesfatin-1 treated pups were injected with capsaicin (50 μg/g) for the chemical ablation of afferent neurons. On the 4th day, clinical state and macroscopic gut assessments were made. In intestines, immunohistochemical staining of cycloxygenase-2 (COX-2), nuclear factor (NF)-κB-p65 (RelA), vascular endothelial growth factor (VEGF), claudin-3 and zonula occludens-1 (ZO-1) were performed, while gene expressions of COX-2, occludin, claudin-3, NF-κB-p65 (RelA) and VEGF were determined using q-PCR. In fecal samples, relative abundance of bacteria was quantified by q-PCR. Biochemical evaluation of oxidant/antioxidant parameters was performed in both intestinal and cerebral tissues.

RESULTS

Claudin-3 and ZO-1 immunoreactivity scores were significantly elevated in the nesfatin-1 treated control pups. Nesfatin-1 reduced NEC-induced high macroscopic and clinical scores, inhibited NF-κB-65 pathway and maintained the balance of oxidant/antioxidant systems. NEC increased the abundance of Proteobacteria with a concomitant reduction in Actinobacteria and Bacteroidetes, while nesfatin-1 treatment reversed these alterations. Modulatory effects of nesfatin-1 on microbiota and oxidative injury were partially reversed by capsaicin. Immunohistochemistry demonstrated that nesfatin-1 abolished NEC-induced reduction in claudin-3. Gene expressions of COX-2, NF-κB, occludin and claudin-3 were elevated in saline-treated NEC pups, while these up-regulated mRNA levels were not further altered in nesfatin-1-treated NEC pups.

CONCLUSION

Nesfatin-1 could be regarded as a potential preventive agent for the treatment of NEC.

New directions in necrotizing enterocolitis with early-stage investigators

The 2019 Necrotizing Enterocolitis (NEC) Symposium expanded upon the NEC Society's goals of bringing stakeholders together to discuss cutting-edge science, potential therapeutics and preventative measures, as well as the patient-family perspectives of NEC. The Symposium facilitated discussions and shared knowledge with the overarching goal of creating "A World Without NEC." To accomplish this goal, new research to advance the state of the science is necessary. Over the last decade, several established investigators have significantly improved our understanding of the pathophysiology of NEC and they have paved the way for the next generation of clinician-scientists funded to perform NEC research. This article will serve to highlight the contributions of these young clinician-scientists that seek to elucidate how immune, microbial and nervous system dysregulation contributes to the pathophysiology of NEC.

Cell death of intestinal epithelial cells in intestinal diseases

Gut injury continues to be the devastating and unpredictable critical illness associated with increased cell death of intestinal epithelial cells (IECs). The IECs, immune system and microbiome are the interrelated entities to maintain normal intestinal homeostasis and barrier integrity. In response to microbial invasion, IEC cell death occurs to maintain intestinal epithelium function and retain the continuous renewal and tissue homeostasis. But the imbalance of IEC cell death results in increased intestinal permeability and barrier dysfunction that leads to several acute and chronic intestinal diseases, such as intestinal ischemia/reperfusion (I/R), sepsis, inflammatory bowel diseases (IBD), necrotizing enterocolitis (NEC), etc. During the pathophysiological state, the excessive IEC apoptotic cell death leads to a chronic inflammatory condition, later switches to necroptotic cell death mechanism that induces more pathological features than apoptosis and may also induce other lytic cell death mechanisms like pyroptosis and ferroptosis to increase the pathogenesis of the intestinal diseases. But still, there remains gaps in the fundamental knowledge about the IEC cell death mechanisms in chronic intestinal diseases. Together, a deep understanding of the specific cell death mechanisms underlying chronic intestinal diseases, including sepsis, IBD, NEC, and intestinal I/R, is desperately needed to develop emerging novel promising therapeutic strategies. This review aims to show how the acute and critical illness in the gut are driven by IEC cell death mechanism, such as apoptosis, necrosis, necroptosis, pyroptosis, and ferroptosis.

Feeding Formula Eliminates the Necessity of Bacterial Dysbiosis and Induces Inflammation and Injury in the Paneth Cell Disruption Murine NEC Model in an Osmolality-Dependent Manner

Necrotizing enterocolitis (NEC) remains a significant cause of morbidity and mortality in preterm infants. Formula feeding is a risk factor for NEC and osmolality, which is increased by the fortification that is required for adequate growth of the infant, has been suggested as a potential cause. Our laboratory has shown that Paneth cell disruption followed by induction of dysbiosis can induce NEC-like pathology in the absence of feeds. We hypothesized adding formula feeds to the model would exacerbate intestinal injury and inflammation in an osmolality-dependent manner. NEC-like injury was induced in 14-16 day-old C57Bl/6J mice by Paneth cell disruption with dithizone or diphtheria toxin, followed by feeding rodent milk substitute with varying osmolality (250-1491 mOsm/kg H₂O). Animal weight, serum cytokines and osmolality, small intestinal injury, and cecal microbial composition were quantified. Paneth cell-disrupted mice fed formula had significant NEC scores compared to controls and no longer required induction of bacterial dysbiosis. Significant increases in serum inflammatory markers, small intestinal damage, and overall mortality were osmolality-dependent and not related to microbial changes. Overall, formula feeding in combination with Paneth cell disruption induced NEC-like injury in an osmolality-dependent manner, emphasizing the importance of vigilance in designing preterm infant feeds.

C. sakazakii activates AIM2 pathway accompanying with excessive ER stress response in mammalian mammary gland epithelium

Bovine mastitis is a common inflammatory disease caused by various factors. The main factor of mastitis is pathogenic microorganism infection, such as Staphylococcus aureus, Escherichia coli, and Streptococcus. Cronobacter sakazakii (C. sakazakii) is a newly discovered pathogenic bacteria in milk products, which seriously threat human health in recent years. At present, it has not been reported that the pathogenesis of mastitis is caused by C. sakazakii. This study investigated the inflammation of mammary gland epithelium, which was induced by C. sakazakii for the first time. We focused on bacterial isolation, histological observation, AIM2 inflammasome pathways, endoplasmic reticulum stress, and apoptosis. The results showed that C. sakazakii-induced inflammation caused damage of tissue, significantly increased the production of pro-inflammatory cytokines (including TNF-α, IL-1β, and IL-6), activated the AIM2 inflammasome pathway (increased the expression of AIM2 and cleaved IL-1β), and induced endoplasmic reticulum stress (increased the expression of ERdj4, Chop, Grp78) and apoptosis (increased the ratio of Bax/Bcl-2, a marker of apoptosis). In conclusion, it is suggested that it maybe inhibite AIM2 inflammasome pathways and alleviate endoplasmic reticulum stress (ER stress) against the C. sakazakii-induced inflammation.

Effects of artificially introduced Enterococcus faecalis strains in experimental necrotizing enterocolitis

Enterococcus faecalis is a ubiquitous intestinal symbiont and common early colonizer of the neonatal gut. Although colonization with E. faecalis has been previously associated with decreased pathology of necrotizing enterocolitis (NEC), these bacteria have been also implicated as opportunistic pathogens. Here we characterized 21 strains of E. faecalis, naturally occurring in 4-day-old rats, for potentially pathogenic properties and ability to colonize the neonatal gut. The strains differed in hemolysis, gelatin liquefaction, antibiotic resistance, biofilm formation, and ability to activate the pro-inflammatory transcription factor NF-κB in cultured enterocytes. Only 3 strains, BB70, 224, and BB24 appreciably colonized the neonatal intestine on day 4 after artificial introduction with the first feeding. The best colonizer, strain BB70, effectively displaced E. faecalis of maternal origin. Whereas BB70 and BB24 significantly increased NEC pathology, strain 224 significantly protected from NEC. Our results show that different strains of E. faecalis may be pathogenic or protective in experimental NEC.

Bacteroides fragilis Strain ZY-312 Defense against Cronobacter sakazakii-Induced Necrotizing Enterocolitis In Vitro and in a Neonatal Rat Model

Cronobacter sakazakii is an important pathogen associated with the development of necrotizing enterocolitis (NEC), infant sepsis, and meningitis. Several randomized prospective clinical trials demonstrated that oral probiotics could decrease the incidence of NEC. Previously, we isolated and characterized a novel probiotic, Bacteroides fragilis strain ZY-312. However, it remains unclear how ZY-312 protects the host from the effects of C. sakazakii infection. To understand the underlying mechanisms triggering the probiotic effects, we tested the hypothesis that there was cross talk between probiotics/probiotics-modulated microbiota and the local immune system, governed by the permeability of the intestinal mucosa, using in vitro and in vivo models for the intestinal permeability. The probiotic effects of ZY-312 on intestinal epithelial cells were first examined, and the results revealed that ZY-312 inhibited C. sakazakii invasion, C. sakazakii-induced dual cell death (pyroptosis and apoptosis), and epithelial barrier dysfunction in vitro and in vivo The presence of ZY-312 also resulted in decreased expression of an inflammasome (NOD-like receptor family member pyrin domain-containing protein 3 [NLRP3]), caspase-3, and serine protease caspase-1 in a neonatal rat model. Furthermore, ZY-312 significantly modulated the compositions of the intestinal bacterial communities and decreased the relative abundances of Proteobacteria and Gammaproteobacteria but increased the relative abundances of Bacteroides and Bacillus in neonatal rats. In conclusion, our findings have shown for the first time that the probiotic B. fragilis ZY-312 suppresses C. sakazakii-induced NEC by modulating the proinflammatory response and dual cell death (apoptosis and pyroptosis).IMPORTANCE Cronobacter sakazakii is an opportunistic pathogenic bacterium that can cause necrotizing enterocolitis (NEC). However, the mechanism of pathogenicity of C. sakazakii is largely unknown. Here we have now demonstrated that apoptotic and pyroptotic stimuli are effectors of C. sakazakii-induced NEC. Previously, we isolated a novel probiotic strain candidate from fecal samples from healthy infants and characterized it as Bacteroides fragilis strain ZY-312. Functional characterization reveals that ZY-312 inhibited C. sakazakii invasion, restoring epithelial barrier dysfunction, decreasing the expression of inflammatory cytokines, and reducing dual cell death (pyroptosis and apoptosis). Furthermore, the presence of ZY-132 was sufficient to hinder the adverse reaction seen with C. sakazakii in a C. sakazakii-induced NEC model. Taking the results together, our study demonstrated the utility of ZY-312 as a promising probiotic agent for the prevention of NEC.

Caveolin 1 is Associated with Upregulated Claudin 2 in Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal emergency of neonates. Epithelial tight junction (TJ) proteins, such as claudins, are essential for regulation and function of the intestinal barrier. Rho kinase (ROCK) affects cellular permeability and TJ regulation. We hypothesized that TJ protein changes would correlate with increased permeability in experimental NEC, and ROCK inhibitors would be protective against NEC by regulation of key claudin proteins. We tested this hypothesis using an in vivo rat pup model, an in vitro model of experimental NEC, and human intestinal samples from patients with and without NEC. Experimental NEC was induced in rats via hypoxia and bacteria-containing formula, and in Caco-2 cells by media inoculated with LPS. The expression of claudins was measured by gene and protein analysis. Experimental NEC in rat pups and Caco-2 cells had increased permeability compared to controls. Gene and protein expression of claudin 2 was increased in experimental NEC. Sub-cellular fractionation localized increased claudin 2 protein to the cytoskeleton. ROCK inhibition was associated with normalization of these alterations and decreased severity of experimental NEC. Co-immunoprecipitation of caveolin-1 with claudin 2 suggests that caveolin-1 may act as a shuttle for the internalization of claudin 2 seen in experimental NEC. In conclusion, NEC is associated with intestinal permeability and increased expression of claudin 2, increased binding of caveolin-1 and claudin 2, and increased trafficking of claudin 2 to the cytoskeleton.

Bacterial isolation from internal organs of rats (Rattus rattus) captured in Baghdad city of Iraq

Aim

Rats are accused in disseminating many zoonotic diseases. This study aimed to isolate and identify bacteria from internal organs of rats captured in Baghdad City, Iraq.

Materials and Methods

A total of 120 black rats (R. rattus) were trapped from different areas in Baghdad city. Rats were kept in individual plastic cages for 3 h before euthanizing. Deep pharyngeal swab, intestinal content, urine, and pieces of the liver and spleen, lung, kidney, and brain were obtained aseptically. The specimens were inoculated into peptone water and incubated at 37°C for 24 h for enrichment. A loopful of each specimen was then subcultured onto MacConkey Agar, Blood Agar, and Mannitol Salt Agar. CHROMagar O157 H7 and CHROMagar Listeria were used to detect Escherichia coli 157:7 and Listeria spp., respectively. Biochemical tests on analytical profile index, microscopic examination, and commercial kit for latex agglutination test for serotyping E. coli O157:H7 were used.

Results

Mixed bacterial isolates were recorded as 116, 52, 36, 28, 18, 6, and 4 from intestinal contents, deep pharyngeal, liver and spleen, urine, lung, brain, and kidney, respectively. Microorganisms included E. coli, Staphylococcus aureus, Streptococcus spp., Bacillus spp., Pseudomonas aeruginosa, Citrobacter freundii, Proteus vulgaris, E. coli O157:H7, Enterobacter cloacae, Listeria spp., Klebsiella spp., Ochrobactrum anthropi, Aeromonas spp., Brucella spp., Pseudomonas fluorescens, Escherichia fergusonii, Micrococcus spp., Morganella spp., Proteus mirabilis, Pseudomonas luteola, and Streptobacillus spp. The highest bacterial prevalence (88; 73.33%) was recorded for E. coli, where 68 isolates were identified from the intestinal contents. Of these, four isolates were E. coli O157:H7.

Conclusion

Rats are important carriers and transmitters of a number of pathogens and can disseminate these microorganisms to humans and animals.

Pathophysiology of Necrotizing Enterocolitis: An Update

NEC is a devastating disease that, once present, is very difficult to treat. In the absence of an etiologic treatment, preventive measures are required. Advances in decoding the pathophysiology of NEC are being made but a more comprehensive understanding is needed for the targeting of preventative strategies. A better definition of the disease as well as diagnostic criteria are needed to be able to specifically label a disease as NEC. Multiple environmental factors combined with host susceptibility appear to contribute to enhanced risks for developing this disease. Several different proximal pathways are involved, all leading to a common undesired outcome: Intestinal necrosis. The most common form of this disease appears to involve inflammatory pathways that are closely meshed with the intestinal microbiota, where a dysbiosis may result in dysregulated inflammation. The organisms present in the intestinal tract prior to the onset of NEC along with their diversity and functional capabilities are just beginning to be understood. Fulfillment of postulates that support causality for particular microorganisms is needed if bacteriotherapies are to be intelligently applied for the prevention of NEC. Identification of molecular effector pathways that propagate inflammation, understanding of, even incipient role of genetic predisposition and of miRNAs may help solve the puzzle of this disease and may bring the researchers closer to finding a treatment. Despite recent progress, multiple limitations of the current animal models, difficulties related to studies in humans, along with the lack of a "clear" definition will continue to make it a very challenging disease to decipher.

Occurrence of virulence factors in Cronobacter sakazakii and Cronobacter malonaticus originated from clinical samples

BACKGROUND

Cronobacter spp. are Gram-negative, facultative-anaerobic, non-spore forming, enteric coliform bacteria, which belongs to the Enterobacteriaceae family. Cronobacter spp. are opportunistic pathogens that have brought rare but life-threatening infections such as meningitis, necrotizing enterocolitis and bloodstream infections in neonates and infants. Information on the diversity, pathogenicity and virulence of Cronobacter species obtained from various sources is still relatively scarce and fragmentary. The aim of this study was to examine and analyse different pathogenicity and virulence factors among C. sakazakii and C. malonaticus strains isolated from clinical samples.

METHODS

The thirty-six clinical Cronobacter strains have been used in this study. This bacterial collection consists of 25 strains of C. sakazakii and 11 strains of C. malonaticus, isolated from different clinical materials. Seven genes (ompA, inv, sip, aut, hly, fliC, cpa) were amplified by PCR. Moreover, the motility and the ability of these strains to adhere and invade human colorectal adenocarcinoma (HT-29) and mouse neuroblastoma (N1E-115) cell lines were investigated.

RESULTS

Our results showed that all tested strains were able to adhere to both used cell lines, HT-29 and N1E-115 cells. The invasion assay showed that 66.7% (24/36) of isolates were able to invade N1-E115 cells while 83% (30/36) of isolates were able to invade HT-29 cells. On the average, 68% of the C. sakazakii strains exhibited seven virulence factors and only 18% in C. malonaticus. All strains amplified ompA and fliC genes. The other genes were detected as follow: sip 97% (35/36), hlyA 92% (33/36), aut 94% (34/36), cpa 67% (24/36), and inv 69% (25/36).

CONCLUSIONS

C. sakazakii and C malonaticus strains demonstrate the diversity of the virulence factors present among these pathogens. It is necessary to permanently monitor the hospital environment to appropriately treat and resolve cases associated with disease. Furthermore, in-depth knowledge is needed about the source and transmission vehicles of pathogens in hospitals to adopt pertinent prevention measures.

Probiotic Lactococcus lactis decreases incidence and severity of necrotizing enterocolitis in a preterm animal model

BACKGROUND

Necrotizing enterocolitis (NEC) persists as the most common and serious gastrointestinal disorder among premature infants. Lactococcus lactis (LL), a lactic acid producing bacteria commonly found in buttermilk and cheese products, has several unique properties making it an ideal probiotic for neonates. We evaluated if the probiotic LL prevents development of NEC in a preterm rabbit model with Cronobacter sakazakii (CS).

METHODS

Two-day preterm New Zealand white rabbit pups were randomly assigned to three diets: control (no additives), CS, and CS+LL. Pups were gavage fed and given daily oral ranitidine and indomethacin. Anal blockage was performed using tissue adhesive. Subjects were sacrificed on day four, with tissue from distal ileum and proximal colon graded for NEC by a pediatric pathologist blinded to group assignments. Outcomes were compared using Fisher's exact test.

RESULTS

All pups in the control group survived to sacrifice and none developed NEC. Survival was 26% higher (p = 0.03) and incidence of NEC 51% less (P < 0.001) in CS+LL group compared to CS group. Of the pups that developed NEC, all pups in the CS+LL group had Grade 1 NEC, while one-third of pups in the CS group developed Grades 2-4 NEC.

CONCLUSIONS

In the presence of CS, LL is protective against development of NEC in a preterm rabbit model. Future studies are needed that evaluate utilization of prophylactic probiotics in the neonatal intensive care unit to determine if this intervention can successfully decrease rates of NEC in preterm infants.

Rho kinase inhibition maintains intestinal and vascular barrier function by upregulation of occludin in experimental necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a deadly disease that occurs in 5-10% of neonates. Although NEC has been extensively studied, no single therapeutic target has been identified. Rho kinase (ROCK) is a serine/threonine kinase that affects multiple cellular processes, including tight junction (TJ) function, cellular permeability, and apoptosis. We hypothesized that ROCK inhibition would decrease cellular permeability, stabilize TJ proteins (occludin), and decrease the severity of NEC. To test this hypothesis, human colon epithelial cells (Caco-2) and human endothelial cells were studied. Cells were treated with lipopolysaccharide to simulate an in vitro model of NEC. The effect of ROCK inhibition was measured by transepithelial membrane resistance (TEER) and cellular permeability to FITC-dextran. The effects of ROCK inhibition in vivo were analyzed in the rat pup model of NEC. NEC was induced by feeding formula supplemented with Cronobacter sakazakii with or without gavaged ROCK inhibitor. Rat intestines were scored based on histological degree of injury. RNA and protein assays for occludin protein were performed for all models of NEC. Treatment with ROCK inhibitor significantly decreased cellular permeability in Caco-2 cells and increased TEER. Intestinal injury scoring revealed decreased scores in ROCK inhibitor-treated pups compared with NEC only. Both cell and rat pup models demonstrated an upregulation of occludin expression in the ROCK inhibitor-treated groups. Therefore, we conclude that ROCK inhibition protects against experimental NEC by strengthening barrier function via upregulation of occludin. These data suggest that ROCK may be a potential therapeutic target for patients with NEC. NEW & NOTEWORTHY These studies are the first to demonstrate an upregulation of occludin tight junction protein in response to Rho kinase (ROCK) inhibition. Furthermore, we have demonstrated that ROCK inhibition in experimental models of necrotizing enterocolitis (NEC) is protective against NEC in both in vitro and in vivo models of disease.

Lactobacillus murinus HF12 colonizes neonatal gut and protects rats from necrotizing enterocolitis

The use of lactobacilli in prevention of necrotizing enterocolitis (NEC) is hampered by insufficient knowledge about optimal species/strains and effects on intestinal bacterial populations. We therefore sought to identify lactobacilli naturally occurring in postnatal rats and examine their ability to colonize the neonatal intestine and protect from NEC. L. murinus, L. acidophilus, and L. johnsonii were found in 42, 20, and 1 out of 51 4-day old rats, respectively. Higher proportion of L. murinus in microbiota correlated with lower NEC scores. Inoculation with each of the three species during first feeding significantly augmented intestinal populations of lactobacilli four days later, indicating successful colonization. L. murinus, but not L. acidophilus or L. johnsonii, significantly protected against NEC. Thus, lactobacilli protect rats from NEC in a species- or strain-specific manner. Our results may help rationalizing probiotic therapy in NEC.

Evolving understanding of neonatal necrotizing enterocolitis

PURPOSE OF REVIEW

Necrotizing enterocolitis (NEC) is a devastating disease that predominately affects premature neonates. The pathogenesis of NEC is multifactorial and poorly understood. Risk factors include low birth weight, formula-feeding, hypoxic/ischemic insults, and microbial dysbiosis. This review focuses on our current understanding of the diagnosis, management, and pathogenesis of NEC.

RECENT FINDINGS

Recent findings identify specific mucosal cell types as potential therapeutic targets in NEC. Despite a broadly accepted view that bacterial colonization plays a key role in NEC, characteristics of bacterial populations associated with this disease remain elusive. The use of probiotics such as lactobacilli and bifidobacteria has been studied in numerous trials, but there is a lack of consensus regarding specific strains and dosing. Although growth factors found in breast milk such as epidermal growth factor and heparin-binding epidermal growth factor may be useful in disease prevention, developing new therapeutic interventions in NEC critically depends on better understanding of its pathogenesis.

SUMMARY

NEC is a leading cause of morbidity and mortality in premature neonates. Recent data confirm that growth factors and certain bacteria may offer protection against NEC. Further studies are needed to better understand the complex pathogenesis of NEC.

The science and necessity of using animal models in the study of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) remains one of the highest causes of mortality and of acute and long-term morbidity in premature infants. Multiple factors are involved in the pathophysiology of NEC including the immaturity of the immune system and the complex changing composition of the intestinal microbiome. This is compounded by the fact that the premature infant should ideally still be a developing fetus and has an immature intestinal tract. Because these complexities are beyond the scope of studies in single-cell cultures, animal models are absolutely essential to understand the mechanisms involved in the pathophysiology of NEC and the effects of inflammation on the immature intestinal tract. To this end, investigators have utilized many different species (e.g., rats, mice, rabbits, quails, piglets, and non-human primates) and conditions to develop models of NEC. Each animal has distinct advantages and drawbacks related to its preterm viability, body size, genetic variability, and cost. The choice of animal model is strongly influenced by the scientific question being addressed. While no model perfectly mimics human NEC, each has greatly improved our understanding of disease. Examples of recent discoveries in NEC pathogenesis and prevention underscore the importance of continued animal research in NEC.

New virulence factor CSK29544_02616 as LpxA binding partner in Cronobacter sakazakii

Cronobacter sakazakii is an opportunistic pathogen that can cause meningitis and necrotizing enterocolitis in premature infants, but its virulence determinants remain largely unknown. In this study, a transposon-mediated random-mutant library of C. sakazakii was used to identify new virulence factors. Compared to wild-type bacteria, a mutant lacking CSK29544_02616 (referred to as labp) was defective in invasion into intestinal epithelial cells (by at least 1000-fold) and showed less phagocytosis by macrophages (by at least 50-fold). The lack of labp in C. sakazakii changed the profile of outer membrane proteins, decreased the production of lipopolysaccharides, and increased the production of membrane phospholipids. Bacterial physiological characteristics including surface hydrophobicity and motility were also altered in the absence of labp, presumably because of changes in the bacterial-envelope structure. To systematically determine the role of labp, ligand fishing was conducted using Labp as a bait, which revealed LpxA as a binding partner of Labp. LpxA is UDP-N-acetylglucosamine (GlcNAc) acyltransferase, the first enzyme in the pathway of lipid A biosynthesis. Labp increased the enzymatic activity of LpxA without influencing lpxA expression. Considering multifaceted roles of lipopolysaccharides in virulence regulation, Labp is a novel virulence factor that promotes the production of lipid A by LpxA in Cronobacter.

Colonization with Escherichia coli EC 25 protects neonatal rats from necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a significant cause of morbidity and mortality in premature infants; yet its pathogenesis remains poorly understood. To evaluate the role of intestinal bacteria in protection against NEC, we assessed the ability of naturally occurring intestinal colonizer E. coli EC25 to influence composition of intestinal microbiota and NEC pathology in the neonatal rat model. Experimental NEC was induced in neonatal rats by formula feeding/hypoxia, and graded histologically. Bacterial populations were characterized by plating on blood agar, scoring colony classes, and identifying each class by sequencing 16S rDNA. Binding of bacteria to, and induction of apoptosis in IEC-6 enterocytes were examined by plating on blood agar and fluorescent staining for fragmented DNA. E. coli EC 25, which was originally isolated from healthy rats, efficiently colonized the intestine and protected from NEC following introduction to newborn rats with formula at 10⁶ or 10⁸ cfu. Protection did not depend significantly on EC25 inoculum size or load in the intestine, but positively correlated with the fraction of EC25 in the microbiome. Introduction of EC25 did not prevent colonization with other bacteria and did not significantly alter bacterial diversity. EC25 neither induced cultured enterocyte apoptosis, nor protected from apoptosis induced by an enteropathogenic strain of Cronobacter muytjensii. Our results show that E. coli EC25 is a commensal strain that efficiently colonizes the neonatal intestine and protects from NEC.

Thymoquinone Inhibits Virulence Related Traits of Cronobacter sakazakii ATCC 29544 and Has Anti-biofilm Formation Potential

The aim of this study was to determine whether thymoquinone, the principal active ingredient in the volatile oil of Nigella sativa seeds, could suppress certain virulence traits of Cronobacter sakazakii ATCC 29544 which contribute to infection. Sub-inhibitory concentrations of thymoquinone significantly decreased motility, quorum sensing, and endotoxin production of C. sakazakii ATCC 29544 and biofilm formation of C. sakazakii 7-17. Thymoquinone substantially reduced the adhesion and invasion of C. sakazakii ATCC 29544 to HT-29 cells and decreased the number of intracellular bacterial cells within the RAW 264.7 macrophage cells. Thymoquinone also repressed the transcription of sixteen genes involved in the virulence. These findings suggest that thymoquinone could attenuated virulence-related traits of C. sakazakii ATCC 29544, and its effects on other C. sakazakii strains and in vivo C. sakazakii infection need further investigation.

Biomarkers of necrotizing enterocolitis: a review of literature

Necrotizing enterocolitis (NEC) is among the most serious gastrointestinal emergency in very low birth weight (VLBW), extremely low birth weight (ELBW) and extremely low gestational age neonates (ELGAN), affecting 7-14% of these neonates. Despite extensive research, the underlying aetiology of NEC still remains blurred. Due to high mortality, morbidity and its delayed presentation, early detection of NEC is considered to be lifesaving. A number of biomarkers have been studied for early detection and prediction of severity of NEC but till date, no ideal marker has been discovered. Molecular techniques like proteomic and metabolomic have recently emerged in the field for the development of biomarkers for early detection and understanding the pathophysiology of NEC. We did literature search for identifying all biomarkers that have been used for the detection of NEC and, in this review article, we discuss these biomarkers along with the available current evidence.

Pathogens of Food Animals: Sources, Characteristics, Human Risk, and Methods of Detection

Pathogens associated with food production (livestock) animals come in many forms causing a multitude of disease for humans. For the purpose of this review, these infectious agents can be divided into three broad categories: those that are associated with bacterial disease, those that are associated with viruses, and those that are parasitic in nature. The goal of this chapter is to provide the reader with an overview of the most common pathogens that cause disease in humans through exposure via the food chain and the consequence of this exposure as well as risk and detection methods. We have also included a collection of unusual pathogens that although rare have still caused disease, and their recognition is warranted in light of emerging and reemerging diseases. These provide the reader an understanding of where the next big outbreak could occur. The influence of the global economy, the movement of people, and food makes understanding production animal-associated disease paramount to being able to address new diseases as they arise.

Probiotic Lactobacillus Species Strengthen Intestinal Barrier Function and Tight Junction Integrity in Experimental Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a serious intestinal disease that occurs in newborn infants. It is associated with major morbidity and affects 5% of all infants admitted to neonatal intensive care units. Probiotics have variable efficacy in preventing necrotizing enterocolitis. Tight junctions (TJ) are protein complexes that maintain epithelial barrier integrity. We hypothesized that the probiotics Lactobacillus rhamnosus and Lactobacillus plantarum strengthen intestinal barrier function, promote TJ integrity, and protect against experimental NEC. Both an in vitro and an in vivo experimental model of NEC were studied. Cultured human intestinal Caco-2 cells were pretreated with L. rhamnosus and L. plantarum probiotics. TJ were then disrupted by EGTA calcium switch or LPS to mimic NEC in vitro. Trans-epithelial resistance (TER) and flux of fluorescein isothiocynate dextran was measured. TJ structure was evaluated by ZO-1 immunofluorescence. In vivo effects of ingested probiotics on intestinal injury and ZO-1 expression were assessed in a rat model of NEC infected with Cronobacter sakazakii (CS). Caco-2 cells treated with individual probiotics demonstrated higher TER and lower permeability compared to untreated cells (p<0.0001). ZO-1 immunofluorescence confirmed TJ stability in treated cells. Rat pups fed probiotics alone had more intestinal injury compared with controls (p=0.0106). Probiotics were protective against injury when given in combination with CS, with no difference in intestinal injury compared to controls (p=0.21). Increased permeability was observed in the probiotic and CS groups (p=0.03, p=0.05), but not in the probiotic plus CS group (p=0.79). Lactobacillus sp. strengthened intestinal barrier function and preserved TJ integrity in an in vitro experimental model of NEC. In vivo, probiotic bacteria were not beneficial when given alone, but were protective in the presence of CS in a rat model of NEC.

A Role for cAMP and Protein Kinase A in Experimental Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intestinal disease that has been associated with Cronobacter sakazakii and typically affects premature infants. Although NEC has been actively investigated, little is known about the mechanisms underlying the pathophysiology of epithelial injury and intestinal barrier damage. Cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) are important mediators and regulators of apoptosis. To test the hypothesis that C. sakazakii increases cAMP and PKA activation in experimental NEC resulting in increased epithelial apoptosis, we investigated the effects of C. sakazakii on cAMP and PKA in vitro and in vivo. Specifically, rat intestinal epithelial cells and a human intestinal epithelial cell line were infected with C. sakazakii, and cAMP levels and phosphorylation of PKA were measured. An increase in cAMP was demonstrated after infection, as well as an increase in phosphorylated PKA. Similarly, increased intestinal cAMP and PKA phosphorylation were demonstrated in a rat pup model of NEC. These increases were correlated with increased intestinal epithelial apoptosis. The additional of a PKA inhibitor (KT5720) significantly ameliorated these effects and decreased the severity of experimental NEC. Findings were compared with results from human tissue samples. Collectively, these observations indicate that cAMP and PKA phosphorylation are associated with increased apoptosis in NEC and that inhibition of PKA activation protects against apoptosis and experimental NEC.

Transcriptome analysis of Cronobacter sakazakii ATCC BAA-894 after interaction with human intestinal epithelial cell line HCT-8

Cronobacter spp. are opportunistic pathogens that are responsible for infections including severe meningitis, septicemia, and necrotizing enterocolitis in neonates and infants. To date, questions still remain regarding the mechanisms of pathogenicity and virulence determinants for each bacterial strain. In this study, we established an in vitro model for Cronobacter sakazakii ATCC BAA-894 infection of HCT-8 human colorectal epithelial cells. The transcriptome profile of C. sakazakii ATCC BAA-894 after interaction with HCT-8 cells was determined using high-throughput whole-transcriptome sequencing (RNA sequencing (RNA-seq)). Gene expression profiles indicated that 139 genes were upregulated and 72 genes were downregulated in the adherent C. sakazakii ATCC BAA-894 strain on HCT-8 cells compared to the cultured bacteria in the cell-free medium. Expressions of some flagella genes and virulence factors involved in adherence were upregulated. High osmolarity and osmotic stress-associated genes were highly upregulated, as well as genes responsible for the synthesis of lipopolysaccharides and outer membrane proteins, iron acquisition systems, and glycerol and glycerophospholipid metabolism. In sum, our study provides further insight into the mechanisms underlying C. sakazakii pathogenesis in the human gastrointestinal tract.

Smad7 interrupts TGF-β signaling in intestinal macrophages and promotes inflammatory activation of these cells during necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is an inflammatory bowel necrosis of premature infants. Based on our recent findings of increased Smad7 expression in surgically resected bowel affected by NEC, we hypothesized that NEC macrophages undergo inflammatory activation because increased Smad7 expression renders these cells resistant to normal, gut-specific, transforming growth factor (TGF)-β-mediated suppression of inflammatory pathways.

METHODS

We used surgically resected human NEC tissue, murine models of NEC-like injury, bone marrow-derived and intestinal macrophages, and RAW264.7 cells. Smad7 and IκB kinase-beta (IKK-β) were measured by quantitative PCR, western blots, and immunohistochemistry. Promoter activation was confirmed in luciferase reporter and chromatin immunoprecipitation assays.

RESULTS

NEC macrophages showed increased Smad7 expression, particularly in areas with severe tissue damage and high bacterial load. Lipopolysaccharide-induced Smad7 expression suppressed TGF-β signaling and augmented nuclear factor-kappa B (NF-κB) activation and cytokine production in macrophages. Smad7-mediated NF-κB activation was likely mediated via increased expression of IKK-β, which, further increased Smad7 expression in a feed-forward loop. We show that Smad7 induced IKK-β expression through direct binding to the IKK-β promoter and its transcriptional activation.

CONCLUSION

Smad7 expression in NEC macrophages interrupts TGF-β signaling and promotes NF-κB-mediated inflammatory signaling in these cells through increased expression of IKK-β.

Cronobacter spp

The Cronobacter group of pathogens, associated with severe and potentially life-threatening diseases, until recently were classified as a single species, Enterobacter sakazakii. The group was reclassified in 2007 into the genus Cronobacter as a member of the Enterobacteriaceae. This chapter outlines the history behind the epidemiology, analyzes how our understanding of these bacteria has evolved, and highlights the clinical significance the Cronobacter spp. have for neonatal and elderly patient populations and treatment of the associated infections.

Roles of nitric oxide and intestinal microbiota in the pathogenesis of necrotizing enterocolitis

Necrotizing enterocolitis remains one of the most vexing problems in the neonatal intensive care unit. Risk factors for NEC include prematurity, formula feeding, and inappropriate microbial colonization of the GI tract. The pathogenesis of NEC is believed to involve weakening of the intestinal barrier by perinatal insults, translocation of luminal bacteria across the weakened barrier, an exuberant inflammatory response, and exacerbation of the barrier damage by inflammatory factors, leading to a vicious cycle of inflammation-inflicted epithelial damage. Nitric oxide (NO), produced by inducible NO synthase (iNOS) and reactive NO oxidation intermediates play a prominent role in the intestinal barrier damage by inducing enterocyte apoptosis and inhibiting the epithelial restitution processes, namely enterocyte proliferation and migration. The factors that govern iNOS upregulation in the intestine are not well understood, which hampers efforts in developing NO/iNOS-targeted therapies. Similarly, efforts to identify bacteria or bacterial colonization patterns associated with NEC have met with limited success, because the same bacterial species can be found in NEC and in non-NEC subjects. However, microbiome studies have identified the three important characteristics of early bacterial populations of the GI tract: high diversity, low complexity, and fluidity. Whether NEC is caused by specific bacteria remains a matter of debate, but data from hospital outbreaks of NEC strongly argue in favor of the infectious nature of this disease. Studies in Cronobacter muytjensii have established that the ability to induce NEC is the property of specific strains rather than the species as a whole. Progress in our understanding of the roles of bacteria in NEC will require microbiological experiments and genome-wide analysis of virulence factors.

A spectrum of intestinal injury models in neonatal mice

PURPOSE

To compare the degree of necrotizing enterocolitis (NEC)-like damage under different stress conditions in neonatal mice.

METHODS

5-day-old C57BL/6 mice were assigned to: (A) breastfed and no stress factors; (B) breastfed+maternal separation (3 h daily); (C) breastfed+hypoxia+lipopolysaccharide (LPS-4 mg/kg/day); (D) hyperosmolar formula+hypoxia+LPS. Mice were killed at 9 days of life. Ileum and colon were stained for hematoxylin/eosin and blindly assessed. A scoring ≥2 was considered NEC. Data were compared using one-way ANOVA and reported as median (range).

RESULTS

Ileum-Mucosal injury was mild in group B (0.0-1). Hypoxia+LPS induced greater injury in group C (1.6, 1-2.5; p < 0.0001 to B) and D (2, 0.5-3.5; p < 0.0001 to B). There were no differences between group C and D (p = n.s.). There were no cases of NEC in group A or B, whereas NEC was present in 36 % group C and 68 % group D mice. Colon-a similar degree of mucosal injury was observed among group B (2, 1-3), C (1.7, 0-3) and D (1.5, 1-3; p = n.s.). NEC was present in 75 % of group B, 50 % of group C and 86 % of group D.

CONCLUSION

These models establish a spectrum of intestinal injury and are useful to investigate the variability of neonatal intestinal diseases, such as NEC.

Pathogenesis of neonatal necrotizing enterocolitis

Although necrotizing enterocolitis (NEC) is the most lethal gastrointestinal disease in the neonatal population, its pathogenesis is poorly understood. Risk factors include prematurity, bacterial colonization, and formula feeding. This review examines how mucosal injury permits opportunistic pathogens to breach the gut barrier and incite an inflammatory response that leads to sustained overproduction of mediators such as nitric oxide and its potent adduct, peroxynitrite. These mediators not only exacerbate the initial mucosal injury, but they also suppress the intestinal repair mechanisms, which further compromises the gut barrier and culminates in bacterial translocation, sepsis, and full-blown NEC.

Insights into virulence factors determining the pathogenicity of Cronobacter sakazakii

Cronobacter sakazakii is an opportunistic pathogen associated with outbreaks of life-threatening necrotizing enterocolitis, meningitis and sepsis in neonates and infants. The pathogen possesses an array of virulence factors which aid in tissue adhesion, invasion and host cell injury. Although the identification and validation of C. sakazakii virulence factors has been hindered by availability of suitable neonatal animal model, various studies has reported outer membrane protein A (ompA) as a potential virulence marker. Various other plasmid associated genes such as filamentous hemagglutinin (fhaBC), Cronobacter plasminogen activator (cpa) and genes responsible for iron acquisition (eitCBAD and iucABD/iutA) have been reported in different strains of C. sakazakii. Besides these proposed virulence factors, several biophysical growth factors such as formation of biofilms and resistance to various environmental stresses also contributes to the pathogenic potential of this pathogen. This review provides an update on virulence determinants associated with the pathogenesis of C. sakazakii. The potential reservoirs of the pathogen, mode of transmission and epidemiology are also discussed.

Development of Bioluminescent Cronobacter sakazakii ATCC 29544 in a Mouse Model

Cronobacter sakazakii is an emerging pathogen that causes severe and life-threatening conditions including meningitis, bacteremia, and necrotizing enterocolitis. An animal model study for extrapolation of C. sakazakii infection can provide a better understanding of pathogenesis. However, methods for real-time monitoring of the course of C. sakazakii infection in living animals have been lacking. We developed a bioluminescent C. sakazakii strain (ATCC 29544) that can be used for real-time monitoring of C. sakazakii infection in BALB/c mice. C. sakazakii ATCC 29544 mainly colonized brain, liver, spleen, kidney, and gastrointestinal tract, as indicated by bioluminescence imaging. This work provides a novel approach for studying the progression of C. sakazakii infection and evaluating therapeutics in a living mouse model.

Hfq plays important roles in virulence and stress adaptation in Cronobacter sakazakii ATCC 29544

Cronobacter spp. are opportunistic pathogens that cause neonatal meningitis and sepsis with high mortality in neonates. Despite the peril associated with Cronobacter infection, the mechanisms of pathogenesis are still being unraveled. Hfq, which is known as an RNA chaperone, participates in the interaction with bacterial small RNAs (sRNAs) to regulate posttranscriptionally the expression of various genes. Recent studies have demonstrated that Hfq contributes to the pathogenesis of numerous species of bacteria, and its roles are varied between bacterial species. Here, we tried to elucidate the role of Hfq in C. sakazakii virulence. In the absence of hfq, C. sakazakii was highly attenuated in dissemination in vivo, showed defects in invasion (3-fold) into animal cells and survival (10(3)-fold) within host cells, and exhibited low resistance to hydrogen peroxide (10(2)-fold). Remarkably, the loss of hfq led to hypermotility on soft agar, which is contrary to what has been observed in other pathogenic bacteria. The hyperflagellated bacteria were likely to be attributable to the increased transcription of genes associated with flagellar biosynthesis in a strain lacking hfq. Together, these data strongly suggest that hfq plays important roles in the virulence of C. sakazakii by participating in the regulation of multiple genes.

Longitudinal analysis of the premature infant intestinal microbiome prior to necrotizing enterocolitis: a case-control study

Necrotizing enterocolitis (NEC) is an inflammatory disease of the newborn bowel, primarily affecting premature infants. Early intestinal colonization has been implicated in the pathogenesis of NEC. The objective of this prospective case-control study was to evaluate differences in the intestinal microbiota between infants who developed NEC and unaffected controls prior to disease onset. We conducted longitudinal analysis of the 16S rRNA genes of 312 samples obtained from 12 NEC cases and 26 age-matched controls with a median frequency of 7 samples per subject and median sampling interval of 3 days. We found that the microbiome undergoes dynamic development during the first two months of life with day of life being the major factor contributing to the colonization process. Depending on when the infant was diagnosed with NEC (i.e. early vs. late onset), the pattern of microbial progression was different for cases and controls. The difference in the microbiota was most overt in early onset NEC cases and controls. In proximity to NEC onset, the abundances of Clostridium sensu stricto from Clostridia class were significantly higher in early onset NEC subjects comparing to controls. In late onset NEC, Escherichia/Shigella among Gammaproteobacteria, showed an increasing pattern prior to disease onset, and was significantly higher in cases than controls six days before NEC onset. Cronobacter from Gammaproteobacteria was also significantly higher in late onset NEC cases than controls 1-3 days prior to NEC onset. Thus, the specific infectious agent associated with NEC may vary by the age of infant at disease onset. We found that intravenously administered antibiotics may have an impact on the microbial diversity present in fecal material. Longitudinal analysis at multiple time points was an important strategy utilized in this study, allowing us to appreciate the dynamics of the premature infant intestinal microbiome while approaching NEC at various points.

Infectious causes of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency among premature infants. Although a large body of research has focused on understanding its pathogenesis, the exact mechanism has not been elucidated. Of particular interest is the potential causative role of infectious culprits in the development of NEC. A variety of reports describe bacterial, viral, and fungal infections occurring in association with NEC; however, no single organism has emerged as being definitively involved in NEC pathogenesis. In this review, the authors summarize the literature on infectious causes of NEC.

Novel approaches to improve the intrinsic microbiological safety of powdered infant milk formula

Human milk is recognised as the best form of nutrition for infants. However; in instances where breast-feeding is not possible, unsuitable or inadequate, infant milk formulae are used as breast milk substitutes. These formulae are designed to provide infants with optimum nutrition for normal growth and development and are available in either powdered or liquid forms. Powdered infant formula is widely used for convenience and economic reasons. However; current manufacturing processes are not capable of producing a sterile powdered infant formula. Due to their immature immune systems and permeable gastro-intestinal tracts, infants can be more susceptible to infection via foodborne pathogenic bacteria than other age-groups. Consumption of powdered infant formula contaminated by pathogenic microbes can be a cause of serious illness. In this review paper, we discuss the current manufacturing practices present in the infant formula industry, the pathogens of greatest concern, Cronobacter and Salmonella and methods of improving the intrinsic safety of powdered infant formula via the addition of antimicrobials such as: bioactive peptides; organic acids; probiotics and prebiotics.

Plasmid-encoded MCP is involved in virulence, motility, and biofilm formation of Cronobacter sakazakii ATCC 29544

The aim of this study was to elucidate the function of the plasmid-borne mcp (methyl-accepting chemotaxis protein) gene, which plays pleiotropic roles in Cronobacter sakazakii ATCC 29544. By searching for virulence factors using a random transposon insertion mutant library, we identified and sequenced a new plasmid, pCSA2, in C. sakazakii ATCC 29544. An in silico analysis of pCSA2 revealed that it included six putative open reading frames, and one of them was mcp. The mcp mutant was defective for invasion into and adhesion to epithelial cells, and the virulence of the mcp mutant was attenuated in rat pups. In addition, we demonstrated that putative MCP regulates the motility of C. sakazakii, and the expression of the flagellar genes was enhanced in the absence of a functional mcp gene. Furthermore, a lack of the mcp gene also impaired the ability of C. sakazakii to form a biofilm. Our results demonstrate a regulatory role for MCP in diverse biological processes, including the virulence of C. sakazakii ATCC 29544. To the best of our knowledge, this study is the first to elucidate a potential function of a plasmid-encoded MCP homolog in the C. sakazakii sequence type 8 (ST8) lineage.