Showing papers by "B. Brett Finlay published in 2014"

The Intestinal Microbiome in Early Life: Health and Disease

Abstract: Human microbial colonization begins at birth and continues to develop and modulate in species abundance for about three years, until the microbiota becomes adult-like. During the same time period, children experience significant developmental changes that influence their current health status as well as their immune system. An ever-expanding number of articles associate several diseases with early life imbalances of the gut microbiota, also referred to as gut microbial dysbiosis. Whether early life dysbiosis precedes and plays a role in disease pathogenesis, or simply originates from the disease process itself is a question that is beginning to be answered in a few diseases, including IBD, obesity and asthma. This review describes the gut microbiome structure and function during the formative first years of life, as well as the environmental factors that determine its composition. It also aims to discuss the recent advances in understanding the role of the early life gut microbiota in the development of immune-mediated, metabolic, and neurological diseases. A greater understanding of how the early life gut microbiota impacts our immune development could potentially lead to novel microbial-derived therapies that target disease prevention at an early age.

Citrobacter rodentium: infection, inflammation and the microbiota

Abstract: Citrobacter rodentium is a mucosal pathogen of mice that shares several pathogenic mechanisms with enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli (EHEC), which are two clinically important human gastrointestinal pathogens. Thus, C. rodentium has long been used as a model to understand the molecular basis of EPEC and EHEC infection in vivo. In this Review, we discuss recent studies in which C. rodentium has been used to study mucosal immunology, including the deregulation of intestinal inflammatory responses during bacteria-induced colitis and the role of the intestinal microbiota in mediating resistance to colonization by enteric pathogens. These insights should help to elucidate the roles of mucosal inflammatory responses and the microbiota in the virulence of enteric pathogens.

Effects of Antibiotics on Human Microbiota and Subsequent Disease

Abstract: Although antibiotics have significantly improved human health and life expectancy, their disruption of the existing microbiota has been linked to significant side effects such as antibiotic-associated diarrhea, pseudomembranous colitis, and increased susceptibility to subsequent disease. By using antibiotics to break colonization resistance against Clostridium, Salmonella, and Citrobacter species, researchers are now exploring mechanisms for microbiota-mediated modulation against pathogenic infection, revealing potential roles for different phyla and family members as well as microbiota-liberated sugars, hormones, and short-chain fatty acids in regulating pathogenicity. Furthermore, connections are now being made between microbiota dysbiosis and a variety of different diseases such as rheumatoid arthritis, inflammatory bowel disease, type 1 diabetes, atopy, and obesity. Future advances in the rapidly developing field of microbial bioinformatics will enable researchers to further characterize the mechanism...

Commensal-pathogen interactions in the intestinal tract: Lactobacilli promote infection with, and are promoted by, helminth parasites

Abstract: The intestinal microbiota are pivotal in determining the developmental, metabolic and immunological status of the mammalian host. However, the intestinal tract may also accommodate pathogenic organisms, including helminth parasites which are highly prevalent in most tropical countries. Both microbes and helminths must evade or manipulate the host immune system to reside in the intestinal environment, yet whether they influence each other’s persistence in the host remains unknown. We now show that abundance of Lactobacillus bacteria correlates positively with infection with the mouse intestinal nematode parasite, Heligmosomoides polygyrus, as well as with heightened regulatory T cell (Treg) and Th17 responses. Moreover, H. polygyrus raises Lactobacillus species abundance in the duodenum of C57BL/6 mice, which are highly susceptible to H. polygyrus infection, but not in BALB/c mice, which are relatively resistant. Sequencing of samples at the bacterial gyrB locus identified the principal Lactobacillus species as L. taiwanensis, a previously characterized rodent commensal. Experimental administration of L. taiwanensis to BALB/c mice elevates regulatory T cell frequencies and results in greater helminth establishment, demonstrating a causal relationship in which commensal bacteria promote infection with an intestinal parasite and implicating a bacterially-induced expansion of Tregs as a mechanism of greater helminth susceptibility. The discovery of this tripartite interaction between host, bacteria and parasite has important implications for both antibiotic and anthelmintic use in endemic human populations.

Autophagy Facilitates Salmonella Replication in HeLa Cells

Abstract: Autophagy is a process whereby a double-membrane structure (autophagosome) engulfs unnecessary cytosolic proteins, organelles, and invading pathogens and delivers them to the lysosome for degradation. We examined the fate of cytosolic Salmonella targeted by autophagy and found that autophagy-targeted Salmonella present in the cytosol of HeLa cells correlates with intracellular bacterial replication. Real-time analyses revealed that a subset of cytosolic Salmonella extensively associates with autophagy components p62 and/or LC3 and replicates quickly, whereas intravacuolar Salmonella shows no or very limited association with p62 or LC3 and replicates much more slowly. Replication of cytosolic Salmonella in HeLa cells is significantly decreased when autophagy components are depleted. Eventually, hyperreplication of cytosolic Salmonella potentiates cell detachment, facilitating the dissemination of Salmonella to neighboring cells. We propose that Salmonella benefits from autophagy for its cytosolic replication in HeLa cells. IMPORTANCE As a host defense system, autophagy is known to target a population of Salmonella for degradation and hence restricting Salmonella replication. In contrast to this concept, a recent report showed that knockdown of Rab1, a GTPase required for autophagy of Salmonella, decreases Salmonella replication in HeLa cells. Here, we have reexamined the fate of Salmonella targeted by autophagy by various cell biology-based assays. We found that the association of autophagy components with cytosolic Salmonella increases shortly after initiation of intracellular bacterial replication. Furthermore, through a live-cell imaging method, a subset of cytosolic Salmonella was found to be extensively associated with autophagy components p62 and/or LC3, and they replicated quickly. Most importantly, depletion of autophagy components significantly reduced the replication of cytosolic Salmonella in HeLa cells. Hence, in contrast to previous reports, we propose that autophagy facilitates Salmonella replication in the cytosol of HeLa cells.

Mycobacterium leprae intracellular survival relies on cholesterol accumulation in infected macrophages: a potential target for new drugs for leprosy treatment

Abstract: We recently showed that Mycobacterium leprae (ML) is able to induce lipid droplet formation in infected macrophages. We herein confirm that cholesterol (Cho) is one of the host lipid molecules that accumulate in ML-infected macrophages and investigate the effects of ML on cellular Cho metabolism responsible for its accumulation. The expression levels of LDL receptors (LDL-R, CD36, SRA-1, SR-B1, and LRP-1) and enzymes involved in Cho biosynthesis were investigated by qRT-PCR and/or Western blot and shown to be higher in lepromatous leprosy (LL) tissues when compared to borderline tuberculoid (BT) lesions. Moreover, higher levels of the active form of the sterol regulatory element-binding protein (SREBP) transcriptional factors, key regulators of the biosynthesis and uptake of cellular Cho, were found in LL skin biopsies. Functional in vitro assays confirmed the higher capacity of ML-infected macrophages to synthesize Cho and sequester exogenous LDL-Cho. Notably, Cho colocalized to ML-containing phagosomes, and Cho metabolism impairment, through either de novo synthesis inhibition by statins or depletion of exogenous Cho, decreased intracellular bacterial survival. These findings highlight the importance of metabolic integration between the host and bacteria to leprosy pathophysiology, opening new avenues for novel therapeutic strategies to leprosy.

Targeting the type III secretion system to treat bacterial infections.

Abstract: Introduction: Causative agents of pneumonia, gastroenteritis, typhoid fever, and plague all utilize a type III secretion system (T3SS) to directly inject proteins into human cells and cause disease...

Gastrointestinal Microbiota–Mediated Control of Enteric Pathogens

Abstract: The gastrointestinal (GI) microbiota is a complex community of microorganisms residing within the mammalian gastrointestinal tract. The GI microbiota is vital to the development of the host immune system and plays a crucial role in human health and disease. The composition of the GI microbiota differs immensely among individuals yet specific shifts in composition and diversity have been linked to inflammatory bowel disease, obesity, atopy, and susceptibility to infection. In this review, we describe the GI microbiota and its role in enteric diseases caused by pathogenic Escherichia coli, Salmonella enterica, and Clostridium difficile. We discuss the central role of the GI microbiota in protective immunity, resistance to enteric pathogens, and resolution of enteric colitis.

Antivirulence Activity of the Human Gut Metabolome

Abstract: The mammalian gut contains a complex assembly of commensal microbes termed microbiota. Although much has been learned about the role of these microbes in health, the mechanisms underlying these functions are ill defined. We have recently shown that the mammalian gut contains thousands of small molecules, most of which are currently unidentified. Therefore, we hypothesized that these molecules function as chemical cues used by hosts and microbes during their interactions in health and disease. Thus, a search was initiated to identify molecules produced by the microbiota that are sensed by pathogens. We found that a secreted molecule produced by clostridia acts as a strong repressor of Salmonella virulence, obliterating expression of the Salmonella pathogenicity island 1 as well as host cell invasion. It has been known for decades that the microbiota protects its hosts from invading pathogens, and these data suggest that chemical sensing may be involved in this phenomenon. Further investigations should reveal the exact biological role of this molecule as well as its therapeutic potential. Importance: Microbes can communicate through the production and sensing of small molecules. Within the complex ecosystem formed by commensal microbes living in and on the human body, it is likely that these molecular messages are used extensively during the interactions between different microbial species as well as with host cells. Deciphering such a molecular dialect will be fundamental to our understanding of host-microbe interactions in health and disease and may prove useful for the design of new therapeutic strategies that target these mechanisms of communication.

Human microbiome science: vision for the future,

Abstract: A conference entitled ‘Human microbiome science: Vision for the future’ was organized in Bethesda, MD from July 24 to 26, 2013. The event brought together experts in the field of human microbiome research and aimed at providing a comprehensive overview of the state of microbiome research, but more importantly to identify and discuss gaps, challenges and opportunities in this nascent field. This report summarizes the presentations but also describes what is needed for human microbiome research to move forward and deliver medical translational applications.

Lyn Deficiency Leads to Increased Microbiota-Dependent Intestinal Inflammation and Susceptibility to Enteric Pathogens

Abstract: The Lyn tyrosine kinase governs the development and function of various immune cells, and its dysregulation has been linked to malignancy and autoimmunity. Using models of chemically induced colitis and enteric infection, we show that Lyn plays a critical role in regulating the intestinal microbiota and inflammatory responses as well as protection from enteric pathogens. Lyn(-/-) mice were highly susceptible to dextran sulfate sodium (DSS) colitis, characterized by significant wasting, rectal bleeding, colonic pathology, and enhanced barrier permeability. Increased DSS susceptibility in Lyn(-/-) mice required the presence of T but not B cells and correlated with dysbiosis and increased IFN-γ(+) and/or IL-17(+) colonic T cells. This dysbiosis was characterized by an expansion of segmented filamentous bacteria, associated with altered intestinal production of IL-22 and IgA, and was transmissible to wild-type mice, resulting in increased susceptibility to DSS. Lyn deficiency also resulted in an inability to control infection by the enteric pathogens Salmonella enterica serovar Typhimurium and Citrobacter rodentium. Lyn(-/-) mice exhibited profound cecal inflammation, bacterial dissemination, and morbidity following S. Typhimurium challenge and greater colonic inflammation throughout the course of C. rodentium infection. These results identify Lyn as a key regulator of the mucosal immune system, governing pathophysiology in multiple models of intestinal disease.

An antibiotic-altered microbiota provides fuel for the enteric foe.

Abstract: Antibiotic therapies disrupt the intestinal microbiota and render the host susceptible to enteric infections. A recent report by Ng et al. explores the ability of two intestinal pathogens (Salmonella enterica serovar Typhimurium and Clostridium difficile) to use this disruption to their advantage and consume host carbohydrates that would otherwise be unavailable in the presence of a normal gut microbiota.

The early life gut microbiota and atopic disease

Abstract: Background Asthma is the most prevalent of all childhood diseases and accounts for the majority of hospitalizations and school absences in children [1]. Current mouse model research has identified the early life gut microbiota as a potential therapeutic target for the prevention of asthma and atopic diseases [2-4]. We hypothesize that the early life gut microbiota could play a similar preventative role against atopic disease development in humans. Methods 1262 children enrolled in the Canadian Healthy Infant Longitudinal Development (CHILD) Study with complete skin prick test and wheeze data at one year were grouped into four clinically relevant phenotypes: atopy + wheeze, atopy only, wheeze only, and control. Bacterial 16S rDNA from 3-month and 1-year stool samples of 319 children in these four phenotypes was extracted, amplified, and subjected to high throughput Illumina sequencing. Quantitative polymerase chain reaction (qPCR) and short chain fatty acid (SCFA) analysis were also conducted on 44 children in the two extreme phenotypes (atopy + wheeze vs. control). Results 16S sequence analysis of our sample cohort (319 subjects) identified bacterial populations that differed in abundance in the atopy + wheeze group at 3-months of age but not at 1-year of age. Additionally, significant changes in the abundance of certain bacterial genera were found in the atopy + wheeze group when compared to controls by qPCR at 3-months of age only. Changes in stool short chain fatty acid production between the atopy + wheeze group and the control group were also observed at 3months of age only. Conclusions Shifts in the relative abundance of certain gut bacterial populations and differences in the levels of stool SCFAs before 3-months of age are associated with atopy and wheeze at one year of age.

The impact of the intestinal microbiome on human immune development and atopic disease

Abstract: Background Asthma is a chronic inflammatory disease characterized by bronchial hyper-responsiveness [1]. As the most endemic of all childhood diseases, asthma accounts for the majority of hospitalizations and school absences in children [2]. Exciting new research focuses on the involvement of the gut microbiome in asthma development. Murine studies support the hypothesis that the administration of probiotics or antibiotics during post-natal life alters the gut microbiome and ultimately the asthmatic symptoms of these mice [3-5]. This study will translate these findings into humans using stool samples obtained from the Canadian Healthy Infant Longitudinal Development (CHILD) study.

Microbiota-Mediated Control of Enteric Pathogens

Abstract: The gastrointestinal (GI) microbiota is a complex community of microorganisms residing within the mammalian gastrointestinal tract. The GI microbiota is vital to the development of the host immune system and plays a crucial role in human health and disease. The composition of the GI microbiota differs immensely among individuals yet specific shifts in composition and diversity have been linked to inflammatory bowel disease, obesity, atopy, and susceptibility to infection. In this review, we describe the GI microbiota and its role in enteric diseases caused by pathogenic Escherichia coli, Salmonella enterica ,a ndClostridium difficile. We discuss the central role of the GI microbiota in protective immunity, resistance to enteric pathogens, and resolution of enteric colitis.