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PubMed2004

Spatial distribution and stability of the eight microbial species of the altered schaedler flora in the mouse gastrointestinal tract.

The overall complexity of the microbial communities in the gastrointestinal (GI) tracts of mammals has hindered observations of dynamics and interactions of individual bacterial populations. However, such information is crucial for understanding the diverse disease-causing and protective roles that gut microbiota play in their hosts. Here, we determine the spatial distribution, interanimal variation, and persistence of bacteria in the most complex defined-flora (gnotobiotic) model system to date, viz., mice colonized with the eight strains of the altered Schaedler flora (ASF). Quantitative PCR protocols based on the 16S rRNA sequence of each ASF strain were developed and optimized to specifically detect as few as 10 copies of each target. Total numbers of the ASF strains were determined in the different regions of the GI tracts of three C.B-17 SCID mice. Individual strain abundance was dependent on oxygen sensitivity, with microaerotolerant Lactobacillus murinus ASF361 present at 10(5) to 10(7) cells/g of tissue in the upper GI tract and obligate anaerobic ASF strains being predominant in the cecal and colonic flora at 10(8) to 10(10) cells/g of tissue. The variation between the three mice was small for most ASF strains, except for Clostridium sp. strain ASF502 and Bacteroides sp. strain ASF519 in the cecum. A comparison of the relative distribution of the ASF strains in feces and the colon indicated large differences, suggesting that fecal bacterial levels may provide a poor approximation of colonic bacterial levels. All ASF strains were detected by PCR in the feces of C57BL/6 restricted flora mice, which had been maintained in an isolator without sterile food, water, or bedding for several generations, providing evidence for the stability of these strains in the face of potential competition by bacteria introduced into the gut.

Animals↗
PubMed1995

Of microbes and macrophages: entry, survival and persistence.

The macrophage is capable of fulfilling the roles of both host cell and effector cell in the immune clearance of many microbial infections. This dual capacity has led to the evolution of intriguing mechanisms whereby pathogens ensure the establishment and maintenance of intracellular infections. The strategies developed range from passive avoidance mechanisms to extremely active modulation of cell function. Recent advances have been made in our appreciation of the processes of intramacrophage parasitization from initial ligand-receptor interactions, through establishment of a stable intracellular environment, to the maintenance of a persistent infection.

Animals↗
PubMed2000

NADPH oxidase, Nramp1 and nitric oxide synthase 2 in the host antimicrobial response.

Using highly conserved, complex enzyme systems, leukocytes utilize the toxic nature of free radical intermediates, derived from oxygen and nitrogen, to control microbial pathogens as part of the innate immune response. Upon activation, NADPH oxidase generates superoxide anion radicals, which in turn give rise to further reactive oxygen intermediates. Similarly, activated nitric oxide synthase 2 catalyses the production of nitric oxide radicals, which leads to the formation of reactive nitrogen intermediates. Nitrogen- and oxygen-centered reactive intermediates can interact to form further reactive species. In addition, presence of the cationic transporter, Nrampl, may exacerbate the effects of these toxic compounds on invading microbes. While each of these antimicrobial systems can operate independently, the combination of their activities is synergistic in the successful containment of almost all invading pathogens. These systems are activated and modulated by microbial products and a series of temporally expressed cytokines. They also feed directly into the initiation of the adaptive immune response, which culminates in lasting specific immunity. The effector molecules, generated in the early innate immune response, are not specific to the invading pathogen and may also cause damage to the host. It is the critical balance of these processes in the initial stages of infection that determines the outcome of infectious disease.

Animals↗
PubMed2004

TLRs: Professor Mechnikov, sit on your hat.

Toll-like receptors (TLRs) are sensors of foreign microbial products, which initiate host defense responses in all multicellular organisms examined to date. They are the target for most adjuvants, are essential for the establishment of memory in T and B cells and provoke inflammation. They program dendritic cells in their interaction with Th1 cells and their signalling pathways enable a tailoring of host defense responses to the provoking microbe previously unsuspected in the innate arm of immunity. Their discovery and characterisation fills a void in immunology and is the culmination of an effort that began with one of immunology's founding fathers, Elie Mechnikov. Targeting TLRs therapeutically now has the potential to impact on how we treat infectious and inflammatory diseases.

Allergy and Immunology↗
PubMed1996

The pathogenesis of Staphylococcus aureus in the trauma patient and potential future therapies.

BACKGROUND: Staphylococcus aureus is the most frequently isolated pathogen in the trauma patient and uses multiple virulent factors to cause infection. At the cellular level, infection begins with the prokaryotic bacterial cell manipulating the eukaryotic host cell through its virulent factors. Researching this cellular interaction by describing the mechanisms of actions of various virulent factors may lead to new preventive therapies which will make the trauma patient less susceptible to S aureus infections. METHODS: Surgical, medical, and microbial literature was reviewed to provide an update on S aureus pathogenesis. RESULTS: Novel future therapies, in addition to antibiotics, are being devised based on understanding the molecular nature of S aureus pathogenesis. CONCLUSION: The impact of S aureus on trauma will increase as S aureus develops more antibiotic resistance and as the trauma population becomes older and includes an increasing proportion of immunocompromised patients. To meet the challenge of increased virulence, trauma surgeons should be directly involved in the research of microbial pathogenesis.

Bacterial Adhesion↗
PubMed2001

Clinical applications of probiotic agents.

In the past century the beneficial roles of nonpathogenic bacteria in the intestinal lumen were described. In the past decade there has been a dramatic increase in scientific work supporting the concept that there are clinical benefits to ingesting specific nonpathogenic organisms (probiotics). The potential benefits of modifying the intestinal flora composition of certain high-risk groups, eg, premature infants, travelers, and children receiving antibiotics, are emerging in the literature. Studies documenting prophylactic and therapeutic benefits in acute viral gastroenteritis and in atopic disease point not only to the potential applications, but also to the fact that the mechanisms of action of these agents may be due to their interaction with the gut as an immunologic organ. The benefits documented thus far are of varying degree and are most likely dependent on the number of agents, the dose, the dosing patterns, and the characteristics of the host and its underlying luminal microbial environment. Consequently, the safety and specification of a particular probiotic agent and methods of delivery to a particular population for a particular purpose should be carefully documented before making broad recommendations. The cost-benefit assessment of adding probiotics to our diet for prophylactic or therapeutic purposes, as well as better regulation of these agents as commercial products, is also needed.

Child↗
PubMed2004

The hygiene hypothesis of atopic disease--an extended version.

The hygiene hypothesis of atopic disease suggests that environmental changes in the industrialized world have lead to reduced microbial contact at an early age and thus resulted in the growing epidemic of atopic eczema, allergic rhinoconjunctivitis, and asthma. The epidemiological findings have been combined with the Th1/Th2 paradigm of immune responsiveness to provide a coherent theory. Recent advances in epidemiology and immunology demonstrate, however, that the hygiene hypothesis may need to be extended in three respects. First, the importance of infections in causing immune deviance may be outweighed by other sources of microbial stimulation, perhaps most importantly by the indigenous intestinal microbiota. Second, immunomodulatory and suppressive immune responses complement the Th1/Th2 paradigm. Third, in addition to protection against atopy, protection against infectious, inflammatory, and autoimmune diseases may also depend upon healthy host-microbe interactions implicated in the hygiene hypothesis.

Child, Preschool↗
PubMed2004

Multilayer polyelectrolyte films functionalized by insertion of defensin: a new approach to protection of implants from bacterial colonization.

Infection of implanted materials by bacteria constitutes one of the most serious complications following prosthetic surgery. In the present study, we developed a new strategy based on the insertion of an antimicrobial peptide (defensin from Anopheles gambiae mosquitoes) into polyelectrolyte multilayer films built by the alternate deposition of polyanions and polycations. Quartz crystal microbalance and streaming potential measurements were used to follow step by step the construction of the multilayer films and embedding of the defensin within the films. Antimicrobial assays were performed with two strains: Micrococcus luteus (a gram-positive bacterium) and Escherichia coli D22 (a gram-negative bacterium). The inhibition of E. coli D22 growth at the surface of defensin-functionalized films was found to be 98% when 10 antimicrobial peptide layers were inserted in the film architecture. Noticeably, the biofunctionalization could be achieved only when positively charged poly(l-lysine) was the outermost layer of the film. On the basis of the results of bacterial adhesion experiments observed by confocal or electron microscopy, these observations could result from the close interaction of the bacteria with the positively charged ends of the films, which allows defensin to interact with the bacterial membrane structure. These results open new possibilities for the use of such easily built and functionalized architectures onto any type of implantable biomaterial. The modified surfaces are active against microbial infection and represent a novel means of local host protection.

Adsorption↗
PubMed1981

[Systems analysis in pathology and its potential use in studying the morphogenesis of infections].

A total systems approach is necessary to draw in integral concept of the pathological process as exemplified by investigations of morphogenesis of the infectious process. For this purpose a concept of the Mm-system is introduced and analysed which helps to study the infectious process as a special object: a system of microbial population (m) and macroorganism cells (M). The ontogenesis of the Mm-system is suggested consisting of 3 stages: formation, existence, and death. Considering the infectious process from the systemic point of view the author found many microbe-host cell interactions observed in infections to be characteristic not for the infectious pathology but to the particular manifestations of well-known but frequently ignored general biological regularities. A number of models of infectious diseases demonstrate the earliest morphological changes of the disturbed homeostasis in tissues containing microbes and the associated features of the infectious process. Comparing the time evolution of the Mm-system with the course of real infectious processes, one may approach the solution of some disputable aspects of the pathogenesis of infections, in particular, to elucidate the importance of intracellular accumulation of microbes observed in enteric infections. The Mm-system concept may find practical application in explaining pathomorphosis of infectious lesions under conditions of current methods of intensive specific therapy as well as in evaluating the mechanism of action of drugs when tested on models.

Animals↗
PubMed1999

Cell adhesion molecules in the pathogenesis of and host defence against microbial infection.

Eukaryotic cell adhesion molecules (CAMs) are used by various cells and extracellular molecules in host defence against infection. They are involved in many processes including recognition by circulating phagocytes of a site of inflammation, transmigration through the endothelial barrier, diapedesis through basement membrane and extracellular matrix, and release of effector mechanisms at the infected site. CAMs involved in leucocyte-endothelial cell interaction include the selectins, integrins, and members of the immunoglobulin superfamily. However, CAMs are also used by various microorganisms (protozoa, fungi, bacteria, and viruses) during their pathogenesis. For example, bacteria that utilise CAMs include Mycobacterium tuberculosis, Listeria monocytogenes, Yersinia spp, enteropathogenic Escherichia coli, Shigella spp, Neisseria spp, Bordetella spp, and Borrelia burgdorferi. In addition, CAMs are involved in the pathogenetic effects of the RTX toxins of Pasteurella haemolytica, Actinobacillus actinomycetemcomitans, and the superantigen exotoxins of Staphylococcus aureus and Streptococcus pyogenes. A recurrent and topical theme of potential importance within the bacterial group is the intimate relation between CAMs, bacterial protein receptors, and type III secretion systems. For example, the IpaBCD protein complex is secreted by the type III system of Shigella flexneri and interacts with alpha 5 beta 1 integrin on the eukaryotic cell surface, followed by Rho mediated internalisation; this illustrates the relevance of cellular microbiology. CAMs might prove to be novel therapeutic targets. Comparative genomics has provided the knowledge of shared virulence determinants among diverse bacterial genera, and will continue to deepen our understanding of microbial pathogenesis, particularly in the context of the interaction of prokaryotic and eukaryotic molecules.

Cell Adhesion Molecules↗
PubMed2001

Pathogenesis of septic shock: implications for prevention and treatment.

The innate immune system is in the vanguard of host defenses against infection. Recognition of invasive microbial pathogens is mediated by pattern recognition receptors on the surface of immune cells that recognize pathogen-associated molecular motifs. Considerable progress has been made in recent years in understanding how bacterial products initiate sepsis. In gram-negative sepsis, the LPS-binding protein (LBP), CD14 and the recently identified Toll-like receptor 4 (TLR4) are key molecules for the recognition of endotoxin (lipopolysaccharide, LPS) by cells of the myelomonocytic lineage. In gram-positive sepsis, components of the bacterial cell wall (peptidoglycan, PGN; lipoteichoic acids, LTA) have been shown to activate myeloid cells through an interaction with a receptor complex composed of CD14, TLR2 and perhaps also TLR6 (PGN) or CD14 and TLR4 (LTA). By contrast, gram-positive exotoxins act as superantigens and directly stimulate T lymphocytes by cross-linking the MHC class II of antigen presenting cells to specific chains of the T cell receptor. Immune cells activated by microbial pathogens release numerous effector molecules, which orchestrate the innate and adaptive host defenses. Furthermore, bacteria and microbial toxins directly activate the complement and coagulation systems, which play an important part in the host defensive response. Severe sepsis and septic shock can be viewed as clinical manifestations of a failing innate immune response that ultimately results in an overstimulation of the physiological host response. The pathogenesis of sepsis is far more complex that was initially anticipated. However, combined research efforts of basic scientists and clinical investigators continue to provide critical information for the identification of novel therapeutic targets. The exciting results obtained recently with treatment strategies designed to correct coagulation abnormalities occurring during sepsis are an example of how research may ultimately translate into improved patient care.

Drosophila Proteins↗
PubMed1992

Consequences of microbial attachment: directing host cell functions with adhesins.

We take the view that adherence is not just a static process of holding hands but rather elicits a response in the targeted cell. From this point of view, adherence is an active process with an outcome. This outcome or fate is predictable only when several parameters of the host cell-adhesin interaction are known: is the adhesin acting alone or in series with other products, is the receptor up- or down-regulated at the time of ligation, which domain of the receptor is bound, and finally, which intracellular response circuits are connected to the receptor in the cell type targeted? Variations in these parameters are the basis for the ability of the adhesins of pathogens to orchestrate outcomes as disparate as simple address recognition versus actin nucleation, cytokine induction, activation of plasmin, derangement of leukocyte migration, or deposition of antibody on host cell membranes. The recognition of the relatedness of some eukaryotic and prokaryotic adhesive domains and the shared use of existing eukaryotic cell-cell interaction systems between host and pathogen suggest that the cellular interactions of interest in eukaryotic cell biology can be revealed by taking clues from the pathogens, which have studied and adapted to them the longest.

Animals↗
PubMed2002

Evidence of participation of soluble CD14 in the host response to microbial invasion of the amniotic cavity and intra-amniotic inflammation in term and preterm gestations.

OBJECTIVE: Endotoxin has been implicated in the mechanism responsible for the setting of infection in preterm labor. To exert its biological effects, endotoxin binds to a circulating protein known as lipopolysaccharide binding protein (LBP) and presents endotoxin monomers to CD14, which may be a membrane-bound receptor or a soluble molecule. The endotoxin-LBP-CD14 complex interacts with Toll-like receptor 4 and other regulatory proteins leading to cellular activation and an inflammatory response. The purpose of this study was to determine whether microbial invasion of the amniotic cavity (MIAC)/intra-amniotic inflammation (both preterm and term) and parturition at term are associated with changes in the amniotic fluid and umbilical plasma soluble concentrations of CD14 (sCD14). STUDY DESIGN: Amniotic fluid was retrieved by amniocentesis from 88 patients in the following groups: group 1, preterm labor with intact membranes with MIAC/intra-amniotic inflammation (n = 18) and without these conditions (n = 26); group 2, term gestations not in labor without MIAC/intra-amniotic inflammation (n = 11), in labor without MIAC/intra-amniotic inflammation (n = 12) and in labor with MIAC/intra-amniotic inflammation (n = 13); and group 3, patients who underwent genetic amniocentesis at mid-trimester (n = 8). A sample of cord blood was obtained after delivery in all patients except those in group 3. sCD14 was assayed with a sensitive and specific immunoassay. Non-parametric statistics were used for analysis. A p value of < 0.05 was considered significant. RESULTS: sCD14 was detectable in 97% (85/88) of the amniotic fluid samples. Amniotic fluid sCD14 concentrations were lower in patients at term than in the mid-trimester of pregnancy (mid-trimester: median 482 ng/ml, range 258-838 ng/ml vs. term no labor: median 7 ng/ml, range 2-274 ng/ml, p = 0.01). Among patients with preterm labor with intact membranes, the median amniotic fluid sCD14 level of patients with MIAC/intra-amniotic inflammation was higher than in patients without these conditions (median 1568 ng/ml, range 98-5887 ng/ml vs. median 645 ng/ml, range 0-3961 ng/ml, respectively; p = 0.01). Among women at term in labor, those with MIAC/intra-amniotic inflammation had a higher median amniotic fluid sCD14 concentration than those without these conditions (median 85 ng/ml, range 2-1113 ng/ml vs. median 17 ng/ml, range 0-186 ng/ml; p = 0.01). MIAC/intra-amniotic inflammation in women with preterm labor with intact membranes was associated with a higher median umbilical venous plasma sCD14 concentration (median 744 ng/ml, range 0-3620 ng/ml vs. median 0 ng/ml, range 0-2060 ng/ml; p = 0.04). sCD14 was undetectable in plasma from umbilical cords of all neonates born to women at term. An increase in amniotic fluid concentration of sCD14 was observed in cases of intrauterine infection, not only by gram-negative bacteria, but also gram-positive bacteria and Ureaplasma spp. CONCLUSION: sCD14 is a physiological constituent of amniotic fluid, and its concentrations at term are lower than in the mid-trimester. Intrauterine infection/inflammation is associated with a higher median amniotic fluid sCD14 concentration in both preterm and term parturition. Neonates born from mothers with preterm labor with intact membranes and MIAC/intra-amniotic inflammation had a higher median concentration of sCD14 in umbilical cord plasma than those without these conditions. sCD14 concentrations are increased in the amniotic fluid and umbilical cord blood even in the absence of a microbiologically proven gram-negative infection. CD14 appears to participate in the host response to intrauterine infection even in cases involving genital mycoplasmas.

Amniocentesis↗
PubMed2003

Interspecific evolution: microbial symbiosis, endosymbiosis and gene transfer.

Microbial symbioses are interesting in their own right and also serve as exemplary models to help biologists to understand two important symbioses in the evolutionary past of eukaryotic cells: the origins of chloroplasts and mitochondria. Most, if not all, microbial symbioses have a chemical basis: compounds produced by one partner are useful for the other. But symbioses can also entail the transfer of genes from one partner to the other, which in some cases cements two cells into a bipartite, co-evolving unit. Here, we discuss some microbial symbioses in which progress is being made in uncovering the nature of symbiotic interactions: anaerobic methane-oxidizing consortia, marine worms that possess endosymbionts instead of a digestive tract, amino acid-producing endosymbionts of aphids, prokaryotic endosymbionts living within a prokaryotic host within mealybugs, endosymbionts of an insect vector of human disease and a photosynthetic sea slug that steals chloroplasts from algae. In the case of chloroplasts and mitochondria, examples of recent and ancient gene transfer to the chromosomes of their host cell illustrate the process of genetic merger in the wake of organelle origins.

Animals↗
PubMed2005

The rhizosphere as a reservoir for opportunistic human pathogenic bacteria.

During the last years, the number of human infections caused by opportunistic pathogens has increased dramatically. One natural reservoir of opportunistic pathogens is the rhizosphere, the zone around roots that is influenced by the plant. Due to a high content of nutrients, this habitat is a 'microbial hot-spot', where bacterial abundances including those with strong antagonistic traits are enhanced. Various bacterial genera, including Burkholderia, Enterobacter, Herbaspirillum, Ochrobactrum, Pseudomonas, Ralstonia, Staphylococcus and Stenotrophomonas, contain root-associated strains that can encounter bivalent interactions with both plant and human hosts. Mechanisms responsible for colonization of the rhizosphere and antagonistic activity against plant pathogens are similar to those responsible for colonization of human organs and tissues, and pathogenicity. Multiple resistances against antibiotics are not only found with clinical strains but also with strains isolated from the rhizosphere. High competition, the occurrence of diverse antibiotics in the rhizosphere, and enhanced horizontal gene transfer rates in this microenvironment appear to contribute to the high levels of natural resistances. While opportunistic bacteria from the rhizosphere have some properties in common, each of these emerging pathogens has its own features, which are discussed in detail for Burkholderia, Ochrobactrum and Stenotrophomonas.

Bacteria↗
PubMed2025

Pangenome analysis of Lactobacillus mulieris strains reveals distinct subspecies clusters with defined ecological adaptations.

Lactobacillus mulieris is a recently described species, reportedly isolated from human urine, vagina, and gut. Previous genomic studies of L. mulieris highlighted significant genetic diversity among its strains. To gain a deeper understanding of this genomic diversity, we conducted a comprehensive genomic comparison of 70 L. mulieris strains from diverse sources. Phylogenomic and genome relatedness analysis identified three distinct clades, each representing a potential subspecies cluster. Pangenome analysis revealed distinct gene clusters shaping the functional characteristics and unique ecological adaptations of each clade. Clade 1 demonstrated a generalist lifestyle, with strains isolated from diverse sources and enriched in serine/threonine protein kinases, suggesting adaptive versatility. Clade 2, predominantly composed of urinary isolates, displayed enrichment in genes facilitating nutrient acquisition and osmotic regulation, enabling survival in the nutrient-limited and high osmolarity conditions of the urinary tract. Clade 3, exclusively composed of vaginal isolates, exhibited significant enrichment in genes supporting glycogen metabolism, carbohydrate transport, and capsular polysaccharide biosynthesis-features indicative of adaptation to the vaginal environment. Collectively, our findings provide essential genomic insights into the ecological specialization of L. mulieris, shedding light on their genetic variability and adaptive traits within their respective ecological niches.IMPORTANCERecognizing the genomic diversity within Lactobacillus mulieris is essential for understanding its ecological specialization and adaptation strategies across distinct human-associated environments. By identifying three distinct clades with unique functional traits, our study highlights the critical role of niche-specific genetic adaptations in microbial survival. The presence of specialized gene functions within each clade underscores how evolutionary pressures shape bacterial resilience in different environments. Despite their coexistence in overlapping environments, these clades exhibit distinct genomic profiles that may influence their colonization potential and interactions with the host and within the host-associated microbiota. Our findings emphasize the need for a classification framework that accounts for these genetic and functional differences and the necessity for further investigation to understand their distinct roles and impact on human health.

Humans↗
PubMed1999

A viral enterotoxin. A new mechanism of virus-induced pathogenesis.

Acute infectious gastroenteritis is a major cause of infant morbidity in developed countries and of infant mortality in developing areas of the world. Rotavirus is recognized as the most important etiologic agent of infantile gastroenteritis, and studies of rotavirus serve as models to understand the complex interactions between enteric viruses and the multifunctional cells of the gastrointestinal tract. Understanding such interactions is significant for microbial pathogenesis because most (> 80%) infections are initiated at mucosal surfaces. Rotaviruses are pathogens that infect the mature enterocytes of the villi in the intestine and infection appears to be limited to these highly differentiated cells in immunologically competent hosts. In such hosts, infections are generally acute yet diarrheal disease can be severe and life-threatening. Disease generally is resolved within 2-5 days after infection if affected hosts receive adequate rehydration. In immunocompromised hosts, virus infections persist, virus can be detected extraintestinally and virus excretion may be detected for extended periods of time (many months). Rotaviruses infect almost all mammalian and some avian species and much of our understanding of rotavirus pathogenesis has come from studies in animal models, particularly in small animal models (mice and rabbits), but also in larger animals (cows and piglets). Studies in children are limited due to the difficulty and lack of clinical need of obtaining biopsies from infants and the inability to determine the precise time of natural infections. In all animal species where naïve animals can be infected, disease is age-dependent; for example, in mice and rabbits, diarrheal disease is the outcome of infections that occur only during the first two weeks of life (Ciarlet et al., 1998; Starkey et al., 1986; Ramig 1988; Ward et al., 1990; Burns et al., 1995), while animals remain susceptible to viral infection into adulthood. Rotavirus infections have been reported to occur repeatedly in humans from birth to old age, but the majority of infections after the first 2 years of life are asymptomatic or associated with mild gastrointestinal symptoms. The age-related resistance to rotavirus-induced diarrhea in humans is thought to be mediated primarily by acquired immunity, but it is not possible to directly test if humans also exhibit an age-dependent resistance to disease based on other factors such as intestinal development and maturation. Currently, our best understanding of the mechanisms of rotavirus pathogenesis rely on results obtained in animal models.

Animals↗