Pro-inflammatory cytokines can act as intracellular modulators of commensal bacterial virulence

Interactions between commensal pathogens and hosts are critical for disease development but the underlying mechanisms for switching between the commensal and virulent states are unknown. We show that the human pathogen Neisseria meningitidis, the leading cause of pyogenic meningitis, can modulate gene expression via uptake of host pro-inflammatory cytokines leading to increased virulence. This uptake is mediated by type IV pili (Tfp) and reliant on the PilT ATPase activity. Two Tfp subunits, PilE and PilQ, are identified as the ligands for TNF-α and IL-8 in a glycan-dependent manner, and their deletion results in decreased virulence and increased survival in a mouse model. We propose a novel mechanism by which pathogens use the twitching motility mode of the Tfp machinery for sensing and importing host elicitors, aligning with the inflamed environment and switching to the virulent state.     

A New Zebrafish Model of Oro-Intestinal Pathogen Colonization Reveals a Key Role for Adhesion in Protection by Probiotic Bacteria

The beneficial contribution of commensal bacteria to host health and homeostasis led to the concept that exogenous non-pathogenic bacteria called probiotics could be used to limit disease caused by pathogens. However, despite recent progress using gnotobiotic mammal and invertebrate models, mechanisms underlying protection afforded by commensal and probiotic bacteria against pathogens remain poorly understood. Here we developed a zebrafish model of controlled co-infection in which germ-free zebrafish raised on axenic living protozoa enabled the study of interactions between host and commensal and pathogenic bacteria. We screened enteric fish pathogens and identified Edwardsiella ictaluri as a virulent strain inducing a strong inflammatory response and rapid mortality in zebrafish larvae infected by the natural oro-intestinal route. Using mortality induced by infection as a phenotypic read-out, we pre-colonized zebrafish larvae with 37 potential probiotic bacterial strains and screened for survival upon E. ictaluri infection. We identified 3 robustly protective strains, including Vibrio parahaemolyticus and 2 Escherichia coli strains. We showed that the observed protective effect of E. coli was not correlated with a reduced host inflammatory response, nor with the release of biocidal molecules by protective bacteria, but rather with the presence of specific adhesion factors such as F pili that promote the emergence of probiotic bacteria in zebrafish larvae. Our study therefore provides new insights into the molecular events underlying the probiotic effect and constitutes a potentially high-throughput in vivo approach to the study of the molecular basis of pathogen exclusion in a relevant model of vertebrate oro-intestinal infection.     

The probability of severe disease in zoonotic and commensal infections

Cross-species transfers of pathogens (zoonoses) cause some of the most virulent diseases, including anthrax, hantavirus and Q fever. Zoonotic infections occur when a pathogen moves from its reservoir host species into a secondary host species. Similarly, commensal infections often have a primary reservoir location within their hosts' bodies from which they rarely cause disease symptoms, but commensals such as Neisseria meningitidis cause severe disease when they cross into a different body compartment from their normal location. Both zoonotic and commensal infections cause either mild symptoms or severe disease, but rarely intermediate symptoms. We develop a mathematical model for studying three factors that affect the probability of severe disease: the size of the inoculum, the route of inoculation and the frequency of naturally occurring infections that do not cause symptoms but do induce protective immunity (vaccinating inoculations). With a single route of infection, increasing pathogen density causes inoculations to develop more often into disease rather than asymptomatic vaccinations that provide protective immunity. With two routes of infection, it may happen that a lower density of a pathogen or of a particular antigenic variant leads to a relatively higher frequency of disease-inducing versus vaccinating inoculations. This reversal occurs when one route of infection tends to vaccinate against relatively common pathogens but less often vaccinates against relatively rare pathogens, whereas the other route of infection is susceptible to disease-inducing inoculation even at relatively low pathogen density.     

Comparative Genomic Analysis Identifies Divergent Genomic Features of Pathogenic Enterococcus cecorum Including a Type IC CRISPR-Cas System,a Capsule Locus,an epa-Like Locus,and Putative Host Tissue Binding Proteins

Enterococcus cecorum (EC) is the dominant enteric commensal of adult chickens and contributes to the gut consortia of many avian and mammalian species. While EC infection is an uncommon zoonosis, like other enterococcal species it can cause life-threating nosocomial infection in people. In contrast to other enterococci which are considered opportunistic pathogens, emerging pathogenic strains of EC cause outbreaks of musculoskeletal disease in broiler chickens. Typical morbidity and mortality is comparable to other important infectious diseases of poultry. In molecular epidemiologic studies, pathogenic EC strains were found to be genetically clonal. These findings suggested acquisition of specific virulence determinants by pathogenic EC. To identify divergent genomic features and acquired virulence determinants in pathogenic EC; comparative genomic analysis was performed on genomes of 3 pathogenic and 3 commensal strains of EC. Pathogenic isolates had smaller genomes with a higher GC content, and they demonstrated large regions of synteny compared to commensal isolates. A molecular phylogenetic analysis demonstrated sequence divergence in pathogenic EC genomes. At a threshold of 98% identity, 414 predicted proteins were identified that were highly conserved in pathogenic EC but not in commensal EC. Among these, divergent CRISPR-cas defense loci were observed. In commensal EC, the type IIA arrangement typical for enterococci was present; however, pathogenic EC had a type IC locus, which is novel in enterococci but commonly observed in streptococci. Potential mediators of virulence identified in this analysis included a polysaccharide capsular locus similar to that recently described for E. faecium, an epa-like locus, and cell wall associated proteins which may bind host extracellular matrix. This analysis identified specific genomic regions, coding sequences, and predicted proteins which may be related to the divergent evolution and increased virulence of emerging pathogenic strains of EC.     

In Vitro Protective Efficacy of Clostridium butyricum Against Fish Pathogen Infections

Most pathogens in intestine are opportunist, called “opportunistic pathogens” that usually do not cause disease in a healthy host. Only when the host’s resistance is lowered or the intestinal microecological balance is destroyed, the opportunistic pathogens are capable of causing disease. Here, two opportunistic pathogens, Salmonella enteritidis and Vibrio parahaemolyticus were chosen to test the possible antagonistic effect of the probiotic agent Clostridium butyricum on these pathogens infections in vitro using fish intestinal epithelial cells (FIECs). The C. butyricum and its spent culture supernatants exhibited significant inhibitory activity on S. enteritidis and V. parahaemolyticus growth and adherence to FIECs. The C. butyricum also showed significant inhibitory effects on S. enteritidis and V. parahaemolyticus induced apoptosis, which may due to its growth and adhesion inhibitory effects. These results indicated that the probiotic bacterium C. butyricum has preventive and therapeutic effects on S. enteritidis and V. parahaemolyticus infections in fish.     

Saliva,Salivary Gland,and Hemolymph Collection from Ixodes scapularis Ticks

Ticks are found worldwide and afflict humans with many tick-borne illnesses. Ticks are vectors for pathogens that cause Lyme disease and tick-borne relapsing fever (Borrelia spp.), Rocky Mountain Spotted fever (Rickettsia rickettsii), ehrlichiosis (Ehrlichia chaffeensis and E. equi), anaplasmosis (Anaplasma phagocytophilum), encephalitis (tick-borne encephalitis virus), babesiosis (Babesia spp.), Colorado tick fever (Coltivirus), and tularemia (Francisella tularensis) ^1-8. To be properly transmitted into the host these infectious agents differentially regulate gene expression, interact with tick proteins, and migrate through the tick ^3,9-13. For example, the Lyme disease agent, Borrelia burgdorferi, adapts through differential gene expression to the feast and famine stages of the tick''s enzootic cycle ^14,15. Furthermore, as an Ixodes tick consumes a bloodmeal Borrelia replicate and migrate from the midgut into the hemocoel, where they travel to the salivary glands and are transmitted into the host with the expelled saliva ^9,16-19.As a tick feeds the host typically responds with a strong hemostatic and innate immune response ^11,13,20-22. Despite these host responses, I. scapularis can feed for several days because tick saliva contains proteins that are immunomodulatory, lytic agents, anticoagulants, and fibrinolysins to aid the tick feeding ^{3,11,20,21,23}. The immunomodulatory activities possessed by tick saliva or salivary gland extract (SGE) facilitate transmission, proliferation, and dissemination of numerous tick-borne pathogens ^3,20,24-27. To further understand how tick-borne infectious agents cause disease it is essential to dissect actively feeding ticks and collect tick saliva. This video protocol demonstrates dissection techniques for the collection of hemolymph and the removal of salivary glands from actively feeding I. scapularis nymphs after 48 and 72 hours post mouse placement. We also demonstrate saliva collection from an adult female I. scapularis tick.     

Salmonella Pathogenicity and Host Adaptation in Chicken-Associated Serovars

SUMMARY

Enteric pathogens such as Salmonella enterica cause significant morbidity and mortality. S. enterica serovars are a diverse group of pathogens that have evolved to survive in a wide range of environments and across multiple hosts. S. enterica serovars such as S. Typhi, S. Dublin, and S. Gallinarum have a restricted host range, in which they are typically associated with one or a few host species, while S. Enteritidis and S. Typhimurium have broad host ranges. This review examines how S. enterica has evolved through adaptation to different host environments, especially as related to the chicken host, and continues to be an important human pathogen. Several factors impact host range, and these include the acquisition of genes via horizontal gene transfer with plasmids, transposons, and phages, which can potentially expand host range, and the loss of genes or their function, which would reduce the range of hosts that the organism can infect. S. Gallinarum, with a limited host range, has a large number of pseudogenes in its genome compared to broader-host-range serovars. S. enterica serovars such as S. Kentucky and S. Heidelberg also often have plasmids that may help them colonize poultry more efficiently. The ability to colonize different hosts also involves interactions with the host''s immune system and commensal organisms that are present. Thus, the factors that impact the ability of Salmonella to colonize a particular host species, such as chickens, are complex and multifactorial, involving the host, the pathogen, and extrinsic pressures. It is the interplay of these factors which leads to the differences in host ranges that we observe today.     

Fungal Chitin Induces Trained Immunity in Human Monocytes during Cross-talk of the Host with Saccharomyces cerevisiae

The immune system is essential to maintain the mutualistic homeostatic interaction between the host and its micro- and mycobiota. Living as a commensal, Saccharomyces cerevisiae could potentially shape the immune response in a significant way. We observed that S. cerevisiae cells induce trained immunity in monocytes in a strain-dependent manner through enhanced TNFα and IL-6 production upon secondary stimulation with TLR ligands, as well as bacterial and fungal commensals. Differential chitin content accounts for the differences in training properties observed among strains, driving induction of trained immunity by increasing cytokine production and direct antimicrobial activity both in vitro and in vivo. These chitin-induced protective properties are intimately associated with its internalization, identifying a critical role of phagosome acidification to facilitate microbial digestion. This study reveals how commensal and passenger microorganisms could be important in promoting health and preventing mucosal diseases by modulating host defense toward pathogens and thus influencing the host microbiota-immune system interactions.     

Gastrointestinal Colonization of Fungi

The human gastrointestinal tract is colonized with trillions of commensal microbes, and disturbances in the equilibrium of the gut microbiota have now been shown to be associated with a number of human diseases. Fungi, particularly Candida spp., are normal, harmless residents of the human gut, but in certain instances can cause invasive infections and inflammatory disorders. This paper will review the fungal diversity in the human gut, host and fungal factors that regulate GI colonization, and how these factors play into the pathogenesis of human disease.     

Bacterial Virulence Factors: Secreted for Survival

Virulence is described as an ability of an organism to infect the host and cause a disease. Virulence factors are the molecules that assist the bacterium colonize the host at the cellular level. These factors are either secretory, membrane associated or cytosolic in nature. The cytosolic factors facilitate the bacterium to undergo quick adaptive—metabolic, physiological and morphological shifts. The membrane associated virulence factors aid the bacterium in adhesion and evasion of the host cell. The secretory factors are important components of bacterial armoury which help the bacterium wade through the innate and adaptive immune response mounted within the host. In extracellular pathogens, the secretory virulence factors act synergistically to kill the host cells. In this review, we revisit the role of some of the secreted virulence factors of two human pathogens: Mycobacterium tuberculosis—an intracellular pathogen and Bacillus anthracis—an extracellular pathogen. The advances in research on the role of secretory factors of these pathogens during infection are discussed.     

The complex interactions between host immunity and non-biotrophic fungal pathogens of wheat leaves

Significant progress has been made in elucidating the mechanisms used by plants to recognize pathogens and activate “immune” responses. A “first line” of defense can be triggered through recognition of conserved Pathogen or Microbe Associated Molecular Patterns (PAMPs or MAMPs), resulting in activation of basal (or non-host) plant defenses, referred to as PAMP-triggered immunity (PTI). Disease resistance responses can also subsequently be triggered via gene-for-gene type interactions between pathogen avirulence effector genes and plant disease resistance genes (Avr-R), giving rise to effector triggered immunity (ETI). The majority of the conceptual advances in understanding these systems have been made using model systems, such as Arabidopsis, tobacco, or tomato in combination with biotrophic pathogens that colonize living plant tissues. In contrast, how these disease resistance mechanisms interact with non-biotrophic (hemibiotrophic or necrotrophic) fungal pathogens that thrive on dying host tissue during successful infection, is less clear. Several lines of recent evidence have begun to suggest that these organisms may actually exploit components of plant immunity in order to infect, successfully colonize and reproduce within host tissues. One underlying mechanism for this strategy has been proposed, which has been referred to as effector triggered susceptibility (ETS). This review aims to highlight the complexity of interactions between plant recognition and defense activation towards non-biotrophic pathogens, with particular emphasis on three important fungal diseases of wheat (Triticum aestivum) leaves.     

Pathogenic conversion of coagulase-negative staphylococci

Humans and animals are colonized by members of the genus Staphylococcus, however only some of these species evolved to cause invasive disease. The genetic basis for conversion of commensal staphylococci into pathogens is not known. We hypothesized that Staphylococcus aureus genes for coagulation and agglutination in vertebrate blood (coa, vwb and clfA) may support pathogenic conversion. Expression of coa and vwb in Staphylococcus epidermidis or Staphylococcus simulans supported a coagulase-positive phenotype but not the ability to cause disease in a mouse model of bloodstream infection. However, the simultaneous expression of coa, vwb and clfA in coagulase-negative staphylococci enabled bacterial agglutination in plasma and enhanced survival of S. simulans in human whole blood. Agglutination of S. simulans in the bloodstream of infected mice upon expression of coa, vwb and clfA provided also a mean for dissemination and replication in distal organs. Thus, the acquisition of genes for bacterial agglutination with fibrin appear sufficient for the conversion of commensal staphylococci into invasive pathogens.     

MicroMeeting: Who's talking to whom? Epithelial–bacterial pathogen interactions

Our perception that host-bacterial interactions lead to disease comes from rare, unsuccessful interactions resulting in the development of detectable symptoms. In contrast, the majority of host-bacterial interactions go unnoticed as the host and bacteria perceive each other to be no threat. In July 2004, a focused international symposium on epithelial-bacterial pathogen interactions was held in Newcastle upon Tyne (UK). The symposium concentrated on recent advances in our understanding of bacterial interactions at respiratory and gastrointestinal mucosal epithelial layers. For the host these epithelial tissues represent a first line of defence against invading bacterial pathogens. Through the discovery that the innate immune system plays a pivotal role during host-bacterial interactions, it has become clear that epithelia are being utilized by the host to monitor or communicate with both pathogenic and commensal bacteria. Interest in understanding the bacterial perspective of these interactions has lead researchers to realize that the bacteria utilize the same factors associated with disease to establish successful long-term interactions. Here we discuss several common themes and concepts that emerged from recent studies that have allowed physiologists and microbiologists to interact at a common interface similar to their counterparts -- epithelia and bacterial pathogens. These studies highlight the need for further multidisciplinary studies into how the host differentiates between pathogenic and commensal bacteria.     

内生真菌感染对宿主羊草抗病性的影响

以感染内生真菌的天然禾草羊草为实验材料,通过体外纯培养条件下的内生真菌、感染内生真菌的离体叶片和在体叶片对3种病原菌的抑菌实验,以探讨内生真菌对宿主植物羊草在抗病性方面的贡献。结果表明:体外纯培养条件下,分离自羊草的内生真菌Epichlobromicola对新月弯孢(Curvularia lunata)、根腐离蠕孢(Bipolaris sorokiniana)和枝孢霉(Cladosporium sp.)这3种病原菌都具有抑制作用,抑菌率分别达56.22%,46.93%和45.15%,且内生真菌培养滤液可以有效抑制这3种病原菌的孢子萌发,平均萌发率分别为30.4%,15.7%和16.4%;宿主植物叶片在离体条件下,内生真菌感染可以有效降低羊草叶片受C.lunata和C.sp.侵染后的病斑数或病斑长度,但对B.sorokiniana不起作用,甚至提高了叶片的病斑数及病斑长度,而离体叶片提取液对不同病原菌均有不同程度的抑制作用;在体条件下,内生真菌均可以通过降低叶片病斑数来增强羊草植株对这3种病原菌的抗性。由此看来,内生真菌E.bromicola对宿主植物羊草在抗病原菌侵染方面有一定的增益作用。     

The role of microbiota in infectious disease

The intestine harbors an ecosystem composed of the intestinal mucosa and the commensal microbiota. The microbiota fosters development, aids digestion and protects host cells from pathogens - a function referred to as colonization resistance. Little is known about the molecular basis of colonization resistance and how it can be overcome by enteropathogenic bacteria. Recently, studies on inflammatory bowel diseases and on animal models for enteric infection have provided new insights into colonization resistance. Gut inflammation changes microbiota composition, disrupts colonization resistance and enhances pathogen growth. Thus, some pathogens can benefit from inflammatory defenses. This new paradigm will enable the study of host factors enhancing or inhibiting bacterial growth in health and disease.     

Can bacterial interference prevent infection?

The concept that one bacterial species can interfere with the ability of another to colonize and infect the host has at its foundation the prerequisite that bacteria must attach to biological surfaces to cause infection. Although this is an over-simplification of pathogenesis, it has led to studies aimed at creating vaccines that block adhesion events. Arguably, the use of commensal bacteria (also referred to as "normal flora", "indigenous" or "autochthonous" microorganisms) to inhibit pathogens has even greater potential than vaccine use, because these bacteria are natural competitors of pathogens and their action does not require host immune stimulation. Exogenous application of commensal organisms (probiotics) has been shown to reduce the risk of infections in the gut, urogenital tract and wound sites. To manipulate and optimize these effects, further studies are required to understand cell signaling amongst commensals and pathogens within biofilms adherent to host tissues. The potential for new therapeutic regimens using probiotics is significant and worthy of further study.     

Botryosphaeriaceae species overlap on four unrelated,native South African hosts

Botryosphaeriaceae represents an important and diverse family of latent fungal pathogens of woody plants. We address the question of host range of these fungi by sampling leaves and branches of four native South African trees, including Acacia karroo (Fabaceae), Celtis africana (Cannabaceae), Searsia lancea (Anacardiaceae), and Gymnosporia buxifolia (Celastraceae). Two new species of the Botryosphaeriaceae, namely Tiarosporella africana sp. nov. and Aplosporella javeedii sp. nov. were identified, together with five known species, including Neofusicoccum parvum, Neofusicoccum kwambonambiense, Spencermartinsia viticola, Diplodia pseudoseriata, and Botryosphaeria dothidea. Most Botryosphaeriaceae occurred on more than one host. With the exception of S. lancea, which was infected by A. javeedii all the hosts were infected by more than one Botryosphaeriaceae species. Collectively, the results suggest that some intrinsic host factors, possibly combined with local environmental conditions, affect the distribution and co-infectivity of various hosts by the Botryosphaeriaceae. This would counteract the general ability of a species in the Botryosphaeriaceae to infect a broad range of plants. The combination of host and environmental factors might also explain why some Botryosphaeriaceae with apparently broad host ranges, are found on different suites of hosts in different areas of the world.     

Genome Reduction Is Associated with Bacterial Pathogenicity across Different Scales of Temporal and Ecological Divergence

Emerging bacterial pathogens threaten global health and food security, and so it is important to ask whether these transitions to pathogenicity have any common features. We present a systematic study of the claim that pathogenicity is associated with genome reduction and gene loss. We compare broad-scale patterns across all bacteria, with detailed analyses of Streptococcus suis, an emerging zoonotic pathogen of pigs, which has undergone multiple transitions between disease and carriage forms. We find that pathogenicity is consistently associated with reduced genome size across three scales of divergence (between species within genera, and between and within genetic clusters of S. suis). Although genome reduction is also found in mutualist and commensal bacterial endosymbionts, genome reduction in pathogens cannot be solely attributed to the features of their ecology that they share with these species, that is, host restriction or intracellularity. Moreover, other typical correlates of genome reduction in endosymbionts (reduced metabolic capacity, reduced GC content, and the transient expansion of nonfunctional elements) are not consistently observed in pathogens. Together, our results indicate that genome reduction is a consistent correlate of pathogenicity in bacteria.     

The immunopathogenesis of Entamoeba histolytica

Amebiasis is the disease caused by the enteric dwelling protozoan parasite Entamoeba histolytica. The WHO considers amebiasis as one of the major health problems in developing countries; it is surpassed by only malaria and schistosomiasis for death caused by parasitic infection. E. histolytica primarily lives in the colon as a harmless commensal, but is capable of causing devastating dysentery, colitis and liver abscess. What triggers the switch to a pathogenic phenotype and the onset of disease is unknown. We are becoming increasingly aware of the complexity of the host-parasite interaction. During chronic stages of amebiasis, the host develops an immune response that is incapable of eliminating tissue resident parasites, while the parasite actively immunosuppresses the host. However, most individuals with symptomatic infections succumb only to an episode of dysentery. Why most halt invasion and a minority progress to chronic disease remains poorly understood. This review presents a current understanding of the immune processes that shape the outcome of E. histolytica infections during its different stages.     

An Experimental Model to Study Tuberculosis-Malaria Coinfection upon Natural Transmission of Mycobacterium tuberculosis and Plasmodium berghei

Coinfections naturally occur due to the geographic overlap of distinct types of pathogenic organisms. Concurrent infections most likely modulate the respective immune response to each single pathogen and may thereby affect pathogenesis and disease outcome. Coinfected patients may also respond differentially to anti-infective interventions. Coinfection between tuberculosis as caused by mycobacteria and the malaria parasite Plasmodium, both of which are coendemic in many parts of sub-Saharan Africa, has not been studied in detail. In order to approach the challenging but scientifically and clinically highly relevant question how malaria-tuberculosis coinfection modulate host immunity and the course of each disease, we established an experimental mouse model that allows us to dissect the elicited immune responses to both pathogens in the coinfected host. Of note, in order to most precisely mimic naturally acquired human infections, we perform experimental infections of mice with both pathogens by their natural routes of infection, i.e. aerosol and mosquito bite, respectively.