Characterization of the O-antigen gene clusters of Yersinia pseudotuberculosis and the cryptic O-antigen gene cluster of Yersinia pestis shows that the plague bacillus is most closely related to and has evolved from Y. pseudotuberculosis serotype O:1b

The CpxAR signaling system confers a fitness advantage for flea gut colonization by the plague bacillus

The adaptation of Yersinia pestis, the flea-borne plague agent, to fluctuating environmental conditions is essential for the successful colonization of the flea vector. A previous comparative transcriptomic analysis showed that the Cpx pathway of Y. pestis is up-regulated in infected fleas. The CpxAR two-component system is a component of the envelope stress response and is critical for maintaining the integrity of the cell. Here, a phenotypic screening revealed a survival defect of the cpxAR mutant to oxidative stress and copper. The measured copper concentration in the digestive tract contents of fed fleas increased fourfold during the digestive process. By direct analysis of phosphorylation of CpxR by a Phos-Tag gel approach, we demonstrated that biologically relevant concentrations of copper triggered the system. Then, a competitive challenge highlighted the role of the CpxAR system in bacterial fitness during flea infection. Lastly, an in vitro sequential exposure to copper and then H2O2 to mimic the flea suggests a model in which, within the insect digestive tract, the CpxAR system would be triggered by copper, establishing an oxidative stress response.

IMPORTANCE

The bacterium Yersinia pestis is the agent of flea-borne plague. Our knowledge of the mechanisms used by the plague bacillus to infect the flea vector is limited. The up-regulation of the envelope stress response under the control of the Cpx signaling pathway was previously shown in a transcriptomic study. Here, our in vivo and in vitro approaches suggest a model in which Y. pestis uses the CpxAR phosphorelay system to sense and respond to the copper present in the flea gut, thereby optimizing the flea gut colonization. In other words, the system is essential for bacterial fitness in the flea.

Yersinia pestis can infect the Pawlowsky glands of human body lice and be transmitted by louse bite

Yersinia pestis, the causative agent of plague, is a highly lethal vector-borne pathogen responsible for killing large portions of Europe's population during the Black Death of the Middle Ages. In the wild, Y. pestis cycles between fleas and rodents; occasionally spilling over into humans bitten by infectious fleas. For this reason, fleas and the rats harboring them have been considered the main epidemiological drivers of previous plague pandemics. Human ectoparasites, such as the body louse (Pediculus humanus humanus), have largely been discounted due to their reputation as inefficient vectors of plague bacilli. Using a membrane-feeder adapted strain of body lice, we show that the digestive tract of some body lice become chronically infected with Y. pestis at bacteremia as low as 1 × 105 CFU/ml, and these lice routinely defecate Y. pestis. At higher bacteremia (≥1 × 107 CFU/ml), a subset of the lice develop an infection within the Pawlowsky glands (PGs), a pair of putative accessory salivary glands in the louse head. Lice that developed PG infection transmitted Y. pestis more consistently than those with bacteria only in the digestive tract. These glands are thought to secrete lubricant onto the mouthparts, and we hypothesize that when infected, their secretions contaminate the mouthparts prior to feeding, resulting in bite-based transmission of Y. pestis. The body louse's high level of susceptibility to infection by gram-negative bacteria and their potential to transmit plague bacilli by multiple mechanisms supports the hypothesis that they may have played a role in previous human plague pandemics and local outbreaks.

Molecular phylogenies of the plague microbe Yersinia pestis: an environmental assessment

Two approaches are applied to studies of the phylogeny of the plague microbe Yersinia pestis, i.e., the reconstruction of its history: Molecular genetic (MG) and ecological (ECO). The MG approach dominates. Phylogenies created with MG and ECO methods are not congruent. MG conclusions contradict the known facts and patterns of ecology, biogeography, paleontology, etc. We discuss some obvious contradictions and inconsistencies and suggest that real phylogenies of the plague microbe can be constructed only on the basis of the integration of MG and ECO approaches.

Parallelism in Speciation and Intraspecific Diversification of the Plague Microbe Yersinia pestis

Modern "molecular genetic (MG) phylogenies" of the plague microbe Yersinia pestis, built on models of neutral evolution using statistical methods of phylogenetic analysis, contradict numerous obvious environmental (ECO) patterns and are not consistent with the concept of adaptatiogenesis. The reason for the discrepancy between MG and ECO phylogenies is seen in the underestimation by the MG approach of parallelisms in the processes of speciation and intraspecific diversification of the plague microbe. ECO methods showed the parallel tritope (almost) simultaneous speciation of three primary genovariants (populations, subspecies) Y. pestis 2.ANT3, 3.ANT2, and 4.ANT1 in three geographical populations of the Mongolian marmot (Marmota sibirica), which in the MG approach is mistaken for polytomy ("Big Bang"), caused by unknown natural phenomena on the eve of the first pandemic (Justinian's plague, 6th-8th centuries AD). The discrepancy between the MG and ECO interpretations of the evolution of intraspecifically-derived phylogenetic subbranches 0.PE and 2.MED is also associated with parallel evolutionary processes in independent lines, based on genovariants 2.ANT3, 3.ANT2, and 4.ANT1. The independence of these phylogenetic lines and parallelisms of sub-branches 0.PE and 2.MED associated with them are not taken into account in the MG approach. The prospect of creating a real phylogenetic tree for Y. pestis depends on a creative synthesis of the two approaches-MG and ECO.

Ecological scenario of the plague microbe <i>Yersinia pestis</i> speciation underlying adequate molecular evolutionary model

It is known that the psychrophilic pseudotuberculosis microbe serotype 1 (Y. pseudotuberculosis 0:1b) causing Far East scarlet-like fever (FESLF) an intestinal infection found in a wide range of invertebrates and vertebrates inhabiting cold regions in the Northern and Central Asia as well as Far East is direct ancestor of the plague causative agent Yersinia pestis. However, the mechanism of Y. pestis speciation remains poorly elucidated. Numerous Y. pestis phylogenies created by using molecular genetic (MG) technologies are largely contradictory, being not in line with reliable data obtained by natural science approaches (e.g., ecology, epizootology, biogeography, and paleontology), which disagree with current evolutionary doctrine (synthetic theory of evolution). The MG approach provides no definitive answer to the questions of where, when, how, and under what circumstances the species Y. pestis arose. One of the reasons for such situation might be due to inadequacy of using the molecular evolutionary model for Y. pestis phylogenetics. Knowledge of the life cycles for the ancestral pseudotuberculosis and derivative plague microbes as well as related unique environmental features allows to create a reliable ecological model for the plague microbe evolution to be further used for assessing patterns of molecular variability and building proper molecular model that might be accepted for MG-reconstruction of plague microbe history. According to the ecological model, the species Y. pestis was formed in a tritopic manner (almost) simultaneously from FESLF clones (populations) in the three geographical populations of the Mongolian marmot-tarbagan (Marmota sibirica) and the flea Oropsylla silantiewi parasitizing on it. The inducer of speciation was coupled to the last maximum (Sartan) cooling in Central Asia occurred 2215 thousand years ago. Soil cooling and deep freezing resulted in altered behavior of the marmot flea larvae with emergence of facultative hematophagy, which, in turn, led to a unique traumatic (compared to routine alimentary) infection route of sleeping marmots with FESLF and, as a result, a unique way of Y. pestis speciation. The molecular model should predict a Y. pestis peripatric tritope speciation, existing numerous parallelisms in intraspecific variability associated with tritope speciation, and the quantum principle of speciation in the highly variable heterothermic (heteroimmune) stressful marmot-flea (Marmota sibirica Oropsylla silantiewi) host-vector environment involving stress-induced mutagenesis. Such molecular model of evolution may be useful for improving molecular methodology of phylogenetic constructions for a wide range of parasitic microorganisms.

Climate Changes in Central Asia as a Prerequisite and Trigger of Plague Microbe (Yersinia pestis) Speciation

Two physical and climatic factors that were distant and recent prerequisites and a transformation trigger for a clone of the ancestral pseudotuberculous microbe Yersinia pseudotuberculosis O:1b (the causative agent of the Far East scarlet-like fever (FESLF)) into a population of the plague microbe derivative Y. pestis are considered. One remote prerequisite was the aridification of the Central Asian landscapes in the second half of the Cenozoic period and the formation of the Gobi Arid Zone. The arid conditions of Central Asia determined the formation of adaptive species-specific protective behavior in the Tarbagan marmot (Marmota sibirica) when installing the plug of a wintering hole, which later contributed to the massive infection of the animals with FESLF by the aberrant (traumatic, not alimentary) method during hibernation. A recent prerequisite and a real trigger of Y. pestis speciation was the onset of the last maximum (Sartan) ice age in Central Asia at the turn of the Pleistocene and Holocene, 22 000-15 000 years ago. Freezing of the cooling burrows of the Tarbagan marmot caused a behavioral shift in the larval population of the marmot flea Oropsylla silantiewi and the transition to the cold winter-spring months of the year from saprophagy in the nesting litter to hematophagy on the bodies of sleeping animals. Larval scarifications in the oral cavity of sleeping marmots have become the entrance gate for a unique traumatic FESLF infection. The constellation of climatic changes, the heterothermal (and, accordingly, heteroimmune) condition of the family groups of sleeping marmots, and the year-round propagation of marmot fleas in wintering burrows, combined with behavioral shifts in marmots and fleas caused by climatic changes, led to the formation of conditions in the parasitic system M. sibirica-O. silantiewi in which the transformation of the FESLF microbe into the causative agent of the plague occurred according to peripatric speciation. Thus, the climatic changes that happened at different times in the Cenozoic initially led to a shift in behavior of the Tarbagan marmot and, subsequently, to a shift in the behavior of the fleas parasitizing it. Ultimately, the change in the behavior of marmots and fleas caused the transition of the clone(s) of the FESLF causative agent into a new ecological niche and adaptive zone, as well as the transformation into a population(s) of the plague microbe.

Subversion of GBP-mediated host defense by E3 ligases acquired during Yersinia pestis evolution

Plague has caused three worldwide pandemics in history, including the Black Death in medieval ages. Yersinia pestis, the etiological agent of plague, has evolved a powerful arsenal to disrupt host immune defenses during evolution from enteropathogenic Y. pseudotuberculosis. Here, we find that two functionally redundant E3 ligase of Y. pestis, YspE1 and YspE2, can be delivered via type III secretion injectisome into host cytosol where they ubiquitinate multiple guanylate-binding proteins (GBPs) for proteasomal degradation. However, Y. pseudotuberculosis has no such capability due to lacking functional YspE1/2 homologs. YspE1/2-mediated GBP degradations significantly promote the survival of Y. pestis in macrophages and strongly inhibit inflammasome activation. By contrast, Gbp^{chr3−/−, chr5−/−} macrophages exhibit much lowered inflammasome activation independent of YspE1/2, accompanied with an enhanced replication of Y. pestis. Accordingly, Gbp^{chr3−/−, chr5−/−} mice are more susceptible to Y. pestis. We demonstrate that Y. pestis utilizes E3 ligases to subvert GBP-mediated host defense, which appears to be newly acquired by Y. pestis during evolution.

Guanylate-binding proteins (GBPs) recognize pathogen containing vacuoles, leading to lysis of this intracellular niche and induction of inflammasomes. Here, Cao et al. show that Y. pestis, the causative agent of plague, secret two functionally redundant E3 ligase, YspE1 and YspE2, into the host’s cytosol to ubiquitinate multiple GBPs for proteasomal degradation to subvert host immune defense. This capability appears to be newly acquired by Y. pestis during evolution, since its closely related progenitor Y. pseudotuberculosis is unable to do so.

Contributions of Yersinia pestis outer membrane protein Ail to plague pathogenesis

PURPOSE OF REVIEW

Pathogenic Yersinia have been a productive model system for studying bacterial pathogenesis. Hallmark contributions of Yersinia research to medical microbiology are legion and include: (i) the first identification of the role of plasmids in virulence, (ii) the important mechanism of iron acquisition from the host, (iii) the first identification of bacterial surface proteins required for host cell invasion, (iv) the archetypical type III secretion system, and (v) elucidation of the role of genomic reduction in the evolutionary trajectory from a fairly innocuous pathogen to a highly virulent species.

RECENT FINDINGS

The outer membrane (OM) protein Ail (attachment invasion locus) was identified over 30 years ago as an invasin-like protein. Recent work on Ail continues to provide insights into Gram-negative pathogenesis. This review is a synopsis of the role of Ail in invasion, serum resistance, OM stability, thermosensing, and vaccine development.

SUMMARY

Ail is shown to be an essential virulence factor with multiple roles in pathogenesis. The recent adaptation of Yersinia pestis to high virulence, which included genomic reduction to eliminate redundant protein functions, is a model to understand the emergence of new bacterial pathogens.

Plague Prevention and Therapy: Perspectives on Current and Future Strategies

Plague, caused by the bacterial pathogen Yersinia pestis, is a vector-borne disease that has caused millions of human deaths over several centuries. Presently, human plague infections continue throughout the world. Transmission from one host to another relies mainly on infected flea bites, which can cause enlarged lymph nodes called buboes, followed by septicemic dissemination of the pathogen. Additionally, droplet inhalation after close contact with infected mammals can result in primary pneumonic plague. Here, we review research advances in the areas of vaccines and therapeutics for plague in context of Y. pestis virulence factors and disease pathogenesis. Plague continues to be both a public health threat and a biodefense concern and we highlight research that is important for infection mitigation and disease treatment.

Lipopolysaccharide of the Yersinia pseudotuberculosis Complex

Lipopolysaccharide (LPS), localized in the outer leaflet of the outer membrane, serves as the major surface component of the Gram-negative bacterial cell envelope responsible for the activation of the host's innate immune system. Variations of the LPS structure utilized by Gram-negative bacteria promote survival by providing resistance to components of the innate immune system and preventing recognition by TLR4. This review summarizes studies of the biosynthesis of Yersinia pseudotuberculosis complex LPSs, and the roles of their structural components in molecular mechanisms of yersiniae pathogenesis and immunogenesis.

The glycan alphabet is not universal: a hypothesis

Several monosaccharides constitute naturally occurring glycans, but it is uncertain whether they constitute a universal set like the alphabets of proteins and DNA. Based on the available experimental observations, it is hypothesized herein that the glycan alphabet is not universal. Data on the presence/absence of pathways for the biosynthesis of 55 monosaccharides in 12 939 completely sequenced archaeal and bacterial genomes are presented in support of this hypothesis. Pathways were identified by searching for homologues of biosynthesis pathway enzymes. Substantial variations were observed in the set of monosaccharides used by organisms belonging to the same phylum, genera and even species. Monosaccharides were grouped as common, less common and rare based on their prevalence in Archaea and Bacteria. It was observed that fewer enzymes are sufficient to biosynthesize monosaccharides in the common group. It appears that the common group originated before the formation of the three domains of life. In contrast, the rare group is confined to a few species in a few phyla, suggesting that these monosaccharides evolved much later. Fold conservation, as observed in aminotransferases and SDR (short-chain dehydrogenase reductase) superfamily members involved in monosaccharide biosynthesis, suggests neo- and sub-functionalization of genes led to the formation of the rare group monosaccharides. The non-universality of the glycan alphabet begets questions about the role of different monosaccharides in determining an organism’s fitness.

Loss of the virulence plasmid by Shigella sonnei promotes its interactions with CD207 and CD209 receptors

Introduction. Shigella sonnei, the cause of bacillary dysentery, belongs to Gram-negative enteropathogenic bacteria. S. sonnei contains a 210 kb virulence plasmid that encodes an O-antigen gene cluster of LPSs. However, this virulence plasmid is frequently lost during replication. It is well-documented that after losing the O-antigen and becoming rough strains, the Gram-negative bacteria may express an LPS core on its surface. Previous studies have suggested that by using the LPS core, Gram-negative bacteria can interact with several C-type lectin receptors that are expressed on antigen-presenting cells (APCs).Hypothesis/Gap Statement. S. sonnei by losing the virulence plasmid may hijack APCs via the interactions of LPS-CD209/CD207.Aim. This study aimed to investigate if the S. sonnei rough strain, by losing the virulence plasmid, interacted with APCs that express C-type lectins of human CD207, human CD209a and mouse CD209b.Methodology. SDS-PAGE silver staining was used to examine the O-antigen expression of S. sonnei WT and its rough strain. Invasion assays and inhibition assays were used to examine the ability of S. sonnei WT and its rough strain to invade APCs and investigate whether CD209 and CD207 are receptors for phagocytosis of rough S. sonnei. Animal assays were used to observe the dissemination of S. sonnei.Results. S. sonnei did not express O-antigens after losing the virulence plasmid. The S. sonnei rough strain invades with APCs, including human dendritic cells (DCs) and mouse macrophages. CD209 and CD207 are receptors for phagocytosis of rough S. sonnei. Expression of the O-antigen reduces the ability of the S. sonnei rough strain to be disseminated to mesenteric lymph nodes and spleens.Conclusion. This work demonstrated that S. sonnei rough strains - by losing the virulence plasmid - invaded APCs through interactions with CD209 and CD207 receptors.

Pan-genomics, drug candidate mining and ADMET profiling of natural product inhibitors screened against Yersinia pseudotuberculosis

Yersinia pseudotuberculosis belongs to the family Enterobacteriaceae and is responsible for scarlatinoid fever, food poisoning, post-infectious complications like erythema nodosum/reactive arthritis as well as pseudoappendicitis in children. Genome sequences of the 23 whole genomes from NCBI were utilized for conducting the pan-genomic analysis. Essential proteins from the core region were obtained and drug targets were identified using a hierarchal in silico approach. Among these, multidrug resistance protein sub-unit mdtC was chosen for further analysis. This protein unit confers resistance to antibiotics upon forming a tripartite complex with units A and B in Escherichia coli. Details of the function have not yet been elucidated experimentally in Yersinia spp. Computational structure modeling and validation were followed by screening against phytochemical libraries of traditional Indian (Ayurveda), North African, and traditional Chinese flora using Molecular Operating Environment software version 2019.0102. ADMET profiling and descriptor study of best docked compounds was studied. Since phytotherapy is the best resort to antibiotic resistance so these compounds should be tested experimentally to further validate the results. The obtained information could aid wet-lab scientists to work on the scaffold of screened drug-like compounds from natural resources. This could be useful in our quest for antibiotic-resistant therapy against Y. pseudotuberculosis.

Induction of Protective Antiplague Immune Responses by Self-Adjuvanting Bionanoparticles Derived from Engineered Yersinia pestis

A Yersinia pestis mutant synthesizing an adjuvant form of lipid A (monophosphoryl lipid A, MPLA) displayed increased biogenesis of bacterial outer membrane vesicles (OMVs). To enhance the immunogenicity of the OMVs, we constructed an Asd-based balanced-lethal host-vector system that oversynthesized the LcrV antigen of Y. pestis, raised the amounts of LcrV enclosed in OMVs by the type II secretion system, and eliminated harmful factors like plasminogen activator (Pla) and murine toxin from the OMVs. Vaccination with OMVs containing MPLA and increased amounts of LcrV with diminished toxicity afforded complete protection in mice against subcutaneous challenge with 8 × 105 CFU (80,000 50% lethal dose [LD50]) and intranasal challenge with 5 × 103 CFU (50 LD50) of virulent Y. pestis This protection was significantly superior to that resulting from vaccination with LcrV/alhydrogel or rF1-V/alhydrogel. At week 4 postimmunization, the OMV-immunized mice showed more robust titers of antibodies against LcrV, Y. pestis whole-cell lysate (YPL), and F1 antigen and more balanced IgG1:IgG2a/IgG2b-derived Th1 and Th2 responses than LcrV-immunized mice. Moreover, potent adaptive and innate immune responses were stimulated in the OMV-immunized mice. Our findings demonstrate that self-adjuvanting Y. pestis OMVs provide a novel plague vaccine candidate and that the rational design of OMVs could serve as a robust approach for vaccine development.

Force interactions between Yersiniae lipopolysaccharides and monoclonal antibodies: An optical tweezers study

This article reports the force spectroscopy investigation of interactions between lipopolysaccharides (LPSs) of two species from Yersinia genus and complementary (or heterologous) monoclonal antibodies (mAbs). We have obtained the experimental data by optical trapping on the "sensitized polystyrene microsphere - sensitized glass substrate" model system at its approach - retraction in vertical plane. We detected non-specific interactions in low-amplitude areas on histograms mainly due to physicochemical properties of abiotic surface and specific interactions in complementary pairs "antigen - antibodies" in high-amplitude areas (100-120 pN) on histograms. The developed measurement procedure can be used for detection of rupture forces in other molecular pairs.

Yersinia pestis Interacts With SIGNR1 (CD209b) for Promoting Host Dissemination and Infection

Yersinia pestis, a Gram-negative bacterium and the etiologic agent of plague, has evolved from Yersinia pseudotuberculosis, a cause of a mild enteric disease. However, the molecular and biological mechanisms of how Y. pseudotuberculosis evolved to such a remarkably virulent pathogen, Y. pestis, are not clear. The ability to initiate a rapid bacterial dissemination is a characteristic hallmark of Y. pestis infection. A distinguishing characteristic between the two Yersinia species is that Y. pseudotuberculosis strains possess an O-antigen of lipopolysaccharide (LPS) while Y. pestis has lost the O-antigen during evolution and therefore exposes its core LPS. In this study, we showed that Y. pestis utilizes its core LPS to interact with SIGNR1 (CD209b), a C-type lectin receptor on antigen presenting cells (APCs), leading to bacterial dissemination to lymph nodes, spleen and liver, and the initiation of a systemic infection. We therefore propose that the loss of O-antigen represents a critical step in the evolution of Y. pseudotuberculosis into Y. pestis in terms of hijacking APCs, promoting bacterial dissemination and causing the plague.

Differential Gene Expression Patterns of Yersinia pestis and Yersinia pseudotuberculosis during Infection and Biofilm Formation in the Flea Digestive Tract

Yersinia pestis, the etiologic agent of plague, emerged as a fleaborne pathogen only within the last 6,000 years. Just five simple genetic changes in the Yersinia pseudotuberculosis progenitor, which served to eliminate toxicity to fleas and to enhance survival and biofilm formation in the flea digestive tract, were key to the transition to the arthropodborne transmission route. To gain a deeper understanding of the genetic basis for the development of a transmissible biofilm infection in the flea foregut, we evaluated additional gene differences and performed in vivo transcriptional profiling of Y. pestis, a Y. pseudotuberculosis wild-type strain (unable to form biofilm in the flea foregut), and a Y. pseudotuberculosis mutant strain (able to produce foregut-blocking biofilm in fleas) recovered from fleas 1 day and 14 days after an infectious blood meal. Surprisingly, the Y. pseudotuberculosis mutations that increased c-di-GMP levels and enabled biofilm development in the flea did not change the expression levels of the hms genes responsible for the synthesis and export of the extracellular polysaccharide matrix required for mature biofilm formation. The Y. pseudotuberculosis mutant uniquely expressed much higher levels of Yersinia type VI secretion system 4 (T6SS-4) in the flea, and this locus was required for flea blockage by Y. pseudotuberculosis but not for blockage by Y. pestis. Significant differences between the two species in expression of several metabolism genes, the Psa fimbrial genes, quorum sensing-related genes, transcription regulation genes, and stress response genes were evident during flea infection. IMPORTANCE Y. pestis emerged as a highly virulent, arthropod-transmitted pathogen on the basis of relatively few and discrete genetic changes from Y. pseudotuberculosis. Parallel comparisons of the in vitro and in vivo transcriptomes of Y. pestis and two Y. pseudotuberculosis variants that produce a nontransmissible infection and a transmissible infection of the flea vector, respectively, provided insights into how Y. pestis has adapted to life in its flea vector and point to evolutionary changes in the regulation of metabolic and biofilm development pathways in these two closely related species.

Necroptosis of infiltrated macrophages drives Yersinia pestis dispersal within buboes

When draining lymph nodes become infected by Yersinia pestis (Y. pestis), a massive influx of phagocytic cells occurs, resulting in distended and necrotic structures known as buboes. The bubonic stage of the Y. pestis life cycle precedes septicemia, which is facilitated by trafficking of infected mononuclear phagocytes through these buboes. However, how Y. pestis convert these immunocytes recruited by host to contain the pathogen into vehicles for bacterial dispersal and the role of immune cell death in this context are unknown. We show that the lymphatic spread requires Yersinia outer protein J (YopJ), which triggers death of infected macrophages by downregulating a suppressor of receptor-interacting protein kinase 1-mediated (RIPK1-mediated) cell death programs. The YopJ-triggered cell death was identified as necroptotic, which released intracellular bacteria, allowing them to infect new neighboring cell targets. Dying macrophages also produced chemotactic sphingosine 1-phosphate, enhancing cell-to-cell contact, further promoting infection. This necroptosis-driven expansion of infected macrophages in buboes maximized the number of bacteria-bearing macrophages reaching secondary lymph nodes, leading to sepsis. In support, necrostatins confined bacteria within macrophages and protected mice from lethal infection. These findings define necrotization of buboes as a mechanism for bacterial spread and a potential target for therapeutic intervention.

Genesis of Flea-Born Transmission of Plague Microbe, Yersinia pestis: Two Approachs – Molecular-Genetic and Ecological Ones

Two approaches to studying the origin and transmission mechanism of the flea-borne plague pathogen, Yersinia pestis: molecular-genetic and ecological ones – are considered in this review. The molecular genetic approach is based on saltation evolutionary ideology and relies upon the phenomenon of horizontal gene transfer of pla and ymt as critical evolutionary events. Further deletion of some structural and regulatory genes optimized “blockage” mechanism of transmission. The Ecological approach is based on the modern synthetic theory of evolution. It posits a gradual population-genetic transformation in the Marmot – Flea (Marmota sibirica – Oropsylla silantiewi) transitional (heterothermal, heteroimmune) host-parasite system in Late Pleistocene – Holocene epochs. The best prospects for disclosing the mechanisms of evolutionary formation of flea-borne Y. pestis transmission consist in the synthesis of molecular-genetic and ecological approaches.

High-throughput analysis of Yersinia pseudotuberculosis gene essentiality in optimised in vitro conditions, and implications for the speciation of Yersinia pestis

Background

Yersinia pseudotuberculosis is a zoonotic pathogen, causing mild gastrointestinal infection in humans. From this comparatively benign pathogenic species emerged the highly virulent plague bacillus, Yersinia pestis, which has experienced significant genetic divergence in a relatively short time span. Much of our knowledge of Yersinia spp. evolution stems from genomic comparison and gene expression studies. Here we apply transposon-directed insertion site sequencing (TraDIS) to describe the essential gene set of Y. pseudotuberculosis IP32953 in optimised in vitro growth conditions, and contrast these with the published essential genes of Y. pestis.

Results

The essential genes of an organism are the core genetic elements required for basic survival processes in a given growth condition, and are therefore attractive targets for antimicrobials. One such gene we identified is yptb3665, which encodes a peptide deformylase, and here we report for the first time, the sensitivity of Y. pseudotuberculosis to actinonin, a deformylase inhibitor. Comparison of the essential genes of Y. pseudotuberculosis with those of Y. pestis revealed the genes whose importance are shared by both species, as well as genes that were differentially required for growth. In particular, we find that the two species uniquely rely upon different iron acquisition and respiratory metabolic pathways under similar in vitro conditions.

Conclusions

The discovery of uniquely essential genes between the closely related Yersinia spp. represent some of the fundamental, species-defining points of divergence that arose during the evolution of Y. pestis from its ancestor. Furthermore, the shared essential genes represent ideal candidates for the development of novel antimicrobials against both species.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1189-5) contains supplementary material, which is available to authorized users.

Differential impact of lipopolysaccharide defects caused by loss of RfaH in Yersinia pseudotuberculosis and Yersinia pestis

RfaH enhances transcription of a select group of operons controlling bacterial surface features such as lipopolysaccharide (LPS). Previous studies have suggested that rfaH may be required for Yersinia pseudotuberculosis resistance to antimicrobial chemokines and survival during mouse infections. In order to further investigate the role of RfaH in LPS synthesis, resistance to host defense peptides, and virulence of Yersinia, we constructed ΔrfaH mutants of Y. pseudotuberculosis IP32953 and Y. pestis KIM6+. Loss of rfaH affected LPS synthesis in both species, resulting in a shorter core oligosaccharide. Susceptibility to polymyxin and the antimicrobial chemokine CCL28 was increased by loss of rfaH in Y. pseudotuberculosis but not in Y. pestis. Transcription of genes in the ddhD-wzz O-antigen gene cluster, but not core oligosaccharide genes, was reduced in ΔrfaH mutants. In addition, mutants with disruptions in specific ddhD-wzz O-antigen cluster genes produced LPS that was indistinguishable from the ΔrfaH mutant. This suggests that both Y. pseudotuberculosis and Y. pestis produce an oligosaccharide core with a single O-antigen unit attached in an RfaH-dependent fashion. Despite enhanced sensitivity to host defense peptides, the Y. pseudotuberculosis ΔrfaH strain was not attenuated in mice, suggesting that rfaH is not required for acute infection.

Genetics and evolution of Yersinia pseudotuberculosis O-specific polysaccharides: a novel pattern of O-antigen diversity

O-antigen polysaccharide is a major immunogenic feature of the lipopolysaccharide of Gram-negative bacteria, and most species produce a large variety of forms that differ substantially from one another. There are 18 known O-antigen forms in the Yersinia pseudotuberculosis complex, which are typical in being composed of multiple copies of a short oligosaccharide called an O unit. The O-antigen gene clusters are located between the hemH and gsk genes, and are atypical as 15 of them are closely related, each having one of five downstream gene modules for alternative main-chain synthesis, and one of seven upstream modules for alternative side-branch sugar synthesis. As a result, many of the genes are in more than one gene cluster. The gene order in each module is such that, in general, the earlier a gene product functions in O-unit synthesis, the closer the gene is to the 5΄ end for side-branch modules or the 3΄ end for main-chain modules. We propose a model whereby natural selection could generate the observed pattern in gene order, a pattern that has also been observed in other species.

Review: Lipopolysaccharide inner core oligosaccharide structure and outer membrane stability in human pathogens belonging to the Enterobacteriaceae

In the Enterobacteriaceae, the outer membrane is primarily comprised of lipopolysaccharides. The lipopolysaccharide molecule is important in mediating interactions between the bacterium and its environment and those regions of the molecule extending further away from the cell surface show a higher amount of structural diversity. The hydrophobic lipid A is highly conserved, due to its important role in the structural integrity of the outer membrane. Attached to the lipid A region is the core oligosaccharide. The inner core oligosaccharide (lipid A proximal) backbone is also well conserved. However, non-stoichiometric substitutions of the basic inner core structure lead to structural variation and microheterogeneity. These include the addition of negatively charged groups (phosphate or galacturonic acid), ethanolamine derivatives, and glycose residues (Kdo, rhamnose, galactose, glucosamine, N-acetylglucosamine, heptose, Ko). The genetics and biosynthesis of these substitutions is beginning to be elucidated. Modification of heptose residues with negatively charged molecules (such as phosphate in Escherichia coli and Salmonella and galacturonic acid in Klebsiella pneumoniae ) has been shown to be involved in maintaining membrane stability. However, the biological role(s) of the remaining substitutions is unknown.

Effect of natural polymorphism on structure and function of the Yersinia pestis outer membrane porin F (OmpF protein): a computational study

The Yersinia pestis outer membrane porin F (OmpF) is a transmembrane protein located in the outer membrane of this Gram-negative bacterium which is the causative agent of plague, where it plays a significant role in controlling the selective permeability of the membrane. The amino acid sequences of OmpF proteins from 48 Y. pestis strains representing all currently available phylogenetic groups of this Gram-negative bacterium were recently deduced. Comparison of these amino acid sequences revealed that the OmpF can be present in four isoforms, the pestis-pestis type, and the pestis-microtus types I, II, and III. OmpF of the most recent pestis-pestis type has an alanine residue at the position 148, where all the pestis-microtus types have threonine there (T148A polymorphism). The variability of different pestis-microtus types is caused by an additional polymorphism at the 193rd position, where the OmpFs of the pestis-microtus type II and type III have isoleucine-glycine (IG⁺₁₉₃) or isoleucine-glycine-isoleucine-glycine (IGIG⁺₁₉₃) insertions, respectively (IG⁺₁₉₃ and IGIG⁺₁₉₃ polymorphism). To investigate potential effects of these sequence polymorphisms on the structural properties of the OmpF protein, we conducted multi-level computational analysis of its isoforms. Analysis of the I-TASSER-generated 3D-models revealed that the Yersinia OmpF is very similar to other non-specific enterobacterial porins. The T148A polymorphism affected a loop located in the external vestibule of the OmpF channel, whereas IG⁺₁₉₃ and IGIG⁺₁₉₃ polymorphisms affected one of its β-strands. Our analysis also suggested that polymorphism has moderate effect on the predicted local intrinsic disorder predisposition of OmpF, but might have some functional implementations.

The symbiotic role of O-antigen of Burkholderia symbiont in association with host Riptortus pedestris

Riptortus pedestris harboring Burkholderia symbiont is a useful symbiosis model to study the molecular interactions between insects and bacteria. We recently reported that the lipopolysaccharide O-antigen is absent in the Burkholderia symbionts isolated from Riptortus guts. Here, we investigated the symbiotic role of O-antigen comprehensively in the Riptortus-Burkholderia model. Firstly, Burkholderia mutant strains deficient of O-antigen biosynthesis genes were generated and confirmed for their different patterns of the lipopolysaccharide by electrophoretic analysis. The O-antigen-deficient mutant strains initially exhibited a reduction of infectivity, having significantly lower level of symbiont population at the second-instar stage. However, both the wild-type and O-antigen mutant symbionts exhibited a similar level of symbiont population from the third-instar stage, indicating that the O-antigen deficiency did not affect the bacterial persistence in the host midgut. Taken together, we showed that the lipopolysaccharide O-antigen of gut symbiont plays an exclusive role in the initial symbiotic association.

Lipopolysaccharide Biosynthesis Genes of Yersinia pseudotuberculosis Promote Resistance to Antimicrobial Chemokines

Antimicrobial chemokines (AMCs) are a recently described family of host defense peptides that play an important role in protecting a wide variety of organisms from bacterial infection. Very little is known about the bacterial targets of AMCs or factors that influence bacterial susceptibility to AMCs. In an effort to understand how bacterial pathogens resist killing by AMCs, we screened Yersinia pseudotuberculosis transposon mutants for those with increased binding to the AMCs CCL28 and CCL25. Mutants exhibiting increased binding to AMCs were subjected to AMC killing assays, which revealed their increased sensitivity to chemokine-mediated cell death. The majority of the mutants exhibiting increased binding to AMCs contained transposon insertions in genes related to lipopolysaccharide biosynthesis. A particularly strong effect on susceptibility to AMC mediated killing was observed by disruption of the hldD/waaF/waaC operon, necessary for ADP-L-glycero-D-manno-heptose synthesis and a complete lipopolysaccharide core oligosaccharide. Periodate oxidation of surface carbohydrates also enhanced AMC binding, whereas enzymatic removal of surface proteins significantly reduced binding. These results suggest that the structure of Y. pseudotuberculosis LPS greatly affects the antimicrobial activity of AMCs by shielding a protein ligand on the bacterial cell surface.

Evaluation of Yersinia pestis Transmission Pathways for Sylvatic Plague in Prairie Dog Populations in the Western U.S

Sylvatic plague, caused by the bacterium Yersinia pestis, is periodically responsible for large die-offs in rodent populations that can spillover and cause human mortalities. In the western US, prairie dog populations experience nearly 100% mortality during plague outbreaks, suggesting that multiple transmission pathways combine to amplify plague dynamics. Several alternate pathways in addition to flea vectors have been proposed, such as transmission via direct contact with bodily fluids or inhalation of infectious droplets, consumption of carcasses, and environmental sources of plague bacteria, such as contaminated soil. However, evidence supporting the ability of these proposed alternate pathways to trigger large-scale epizootics remains elusive. Here we present a short review of potential plague transmission pathways and use an ordinary differential equation model to assess the contribution of each pathway to resulting plague dynamics in black-tailed prairie dogs (Cynomys ludovicianus) and their fleas (Oropsylla hirsuta). Using our model, we found little evidence to suggest that soil contamination was capable of producing plague epizootics in prairie dogs. However, in the absence of flea transmission, direct transmission, i.e., contact with bodily fluids or inhalation of infectious droplets, could produce enzootic dynamics, and transmission via contact with or consumption of carcasses could produce epizootics. This suggests that these pathways warrant further investigation.

Immunochemical Nature of Receptors of Pseudotuberculosis Diagnostic Bacteriophage

The effect of treatment of Yersinia pseudotuberculosis cells with antibodies of various specificities on adhesiveness of pseudotuberculosis bacteriophage was analyzed by competitive inhibition technique. Bacteriophage adsorption to bacteria was sterically inhibited by monoclonal antibodies to protein epitopes of Y. pseudotuberculosis outer membrane. These results suggest that receptors of pseudotuberculosis diagnostic bacteriophage are localized on the LPS core of microbial cell.

Dissociation of Tissue Destruction and Bacterial Expansion during Bubonic Plague

Activation and/or recruitment of the host plasmin, a fibrinolytic enzyme also active on extracellular matrix components, is a common invasive strategy of bacterial pathogens. Yersinia pestis, the bubonic plague agent, expresses the multifunctional surface protease Pla, which activates plasmin and inactivates fibrinolysis inhibitors. Pla is encoded by the pPla plasmid. Following intradermal inoculation, Y. pestis has the capacity to multiply in and cause destruction of the lymph node (LN) draining the entry site. The closely related, pPla-negative, Y. pseudotuberculosis species lacks this capacity. We hypothesized that tissue damage and bacterial multiplication occurring in the LN during bubonic plague were linked and both driven by pPla. Using a set of pPla-positive and pPla-negative Y. pestis and Y. pseudotuberculosis strains in a mouse model of intradermal injection, we found that pPla is not required for bacterial translocation to the LN. We also observed that a pPla-cured Y. pestis caused the same extensive histological lesions as the wild type strain. Furthermore, the Y. pseudotuberculosis histological pattern, characterized by infectious foci limited by inflammatory cell infiltrates with normal tissue density and follicular organization, was unchanged after introduction of pPla. However, the presence of pPla enabled Y. pseudotuberculosis to increase its bacterial load up to that of Y. pestis. Similarly, lack of pPla strongly reduced Y. pestis titers in LNs of infected mice. This pPla-mediated enhancing effect on bacterial load was directly dependent on the proteolytic activity of Pla. Immunohistochemistry of Pla-negative Y. pestis-infected LNs revealed extensive bacterial lysis, unlike the numerous, apparently intact, microorganisms seen in wild type Y. pestis-infected preparations. Therefore, our study demonstrates that tissue destruction and bacterial survival/multiplication are dissociated in the bubo and that the primary action of Pla is to protect bacteria from destruction rather than to alter the tissue environment to favor Y. pestis propagation in the host.

The hallmark of bubonic plague, a disease that ravaged Medieval Europe and is still prevalent in several countries, is the bubo, a highly inflammatory and painful lymph node, which is characterized by high concentrations of bacteria within a severely damaged organ. Yersinia pestis, the causative agent, expresses a surface protease, Pla, critical to the development of bubonic plague. This multitarget protease has the potential to activate the fibrinolytic pathway and to promote destruction of extracellular protein networks within tissues. Hence, it was expected that Pla was responsible for the tissue destructions of the bubo, and consequently, for bacterial propagation and virulence. However, we found, using various engineered Yersinia strains in a mouse model of bubonic plague, that Pla proteolytic activity was dispensable for lymph node alteration, but was required to achieve high bacterial loads in the organ. Further analysis showed that Pla is essential for preventing the bacteria from being destroyed in the host. Therefore, the role of Pla as a virulence factor is to protect Y. pestis survival and integrity in the host, rather than to assist its spread through tissue destruction.

Development of a bead-based Luminex assay using lipopolysaccharide specific monoclonal antibodies to detect biological threats from Brucella species

BACKGROUND

Brucella, a Gram-negative bacterium, is classified as a potential bioterrorism agent mainly due to the low dose needed to cause infection and the ability to transmit the bacteria via aerosols. Goats/sheep, cattle, pigs, dogs, sheep and rodents are infected by B. melitensis, B. abortus, B. suis, B. canis, B. ovis and B. neotomae, respectively, the six classical Brucella species. Most human cases are caused by B. melitensis and B. abortus. Our aim was to specifically detect Brucellae with 'smooth' lipopolysaccharide (LPS) using a highly sensitive monoclonal antibody (mAb) based immunological assay.

METHODS

To complement molecular detection systems for potential bioterror agents, as required by international biodefense regulations, sets of mAbs were generated by B cell hybridoma technology and used to develop immunological assays. The combination of mAbs most suitable for an antigen capture assay format was identified and an immunoassay using the Luminex xMAP technology was developed.

RESULTS

MAbs specific for the LPS O-antigen of Brucella spp. were generated by immunising mice with inactivated B. melitensis or B. abortus cells. Most mAbs recognised both B. melitensis and B. abortus and antigen binding was not impeded by inactivation of the bacterial cells by γ irradiation, formalin or heat treatment, a step required to analyse the samples immunologically under biosafety level two conditions. The Luminex assay recognised all tested Brucella species with 'smooth' LPS with detection limits of 2×10(2) to 8×10(4) cells per mL, depending on the species tested. Milk samples spiked with Brucella spp. cells were identified successfully using the Luminex assay. In addition, the bead-based immunoassay was integrated into a multiplex format, allowing for simultaneous, rapid and specific detection of Brucella spp., Bacillus anthracis, Francisella tularensis and Yersinia pestis within a single sample.

CONCLUSION

Overall, the robust Luminex assay should allow detection of Brucella spp. in both natural outbreak and bio-threat situations.

Host Langerin (CD207) is a receptor for Yersinia pestis phagocytosis and promotes dissemination

Yersinia pestis is a Gram-negative bacterium that causes plague. After Y. pestis overcomes the skin barrier, it encounters antigen-presenting cells (APCs), such as Langerhans and dendritic cells. They transport the bacteria from the skin to the lymph nodes. However, the molecular mechanisms involved in bacterial transmission are unclear. Langerhans cells (LCs) express Langerin (CD207), a calcium-dependent (C-type) lectin. Furthermore, Y. pestis possesses exposed core oligosaccharides. In this study, we show that Y. pestis invades LCs and Langerin-expressing transfectants. However, when the bacterial core oligosaccharides are shielded or truncated, Y. pestis propensity to invade Langerhans and Langerin-expressing cells decreases. Moreover, the interaction of Y. pestis with Langerin-expressing transfectants is inhibited by purified Langerin, a DC-SIGN (DC-specific intercellular adhesion molecule 3 grabbing nonintegrin)-like molecule, an anti-CD207 antibody, purified core oligosaccharides and several oligosaccharides. Furthermore, covering core oligosaccharides reduces the mortality associated with murine infection by adversely affecting the transmission of Y. pestis to lymph nodes. These results demonstrate that direct interaction of core oligosaccharides with Langerin facilitates the invasion of LCs by Y. pestis. Therefore, Langerin-mediated binding of Y. pestis to APCs may promote its dissemination and infection.

Early emergence of Yersinia pestis as a severe respiratory pathogen

Yersinia pestis causes the fatal respiratory disease pneumonic plague. Y. pestis recently evolved from the gastrointestinal pathogen Y. pseudotuberculosis; however, it is not known at what point Y. pestis gained the ability to induce a fulminant pneumonia. Here we show that the acquisition of a single gene encoding the protease Pla was sufficient for the most ancestral, deeply rooted strains of Y. pestis to cause pneumonic plague, indicating that Y. pestis was primed to infect the lungs at a very early stage in its evolution. As Y. pestis further evolved, modern strains acquired a single amino-acid modification within Pla that optimizes protease activity. While this modification is unnecessary to cause pneumonic plague, the substitution is instead needed to efficiently induce the invasive infection associated with bubonic plague. These findings indicate that Y. pestis was capable of causing pneumonic plague before it evolved to optimally cause invasive infections in mammals.

Two host clades, two bacterial arsenals: evolution through gene losses in facultative endosymbionts

Bacterial endosymbiosis is an important evolutionary process in insects, which can harbor both obligate and facultative symbionts. The evolution of these symbionts is driven by evolutionary convergence, and they exhibit among the tiniest genomes in prokaryotes. The large host spectrum of facultative symbionts and the high diversity of strategies they use to infect new hosts probably impact the evolution of their genome and explain why they undergo less severe genomic erosion than obligate symbionts. Candidatus Hamiltonella defensa is suitable for the investigation of the genomic evolution of facultative symbionts because the bacteria are engaged in specific relationships in two clades of insects. In aphids, H. defensa is found in several species with an intermediate prevalence and confers protection against parasitoids. In whiteflies, H. defensa is almost fixed in some species of Bemisia tabaci, which suggests an important role of and a transition toward obligate symbiosis. In this study, comparisons of the genome of H. defensa present in two B. tabaci species (Middle East Asia Minor 1 and Mediterranean) and in the aphid Acyrthosiphon pisum revealed that they belong to two distinct clades and underwent specific gene losses. In aphids, it contains highly virulent factors that could allow protection and horizontal transfers. In whiteflies, the genome lost these factors and seems to have a limited ability to acquire genes. However it contains genes that could be involved in the production of essential nutrients, which is consistent with a primordial role for this symbiont. In conclusion, although both lineages of H. defensa have mutualistic interactions with their hosts, their genomes follow distinct evolutionary trajectories that reflect their phenotype and could have important consequences on their evolvability.

The outer membrane protease PgtE of Salmonella enterica interferes with the alternative complement pathway by cleaving factors B and H

The virulence factor PgtE is an outer membrane protease (omptin) of the zoonotic pathogen Salmonella enterica that causes diseases ranging from gastroenteritis to severe enteric fever. It is surface exposed in bacteria that have a short-chain, i.e., rough LPS, as observed e.g., in bacteria residing inside macrophages or just emerging from them. We investigated whether PgtE cleaves the complement factors B (B) and H (H), key proteins controlling formation and inactivation of the complement protein C3b and thereby the activity of the complement system. S. enterica serovar Typhimurium or omptin-expressing recombinant E. coli bacteria were incubated with purified human complement proteins or recombinant H fragments. PgtE cleaved both B and H, whereas its close homolog Pla of Yersinia pestis cleaved only H. H was cleaved at both N- and C-termini, while the central region resisted proteolysis. Because of multiple effects of PgtE on complement components (cleavage of C3, C3b, B, and H) we assessed its effect on the opsonophagocytosis of Salmonella. In human serum, C3 cleavage was dependent on proteolytically active PgtE. Human neutrophils interacted less with serum-opsonized FITC-stained S. enterica 14028R than with the isogenic ΔpgtE strain, as analyzed by flow cytometry. In conclusion, cleavage of B and H by PgtE, together with C3 cleavage, affects the C3-mediated recognition of S. enterica by human neutrophils, thus thwarting the immune protection against Salmonella.

Combinational deletion of three membrane protein-encoding genes highly attenuates yersinia pestis while retaining immunogenicity in a mouse model of pneumonic plague

Previously, we showed that deletion of genes encoding Braun lipoprotein (Lpp) and MsbB attenuated Yersinia pestis CO92 in mouse and rat models of bubonic and pneumonic plague. While Lpp activates Toll-like receptor 2, the MsbB acyltransferase modifies lipopolysaccharide. Here, we deleted the ail gene (encoding the attachment-invasion locus) from wild-type (WT) strain CO92 or its lpp single and Δlpp ΔmsbB double mutants. While the Δail single mutant was minimally attenuated compared to the WT bacterium in a mouse model of pneumonic plague, the Δlpp Δail double mutant and the Δlpp ΔmsbB Δail triple mutant were increasingly attenuated, with the latter being unable to kill mice at a 50% lethal dose (LD50) equivalent to 6,800 LD50s of WT CO92. The mutant-infected animals developed balanced TH1- and TH2-based immune responses based on antibody isotyping. The triple mutant was cleared from mouse organs rapidly, with concurrent decreases in the production of various cytokines and histopathological lesions. When surviving animals infected with increasing doses of the triple mutant were subsequently challenged on day 24 with the bioluminescent WT CO92 strain (20 to 28 LD50s), 40 to 70% of the mice survived, with efficient clearing of the invading pathogen, as visualized in real time by in vivo imaging. The rapid clearance of the triple mutant, compared to that of WT CO92, from animals was related to the decreased adherence and invasion of human-derived HeLa and A549 alveolar epithelial cells and to its inability to survive intracellularly in these cells as well as in MH-S murine alveolar and primary human macrophages. An early burst of cytokine production in macrophages elicited by the triple mutant compared to WT CO92 and the mutant's sensitivity to the bactericidal effect of human serum would further augment bacterial clearance. Together, deletion of the ail gene from the Δlpp ΔmsbB double mutant severely attenuated Y. pestis CO92 to evoke pneumonic plague in a mouse model while retaining the required immunogenicity needed for subsequent protection against infection.

LPS modification promotes maintenance of Yersinia pestis in fleas

Yersinia pestis, the causative agent of plague, can be transmitted by fleas by two different mechanisms: by early-phase transmission (EPT), which occurs shortly after flea infection, or by blocked fleas following long-term infection. Efficient flea-borne transmission is predicated upon the ability of Y. pestis to be maintained within the flea. Signature-tagged mutagenesis (STM) was used to identify genes required for Y. pestis maintenance in a genuine plague vector, Xenopsylla cheopis. The STM screen identified seven mutants that displayed markedly reduced fitness in fleas after 4 days, the time during which EPT occurs. Two of the mutants contained insertions in genes encoding glucose 1-phosphate uridylyltransferase (galU) and UDP-4-amino-4-deoxy-l-arabinose-oxoglutarate aminotransferase (arnB), which are involved in the modification of lipid A with 4-amino-4-deoxy-l-arabinose (Ara4N) and resistance to cationic antimicrobial peptides (CAMPs). These Y. pestis mutants were more susceptible to the CAMPs cecropin A and polymyxin B, and produced lipid A lacking Ara4N modifications. Surprisingly, an in-frame deletion of arnB retained modest levels of CAMP resistance and Ara4N modification, indicating the presence of compensatory factors. It was determined that WecE, an aminotransferase involved in biosynthesis of enterobacterial common antigen, plays a novel role in Y. pestis Ara4N modification by partially offsetting the loss of arnB. These results indicated that mechanisms of Ara4N modification of lipid A are more complex than previously thought, and these modifications, as well as several factors yet to be elucidated, play an important role in early survival and transmission of Y. pestis in the flea vector.

LcrV delivered via type III secretion system of live attenuated Yersinia pseudotuberculosis enhances immunogenicity against pneumonic plague

Here, we constructed a Yersinia pseudotuberculosis mutant strain with arabinose-dependent regulated and delayed shutoff of crp expression (araC P(BAD) crp) and replacement of the msbB gene with the Escherichia coli msbB gene to attenuate it. Then, we inserted the asd mutation into this construction to form χ10057 [Δasd-206 ΔmsbB868::P(msbB) msbB(EC) ΔP(crp21)::TT araC P(BAD) crp] for use with a balanced-lethal Asd-positive (Asd(+)) plasmid to facilitate antigen synthesis. A hybrid protein composed of YopE (amino acids [aa]1 to 138) fused with full-length LcrV (YopE(Nt138)-LcrV) was synthesized in χ10057 harboring an Asd(+) plasmid (pYA5199, yopE(Nt138)-lcrV) and could be secreted through a type III secretion system (T3SS) in vitro and in vivo. Animal studies indicated that mice orally immunized with χ10057(pYA5199) developed titers of IgG response to whole-cell lysates of Y. pestis (YpL) and subunit LcrV similar to those seen with χ10057(pYA3332) (χ10057 plus an empty plasmid). However, only immunization of mice with χ10057(pYA5199) resulted in a significant secretory IgA response to LcrV. χ10057(pYA5199) induced a higher level of protection (80% survival) against intranasal (i.n.) challenge with ~240 median lethal doses (LD50) (2.4 × 10(4) CFU) of Y. pestis KIM6+(pCD1Ap) than χ10057(pYA3332) (40% survival). Splenocytes from mice vaccinated with χ10057(pYA5199) produced significant levels of gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin-17 (IL-17) after restimulation with LcrV and YpL antigens. Our results suggest that it is possible to use an attenuated Y. pseudotuberculosis strain delivering the LcrV antigen via the T3SS as a potential vaccine candidate against pneumonic plague.

Prophylaxis and therapy of plague

Plague has been a scourge of mankind for centuries, and outbreaks continue to the present day. The virulence mechanisms employed by the etiological agent Yersinia pestis are reviewed in the context of the available prophylactic and therapeutic strategies for plague. Although antibiotics are available, resistance is emerging in this dangerous pathogen. Therapeutics used in the clinic are discussed and innovative approaches to the design and development of new therapeutic compounds are reviewed. Currently there is no licensed vaccine available for prevention of plague in the USA or western Europe, although both live attenuated strains and killed whole-cell extracts have been used historically. Live strains are still approved for human use in some parts of the world, such as the former Soviet Union, but poor safety profiles render them unacceptable to many countries. The development of safe, effective next-generation vaccines, including the recombinant subunit vaccine currently used in clinical trials is discussed.