Microneedle array delivery of Yersinia pestis recapitulates bubonic plague

Fleas transmit Yersinia pestis directly within the dermis of mammals to cause bubonic plague. Syringe-mediated inoculation is widely used to recapitulate bubonic plague and study Y. pestis pathogenesis. However, intradermal needle inoculation is tedious, error prone, and poses a significant safety risk for laboratorians. Microneedle arrays (MNAs) are micron-scale polymeric structures that deliver materials to the dermis, while minimizing the risk of needle sticks. We demonstrated that MNA inoculation is a viable strategy to recapitulate bubonic plague and study bacterial virulence by defining the parameters needed to establish a lethal infection in the mouse model and characterizing the course of infection using live-animal optical imaging. Using MNAs, we also demonstrated that Y. pestis must overcome calprotectin-mediated zinc restriction within the dermis and dermal delivery of an attenuated mutant has vaccine potential. Together, these data demonstrate that MNAs are a safe alternative to study Y. pestis pathogenesis in the laboratory.

Type 3 secretion system induced leukotriene B4 synthesis by leukocytes is actively inhibited by Yersinia pestis to evade early immune recognition

Subverting the host immune response to inhibit inflammation is a key virulence strategy of Yersinia pestis. The inflammatory cascade is tightly controlled via the sequential action of lipid and protein mediators of inflammation. Because delayed inflammation is essential for Y. pestis to cause lethal infection, defining the Y. pestis mechanisms to manipulate the inflammatory cascade is necessary to understand this pathogen's virulence. While previous studies have established that Y. pestis actively inhibits the expression of host proteins that mediate inflammation, there is currently a gap in our understanding of the inflammatory lipid mediator response during plague. Here we used the murine model to define the kinetics of the synthesis of leukotriene B4 (LTB4), a pro-inflammatory lipid chemoattractant and immune cell activator, within the lungs during pneumonic plague. Furthermore, we demonstrated that exogenous administration of LTB4 prior to infection limited bacterial proliferation, suggesting that the absence of LTB4 synthesis during plague contributes to Y. pestis immune evasion. Using primary leukocytes from mice and humans further revealed that Y. pestis actively inhibits the synthesis of LTB4. Finally, using Y. pestis mutants in the Ysc type 3 secretion system (T3SS) and Yersinia outer protein (Yop) effectors, we demonstrate that leukocytes recognize the T3SS to initiate the rapid synthesis of LTB4. However, several Yop effectors secreted through the T3SS effectively inhibit this host response. Together, these data demonstrate that Y. pestis actively inhibits the synthesis of the inflammatory lipid LTB4 contributing to the delay in the inflammatory cascade required for rapid recruitment of leukocytes to sites of infection.

Droplet Tn-Seq identifies the primary secretion mechanism for yersiniabactin in Yersinia pestis

Nutritional immunity includes sequestration of transition metals from invading pathogens. Yersinia pestis overcomes nutritional immunity by secreting yersiniabactin to acquire iron and zinc during infection. While the mechanisms for yersiniabactin synthesis and import are well-defined, those responsible for yersiniabactin secretion are unknown. Identification of this mechanism has been difficult because conventional mutagenesis approaches are unable to inhibit trans-complementation by secreted factors between mutants. To overcome this obstacle, we utilized a technique called droplet Tn-seq (dTn-seq), which uses microfluidics to isolate individual transposon mutants in oil droplets, eliminating trans-complementation between bacteria. Using this approach, we first demonstrated the applicability of dTn-seq to identify genes with secreted functions. We then applied dTn-seq to identify an AcrAB efflux system as required for growth in metal-limited conditions. Finally, we showed this efflux system is the primary yersiniabactin secretion mechanism and required for virulence during bubonic and pneumonic plague. Together, these studies have revealed the yersiniabactin secretion mechanism that has eluded researchers for over 30 years and identified a potential therapeutic target for bacteria that use yersiniabactin for metal acquisition.

Fluorescent sensors of siderophores produced by bacterial pathogens

Siderophores are iron-chelating molecules that solubilize Fe³⁺ for microbial utilization and facilitate colonization or infection of eukaryotes by liberating host iron for bacterial uptake. By fluorescently labeling membrane receptors and binding proteins, we created 20 sensors that detect, discriminate, and quantify apo- and ferric siderophores. The sensor proteins originated from TonB-dependent ligand-gated porins (LGPs) of Escherichia coli (Fiu, FepA, Cir, FhuA, IutA, BtuB), Klebsiella pneumoniae (IroN, FepA, FyuA), Acinetobacter baumannii (PiuA, FepA, PirA, BauA), Pseudomonas aeruginosa (FepA, FpvA), and Caulobacter crescentus (HutA) from a periplasmic E. coli binding protein (FepB) and from a human serum binding protein (siderocalin). They detected ferric catecholates (enterobactin, degraded enterobactin, glucosylated enterobactin, dihydroxybenzoate, dihydroxybenzoyl serine, cefidericol, MB-1), ferric hydroxamates (ferrichromes, aerobactin), mixed iron complexes (yersiniabactin, acinetobactin, pyoverdine), and porphyrins (hemin, vitamin B12). The sensors defined the specificities and corresponding affinities of the LGPs and binding proteins and monitored ferric siderophore and porphyrin transport by microbial pathogens. We also quantified, for the first time, broad recognition of diverse ferric complexes by some LGPs, as well as monospecificity for a single metal chelate by others. In addition to their primary ferric siderophore ligands, most LGPs bound the corresponding aposiderophore with ∼100-fold lower affinity. These sensors provide insights into ferric siderophore biosynthesis and uptake pathways in free-living, commensal, and pathogenic Gram-negative bacteria.

Siderophore-mediated zinc acquisition enhances enterobacterial colonization of the inflamed gut

Zinc is an essential cofactor for bacterial metabolism, and many Enterobacteriaceae express the zinc transporters ZnuABC and ZupT to acquire this metal in the host. However, the probiotic bacterium Escherichia coli Nissle 1917 (or "Nissle") exhibits appreciable growth in zinc-limited media even when these transporters are deleted. Here, we show that Nissle utilizes the siderophore yersiniabactin as a zincophore, enabling Nissle to grow in zinc-limited media, to tolerate calprotectin-mediated zinc sequestration, and to thrive in the inflamed gut. We also show that yersiniabactin's affinity for iron or zinc changes in a pH-dependent manner, with increased relative zinc binding as the pH increases. Thus, our results indicate that siderophore metal affinity can be influenced by the local environment and reveal a mechanism of zinc acquisition available to commensal and pathogenic Enterobacteriaceae.

Yersiniabactin contributes to overcoming zinc restriction during Yersinia pestis infection of mammalian and insect hosts

Yersinia pestis causes human plague and colonizes both a mammalian host and a flea vector during its transmission cycle. A key barrier to bacterial infection is the host's ability to actively sequester key biometals (e.g., iron, zinc, and manganese) required for bacterial growth. This is referred to as nutritional immunity. Mechanisms to overcome nutritional immunity are essential virulence factors for bacterial pathogens. Y. pestis produces an iron-scavenging siderophore called yersiniabactin (Ybt) that is required to overcome iron-mediated nutritional immunity and cause lethal infection. Recently, Ybt has been shown to bind to zinc, and in the absence of the zinc transporter ZnuABC, Ybt improves Y. pestis growth in zinc-limited medium. These data suggest that, in addition to iron acquisition, Ybt may also contribute to overcoming zinc-mediated nutritional immunity. To test this hypothesis, we used a mouse model defective in iron-mediated nutritional immunity to demonstrate that Ybt contributes to virulence in an iron-independent manner. Furthermore, using a combination of bacterial mutants and mice defective in zinc-mediated nutritional immunity, we identified calprotectin as the primary barrier for Y. pestis to acquire zinc during infection and that Y. pestis uses Ybt to compete with calprotectin for zinc. Finally, we discovered that Y. pestis encounters zinc limitation within the flea midgut, and Ybt contributes to overcoming this limitation. Together, these results demonstrate that Ybt is a bona fide zinc acquisition mechanism used by Y. pestis to surmount zinc limitation during the infection of both the mammalian and insect hosts.

Lemon Exosome-like Nanoparticles-Manipulated Probiotics Protect Mice from C. d iff Infection

Clostridioides difficile (C. diff) is the leading cause of antibiotic-associated colitis. Here, we report that lemon exosome-like nanoparticles (LELNs) manipulated probiotics to inhibit C. diff infection (CDI). LELN-manipulated Lactobacillus rhamnosus GG (LGG) and Streptococcus thermophilus ST-21 (STH) (LELN-LS) decrease CDI mortality via an LELN-mediated increase in bile resistance and gut survivability. LELN-LS treatment increases the AhR ligands indole-3-lactic acid (I3LA) and indole-3-carboxaldehyde (I3Ald), leading to induction of IL-22, and increases lactic acid leading to a decrease of C. diff fecal shedding by inhibiting C. diff growth and indole biosynthesis. A synergistic effect between STH and LGG was identified. The STH metabolites inhibit gluconeogenesis of LGG and allow fructose-1,6-bisphosphate (FBP) to accumulate in LGG; accumulated FBP then activates lactate dehydrogenase of LGG (LGG-LDH) and enhances production of lactic acid and the AhR ligand. Our findings provide a new strategy for CDI prevention and treatment with a new type of prebiotics.

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LELNs-manipulated probiotics protect mice from C. diff infection

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LELNs manipulation modulates gut metabolomics composition

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Cross talk between LGG and STH enhances production of lactic acid and AhR ligands

Recombinant Human Plasma Gelsolin Improves Survival and Attenuates Lung Injury in a Murine Model of Multidrug-Resistant Pseudomonas aeruginosa Pneumonia

Background

Plasma gelsolin (pGSN) is an abundant circulating protein quickly consumed by extensive tissue damage. Marked depletion is associated with later poor outcomes in diverse clinical circumstances. Repletion with recombinant human (rhu)-pGSN in animal models of inflammation lessens mortality and morbidity.

Methods

Neutropenic mice were treated with different meropenem doses ±12 mg of rhu-pGSN commencing 1 day before an intratracheal challenge with multidrug-resistant Pseudomonas aeruginosa. Survival, bacterial counts, and pulmonary pathology were compared between corresponding meropenem groups with and without rhu-pGSN.

Results

Overall survival was 35/64 (55%) and 46/64 (72%) in mice given meropenem without and with rhu-pGSN, respectively (Δ = 17%; 95% CI, 1-34). In control mice receiving meropenem 1250 mg/kg/d where the majority died, the addition of rhu-pGSN increased survival from 5/16 (31%) to 12/16 (75%) (Δ = 44%; 95% CI, 13-75). Survival with minor lung injury was found in 26/64 (41%) mice receiving only meropenem, vs 38/64 (59%) in mice given meropenem plus rhu-pGSN (Δ = 19%; 95% CI, 2-36).

Conclusions

In a series of dose-ranging experiments, both mortality and lung injury were reduced by the addition of rhu-pGSN to meropenem against carbapenem-resistant P. aeruginosa. Rhu-pGSN offers a novel candidate therapy for antibiotic-resistant pneumonia.

Robust Th1 cellular and humoral responses generated by the Yersinia pestis rF1-V subunit vaccine formulated to contain an agonist of the CD137 pathway do not translate into increased protection against pneumonic plague

Yersinia pestis is the causative agent of plague and is a re-emerging pathogen that also has the potential as a biological weapon, necessitating the development of a preventive vaccine. Despite intense efforts for the last several decades, there is currently not a vaccine approved by the FDA. The rF1-V vaccine adjuvanted with Alhydrogel is a lead candidate subunit vaccine for plague and generates a strong Th2-mediate humoral response with a modest Th1 cellular response. As immune protection against Y. pestis requires both humoral and Th1 cellular responses, modifying the rF1-V subunit vaccine formulation to include a robust inducer of Th1 responses may improve efficacy. Thus, we reformulated the subunit vaccine to include SA-4-1BBL, an agonist of the CD137 costimulatory pathway and a potent inducer of Th1 response, and assessed its protective efficacy against pneumonic plague. We herein show for the first time a sex bias in the prophylactic efficacy of the Alhydrogel adjuvanted rF1-V vaccine, with female mice showing better protection against pneumonic plague than male. The sex bias for protection was irrespective of the generation of comparable levels of rF1-V-specific antibody titers and Th1 cellular responses in both sexes. The subunit vaccine reformulated with SA-4-1BBL generated robust Th1 cellular and humoral responses. A prime-boost vaccination scheme involving prime with rF1-V + Alhydrogel and boost with the rF1-V + SA-4-1BBL provided protection in male mice against pneumonic plague. In marked contrast, prime and boost with rF1-V reformulated with both adjuvants resulted in the loss of protection against pneumonic plague, despite generating high levels of humoral and Th1 cellular responses. While unexpected, these findings demonstrate the complexity of immune mechanisms required for protection. Elucidating mechanisms responsible for these differences in protection will help to guide the development of better prophylactic subunit vaccines effective against pneumonic plague.

The Evolution of SlyA/RovA Transcription Factors from Repressors to Countersilencers in Enterobacteriaceae

Gene duplication and subsequent evolutionary divergence have allowed conserved proteins to develop unique roles. The MarR family of transcription factors (TFs) has undergone extensive duplication and diversification in bacteria, where they act as environmentally responsive repressors of genes encoding efflux pumps that confer resistance to xenobiotics, including many antimicrobial agents. We have performed structural, functional, and genetic analyses of representative members of the SlyA/RovA lineage of MarR TFs, which retain some ancestral functions, including repression of their own expression and that of divergently transcribed multidrug efflux pumps, as well as allosteric inhibition by aromatic carboxylate compounds. However, SlyA and RovA have acquired the ability to countersilence horizontally acquired genes, which has greatly facilitated the evolution of Enterobacteriaceae by horizontal gene transfer. SlyA/RovA TFs in different species have independently evolved novel regulatory circuits to provide the enhanced levels of expression required for their new role. Moreover, in contrast to MarR, SlyA is not responsive to copper. These observations demonstrate the ability of TFs to acquire new functions as a result of evolutionary divergence of both cis-regulatory sequences and in trans interactions with modulatory ligands.IMPORTANCE Bacteria primarily evolve via horizontal gene transfer, acquiring new traits such as virulence and antibiotic resistance in single transfer events. However, newly acquired genes must be integrated into existing regulatory networks to allow appropriate expression in new hosts. This is accommodated in part by the opposing mechanisms of xenogeneic silencing and countersilencing. An understanding of these mechanisms is necessary to understand the relationship between gene regulation and bacterial evolution. Here we examine the functional evolution of an important lineage of countersilencers belonging to the ancient MarR family of classical transcriptional repressors. We show that although members of the SlyA lineage retain some ancestral features associated with the MarR family, their cis-regulatory sequences have evolved significantly to support their new function. Understanding the mechanistic requirements for countersilencing is critical to understanding the pathoadaptation of emerging pathogens and also has practical applications in synthetic biology.

Zinc transporters YbtX and ZnuABC are required for the virulence of Yersinia pestis in bubonic and pneumonic plague in mice

A number of bacterial pathogens require the ZnuABC Zinc (Zn²⁺) transporter and/or a second Zn²⁺ transport system to overcome Zn²⁺ sequestration by mammalian hosts. Previously we have shown that in addition to ZnuABC, Yersinia pestis possesses a second Zn²⁺ transporter that involves components of the yersiniabactin (Ybt), siderophore-dependent iron transport system. Synthesis of the Ybt siderophore and YbtX, a member of the major facilitator superfamily, are both critical components of the second Zn²⁺ transport system. Here we demonstrate that a ybtX znu double mutant is essentially avirulent in mouse models of bubonic and pneumonic plague while a ybtX mutant retains high virulence in both plague models. While sequestration of host Zn is a key nutritional immunity factor, excess Zn appears to have a significant antimicrobial role in controlling intracellular bacterial survival. Here, we demonstrate that ZntA, a Zn²⁺ exporter, plays a role in resistance to Zn toxicity in vitro, but that a zntA zur double mutant retains high virulence in both pneumonic and bubonic plague models and survival in macrophages. We also confirm that Ybt does not directly bind Zn²⁺in vitro under the conditions tested. However, we detect a significant increase in Zn²⁺-binding ability of filtered supernatants from a Ybt⁺ strain compared to those from a strain unable to produce the siderophore, supporting our previously published data that Ybt biosynthetic genes are involved in the production of a secreted Zn-binding molecule (zincophore). Our data suggest that Ybt or a modified Ybt participate in or promote Zn-binding activity in culture supernatants and is involved in Zn acquisition in Y. pestis.

Inflammasome-Independent Leukotriene B4 Production Drives Crystalline Silica-Induced Sterile Inflammation

Silicosis is a lung inflammatory disease caused by chronic exposure to crystalline silica (CS). Leukotriene B₄ (LTB₄) plays an important role in neutrophilic inflammation, which drives silicosis and promotes lung cancer. In this study, we examined the mechanisms involved in CS-induced inflammatory pathways. Phagocytosis of CS particles is essential for the production of LTB₄ and IL-1β in mouse macrophages, mast cells, and neutrophils. Phagosomes enclosing CS particles trigger the assembly of lipidosome in the cytoplasm, which is likely the primary source of CS-induced LTB₄ production. Activation of the JNK pathway is essential for both CS-induced LTB₄ and IL-1β production. Studies with bafilomycin-A1- and NLRP3-deficient mice revealed that LTB₄ synthesis in the lipidosome is independent of inflammasome activation. Small interfering RNA knockdown and confocal microscopy studies showed that GTPases Rab5c, Rab40c along with JNK1 are essential for lipidosome formation and LTB₄ production. BI-78D3, a JNK inhibitor, abrogated CS-induced neutrophilic inflammation in vivo in an air pouch model. These results highlight an inflammasome-independent and JNK activation-dependent lipidosome pathway as a regulator of LTB₄ synthesis and CS-induced sterile inflammation.

Impact of Gentamicin Concentration and Exposure Time on Intracellular Yersinia pestis

The study of intracellular bacterial pathogens in cell culture hinges on inhibiting extracellular growth of the bacteria in cell culture media. Aminoglycosides, like gentamicin, were originally thought to poorly penetrate eukaryotic cells, and thus, while inhibiting extracellular bacteria, these antibiotics had limited effect on inhibiting the growth of intracellular bacteria. This property led to the development of the antibiotic protection assay to study intracellular pathogens in vitro. More recent studies have demonstrated that aminoglycosides slowly penetrate eukaryotic cells and can even reach intracellular concentrations that inhibit intracellular bacteria. Therefore, important considerations, such as antibiotic concentration, incubation time, and cell type need to be made when designing the antibiotic protection assay to avoid potential false positive/negative observations. Yersinia pestis, which causes the human disease known as the plague, is a facultative intracellular pathogen that can infect and replicate in macrophages. Y. pestis is sensitive to gentamicin and this antibiotic is often employed in the antibiotic protection assay to study the Y. pestis intracellular life cycle. However, a large variety of gentamicin concentrations and incubation periods have been reported in the Y. pestis literature without a clear characterization of the potential influences that variations in the gentamicin protection assay could have on intracellular growth of this pathogen. This raised concerns that variations in the gentamicin protection assay could influence phenotypes and reproducibility of data. To provide a better understanding of the potential consequences that variations in the gentamicin protection assay could have on Y. pestis, we systematically examined the impact of multiple variables of the gentamicin protection assay on Y. pestis intracellular survival in macrophages. We found that prolonged incubation periods with low concentrations of gentamicin, or short incubation periods with higher concentrations of the antibiotic, have a dramatic impact on intracellular growth. Furthermore, the degree of sensitivity of intracellular Y. pestis to gentamicin was also cell type dependent. These data highlight the importance to empirically establish cell type specific gentamicin protection assays to avoid potential artificial data in Y. pestis intracellular studies.

Crystal structure of Yersinia pestis virulence factor YfeA reveals two polyspecific metal-binding sites

Gram-negative bacteria use siderophores, outer membrane receptors, inner membrane transporters and substrate-binding proteins (SBPs) to transport transition metals through the periplasm. The SBPs share a similar protein fold that has undergone significant structural evolution to communicate with a variety of differentially regulated transporters in the cell. In Yersinia pestis, the causative agent of plague, YfeA (YPO2439, y1897), an SBP, is important for full virulence during mammalian infection. To better understand the role of YfeA in infection, crystal structures were determined under several environmental conditions with respect to transition-metal levels. Energy-dispersive X-ray spectroscopy and anomalous X-ray scattering data show that YfeA is polyspecific and can alter its substrate specificity. In minimal-media experiments, YfeA crystals grown after iron supplementation showed a threefold increase in iron fluorescence emission over the iron fluorescence emission from YfeA crystals grown from nutrient-rich conditions, and YfeA crystals grown after manganese supplementation during overexpression showed a fivefold increase in manganese fluorescence emission over the manganese fluorescence emission from YfeA crystals grown from nutrient-rich conditions. In all experiments, the YfeA crystals produced the strongest fluorescence emission from zinc and could not be manipulated otherwise. Additionally, this report documents the discovery of a novel surface metal-binding site that prefers to chelate zinc but can also bind manganese. Flexibility across YfeA crystal forms in three loops and a helix near the buried metal-binding site suggest that a structural rearrangement is required for metal loading and unloading.

Host FIH-Mediated Asparaginyl Hydroxylation of Translocated Legionella pneumophila Effectors

FIH-mediated post-translational modification through asparaginyl hydroxylation of eukaryotic proteins impacts regulation of protein-protein interaction. We have identified the FIH recognition motif in 11 Legionella pneumophila translocated effectors, YopM of Yersinia, IpaH4.5 of Shigella and an ankyrin protein of Rickettsia. Mass spectrometry analyses of the AnkB and AnkH effectors of L. pneumophila confirm their asparaginyl hydroxylation. Consistent with localization of the AnkB effector to the Legionella-containing vacuole (LCV) membrane and its modification by FIH, our data show that FIH and its two interacting proteins, Mint3 and MT1-MMP are acquired by the LCV in a Dot/Icm type IV secretion-dependent manner. Chemical inhibition or RNAi-mediated knockdown of FIH promotes LCV-lysosomes fusion, diminishes decoration of the LCV with polyubiquitinated proteins, and abolishes intra-vacuolar replication of L. pneumophila. These data show acquisition of the host FIH by a pathogen-containing vacuole and that asparaginyl-hydroxylation of translocated effectors is indispensable for their function.

Novel Synthesis of Kanamycin Conjugated Gold Nanoparticles with Potent Antibacterial Activity

With a sharp increase in the cases of multi-drug resistant (MDR) bacteria all over the world, there is a huge demand to develop a new generation of antibiotic agents to fight them. As an alternative to the traditional drug discovery route, we have designed an effective antibacterial agent by modifying an existing commercial antibiotic, kanamycin, conjugated on the surface of gold nanoparticles (AuNPs). In this study, we report a single-step synthesis of kanamycin-capped AuNPs (Kan-AuNPs) utilizing the combined reducing and capping properties of kanamycin. While Kan-AuNPs have increased toxicity to a primate cell line (Vero 76), antibacterial assays showed dose-dependent broad spectrum activity of Kan-AuNPs against both Gram-positive and Gram-negative bacteria, including Kanamycin resistant bacteria. Further, a significant reduction in the minimum inhibitory concentration (MIC) of Kan-AuNPs was observed when compared to free kanamycin against all the bacterial strains tested. Mechanistic studies using transmission electron microscopy and fluorescence microscopy indicated that at least part of Kan-AuNPs increased efficacy may be through disrupting the bacterial envelope, resulting in the leakage of cytoplasmic content and the death of bacterial cells. Results of this study provide critical information about a novel method for the development of antibiotic capped AuNPs as potent next-generation antibacterial agents.

Yersinia pestis Requires Host Rab1b for Survival in Macrophages

Yersinia pestis is a facultative intracellular pathogen that causes the disease known as plague. During infection of macrophages Y. pestis actively evades the normal phagosomal maturation pathway to establish a replicative niche within the cell. However, the mechanisms used by Y. pestis to subvert killing by the macrophage are unknown. Host Rab GTPases are central mediators of vesicular trafficking and are commonly targeted by bacterial pathogens to alter phagosome maturation and killing by macrophages. Here we demonstrate for the first time that host Rab1b is required for Y. pestis to effectively evade killing by macrophages. We also show that Rab1b is specifically recruited to the Yersinia containing vacuole (YCV) and that Y. pestis is unable to subvert YCV acidification when Rab1b expression is knocked down in macrophages. Furthermore, Rab1b knockdown also altered the frequency of association between the YCV with the lysosomal marker Lamp1, suggesting that Rab1b recruitment to the YCV directly inhibits phagosome maturation. Finally, we show that Rab1b knockdown also impacts the pH of the Legionella pneumophila containing vacuole, another pathogen that recruits Rab1b to its vacuole. Together these data identify a novel role for Rab1b in the subversion of phagosome maturation by intracellular pathogens and suggest that recruitment of Rab1b to the pathogen containing vacuole may be a conserved mechanism to control vacuole pH.

Yersinia pestis is the bacterial agent that causes the human disease known as plague. While often considered a historic disease, Y. pestis is endemic in rodent populations on several continents and the World Health Organization considers plague to be a reemerging disease. Much of the success of this pathogen comes from its ability to evade clearance by the innate immune system of its host. One weapon in the Y. pestis arsenal is its ability to resist killing when engulfed by macrophages. Upon invasion of macrophages, Y. pestis actively manipulates the cell to generate a protective vacuolar compartment, called the Yersinia containing vacuole (YCV) that allows the bacterium to evade the normal pathogen killing mechanisms of the macrophage. Here we demonstrate that the host protein Rab1b is recruited to the YCV and is required for Y. pestis to inhibit both the acidification and normal maturation of the phagosome to establish a protective niche within the cell. Rab1b is the first protein, either from the host or Y. pestis, shown to contribute to the biogenesis of the YCV. Furthermore, our data suggest a previously unknown impact of Rab1b recruitment in the phagosome maturation pathway.

Nanotechnology's Impact on Medicinal Chemistry

Nanotechnology has intrigued a large number of researchers the world over owing to its unique properties as compared to bulk materials, and the novelty of applications made possible across many fields of science. Researchers, taking advantage of the unique properties of particles in nano (1-100 nm) form, have been developing nanoformulations of various medicinal compounds to enhance drug solubility, dissolution, and bioavailability. There are various methods by which drug compounds are conjugated to nanoparticles, and some bioactive compounds are attached by intermediary agents which are themselves usually part of the formation reaction of nanoparticles. Nanoformulations have been developed involving a range of medicinal compounds of biological and syntheticorigin intended to enhance the compound's pharmacokinetic and pharmacological profiles, or to capitalize on unique properties of nanoparticles for therapeutic or diagnostic purposes. A number of nanodrugs exist on the market today, and many more are in the clinical or pre-clinical pipeline. There are a number of challenges commonly encountered when designing nanodrug formulations as well as challenges to the long term viability of nanodrug formulation strategies, especially in regards to environmental and safety concerns. Some researchers have harnessed the structural and functional relationship of various medicinal compounds to enhance the design of nanoformulations. Other researchers have used structure-activity relationships as a means of enhancing safety and efficacy testing through in silico modeling. This article will touch on each of the above issues within the context of the impact each facet of nanotechnology has on medicinal chemistry.

Development and evaluation of murine lung-specific disease models for Pseudomonas aeruginosa applicable to therapeutic testing

Pseudomonas aeruginosa is an opportunistic bacterial pathogen capable of causing a wide range of disease manifestations, including severe bacterial pneumonia. Recently, clinics have reported a rise in nosocomial infections with multidrug resistant (MDR) species, including MDR strains of P. aeruginosa. In order to quickly evaluate the efficacy of new therapeutics for MDR infections, highly reproducible and validated animal models need to be developed for pre-clinical testing. Here, we describe the characterization of two murine models to study MDR P. aeruginosa respiratory disease. We evaluated and compared these models using a non-invasive intratracheal instillation method and established the 50% lethal dose, course of infection, biometric parameters of disease and degree of pneumonia development for each model. Further, we tested meropenem as a proof-of-concept therapeutic and report efficacy data that suggests that the leukopenic model could serve a robust pre-clinical model to test novel therapeutics.

Intubation-mediated intratracheal (IMIT) instillation: a noninvasive, lung-specific delivery system

Respiratory disease studies typically involve the use of murine models as surrogate systems. However, there are significant physiologic differences between the murine and human respiratory systems, especially in their upper respiratory tracts (URT). In some models, these differences in the murine nasal cavity can have a significant impact on disease progression and presentation in the lower respiratory tract (LRT) when using intranasal instillation techniques, potentially limiting the usefulness of the mouse model to study these diseases. For these reasons, it would be advantageous to develop a technique to instill bacteria directly into the mouse lungs in order to study LRT disease in the absence of involvement of the URT. We have termed this lung specific delivery technique intubation-mediated intratracheal (IMIT) instillation. This noninvasive technique minimizes the potential for instillation into the bloodstream, which can occur during more invasive traditional surgical intratracheal infection approaches, and limits the possibility of incidental digestive tract delivery. IMIT is a two-step process in which mice are first intubated, with an intermediate step to ensure correct catheter placement into the trachea, followed by insertion of a blunt needle into the catheter to mediate direct delivery of bacteria into the lung. This approach facilitates a >98% efficacy of delivery into the lungs with excellent distribution of reagent throughout the lung. Thus, IMIT represents a novel approach to study LRT disease and therapeutic delivery directly into the lung, improving upon the ability to use mice as surrogates to study human respiratory disease. Furthermore, the accuracy and reproducibility of this delivery system also makes it amenable to Good Laboratory Practice Standards (GLPS), as well as delivery of a wide range of reagents which require high efficiency delivery to the lung.

Improving the Th1 cellular efficacy of the lead Yersinia pestis rF1-V subunit vaccine using SA-4-1BBL as a novel adjuvant

The lead candidate plague subunit vaccine is the recombinant fusion protein rF1-V adjuvanted with alum. While alum generates Th2 regulated robust humoral responses, immune protection against Yersinia pestis has been shown to also involve Th1 driven cellular responses. Therefore, the rF1-V-based subunit vaccine may benefit from an adjuvant system that generates a mixed Th1 and humoral immune response. We herein assessed the efficacy of a novel SA-4-1BBL costimulatory molecule as a Th1 adjuvant to improve cellular responses generated by the rF1-V vaccine. SA-4-1BBL as a single adjuvant had better efficacy than alum in generating CD4(+) and CD8(+) T cells producing TNFα and IFNγ, signature cytokines for Th1 responses. The combination of SA-4-1BBL with alum further increased this Th1 response as compared with the individual adjuvants. Analysis of the humoral response revealed that SA-4-1BBL as a single adjuvant did not generate a significant Ab response against rF1-V, and SA-4-1BBL in combination with alum did not improve Ab titers. However, the combined adjuvants significantly increased the ratio of Th1 regulated IgG2c in C57BL/6 mice to the Th2 regulated IgG1. Finally, a single vaccination with rF1-V adjuvanted with SA-4-1BBL+alum had better protective efficacy than vaccines containing individual adjuvants. Taken together, these results demonstrate that SA-4-1BBL improves the protective efficacy of the alum adjuvanted lead rF1-V subunit vaccine by generating a more balanced Th1 cellular and humoral immune response. As such, this adjuvant platform may prove efficacious not only for the rF1-V vaccine but also against other infections that require both cellular and humoral immune responses for protection.

Bioluminescent imaging of bacteria during mouse infection

Diagnostic imaging is a powerful tool that has recently been applied towards the study of infectious diseases. Optical imaging of bioluminescently labeled bacteria in infected animals allows for real-time analysis of bacterial proliferation and dissemination during infection without sacrificing the animal. Imaging also allows for tracking of disease progression in an individual subject over time, has the potential to reveal previously overlooked sites of infection, and reduces the number of research animals used in pathogenesis studies. Here, we describe the use of a deep-cooled CCD camera imager to record light emitted from bacteria during infection. We also describe the process of correlating bioluminescence to bacterial numbers by ex vivo imaging of necropsied tissues. Together these techniques can be used to estimate bacterial burdens in host tissues both in vivo and ex vivo using bioluminescent imaging.

Acquisition of omptin reveals cryptic virulence function of autotransporter YapE in Yersinia pestis

Autotransporters, the largest family of secreted proteins in Gram-negative bacteria, perform a variety of functions, including adherence, cytotoxicity and immune evasion. In Yersinia pestis the autotransporter YapE has adhesive properties and contributes to disease in the mouse model of bubonic plague. Here, we demonstrate that omptin cleavage of Y. pestis YapE is required to mediate bacterial aggregation and adherence to eukaryotic cells. We demonstrate that omptin cleavage is specific for the Y. pestis and Y. pseudotuberculosis YapE orthologues but is not conserved in the Yersinia enterocolitica protein. We also show that cleavage of YapE occurs in Y. pestis but not in the enteric Yersinia species, and requires the omptin Pla (plasminogen activator protease), which is encoded on the Y. pestis-specific plasmid pPCP1. Together, these data show that post-translation modification of YapE appears to be specific to Y. pestis, was acquired along with the acquisition of pPCP1 during the divergence of Y. pestis from Y. pseudotuberculosis, and are the first evidence of a novel mechanism to regulate bacterial adherence.

Development of bioluminescent bioreporters for in vitro and in vivo tracking of Yersinia pestis

Yersinia pestis causes an acute infection known as the plague. Conventional techniques to enumerate Y. pestis can be labor intensive and do not lend themselves to high throughput assays. In contrast, bioluminescent bioreporters produce light that can be detected using plate readers or optical imaging platforms to monitor bacterial populations as a function of luminescence. Here, we describe the development of two Y. pestis chromosomal-based luxCDABE bioreporters, Lux(PtolC) and Lux(PcysZK). These bioreporters use constitutive promoters to drive expression of luxCDABE that allow for sensitive detection of bacteria via bioluminescence in vitro. Importantly, both bioreporters demonstrate a direct correlation between bacterial numbers and bioluminescence, which allows for bioluminescence to be used to compare bacterial numbers. We demonstrate the use of these bioreporters to test antimicrobial inhibitors (Lux(PtolC)) and monitor intracellular survival (Lux(PtolC) and Lux(PcysZK)) in vitro. Furthermore, we show that Y. pestis infection of the mouse model can be monitored using whole animal optical imaging in real time. Using optical imaging, we observed Y. pestis dissemination and differentiated between virulence phenotypes in live animals via bioluminescence. Finally, we demonstrate that whole animal optical imaging can identify unexpected colonization patterns in mutant-infected animals.

Model systems to study plague pathogenesis and develop new therapeutics

The Gram negative bacterium Yersinia pestis can infect humans by multiple routes to cause plague. Three plague pandemics have occurred and Y. pestis has been linked to biowarfare in the past. The continued risk of plague as a bioweapon has prompted increased research to understand Y. pestis pathogenesis and develop new plague therapeutics. Several in vivo models have been developed for this research and are reviewed here.

Comparative analysis of the regulation of rovA from the pathogenic yersiniae

RovA is a MarR/SlyA-type regulator that mediates the transcription of inv in Yersinia enterocolitica and Y. pseudotuberculosis. In Y. pseudotuberculosis, rovA transcription is controlled primarily by H-NS and RovA, which bind to similar regions within the rovA promoter. At 37 degrees C, rovA transcription is repressed by H-NS. Transcription of rovA results when RovA relieves H-NS-mediated repression. The region of the rovA promoter that H-NS and RovA bind is not conserved in the Y. enterocolitica promoter. Using green fluorescent protein reporters, we determined that the Y. enterocolitica rovA (rovA(Yent)) promoter is weaker than the Y. pseudotuberculosis promoter. However, despite the missing H-NS/RovA binding site in the rovA(Yent) promoter, H-NS and RovA are still involved in the regulation of rovA(Yent). DNA binding studies suggest that H-NS and RovA bind with a higher affinity to the Y. pseudotuberculosis/Y. pestis rovA (rovA(Ypstb/Ypestis)) promoter than to the rovA(Yent) promoter. Furthermore, H-NS appears to bind to two regions in a cooperative fashion within the rovA(Yent) promoter that is not observed with the rovA(Ypstb/Ypestis) promoter. Finally, using a transposon mutagenesis approach, we identified a new positive regulator of rovA in Y. enterocolitica, LeuO. In Escherichia coli, LeuO regulates gene expression via changes in levels of RpoS and H-NS, but LeuO-mediated regulation of rovA(Yent) appears to be independent of either of these two proteins. Together, these data demonstrate that while the rovA regulatory factors are conserved in Yersinia, divergence of Y. enterocolitica and Y. pseudotuberculosis/Y. pestis during evolution has resulted in modifications in the mechanisms that are responsible for controlling rovA transcription.

Effects of vlsE complementation on the infectivity of Borrelia burgdorferi lacking the linear plasmid lp28-1

The loss of linear plasmid lp28-1, which contains the vls antigenic variation locus, is associated with reduced infectivity of Borrelia burgdorferi in immunocompetent mice. The recombinant shuttle vector pBBE22, which includes the virulence determinant BBE22 from lp25 and restores infectivity to readily transformable B. burgdorferi lacking lp25 and lp56, was used to determine the effect of trans expression of vlsE on virulence. Spirochetes lacking lp28-1 were complemented with the plasmid pBBE22:vlsE, containing both BBE22 and vlsE. VlsE protein produced by this construct was expressed and surface accessible in in vitro-cultured B. burgdorferi, as determined by surface proteolysis and immunoblot analysis. Clones lacking lp25 but containing lp28-1 and either pBBE22 or pBBE22:vlsE were reisolated consistently from immunocompetent mice 8 weeks after infection. In contrast, a clone lacking both lp25 and lp28-1 and complemented with pBBE22:vlsE was isolated from only a single tissue of one of six C3H/HeN mice 8 weeks postinfection. These results indicate that either an intact vls antigenic variation locus or another determinant on lp28-1 is required to restore complete infectivity. In addition, an isogenic clone that retained lp28-1 was complemented with the vlsE shuttle plasmid and was examined for vlsE sequence variation and infectivity. Sequence variation was not observed for the shuttle plasmid, indicating that the cis arrangement of vlsE and the vls silent cassettes in lp28-1 facilitate vlsE gene conversion. Lack of vlsE sequence variation on the shuttle plasmid thus did not result in clearance of the trans-complemented strain in immunocompetent mice under the conditions tested.

Invasin and beyond: regulation of Yersinia virulence by RovA

RovA, a member of the MarR/SlyA family of winged-helix transcription factors, regulates expression of invasin, the major adhesion and invasion factor in Yersinia enterocolitica and Yersinia pseudotuberculosis. Disruption of rovA increases the LD(50) of the organism when inoculated using the oral route. However, when administered by intraperitoneal injection only a slight difference in LD(50) between mutant and wild-type organisms is apparent. The study of RovA and the genes it regulates provides a unique opportunity to gain insight into the initial stages of a Yersinia infection.

Effect of complement component C3 deficiency on experimental Lyme borreliosis in mice

Mice deficient in complement component C3 (C3(-/-)) and syngeneic C57BL/6 control mice were challenged with Borrelia burgdorferi to determine the role of complement in immune clearance and joint histopathology during experimental Lyme borreliosis. Tibiotarsal joint, ear, and heart tissues were monitored for spirochete numbers at 2, 4, 8, and 12 weeks postinoculation with 10(5) B. burgdorferi B31 clone 5A4 by using quantitative real-time PCR. The spirochete load in joint and ear tissue remained higher in the C3(-/-) mice than in the wild-type counterparts throughout the 12-week study, whereas the numbers in heart tissue of both groups of mice decreased substantially at 8 to 12 weeks postinfection. Histopathology scores for joint tissue were generally higher in the C3(-/-) mice compared to C57BL/6 controls at 2 and 4 weeks postinfection, which may reflect the presence of higher numbers of bacteria in the joints at these early time points. Levels of anti-B. burgdorferi immunoglobulin G tended to be reduced in the C3(-/-) mice compared to control mice. Furthermore, a 5.5-fold-lower number of the complement-sensitive Borrelia garinii was needed to infect C3(-/-) mice compared to C57BL/6 mice, indicating that its sensitivity to complement is one barrier to infection of the mouse model by B. garinii. These results indicate that the complement system may be important in controlling the early dissemination and progression of B. burgdorferi infection.

A plasmid-encoded nicotinamidase (PncA) is essential for infectivity of Borrelia burgdorferi in a mammalian host

Borrelia burgdorferi, a spirochaete that causes Lyme borreliosis, contains 21 linear and circular plasmids thought to be important for survival in mammals or ticks. Our results demonstrate that the gene BBE22 encoding a nicotinamidase is capable of replacing the requirement for the 25 kb linear plasmid lp25 during mammalian infection. Transformation of B. burgdorferi lacking lp25 with a shuttle vector containing the lp25 gene BBE22 (pBBE22) restored infectivity in mice to a level comparable to that of wild-type Borrelia. This complementation also restored the growth and host adaptation of lp25-B. burgdorferi in dialysis membrane chambers (DMCs) implanted in rats. A single Cys to Ala conversion at the putative active site of BBE22 abrogated the ability of pBBE22 to re-establish infectivity or growth in DMCs. Additional Salmonella typhimurium complementation studies and enzymatic analysis demonstrated that the BBE22 gene product has nicotinamidase activity and is most probably required for the biosynthesis of NAD. These results indicate that some plasmid-encoded products fulfil physiological functions required in the enzootic cycle of pathogenic Borrelia.

Decreased electroporation efficiency in Borrelia burgdorferi containing linear plasmids lp25 and lp56: impact on transformation of infectious B. burgdorferi

The presence of the linear plasmids lp25 and lp56 of Borrelia burgdorferi B31 was found to dramatically decrease the rate of transformation by electroporation with the shuttle vector pBSV2, an autonomously replicating plasmid that confers kanamycin resistance (P. E. Stewart, R. Thalken, J. L. Bono, and P. Rosa, Mol. Microbiol. 39:714-721, 2001). B. burgdorferi B31 clones had transformation efficiencies that were either low, intermediate, or high, and this phenotype correlated with the presence or absence of lp25 and lp56. Under the conditions utilized in this study, no transformants were detected in clones that contained both lp25 and lp56; the few kanamycin-resistant colonies isolated did not contain pBSV2, indicating that the resistance was due to mutation. Intermediate electroporation rates (10 to 200 colonies per micro g of DNA) were obtained with B31 clones that were either lp25(-) and lp56(+) or lp25(+) and lp56(-). Clones in this group that initially contained lp25 lacked this plasmid in pBSV2 transformants, a finding consistent with selective transformation of lp25(-) variants. High transformation rates (>1,000 colonies per micro g of DNA) occurred in clones that lacked both lp25 and lp56. Sequence analysis indicated that lp25 and lp56 contain genes that may encode restriction and/or modification systems that could result in the low transformation rates obtained with strains containing these plasmids. The previously reported correlation between lp25 and infectivity in mice, coupled with the barrier lp25 presents to transformation, may explain the difficulty in obtaining virulent transformants of B. burgdorferi.

Crystal structure of Lyme disease variable surface antigen VlsE of Borrelia burgdorferi

VlsE is an outer surface lipoprotein of Borrelia burgdorferi that undergoes antigenic variation through an elaborate gene conversion mechanism and is thought to play a major role in the immune response to the Lyme disease borellia. The crystal structure of recombinant variant protein VlsE1 at 2.3-A resolution reveals that the six variable regions form loop structures that constitute most of the membrane distal surface of VlsE, covering the predominantly alpha-helical, invariant regions of the protein. The surface localization of the variable amino acid segments appears to protect the conserved regions from interaction with antibodies and hence may contribute to immune evasion.

Human antibody responses to VlsE antigenic variation protein of Borrelia burgdorferi

VlsE is a 35-kDa surface-exposed lipoprotein of Borrelia burgdorferi that was shown previously to undergo antigenic variation through segmental recombination of silent vls cassettes with vlsE during experimental mouse infections. Previous data had indicated that sera from North American Lyme disease patients and experimentally infected animals contained antibodies reactive with VlsE. In this study, sera from patients with Lyme disease, syphilis, and autoimmune conditions as well as from healthy controls were examined for reactivity with VlsE by Western blotting and enzyme-linked immunosorbent assay (ELISA). Strong Western blot reactivity to a recombinant VlsE cassette region protein was obtained consistently with Lyme disease sera. Although sera from Lyme disease patients also reacted with a band corresponding to VlsE in B. burgdorferi B31-5A3, interpretation was complicated by low levels of VlsE expression in in vitro-cultured B. burgdorferi and by the presence of comigrating bands. An ELISA using recombinant VlsE was compared with an ELISA using sonically disrupted B. burgdorferi as the antigen. For a total of 93 Lyme disease patient sera examined, the VlsE ELISA yielded sensitivities of 63% for culture-confirmed erythema migrans cases and 92% for later stages, as compared to 61 and 98%, respectively, for the "whole-cell" ELISA. The specificities of the two assays with healthy blood donor sera were comparable, but the VlsE ELISA was 90% specific with sera from syphilis patients, compared to 20% specificity for the whole-cell ELISA with this group. Neither assay showed reactivity with a panel of sera from 20 non-Lyme disease arthritis patients or 20 systemic lupus erythematosus patients. Our results indicate that VlsE may be useful in the immunodiagnosis of Lyme disease and may offer greater specificity than ELISAs using whole B. burgdorferi as the antigen.