Bacillus anthracis, Francisella tularensis and Yersinia pestis. The most important bacterial warfare agents — review

Screening and identification of DNA nucleic acid aptamers against F1 protein of Yersinia pestis using SELEX method

BACKGROUND

Yersinia pestis is a bacterium that causes the disease plague. It has caused the deaths of many people throughout history. The bacterium possesses several virulence factors (pPla, pFra, and PYV). PFra plasmid encodes fraction 1 (F1) capsular antigen. F1 protein protects the bacterium against host immune cells through phagocytosis process. This protein is specific for Y. pestis. Many diagnostic techniques are based on molecular and serological detection and quantification of F1 protein in different food and clinical samples. Aptamers are small nucleic acid sequences that can act as specific ligands for many targets.This study, aimed to isolate the high-affinity ssDNA aptamers against F1 protein.

METHODS AND RESULTS

In this study, SELEX was used as the main strategy in screening aptamers. Moreover, enzyme-linked aptamer sorbent assay (ELASA) and surface plasmon resonance (SPR) were used to determine the affinity and specificity of obtained aptamers to F1 protein. The analysis showed that among the obtained aptamers, the three aptamers of Yer 21, Yer 24, and Yer 25 were selected with a KD value of 1.344E - 7, 2.004E - 8, and 1.68E - 8 M, respectively. The limit of detection (LoD) was found to be 0.05, 0.076, and 0.033 μg/ml for Yer 21, Yer 24, and Yer 25, respectively.

CONCLUSION

This study demonstrated that the synthesized aptamers could serve as effective tools for detecting and analyzing the F1 protein, indicating their potential value in future diagnostic applications.

The Urinary Resistome of Clinically Healthy Companion Dogs: Potential One Health Implications

An interdisciplinary approach to antimicrobial resistance (AMR) is essential to effectively address what is projected to soon become a public health disaster. Veterinary medicine accounts for a majority of antimicrobial use, and mainly in support of industrial food animal production (IFAP), which has significant exposure implications for human and nonhuman animals. Companion dogs live in close proximity to humans and share environmental exposures, including food sources. This study aimed to elucidate the AMR-gene presence in microorganisms recovered from urine from clinically healthy dogs to highlight public health considerations in the context of a species-spanning framework. Urine was collected through cystocentesis from 50 companion dogs in Southern California, and microbial DNA was analyzed using next-generation sequencing. Thirteen AMR genes in urine from 48% of the dogs {n=24} were detected. The most common AMR genes were aph(3')Ia, and ermB, which confer resistance to aminoglycosides and MLS (macrolides, lincosamides, streptogramins) antibiotics, respectively. Antibiotic-resistance profiles based on the AMR genes detected, and the intrinsic resistance profiles of bacterial species, were inferred in 24% of the samples {n=12} for 57 species, with most belonging to Streptococcus, Staphylococcus, and Corynebacterium genera. The presence of AMR genes that confer resistance to medically important antibiotics suggests that dogs may serve as reservoirs of clinically relevant resistomes, which is likely rooted in excessive IFAP antimicrobial use.

Novel Transcriptional and Translational Biomarkers of Tularemia Vaccine Efficacy in a Mouse Inhalation Model: Proof of Concept

Francisella tularensis subspecies tularensis (Ftt) is extremely virulent for humans when inhaled as a small particle aerosol (<5 µm). Inhalation of ≥20 viable bacteria is sufficient to initiate infection with a mortality rate ≥30%. Consequently, in the past, Ftt became a primary candidate for biological weapons development. To counter this threat, the USA developed a live vaccine strain (LVS), that showed efficacy in humans against inhalation of virulent Ftt. However, the breakthrough dose was fairly low, and protection waned with time. These weaknesses triggered extensive research for better vaccine candidates. Previously, we showed that deleting the clpB gene from virulent Ftt strain, SCHU S4, resulted in a mutant that was significantly less virulent than LVS for mice, yet better protected them from aerosol challenge with wild-type SCHU S4. To date, comprehensive searches for correlates of protection for SCHU S4 ΔclpB among molecules that are critical signatures of cell-mediated immunity, have yielded little reward. In this study we used transcriptomics analysis to expand the potential range of molecular correlates of protection induced by vaccination with SCHU S4 ΔclpB beyond the usual candidates. The results provide proof-of-concept that unusual host responses to vaccination can potentially serve as novel efficacy biomarkers for new tularemia vaccines.

Critical Comparison between Large and Mini Vertical Flow Immunoassay Platforms for Yersinia Pestis Detection

Yersinia pestis is a Gram-negative bacterium that is the causative agent of plague and is widely recognized as a potential biological weapon. Due to the high fatality rate of plague when diagnosis is delayed, the development of rapid, sensitive, specific, and cost-effective methods is needed for its diagnosis. The Y. pestis low calcium response V (LcrV) protein has been identified as a potential microbial biomarker for the diagnosis of plague. In this paper, we present a highly sensitive, paper-based, vertical flow immunoassay (VFI) prototype for the detection of LcrV and the diagnosis of plague. An antigen-capture assay using monoclonal antibodies is employed to capture and detect the LcrV protein, using a colorimetric approach. In addition, the effect of miniaturizing the VFI device is explored based on two different sizes of VFI platforms, denoted as "large VFI" and "mini VFI." Also, a comparative analysis is performed between the VFI platform and a lateral flow immunoassay (LFI) platform to exhibit the improved assay sensitivity suitable for point-of-care (POC) diagnostics. The analytical sensitivity or limit of detection (LOD) in the mini VFI is approximately 0.025 ng/mL, that is, 10 times better than that of the large VFI platform or 80 times over a standard lateral flow configuration. The low LOD of the LcrV VFI appears to be highly suitable for testing clinical samples and potentially diagnosing plague at earlier time points. In addition, optimization of the gold nanoparticle (AuNP) concentration, nanomaterial plasmonic properties, and flow velocity analysis could improve the performance of the VFI. Furthermore, we developed automated image analysis software that shows potential for integrating the diagnostic system into a smartphone. These methods and findings demonstrate that the VFI platform is a highly sensitive device for detecting the LcrV and potentially many other biomarkers.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Rapid and sensitive detection of Yersinia pestis by lateral-flow assay in simulated clinical samples

Background

Yersinia pestis is a contributing agent to the epidemic disease, plague, which killed an estimated 200 million people during historical times. In this study, a rapid, cheap, sensitive, and specific technique, the lateral flow assay (F1 strips), has been successfully developed to detect this pathogen, by using paired monoclonal antibodies (MAbs) against Y. pestis capsule like fraction 1 (F1) protein. Compared with the polyclonal antibody (PAb) based F1 strips, the Mab-based F1 strips have a remarkable increased detection limitation (10 to 100 folds). Furthermore, besides the limitation and specificity evaluation, the application of this F1 strip on simulated clinical samples indicate the LFA can be a good candidate to detect plague.

Methods

Recombinant F1 antigen was expressed and purified from a series of works. The various anti-F1 monoclonal antibodies generated from hybridoma cells were screened with the ELISA technique. To evaluate the feasibility of this Y. pestis F1 test strip, the F1 protein/Y. pestis was spiked into simulated clinical samples such as human serum, mouse bronchoalveolar lavage fluids, and mouse blood to mimic natural infection status. Additionally, this technique was applied to detect the Y. pestis in the environment-captured rats, to evaluate the practical usefulness of the strips.

Results

By using this MAb-based-LFA technique, 4 ng/ml of recombinant F1-protein and 10³ CFU/ml of Y. pestis could be detected in less than 10 mins, which is at least 10-folds than that of the PAb format. On the other hand, although various Yersinia strains were applied to the strips, only Y. pestis strain showed a positive result; all other Yersinia species did not produce a positive signal, indicating the high efficiency and specificity of the MAb-based F1-strips.

Conclusion

Based on our findings, we suggest that the MAb-format-LFA will be valuable as a diagnostic tool for the detection of Y. pestis. This report shows that the F1 strip is sufficient to support not only the detection of plague in simulated clinical samples, but also it may be a good candidate to meet the epidemiological surveillance during an outbreak of the biological warfare.

Epidemiological Review of Francisella Tularensis: A Case Study in the Complications of Dual Diagnoses

INTRODUCTION

Tularemia is a rare but potentially fatal disease that develops in numerous wild and domestic animals, including lagomorphs, rodents, cats, and humans.  Francisella tularensis bacterium, the causative agent of tularemia, was identified by veterinary personnel at Fort Riley, Kansas during a routine post-mortum evaluation of a domestic feline. However, before formal diagnosis was confirmed, the sample was sent and prepared for rabies testing at the Department of Defense (DoD) U.S. Army Public Health Command Central (PHC-C), Food Analysis and Diagnostic Laboratory (FADL).  This case report provides insight on how veterinarian staff and laboratory personnel can clinically manage esoteric, unexplained, or post-mortum examinations.  The epidemiologic characteristics of tularemia, F. tularensis as an organism of military interest, potential laboratory management of F. tularensis, and clinical findings on a case of feline tularemia are discussed. It further raises questions as to whether or not dead animals should be treated as sentinels and be pre-screened for select agents, especially in instances of dual diagnoses.

METHODS

A necropsy was performed on the cat by the Fort Riley veterinarian, DNA extraction and PCR analyses were conducted by FADL microbiologists, histology and immunohistology analyses were conducted by the Kansas State Veterinary Diagnostic Laboratory, and feline tissue and blood were sent to the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) for confirmatory testing and strain identification of tularemia.

RESULTS

Tularemia was identified in the spleen of the cat by the Fort Riley veterinarian and during the histological sampling of the spleen by the Kansas State Veterinary Diagnostic Laboratory.  A specific subsequent real-time polymerase chain reaction (RT-PCR) in vitro diagnostic detection of target DNA sequences of F. tularensis was conducted by the FADL microbiologists using a Joint Biological Agent Identification and Diagnostic System (JBAIDS) Tularemia Detection Kit to detect a presumptive qualitative result to detect tularemia in feline and blood samples.   USAMRIID also performed RT-PCR and identified genomic DNA from F. tularensis Type A, (SPL15.013.02), thus confirming the FADL's initial presumptive result of F. tularensis.  USAMRIID attempted to culture F. tularensis from three samples (swab, feline tissue, and transfer pipette tip), but no growth consistent with F. tularensis was observed on the cysteine heart agar with sheep blood and antibiotics (CHAB) and chocolate (CHOC) plates.

DISCUSSIONS

Our case study of a dual diagnosis of presumptive F. tularensis and possible rabies exposure transmission from a pet cat to its owner provides insight on how veterinarian staff and laboratory personnel can clinically manage esoteric, unexplained, or post-mortum examinations.  Our case study also demonstrates the obligation for cooperation between animal health, human health, and public health professionals in the management of zoonotic diseases.

The Fluorocycline TP-271 Is Efficacious in Models of Aerosolized Francisella tularensis SCHU S4 Infection in BALB/c Mice and Cynomolgus Macaques

TP-271 is a novel, fully synthetic fluorocycline in development for complicated bacterial respiratory infections. TP-271 was active in vitro against a panel of 29 Francisella tularensis isolates, showing MICs against 50% and 90% of isolates of 0.25 and 0.5 μg/ml, respectively. In a mouse model of inhalational tularemia, animals were exposed by aerosol to 91 to 283 50% lethal doses (LD₅₀)/mouse of F. tularensis SCHU S4. Following 21 days of once-daily intraperitoneal dosing with TP-271 at 3, 6, 12, and 18 mg/kg of body weight/day, initiating at 24 h postchallenge, survival was 80%, 100%, 100%, and 100%, respectively. When treatment was initiated at 72 h postchallenge, survival was 89%, 100%, 100%, and 100% in the 3-, 6-, 12-, and 18-mg/kg/day TP-271 groups, respectively. No mice treated with the vehicle control survived. Surviving mice treated with TP-271 showed little to no relapse during 14 days posttreatment. In a nonhuman primate model of inhalational tularemia, cynomolgus macaques received an average aerosol exposure of 1,144 CFU of F. tularensis SCHU S4. Once-daily intravenous infusion with 1 or 3 mg/kg TP-271, or vehicle control, for 21 days was initiated within 6 h of confirmed fever. All animals treated with TP-271 survived to the end of the study, with no relapse during 14 days after the last treatment, whereas no vehicle control-treated animals survived. The protection and low relapse afforded by TP-271 treatment in these studies support continued investigation of TP-271 for use in the event of aerosolized exposure to F. tularensis.

The unusual substrate specificity of a virulence associated serine hydrolase from the highly toxic bacterium, Francisella tularensis

Francisella tularensis is the causative agent of the highly, infectious disease, tularemia. Amongst the genes identified as essential to the virulence of F. tularensis was the proposed serine hydrolase FTT0941c. Herein, we purified FTT0941c to homogeneity and then characterized the folded stability, enzymatic activity, and substrate specificity of FTT0941c. Based on phylogenetic analysis, FTT0941c was classified within a divergent Francisella subbranch of the bacterial hormone sensitive lipase (HSL) superfamily, but with the conserved sequence motifs of a bacterial serine hydrolase. FTT0941c showed broad hydrolase activity against diverse libraries of ester substrates, including significant hydrolytic activity across alkyl ester substrates from 2 to 8 carbons in length. Among a diverse library of fluorogenic substrates, FTT0941c preferred α-cyclohexyl ester substrates, matching with the substrate specificity of structural homologues and the broad open architecture of its modeled binding pocket. By substitutional analysis, FTT0941c was confirmed to have a classic catalytic triad of Ser115, His278, and Asp248 and to remain thermally stable even after substitution. Its overall substrate specificity profile, divergent phylogenetic homology, and preliminary pathway analysis suggested potential biological functions for FTT0941c in diverse metabolic degradation pathways in F. tularensis.

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FTT0941c is an unstudied virulence associated hydrolase from F. tularensis (74).

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Classified as a bacterial HSL enzyme within a unique subclade of Francisella (85).

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Broad substrate specificity for alkyl, unsaturated, tertiary, and cyclic esters (79).

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Distinct substrate selectivity for α-cyclohexyl esters (54).

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Proposed metabolic role in cyclohexyl and benzoate ester hydrolysis pathways (76).

Atmospheric dispersion modelling of bioaerosols that are pathogenic to humans and livestock - A review to inform risk assessment studies

In this review we discuss studies that applied atmospheric dispersion models (ADM) to bioaerosols that are pathogenic to humans and livestock in the context of risk assessment studies. Traditionally, ADMs have been developed to describe the atmospheric transport of chemical pollutants, radioactive matter, dust, and particulate matter. However, they have also enabled researchers to simulate bioaerosol dispersion. To inform risk assessment, the aims of this review were fourfold, namely (1) to describe the most important physical processes related to ADMs and pathogen transport, (2) to discuss studies that focused on the application of ADMs to pathogenic bioaerosols, (3) to discuss emission and inactivation rate parameterisations, and (4) to discuss methods for conversion of concentrations to infection probabilities (concerning quantitative microbial risk assessment). The studies included human, livestock, and industrial sources. Important factors for dispersion included wind speed, atmospheric stability, topographic effects, and deposition. Inactivation was mainly governed by humidity, temperature, and ultraviolet radiation. A majority of the reviewed studies, however, lacked quantitative analyses and application of full quantitative microbial risk assessments (QMRA). Qualitative conclusions based on geographical dispersion maps and threshold doses were encountered frequently. Thus, to improve risk assessment for future outbreaks and releases, we recommended determining well-quantified emission and inactivation rates and applying dosimetry and dose-response models to estimate infection probabilities in the population at risk.

Monitoring biothreat agents (Francisella tularensis, Bacillus anthracis and Yersinia pestis) with a portable real-time PCR instrument

In the event of suspected releases or natural outbreaks of contagious pathogens, rapid identification of the infectious agent is essential for appropriate medical intervention and disease containment. The purpose of this study was to compare the performance of a novel portable real-time PCR thermocycler, PikoReal™, to the standard real-time PCR thermocycler, Applied Biosystems® 7300 (ABI 7300), for the detection of three high-risk biothreat bacterial pathogens: Francisella tularensis, Bacillus anthracis and Yersinia pestis. In addition, a novel confirmatory real-time PCR assay for the detection of F. tularensis is presented and validated. The results show that sensitivity of the assays, based on a dilution series, for the three infectious agents ranged from 1 to 100 fg of target DNA with both instruments. No cross-reactivity was revealed in specificity testing. Duration of the assays with the PikoReal and ABI 7300 systems were 50 and 100 min, respectively. In field testing for F. tularensis, results were obtained with the PikoReal system in 95 min, as the pre-PCR preparation, including DNA extraction, required an additional 45 min. We conclude that the PikoReal system enables highly sensitive and rapid on-site detection of biothreat agents under field conditions, and may be a more efficient alternative to conventional diagnostic methods.

Rapid detection of Yersinia pestis recombinant fraction 1 capsular antigen

Yersinia pestis, an infectious bacterium that is a causative agent of plague, a disease which has been shown to be one of the most feared in history and which has caused millions of deaths. The capsule-like fraction 1 (F1) antigen expressed by Y. pestis is a known specific marker for the identification of the bacteria; therefore, the detection of F1 is important for Y. pestis recognition. In this study, a rapid, sensitive, and specific technique, the lateral flow assay (LFA), was successfully developed to detect Y. pestis by the recombinant F1 antigen. The assay that utilized an anti-F1 polyclonal antibody (Pab) to identify the bacteria was based on a double-antibody sandwich format on a nitrocellulose membrane. With the LFA method, 50 ng/ml of recombinant F1 protein and 10(5) CFU/mL of Y. pestis could be detected in less than 10 min. This assay also showed no cross-reaction with other Yersinia spp. or with some selected capsule-producing Enterobacteriaceae strains. Furthermore, detection of Y. pestis in simulated samples has been evaluated. The detection sensitivity of Y. pestis in various matrices was 10(5) CFU/mL, which was identical to that in PBS buffer. The results obtained suggest that LFA is an excellent tool for detection of Y. pestis contamination in an environment and hence can be used to monitor plague diseases when they emerge.

Detection of Yersinia pestis in environmental and food samples by intact cell immunocapture and liquid chromatography-tandem mass spectrometry

Yersinia pestis is the causative agent of bubonic and pneumonic plague, an acute and often fatal disease in humans. In addition to the risk of natural exposure to plague, there is also the threat of a bioterrorist act, leading to the deliberate spread of the bacteria in the environment or food. We report here an immuno-liquid chromatography-tandem mass spectrometry (immuno-LC-MS/MS) method for the direct (i.e., without prior culture), sensitive, and specific detection of Y. pestis in such complex samples. In the first step, a bottom-up proteomics approach highlighted three relevant protein markers encoded by the Y. pestis-specific plasmids pFra (murine toxin) and pPla (plasminogen activator and pesticin). Suitable proteotypic peptides were thoroughly selected to monitor the three protein markers by targeted MS using the selected reaction monitoring (SRM) mode. Immunocapture conditions were optimized for the isolation and concentration of intact bacterial cells from complex samples. The immuno-LC-SRM assay has a limit of detection of 2 × 10(4) CFU/mL in milk or tap water, which compares well with those of state-of-the-art immunoassays. Moreover, we report the first direct detection of Y. pestis in soil, which could be extremely useful in confirming Y. pestis persistence in the ground.

Metabolism-directed structure optimization of benzimidazole-based Francisella tularensis enoyl-reductase (FabI) inhibitors

1. FabI is a potential antibiotic target against Francisella tularensis, which has been classified as a Category A biowarfare agent of high risk to public health. Our previous work demonstrated that N-benzyl benzimidazole compounds possess promising FabI inhibitory activity, but their druggability properties, including metabolic stability, are unknown. 2. The objective of this study was to characterize structure-metabolism relationships of a series of N-benzyl benzimidazole compounds to guide chemical optimization for better metabolic stability. To this end, metabolic stability data were obtained for 22 initial lead compounds using mouse hepatic microsomes. 3. Metabolic hotspots on the benzimidazole core structure as well as the benzyl ring were identified and verified by metabolite identification studies of four model compounds. Interestingly, the proposed structure-metabolism relationships did not apply to nine newly synthesized cyclopentane or oxacyclopentane derivatives of N-benzyl benzimidazole. 4. Subsequently, in silico quantitative structure-property relationship models were developed. Four molecular descriptors representing molecular polarity/polarisability, symmetry and size were identified to best explain variability in metabolic stability of different compounds. Multi-linear and non-linear regression models based on the selected molecular descriptors were developed and validated. 5. The structure-metabolism relationships for N-benzyl benzimidazole compounds should help optimization of N-benzyl benzimidazole compounds for better pharmacokinetic behavior.

Epitope recognition of antibodies against a Yersinia pestis lipopolysaccharide trisaccharide component

Today, the process of selecting carbohydrate antigens as a basis for active vaccination and the generation of antibodies for therapeutic and diagnostic purposes is based on intuition combined with trial and error experiments. In efforts to establish a rational process for glycan epitope selection, we employed glycan array screening, surface plasmon resonance, and saturation transfer difference (STD)-NMR to elucidate the interactions between antibodies and glycans representing the Yersinia pestis lipopolysaccharide (LPS). A trisaccharide epitope of the LPS inner core glycan and different LPS-derived oligosaccharides from various Gram-negative bacteria were analyzed using this combination of techniques. The antibody-glycan interaction with a heptose substructure was determined at atomic-level detail. Antibodies specifically recognize the Y. pestis trisaccharide and some substructures with high affinity and specificity. No significant binding to LPS glycans from other bacteria was observed, which suggests that the epitopes for just one particular bacterial species can be identified. On the basis of these results we are beginning to understand the rules for structure-based design and selection of carbohydrate antigens.

Metabolic network analysis-based identification of antimicrobial drug targets in category A bioterrorism agents

The 2001 anthrax mail attacks in the United States demonstrated the potential threat of bioterrorism, hence driving the need to develop sophisticated treatment and diagnostic protocols to counter biological warfare. Here, by performing flux balance analyses on the fully-annotated metabolic networks of multiple, whole genome-sequenced bacterial strains, we have identified a large number of metabolic enzymes as potential drug targets for each of the three Category A-designated bioterrorism agents including Bacillus anthracis, Francisella tularensis and Yersinia pestis. Nine metabolic enzymes- belonging to the coenzyme A, folate, phosphatidyl-ethanolamine and nucleic acid pathways common to all strains across the three distinct genera were identified as targets. Antimicrobial agents against some of these enzymes are available. Thus, a combination of cross species-specific antibiotics and common antimicrobials against shared targets may represent a useful combinatorial therapeutic approach against all Category A bioterrorism agents.

Deterministic models of inhalational anthrax in New Zealand white rabbits

Computational models describing bacterial kinetics were developed for inhalational anthrax in New Zealand white (NZW) rabbits following inhalation of Ames strain B. anthracis. The data used to parameterize the models included bacterial numbers in the airways, lung tissue, draining lymph nodes, and blood. Initial bacterial numbers were deposited spore dose. The first model was a single exponential ordinary differential equation (ODE) with 3 rate parameters that described mucociliated (physical) clearance, immune clearance (bacterial killing), and bacterial growth. At 36 hours postexposure, the ODE model predicted 1.7×10⁷ bacteria in the rabbit, which agreed well with data from actual experiments (4.0×10⁷ bacteria at 36 hours). Next, building on the single ODE model, a physiological-based biokinetic (PBBK) compartmentalized model was developed in which 1 physiological compartment was the lumen of the airways and the other was the rabbit body (lung tissue, lymph nodes, blood). The 2 compartments were connected with a parameter describing transport of bacteria from the airways into the body. The PBBK model predicted 4.9×10⁷ bacteria in the body at 36 hours, and by 45 hours the model showed all clearance mechanisms were saturated, suggesting the rabbit would quickly succumb to the infection. As with the ODE model, the PBBK model results agreed well with laboratory observations. These data are discussed along with the need for and potential application of the models in risk assessment, drug development, and as a general aid to the experimentalist studying inhalational anthrax.

Comparative evaluation of eleven commercial DNA extraction kits for real-time PCR detection of Bacillus anthracis spores in spiked dairy samples

Spores of Bacillus anthracis are highly resistant and can survive conditions used for food preservation. Sample size and complexity represent the major hurdles for pathogen detection in food-related settings. Eleven commercial DNA extraction kits were evaluated for detection of B. anthracis spores by quantitative real-time PCR (qPCR) in dairy products. DNA was extracted from serial dilutions of B. anthracis spores in milk powder, cream cheese, whole milk and buttermilk. Three kits (QIAamp DNA mini kit, Invisorb Food kit I and II) were determined to produce the lowest limit of detections (LODs) with equally good performance. These kits employed lysozyme and proteinase K treatments or proteinase K in combination with cethyltrimethylamonium bromide-mediated (CTAB) precipitation of cell debris for cell disruption and DNA release. The LODs for these three kits were determined as 10(2) spores/ml of distilled water, 10(3)s pores/20 mg of powdered milk and 10(4) spores/100 mg of cream cheese, respectively. Performance testing of the QIAamp DNA mini kit demonstrated a good reproducibility and appropriate detection limits from 10(3)/ml for butter milk, 10(4)/ml for whole milk and 10(4)/100 mg for low fat cream cheese. However, DNA extraction efficiency was strongly inhibited by cream cheese with higher fat contents with an increased LOD of 10(6)/100 mg spores. This study demonstrated that qPCR detection depends directly on the appropriate DNA extraction method for an individual food matrix and bacterial agent.

MyD88-dependent signaling prolongs survival and reduces bacterial burden during pulmonary infection with virulent Francisella tularensis

Francisella tularensis is the causative agent of the debilitating febrile illness tularemia. The severe morbidity associated with F. tularensis infections is attributed to its ability to evade the host immune response. Innate immune activation is undetectable until more than 48 hours after infection. The ensuing inflammatory response is considered pathological, eliciting a septic-like state characterized by hypercytokinemia and cell death. To investigate potential pathological consequences of the innate immune response, mice deficient in a key innate immune signaling molecule, MyD88, were studied. MyD88 knockout (KO) mice were infected with the prototypical virulent F. tularensis strain, Schu S4. MyD88 KO mice succumbed to infection more rapidly than wild-type mice. The enhanced pathogenicity of Schu S4 in MyD88 KO mice was associated with greater bacterial burdens in lungs and distal organs, and the absence of IFN-γ in the lungs, spleens, and sera. Cellular infiltrates were not observed on histological evaluation of the lungs, livers, or spleens of MyD88 KO mice, the first KO mouse described with this phenotype to our knowledge. Despite the absence of cellular infiltration, there was more cell death in the lungs of MyD88 KO mice. Thus, the host proinflammatory response is beneficial, and MyD88 signaling is required to limit bacterial burden and prolong survival during pulmonary infection by virulent F. tularensis.

Diversity-oriented synthesis of inner core oligosaccharides of the lipopolysaccharide of pathogenic Gram-negative bacteria

Lipopolysaccharide (LPS) is a potent virulence factor of pathogenic Gram-negative bacteria. To better understand the role of LPS in host-pathogen interactions and to elucidate the antigenic and immunogenic properties of LPS inner core region, a collection of well-defined L-glycero-D-manno-heptose (Hep) and 3-deoxy-α-D-manno-oct-2-ulosonic acid (Kdo)-containing inner core oligosaccharides is required. To address this need, we developed a diversity-oriented approach based on a common orthogonal protected disaccharide Hep-Kdo. Utilizing this new approach, we synthesized a range of LPS inner core oligosaccharides from a variety of pathogenic bacteria including Y. pestis, H. influenzae, and Proteus that cause plague, meningitis, and severe wound infections, respectively. Rapid access to these highly branched core oligosaccharides relied on elaboration of the disaccharide Hep-Kdo core as basis for the elongation with various flexible modules including unique Hep and 4-amino-4-deoxy-β-L-arabinose (Ara4N) monosaccharides and branched Hep-Hep disaccharides. A regio- and stereoselective glycosylation of Kdo 7,8-diol was key to selective installation of the Ara4N moiety at the 8-hydroxyl group of Kdo moiety of the Hep-Kdo disaccharide. The structure of the LPS inner core oligosaccharides was confirmed by comparison of (1)H NMR spectra of synthetic antigens and isolated fragments. These synthetic LPS core oligosaccharides can be covalently bound to carrier proteins via the reducing end pentyl amine linker, to explore their antigenic and immunogenic properties as well as potential applications such as diagnostic tools and vaccines.

Large scale structural rearrangement of a serine hydrolase from Francisella tularensis facilitates catalysis

Tularemia is a deadly, febrile disease caused by infection by the gram-negative bacterium, Francisella tularensis. Members of the ubiquitous serine hydrolase protein family are among current targets to treat diverse bacterial infections. Herein we present a structural and functional study of a novel bacterial carboxylesterase (FTT258) from F. tularensis, a homologue of human acyl protein thioesterase (hAPT1). The structure of FTT258 has been determined in multiple forms, and unexpectedly large conformational changes of a peripheral flexible loop occur in the presence of a mechanistic cyclobutanone ligand. The concomitant changes in this hydrophobic loop and the newly exposed hydrophobic substrate binding pocket suggest that the observed structural changes are essential to the biological function and catalytic activity of FTT258. Using diverse substrate libraries, site-directed mutagenesis, and liposome binding assays, we determined the importance of these structural changes to the catalytic activity and membrane binding activity of FTT258. Residues within the newly exposed hydrophobic binding pocket and within the peripheral flexible loop proved essential to the hydrolytic activity of FTT258, indicating that structural rearrangement is required for catalytic activity. Both FTT258 and hAPT1 also showed significant association with liposomes designed to mimic bacterial or human membranes, respectively, even though similar structural rearrangements for hAPT1 have not been reported. The necessity for acyl protein thioesterases to have maximal catalytic activity near the membrane surface suggests that these conformational changes in the protein may dually regulate catalytic activity and membrane association in bacterial and human homologues.

Characterization of systemic and pneumonic murine models of plague infection using a conditionally virulent strain

Yersinia pestis causes bubonic and pneumonic plague in humans. The pneumonic infection is the most severe and invariably fatal if untreated. Because of its high virulence, ease of delivery and precedent of use in warfare, Y. pestis is considered as a potential bioterror agent. No licensed plague vaccine is currently available in the US. Laboratory research with virulent strains requires appropriate biocontainment (i.e., Biosafety Level 3 (BSL-3) for procedures that generate aerosol/droplets) and secure facilities that comply with federal select agent regulations. To assist in the identification of promising vaccine candidates during the early phases of development, we characterized mouse models of systemic and pneumonic plague infection using the Y. pestis strain EV76, an attenuated human vaccine strain that can be rendered virulent in mice under in vivo iron supplementation. Mice inoculated intranasally or intravenously with Y. pestis EV76 in the presence of iron developed a systemic and pneumonic plague infection that resulted in disease and lethality. Bacteria replicated and severely compromised the spleen, liver and lungs. Susceptibility was age dependent, with younger mice being more vulnerable to pneumonic infection. We used these models of infection to assess the protective capacity of newly developed Salmonella-based plague vaccines. The protective outcome varied depending on the route and dose of infection. Protection was associated with the induction of specific immunological effectors in systemic/mucosal compartments. The models of infection described could serve as safe and practical tools for identifying promising vaccine candidates that warrant further potency evaluation using fully virulent strains in BSL-3 settings.

Antimicrobial peptides containing unnatural amino acid exhibit potent bactericidal activity against ESKAPE pathogens

A series of 36 synthetic antimicrobial peptides containing unnatural amino acids were screened to determine their effectiveness to treat Enterococcus faecium, Staphylococcus aureus, Klebsiella pnemoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species (ESKAPE) pathogens, which are known to commonly infect chronic wounds. The primary amino acid sequences of these peptides incorporate either three or six dipeptide units consisting of the unnatural amino acids Tetrahydroisoquinolinecarboxylic acid (Tic) and Octahydroindolecarboxylic acid (Oic). The Tic-Oic dipeptide units are separated by SPACER amino acids with specific physicochemical properties that control how these peptides interact with bacterial cell membranes of different chemical compositions. These peptides exhibited minimum inhibitory concentrations (MIC) against these pathogens in the range from >100 to 6.25 μg/mL. The observed diversity of MIC values for these peptides against the various bacterial strains are consistent with our hypothesis that the complementarity of the physicochemical properties of the peptide and the lipid of the bacteria's cell membrane determines the resulting antibacterial activity of the peptide.

Vectors and vector-borne diseases of horses

Most diseases of horses with zoonotic importance are transmitted by arthropods. The vectors belong to two very distantly related groups, the chelicerate Ixodidae (Acari = ticks) and the hexapod Diptera (true flies). Almost all relevant species are predestined for transmitting pathogens by their blood-sucking habits. Especially species of Diptera, one of the megadiverse orders of holometabolan insects (ca. 150.000 spp.), affect the health status and performance of horses during the grazing period in summer. The severity of pathological effect depends on the pathogen, but also on the group of vectors and the intensity of the infection or infestation. Dipteran species but also blood-sucking representatives of Acari (Ixodidae) can damage their hosts by sucking blood, causing myiasis, allergy, paralysis and intoxication, and also transmit various bacterial, viral, parasitic, spirochetal and rickettsial diseases to animals and also humans. The aim of this review was to provide extensive information on the infectious diseases transmitted by members of the two arthropod lineages (Ixodidae, Diptera) and a systematic overview of the vectors. For each taxon, usually on the ordinal, family, and genus level a short characterisation is given, allowing non-entomologists easy identification. Additionally, the biology of the relevant species (or genera) is outlined briefly.

Novel genomic tools for specific and real-time detection of biothreat and frequently encountered foodborne pathogens

The bacterial genera Escherichia, Salmonella, Shigella, Vibrio, Yersinia, and Francisella include important food safety and biothreat agents. By extensive mining of the whole genome and protein databases of diverse, closely and distantly related bacterial species and strains, we have identified novel genome regions, which we utilized to develop a rapid detection platform for these pathogens. The specific genomic targets we have identified to design the primers in Francisella tularensis subsp. tularensis, F. tularensis subsp. novicida, Shigella dysenteriae, Salmonella enterica serovar Typhimurium, Vibrio cholerae, Yersinia pestis, and Yersinia pseudotuberculosis contained either known genes or putative proteins. Primer sets were designed from the target regions for use in real-time PCR assays to detect specific biothreat pathogens at species or strain levels. The primer sets were first tested by in silico PCR against whole-genome sequences of different species, subspecies, or strains and then by in vitro PCR against genomic DNA preparations from 23 strains representing six biothreat agents (Escherichia coli O157:H7 strain EDL 933, Shigella dysenteriae, S. enterica serovar Typhi, F. tularensis subsp. tularensis, V. cholerae, and Y. pestis) and six foodborne pathogens (Salmonella Typhimurium, Salmonella Saintpaul, Shigella sonnei, F. tularensis subsp. novicida, Vibrio parahaemolyticus, and Y. pseudotuberculosis). Each pathogen was specifically identifiable at the genus and species levels. Sensitivity assays performed with purified DNA showed the lowest detection limit of 128 fg of DNA/μl for F. tularensis subsp. tularensis. A preliminary test to detect Shigella organisms in a milk matrix also enabled the detection of 6 to 60 CFU/ml. These new tools could ultimately be used to develop platforms to simultaneously detect these pathogens.

Prioritizing risks and uncertainties from intentional release of selected Category A pathogens

This paper synthesizes available information on five Category A pathogens (Bacillus anthracis, Yersinia pestis, Francisella tularensis, Variola major and Lassa) to develop quantitative guidelines for how environmental pathogen concentrations may be related to human health risk in an indoor environment. An integrated model of environmental transport and human health exposure to biological pathogens is constructed which 1) includes the effects of environmental attenuation, 2) considers fomite contact exposure as well as inhalational exposure, and 3) includes an uncertainty analysis to identify key input uncertainties, which may inform future research directions. The findings provide a framework for developing the many different environmental standards that are needed for making risk-informed response decisions, such as when prophylactic antibiotics should be distributed, and whether or not a contaminated area should be cleaned up. The approach is based on the assumption of uniform mixing in environmental compartments and is thus applicable to areas sufficiently removed in time and space from the initial release that mixing has produced relatively uniform concentrations. Results indicate that when pathogens are released into the air, risk from inhalation is the main component of the overall risk, while risk from ingestion (dermal contact for B. anthracis) is the main component of the overall risk when pathogens are present on surfaces. Concentrations sampled from untracked floor, walls and the filter of heating ventilation and air conditioning (HVAC) system are proposed as indicators of previous exposure risk, while samples taken from touched surfaces are proposed as indicators of future risk if the building is reoccupied. A Monte Carlo uncertainty analysis is conducted and input-output correlations used to identify important parameter uncertainties. An approach is proposed for integrating these quantitative assessments of parameter uncertainty with broader, qualitative considerations to identify future research priorities.

Discovery of a novel and potent class of F. tularensis enoyl-reductase (FabI) inhibitors by molecular shape and electrostatic matching

Enoyl-acyl carrier protein (ACP) reductase, FabI, is a key enzyme in the bacterial fatty acid biosynthesis pathway (FAS II). FabI is an NADH-dependent oxidoreductase that acts to reduce enoyl-ACP substrates in a final step of the pathway. The absence of this enzyme in humans makes it an attractive target for the development of new antibacterial agents. FabI is known to be unresponsive to structure-based design efforts due to a high degree of induced fit and a mobile flexible loop encompassing the active site. Here we discuss the development, validation, and careful application of a ligand-based virtual screen used for the identification of novel inhibitors of the Francisella tularensis FabI target. In this study, four known classes of FabI inhibitors were used as templates for virtual screens that involved molecular shape and electrostatic matching. The program ROCS was used to search a high-throughput screening library for compounds that matched any of the four molecular shape queries. Matching compounds were further refined using the program EON, which compares and scores compounds by matching electrostatic properties. Using these techniques, 50 compounds were selected, ordered, and tested. The tested compounds possessed novel chemical scaffolds when compared to the input query compounds. Several hits with low micromolar activity were identified and follow-up scaffold-based searches resulted in the identification of a lead series with submicromolar enzyme inhibition, high ligand efficiency, and a novel scaffold. Additionally, one of the most active compounds showed promising whole-cell antibacterial activity against several Gram-positive and Gram-negative species, including the target pathogen. The results of a preliminary structure-activity relationship analysis are presented.

Characterization of the Na⁺/H⁺ antiporter from Yersinia pestis

Yersinia pestis, the bacterium that historically accounts for the Black Death epidemics, has nowadays gained new attention as a possible biological warfare agent. In this study, its Na/H antiporter is investigated for the first time, by a combination of experimental and computational methodologies. We determined the protein's substrate specificity and pH dependence by fluorescence measurements in everted membrane vesicles. Subsequently, we constructed a model of the protein's structure and validated the model using molecular dynamics simulations. Taken together, better understanding of the Yersinia pestis Na/H antiporter's structure-function relationship may assist in studies on ion transport, mechanism of action and designing specific blockers of Na/H antiporter to help in fighting Yersinia pestis -associated infections. We hope that our model will prove useful both from mechanistic and pharmaceutical perspectives.

Rapid onset of ICAM-1 expression is a marker of effective macrophages activation during infection of Francisella tularensis LVS in vitro

Francisella tularensis is capable to modulate immunobiological activities of the host cells. We focused on the expression of ICAM-1 (CD54) on J774.2 mouse macrophage cell line infected by F. tularensis live vaccine strain (LVS) in vitro as a putative marker of subsequent elimination of infection. J774.2 cell line cells were infected by F. tularensis LVS strain (multiplicity of infection, 1:100). Cell cultures were stimulated either 3 h before infection or 3 h after infection by either lipopolysaccharide (LPS) or interferon γ (IFN-γ). The expression of ICAM-1 was determined by flow cytometry 6 h after infection. The intensity of ICAM-1 expression after 6 h of J774.2 macrophage cells infection by F. tularensis is very sensitive indicator of the effective macrophages stimulation resulting in the elimination of F. tularensis infection. The mean fluorescence intensity MFI = 49.8 is set-up by our experiments as a reliable threshold of the effective elimination of F. tularensis experimental infection with 83.3% sensitivity and 96.7% specificity, respectively. Simultaneous stimulation of J774.2 macrophage cells by LPS and IFN-γ was essential to elicit the elimination of F. tularensis infection. The ICAM-1 expression determined by flow cytometry can be considered to be highly sensitive and specific approach to predict elimination of F. tularensis infection by J774.2 macrophages.

J774 macrophage-like cell line cytokine and chemokine patterns are modulated by Francisella tularensis LVS strain infection

Mutual interactions were investigated between intracellular parasitic bacterium Francisella tularensis (F.t.; highly virulent bacterium responsible for tularemia, replicating within the host macrophages) and murine macrophage-like cell line J774. Recombinant murine lymphokine INF-gamma and/or LPS derived from E. coli were determined to stimulate in vitro antimicrobial activity of macrophage-like J774 cell line against the live vaccine strain (LVS) of F.t. through their ability to produce proinflammatory cytokines and chemokines. F.t. infection up-regulated IL-12 p40 production and down-regulated TNF-alpha production by stimulated macrophages; on the other hand, F.t. infection did not affect the production of IL-8, IL-6, MCP-5, and RANTES by stimulated macrophages. This showed that F.t. infection modulates the cytokine synthesis by J774 macrophage cell line.

Selected fluorescent techniques for identification of the physiological state of individual water and soil bacterial cells - review

Stimulated by demands of the natural environment conservation, the need for thorough structural and functional identification of microorganisms colonizing different ecosystems has contributed to an intensive advance in research techniques. The article shows that some of these techniques are also a convenient tool for determination of the physiological state of single cells in a community of microorganisms. The paper presents selected fluorescent techniques, which are used in research on soil, water and sediment microorganisms. It covers the usability of determination of the dehydrogenase activity of an individual bacterial cell (CTC+) and of bacteria with intact, functioning cytoplasmic membranes, bacteria with an integrated nucleiod (NuCC+) as well as fluorescent in situ hybridization (FISH).