Listeria monocytogenes phosphatidylinositol-specific phospholipase C has evolved for virulence by greatly reduced activity on GPI anchors

Microfluidic paper analytic device (μPAD) technology for food safety applications

Foodborne pathogens, food adulterants, allergens, and toxic chemicals in food can cause major health hazards to humans and animals. Stringent quality control measures at all stages of food processing are required to ensure food safety. There is, therefore, a global need for affordable, reliable, and rapid tests that can be conducted at different process steps and processing sites, spanning the range from the sourcing of food to the end-product acquired by the consumer. Current laboratory-based food quality control tests are well established, but many are not suitable for rapid on-site investigations and are costly. Microfluidic paper analytical devices (μPADs) are a fast-growing field in medical diagnostics that can fill these gaps. In this review, we describe the latest developments in the applications of microfluidic paper analytic device (μPAD) technology in the food safety sector. State-of-the-art μPAD designs and fabrication methods, microfluidic assay principles, and various types of μPAD devices with food-specific applications are discussed. We have identified the prominent research and development trends and future directions for maximizing the value of microfluidic technology in the food sector and have highlighted key areas for improvement. We conclude that the μPAD technology is promising in food safety applications by using novel materials and improved methods to enhance the sensitivity and specificity of the assays, with low cost.

Tools and mechanisms of vacuolar escape leading to host egress in Legionella pneumophila infection: Emphasis on bacterial phospholipases

The phenomenon of host cell escape exhibited by intracellular pathogens is a remarkably versatile occurrence, capable of unfolding through lytic or non-lytic pathways. Among these pathogens, the bacterium Legionella pneumophila stands out, having adopted a diverse spectrum of strategies to disengage from their host cells. A pivotal juncture that predates most of these host cell escape modalities is the initial escape from the intracellular compartment. This critical step is increasingly supported by evidence suggesting the involvement of several secreted pathogen effectors, including lytic proteins. In this intricate landscape, L. pneumophila emerges as a focal point for research, particularly concerning secreted phospholipases. While nestled within its replicative vacuole, the bacterium deftly employs both its type II (Lsp) and type IVB (Dot/Icm) secretion systems to convey phospholipases into either the phagosomal lumen or the host cell cytoplasm. Its repertoire encompasses numerous phospholipases A (PLA), including three enzymes-PlaA, PlaC, and PlaD-bearing the GDSL motif. Additionally, there are 11 patatin-like phospholipases A as well as PlaB. Furthermore, the bacterium harbors three extracellular phospholipases C (PLCs) and one phospholipase D. Within this comprehensive review, we undertake an exploration of the pivotal role played by phospholipases in the broader context of phagosomal and host cell egress. Moreover, we embark on a detailed journey to unravel the established and potential functions of the secreted phospholipases of L. pneumophila in orchestrating this indispensable process.

Human Listeriosis

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that can cause severe invasive infections upon ingestion with contaminated food. Clinically, listerial disease, or listeriosis, most often presents as bacteremia, meningitis or meningoencephalitis, and pregnancy-associated infections manifesting as miscarriage or neonatal sepsis. Invasive listeriosis is life-threatening and a main cause of foodborne illness leading to hospital admissions in Western countries. Sources of contamination can be identified through international surveillance systems for foodborne bacteria and strains' genetic data sharing. Large-scale whole genome studies have increased our knowledge on the diversity and evolution of L. monocytogenes, while recent pathophysiological investigations have improved our mechanistic understanding of listeriosis. In this article, we present an overview of human listeriosis with particular focus on relevant features of the causative bacterium, epidemiology, risk groups, pathogenesis, clinical manifestations, and treatment and prevention.

A subtractive proteomics and immunoinformatics approach towards designing a potential multi-epitope vaccine against pathogenic Listeriamonocytogenes

Listeria monocytogenes is the causative agent of listeriosis, which is dangerous for pregnant women, the elderly or individuals with a weakened immune system. Individuals with leukaemia, cancer, HIV/AIDS, kidney transplant and steroid therapy suffer from immunological damage are menaced. World Health Organization (WHO) reports that human listeriosis has a high mortality rate of 20-30% every year. To date, no vaccine is available to treat listeriosis. Thereby, it is high time to design novel vaccines against L. monocytogenes. Here, we present computational approaches to design an antigenic, stable and safe vaccine against the L. monocytogenes that could help to control the infections associated with the pathogen. Three vital pathogenic proteins of L. monocytogenes, such as Listeriolysin O (LLO), Phosphatidylinositol-specific phospholipase C (PI-PLC), and Actin polymerization protein (ActA), were selected using a subtractive proteomics approach to design the multi-epitope vaccine (MEV). A total of 5 Cytotoxic T-lymphocyte (CTL) and 9 Helper T-lymphocyte (HTL) epitopes were predicted from these selected proteins. To design the multi-epitope vaccine (MEV) from the selected proteins, CTL epitopes were joined with the AAY linker, and HTL epitopes were joined with the GPGPG linker. Additionally, a human β-defensin-3 (hBD-3) adjuvant was added to the N-terminal side of the final MEV construct to increase the immune response to the vaccine. The final MEV was predicted to be antigenic, non-allergen and non-toxic in nature. Physicochemical property analysis suggested that the MEV construct is stable and could be easily purified through the E. coli expression system. This in-silico study showed that MEV has a robust binding interaction with Toll-like receptor 2 (TLR2), a key player in the innate immune system. Current subtractive proteomics and immunoinformatics study provides a background for designing a suitable, safe and effective vaccine against pathogenic L. monocytogenes.

Life without air

An early exposure to lipid biochemistry in the laboratory of Konrad Bloch resulted in a fascination with the biosynthesis, structures, and functions of bacterial lipids. The discovery of plasmalogens (1-alk-1'-enyl, 2-acyl phospholipids) in anaerobic Gram-positive bacteria led to studies on the physical chemistry of these lipids and the cellular regulation of membrane lipid polymorphism in bacteria. Later studies in several laboratories showed that the formation of the alk-1-enyl ether bond involves an aerobic process in animal cells and thus is fundamentally different from that in anaerobic organisms. Our work provides evidence for an anaerobic process in which plasmalogens are formed from their corresponding diacyl lipids. Studies on the roles of phospholipases in Listeria monocytogenes revealed distinctions between its phospholipases and those previously discovered in other bacteria and showed how the Listeria enzymes are uniquely fitted to the intracellular lifestyle of this significant human pathogen.

Molecular Signatures Related to the Virulence of Bacillus cereus Sensu Lato, a Leading Cause of Devastating Endophthalmitis

Bacillus endophthalmitis is a devastating eye infection that causes rapid blindness through extracellular tissue-destructive exotoxins. Despite its importance, knowledge of the phylogenetic relationships and population structure of intraocular Bacillus spp. is lacking. In this study, we sequenced the whole genomes of eight Bacillus intraocular pathogens independently isolated from 8/52 patients with posttraumatic Bacillus endophthalmitis infections in the Eye Hospital of Wenzhou Medical University between January 2010 and December 2018. Phylogenetic analysis revealed that the pathogenic intraocular isolates belonged to Bacillus cereus, Bacillus thuringiensis and Bacillus toyonensis To determine the virulence of the ocular isolates, three representative strains were injected into mouse models, and severe endophthalmitis leading to blindness was observed. Through incorporating publicly available genomes for Bacillus spp., we found that the intraocular pathogens could be isolated independently but displayed a similar genetic context. In addition, our data provide genome-wide support for intraocular and gastrointestinal sources of Bacillus spp. belonging to different lineages. Importantly, we identified five molecular signatures of virulence and motility genes associated with intraocular infection, namely, plcA-2, InhA-3, InhA-4, hblA-5, and fliD using pangenome-wide association studies. The characterization of overrepresented genes in the intraocular isolates holds value to predict bacterial evolution and for the design of future intervention strategies in patients with endophthalmitis.IMPORTANCE In this study, we provided a detailed and comprehensive clinicopathological and pathogenic report of Bacillus endophthalmitis over the 8 years of the study period. We first reported the whole-genome sequence of Bacillus spp. causing devastating endophthalmitis and found that Bacillus toyonensis is able to cause endophthalmitis. Finally, we revealed significant endophthalmitis-associated virulence genes involved in hemolysis, immunity inhibition, and pathogenesis. Overall, as more sequencing data sets become available, these data will facilitate comparative research and will reveal the emergence of pathogenic "ocular bacteria."

Staphylococcal phosphatidylinositol-specific phospholipase C potentiates lung injury via complement sensitisation

Staphylococcus aureus is frequently isolated from patients with community-acquired pneumonia and acute respiratory distress syndrome (ARDS). ARDS is associated with staphylococcal phosphatidylinositol-specific phospholipase C (PI-PLC); however, the role of PI-PLC in the pathogenesis and progression of ARDS remains unknown. Here, we showed that recombinant staphylococcal PI-PLC possesses enzyme activity that causes shedding of glycosylphosphatidylinositol-anchored CD55 and CD59 from human umbilical vein endothelial cell surfaces and triggers cell lysis via complement activity. Intranasal infection with PI-PLC-positive S. aureus resulted in greater neutrophil infiltration and increased pulmonary oedema compared with a plc-isogenic mutant. Although indistinguishable proinflammatory genes were induced, the wild-type strain activated higher levels of C5a in lung tissue accompanied by elevated albumin instillation and increased lactate dehydrogenase release in bronchoalveolar lavage fluid compared with the plc^- mutant. Following treatment with cobra venom factor to deplete complement, the wild-type strain with PI-PLC showed a reduced ability to trigger pulmonary permeability and tissue damage. PI-PLC-positive S. aureus induced the formation of membrane attack complex, mainly on type II pneumocytes, and reduced the level of CD55/CD59, indicating the importance of complement regulation in pulmonary injury. In conclusion, S. aureus PI-PLC sensitised tissue to complement activation leading to more severe tissue damage, increased pulmonary oedema, and ARDS progression.

Listeria monocytogenes: cell biology of invasion and intracellular growth

The Gram-positive pathogen Listeria monocytogenes is able to promote its entry into a diverse range of mammalian host cells by triggering plasma membrane remodeling, leading to bacterial engulfment. Upon cell invasion, L. monocytogenes disrupts its internalization vacuole and translocates to the cytoplasm, where bacterial replication takes place. Subsequently, L. monocytogenes uses an actin-based motility system that allows bacterial cytoplasmic movement and cell-to-cell spread. L. monocytogenes therefore subverts host cell receptors, organelles and the cytoskeleton at different infection steps, manipulating diverse cellular functions that include ion transport, membrane trafficking, post-translational modifications, phosphoinositide production, innate immune responses as well as gene expression and DNA stability.

Ceratocystis cacaofunesta genome analysis reveals a large expansion of extracellular phosphatidylinositol-specific phospholipase-C genes (PI-PLC)

BACKGROUND

The Ceratocystis genus harbors a large number of phytopathogenic fungi that cause xylem parenchyma degradation and vascular destruction on a broad range of economically important plants. Ceratocystis cacaofunesta is a necrotrophic fungus responsible for lethal wilt disease in cacao. The aim of this work is to analyze the genome of C. cacaofunesta through a comparative approach with genomes of other Sordariomycetes in order to better understand the molecular basis of pathogenicity in the Ceratocystis genus.

RESULTS

We present an analysis of the C. cacaofunesta genome focusing on secreted proteins that might constitute pathogenicity factors. Comparative genome analyses among five Ceratocystidaceae species and 23 other Sordariomycetes fungi showed a strong reduction in gene content of the Ceratocystis genus. However, some gene families displayed a remarkable expansion, in particular, the Phosphatidylinositol specific phospholipases-C (PI-PLC) family. Also, evolutionary rate calculations suggest that the evolution process of this family was guided by positive selection. Interestingly, among the 82 PI-PLCs genes identified in the C. cacaofunesta genome, 70 genes encoding extracellular PI-PLCs are grouped in eight small scaffolds surrounded by transposon fragments and scars that could be involved in the rapid evolution of the PI-PLC family. Experimental secretome using LC-MS/MS validated 24% (86 proteins) of the total predicted secretome (342 proteins), including four PI-PLCs and other important pathogenicity factors.

CONCLUSION

Analysis of the Ceratocystis cacaofunesta genome provides evidence that PI-PLCs may play a role in pathogenicity. Subsequent functional studies will be aimed at evaluating this hypothesis. The observed genetic arsenals, together with the analysis of the PI-PLC family shown in this work, reveal significant differences in the Ceratocystis genome compared to the classical vascular fungi, Verticillium and Fusarium. Altogether, our analyses provide new insights into the evolution and the molecular basis of plant pathogenicity.

Phospholipases: An Overview

Phospholipases are lipolytic enzymes that hydrolyze phospholipid substrates at specific ester bonds. Phospholipases are widespread in nature and play very diverse roles from aggression in snake venom to signal transduction, lipid mediator production, and metabolite digestion in humans. Phospholipases vary considerably in structure, function, regulation, and mode of action. Tremendous advances in understanding the structure and function of phospholipases have occurred in the last decades. This introductory chapter is aimed at providing a general framework of the current understanding of phospholipases and a discussion of their mechanisms of action and emerging biological functions.

Bacterial Sphingomyelinases and Phospholipases as Virulence Factors

Bacterial sphingomyelinases and phospholipases are a heterogeneous group of esterases which are usually surface associated or secreted by a wide variety of Gram-positive and Gram-negative bacteria. These enzymes hydrolyze sphingomyelin and glycerophospholipids, respectively, generating products identical to the ones produced by eukaryotic enzymes which play crucial roles in distinct physiological processes, including membrane dynamics, cellular signaling, migration, growth, and death. Several bacterial sphingomyelinases and phospholipases are essential for virulence of extracellular, facultative, or obligate intracellular pathogens, as these enzymes contribute to phagosomal escape or phagosomal maturation avoidance, favoring tissue colonization, infection establishment and progression, or immune response evasion. This work presents a classification proposal for bacterial sphingomyelinases and phospholipases that considers not only their enzymatic activities but also their structural aspects. An overview of the main physiopathological activities is provided for each enzyme type, as are examples in which inactivation of a sphingomyelinase- or a phospholipase-encoding gene impairs the virulence of a pathogen. The identification of sphingomyelinases and phospholipases important for bacterial pathogenesis and the development of inhibitors for these enzymes could generate candidate vaccines and therapeutic agents, which will diminish the impacts of the associated human and animal diseases.

Plant phosphoinositide-dependent phospholipases C: variations around a canonical theme

Phosphoinositide-specific phospholipase C (PI-PLC) cleaves, in a Ca(2+)-dependent manner, phosphatidylinositol-4,5-bisphosphate (PI-4,5-P2) into diacylglycerol (DAG) and inositol triphosphate (IP3). PI-PLCs are multidomain proteins that are structurally related to the PI-PLCζs, the simplest animal PI-PLCs. Like these animal counterparts, they are only composed of EF-hand, X/Y and C2 domains. However, plant PI-PLCs do not have a conventional EF-hand domain since they are often truncated, while some PI-PLCs have no EF-hand domain at all. Despite this simple structure, plant PI-PLCs are involved in many essential plant processes, either associated with development or in response to environmental stresses. The action of PI-PLCs relies on the mediators they produce. In plants, IP3 does not seem to be the sole active soluble molecule. Inositol pentakisphosphate (IP5) and inositol hexakisphosphate (IP6) also transmit signals, thus highlighting the importance of coupling PI-PLC action with inositol-phosphate kinases and phosphatases. PI-PLCs also produce a lipid molecule, but plant PI-PLC pathways show a peculiarity in that the active lipid does not appear to be DAG but its phosphorylated form, phosphatidic acid (PA). Besides, PI-PLCs can also act by altering their substrate levels. Taken together, plant PI-PLCs show functional differences when compared to their animal counterparts. However, they act on similar general signalling pathways including calcium homeostasis and cell phosphoproteome. Several important questions remain unanswered. The cross-talk between the soluble and lipid mediators generated by plant PI-PLCs is not understood and how the coupling between PI-PLCs and inositol-kinases or DAG-kinases is carried out remains to be established.

Staphylococcus aureus α-hemolysin promotes platelet-neutrophil aggregate formation

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) causes severe hemorrhagic necrotizing pneumonia associated with high mortality. Exotoxins have been implicated in the pathogenesis of this infection; however, the cellular mechanisms responsible remain largely undefined. Because platelet-neutrophil aggregates (PNAs) can dysregulate inflammatory responses and contribute to tissue destruction, we investigated whether exotoxins from MRSA could stimulate formation of PNAs in human whole blood. Strong PNA formation was stimulated by toxins from stationary phase but not log phase CA-MRSA, and α-hemolysin was singularly identified as the mediator of this activity. MRSA exotoxins also caused neutrophil (polymorphonuclear leukocyte) activation, as measured by increased CD11b expression, although platelet binding was not driven by this mechanism; rather, α-hemolysin-induced PNA formation was solely platelet P-selectin dependent. These findings suggest a role for S. aureus α-hemolysin-induced PNA formation in alveolar capillary destruction in hemorrhagic/necrotizing pneumonia caused by CA-MRSA and offer novel targets for intervention.

Interaction between Bacillus cereus and cultured human enterocytes: effect of calcium, cell differentiation, and bacterial extracellular factors

Bacillus cereus interaction with cultured human enterocytes and the signaling pathways responsible for the biological effects of the infection were investigated. Results demonstrate that calcium depletion increases the ability of strains T1 and 2 to invade cells. Bacteria associated in greater extent to undifferentiated enterocytes and extracellular factors from strain 2 increased its own association and invasion. Inhibitors of signaling pathways related to phosphorylated lipids (U73122 and wortmannin) were able to significantly reduce cytoskeleton disruption induced by B. cereus infection. Adhesion of strain T1 decreased in the presence of U73122 and of wortmannin, as well as when those inhibitors were used together. In contrast, invasion values were diminished only by U73122. Results show that different factors are involved in the interaction between B. cereus and cultured human enterocytes. Following infection, disruption of the cytoskeleton could facilitate invasion of the eukaryotic cells.

A highly dynamic ER-derived phosphatidylinositol-synthesizing organelle supplies phosphoinositides to cellular membranes

Polyphosphoinositides are lipid signaling molecules generated from phosphatidylinositol (PtdIns) with critical roles in vesicular trafficking and signaling. It is poorly understood where PtdIns is located within cells and how it moves around between membranes. Here we identify a hitherto-unrecognized highly mobile membrane compartment as the site of PtdIns synthesis and a likely source of PtdIns of all membranes. We show that the PtdIns-synthesizing enzyme PIS associates with a rapidly moving compartment of ER origin that makes ample contacts with other membranes. In contrast, CDP-diacylglycerol synthases that provide PIS with its substrate reside in the tubular ER. Expression of a PtdIns-specific bacterial PLC generates diacylglycerol also in rapidly moving cytoplasmic objects. We propose a model in which PtdIns is synthesized in a highly mobile lipid distribution platform and is delivered to other membranes during multiple contacts by yet-to-be-defined lipid transfer mechanisms.

Role of phospholipases in fungal fitness, pathogenicity, and drug development - lessons from cryptococcus neoformans

Many pathogenic microbes, including many fungi, produce phospholipases which facilitate survival of the pathogen in vivo, invasion and dissemination throughout the host, expression of virulence traits and evasion of host immune defense mechanisms. These phospholipases are either secreted or produced intracellularly and act by physically disrupting host membranes, and/or by affecting fungal cell signaling and production of immunomodulatory effectors. Many of the secreted phospholipases acquire a glycosylphosphatidylinositol sorting motif to facilitate membrane and/or cell wall association and secretion. This review focuses primarily on the role of two members of the phospholipase enzyme family, phospholipase B (Plb) and phosphatidylinositol (PI)-specific phospholipase C (PI-C/Plc), in fungal pathogenesis and in particular, what has been learnt about their function from studies performed in the model pathogenic yeast, Cryptococcus neoformans. These studies have revealed how Plb has adapted to become an important part of the virulence repertoire of pathogenic fungi and how its secretion is regulated. They have also provided valuable insight into how the intracellular enzyme, Plc1, contributes to fungal fitness and pathogenicity – via a putative role in signal transduction pathways that regulate the production of stress-protecting pigments, polysaccharide capsule, cell wall integrity, and adaptation to growth at host temperature. Finally, this review will address the role fungal phospholipases have played in the development of a new class of antifungal drugs, which mimic their phospholipid substrates.

The Key Events Dose-Response Framework: its potential for application to foodborne pathogenic microorganisms

The Key Events Dose-Response Framework (KEDRF) is an analytical approach that facilitates the use of currently available data to gain insight regarding dose-response relationships. The use of the KEDRF also helps identify critical knowledge gaps that once filled, will reduce reliance on assumptions. The present study considers how the KEDRF might be applied to pathogenic microorganisms, using fetal listeriosis resulting from maternal ingestion of food contaminated with L. monocytogenes as an initial example. Major biological events along the pathway between food ingestion and the endpoint of concern are systematically considered with regard to dose (i.e., number of organisms), pathogen factors (e.g., virulence), and protective host mechanisms (e.g., immune response or other homeostatic mechanisms). It is concluded that the KEDRF provides a useful structure for systematically evaluating the complex array of host and pathogen factors that influence the dose-response relationship. In particular, the KEDRF supports efforts to specify and quantify the sources of variability, a prerequisite to strengthening the scientific basis for food safety decision making.

The ability of Listeria monocytogenes PI-PLC to facilitate escape from the macrophage phagosome is dependent on host PKCbeta

Listeria monocytogenes are facultative intracellular pathogenic bacteria that can infect macrophages as well as non-professional phagocytes. After entry in the host cell, the bacteria escape from the phagosome into the cytoplasm. In murine macrophages and in cell lines derived from these cells, escape of L. monocytogenes from the phagosome is absolutely dependent on listeriolysin O (LLO) and facilitated by a secreted phosphatidylinositol-specific phospholipase C (PI-PLC). Work in this laboratory has previously demonstrated a LLO and PI-PLC-dependent translocation of host PKCbeta isoforms. Pharmacological inhibition of PKCbeta resulted in a significant reduction in permeabilization of the phagosome, and in the number of bacteria reaching the cytosol. These findings led to the prediction that the bacterial PI-PLC promotes escape through the production of diacylglycerol leading to the activation of host PKCbeta. To test this hypothesis, bone marrow-derived macrophages (BMMf) obtained from PKCbeta knockout (PKCbetaKO) or C57Bl/6 mice were infected with L. monocytogenes. We observed that wild-type L. monocytogenes escapes from the phagosome of PKCbetaKO BMMf as well as from C57Bl/6 BMMf. However, in PKCbetaKO BMMf, L. monocytogenes uses a PI-PLC-independent, but phosphatidylcholine-preferring PLC (PC-PLC)-dependent pathway to facilitate escape. These findings strongly support the hypothesis that PI-PLC promotes escape through mobilization of host PKCbeta.

Tools for functional postgenomic analysis of listeria monocytogenes

We describe the development of genetic tools for regulated gene expression, the introduction of chromosomal mutations, and improved plasmid transfer by electroporation in the food-borne pathogen Listeria monocytogenes. pIMK, a kanamycin-resistant, site-specific, integrative listeriophage vector was constructed and then modified for overexpression (pIMK2) or for isopropyl-beta-d-thiogalactopyranoside (IPTG)-regulated expression (pIMK3 and pIMK4). The dynamic range of promoters was assessed by determining luciferase activity, P60 secretion, and internalin A-mediated invasion. These analyses demonstrated that pIMK4 and pIMK3 have a stringently controlled dynamic range of 540-fold. Stable gene overexpression was achieved with pIMK2, giving a range of expression for the three vectors of 1,350-fold. The lactococcal pORI280 system was optimized for the generation of chromosomal mutations and used to create five new prfA star mutants. The combination of pIMK4 and pORI280 allowed streamlined creation of "IPTG-dependent" mutants. This was exemplified by creation of a clean deletion mutant with deletion of the universally essential secA gene, and this mutant exhibited a rapid loss of viability upon withdrawal of IPTG. We also improved plasmid transfer by electroporation into three commonly used laboratory strains of L. monocytogenes. A 125-fold increase in transformation efficiency for EGDe compared with the widely used protocol of Park and Stewart (S. F. Park and G. S. Stewart, Gene 94:129-132, 1990) was observed. Maximal transformation efficiencies of 5.7 x 10(6) and 6.7 x 10(6) CFU per mug were achieved for EGDe and 10403S, respectively, with a replicating plasmid. An efficiency of 2 x 10(7) CFU per mug is the highest efficiency reported thus far for L. monocytogenes F2365.

Bacillus anthracis: interactions with the host and establishment of inhalational anthrax

Due to its potential as a bioweapon, Bacillus anthracis has received a great deal of attention in recent years, and a significant effort has been devoted to understanding how this organism causes anthrax. There has been a particular focus on the inhalational form of the disease, and studies over the past several years have painted an increasingly complex picture of how B. anthracis enters the mammalian host, survives the host's defense mechanisms, disseminates throughout the body and causes death. This article reviews recent advances in these areas, with a focus on how the bacterium interacts with its host in establishing infection and causing anthrax.