Very Early Blood Diffusion of the Active Lethal and Edema Factors of Bacillus anthracis After Intranasal Infection

Early Circulating Edema Factor in Inhalational Anthrax Infection: Does It Matter?

Anthrax toxins are critical virulence factors of Bacillus anthracis and Bacillus cereus strains that cause anthrax-like disease, composed of a common binding factor, the protective antigen (PA), and two enzymatic proteins, lethal factor (LF) and edema factor (EF). While PA is required for endocytosis and activity of EF and LF, several studies showed that these enzymatic factors disseminate within the body in the absence of PA after intranasal infection. In an effort to understand the impact of EF in the absence of PA, we used a fluorescent EF chimera to facilitate the study of endocytosis in different cell lines. Unexpectedly, EF was found inside cells in the absence of PA and showed a pole-dependent endocytosis. However, looking at enzymatic activity, PA was still required for EF to induce an increase in intracellular cAMP levels. Interestingly, the sequential delivery of EF and then PA rescued the rise in cAMP levels, indicating that PA and EF may functionally associate during intracellular trafficking, as well as it did at the cell surface. Our data shed new light on EF trafficking and the potential location of PA and EF association for optimal cytosolic delivery.

Bacillus anthracis, "la maladie du charbon", Toxins, and Institut Pasteur

Institut Pasteur and Bacillus anthracis have enjoyed a relationship lasting almost 120 years, starting from its foundation and the pioneering work of Louis Pasteur in the nascent fields of microbiology and vaccination, and blooming after 1986 following the molecular biology/genetic revolution. This contribution will give a historical overview of these two research eras, taking advantage of the archives conserved at Institut Pasteur. The first era mainly focused on the production, characterisation, surveillance and improvement of veterinary anthrax vaccines; the concepts and technologies with which to reach a deep understanding of this research field were not yet available. The second period saw a new era of B. anthracis research at Institut Pasteur, with the anthrax laboratory developing a multi-disciplinary approach, ranging from structural analysis, biochemistry, genetic expression, and regulation to bacterial-host cell interactions, in vivo pathogenicity, and therapy development; this led to the comprehensive unravelling of many facets of this toxi-infection. B. anthracis may exemplify some general points on how science is performed in a given society at a given time and how a scientific research domain evolves. A striking illustration can be seen in the additive layers of regulations that were implemented from the beginning of the 21st century and their impact on B. anthracis research. B. anthracis and anthrax are complex systems that raise many valuable questions regarding basic research. One may hope that B. anthracis research will be re-initiated under favourable circumstances later at Institut Pasteur.

Early expression of capsule during Bacillus anthracis germination

Bacillus anthracis is a spore-forming bacterium that produces two major virulence factors, a tripartite toxin with two enzymatic toxic activities and a pseudo-proteic capsule. One of the main described functions of the poly-gamma-d-glutamate capsule is to enable B. anthracis bacilli to escape phagocytosis. Thus, kinetics of expression of the capsule filaments at the surface of the emerging bacillus during germination is an important step for the protection of the nascent bacilli. In this study, through immunofluorescence and electron microscopic approaches, we show the emergence of the capsule through a significant surface of the exosporium in the vast majority of the germinating spores, with co-detection of BclA and capsular material. This suggests that, due to an early capsule expression, the extracellular life of B. anthracis might occur earlier than previously thought, once germination is triggered. This raises the prospect that an anti-capsular vaccine may play a protective role at the initial stage of infection by opsonisation of the nascent encapsulated bacilli before their emergence from the exosporium.

Assessment of calcium hypochlorite for Bacillus anthracis spore surface's decontamination

Contamination with microorganisms occurs in laboratories but is also of high concern in the context of bioterrorism. Decontamination is a cornerstone that promotes good laboratory practices and occupational health and safety. Among the most resistant structures formed by microorganisms are spores, produced notably by Clostridium and Bacillus species. Here, we compared six products containing four different molecules (hydrogen peroxide, peracetic acid, sodium and calcium hypochlorite) on B. anthracis Sterne spores. We first selected the most efficient product based on its activity against spore suspensions using French and European standards. Four products showed sporicidal activity, of which only two did so in a time frame consistent with good laboratory practices. Then, we tested one of these two products under laboratory conditions on fully virulent B. anthracis spores, during common use and after contamination through a spill of a highly concentrated spore suspension. We, thus, robustly validated a decontaminant based on calcium hypochlorite not only on its ability to kill spores but also on its effectiveness under laboratory conditions. At the end, we were able to assure a complete disinfection in 1 min after spillover and in 2 min for common use.

Convergent evolution of diverse Bacillus anthracis outbreak strains toward altered surface oligosaccharides that modulate anthrax pathogenesis

Bacillus anthracis, a spore-forming gram-positive bacterium, causes anthrax. The external surface of the exosporium is coated with glycosylated proteins. The sugar additions are capped with the unique monosaccharide anthrose. The West African Group (WAG) B. anthracis have mutations rendering them anthrose deficient. Through genome sequencing, we identified 2 different large chromosomal deletions within the anthrose biosynthetic operon of B. anthracis strains from Chile and Poland. In silico analysis identified an anthrose-deficient strain in the anthrax outbreak among European heroin users. Anthrose-deficient strains are no longer restricted to West Africa so the role of anthrose in physiology and pathogenesis was investigated in B. anthracis Sterne. Loss of anthrose delayed spore germination and enhanced sporulation. Spores without anthrose were phagocytized at higher rates than spores with anthrose, indicating that anthrose may serve an antiphagocytic function on the spore surface. The anthrose mutant had half the LD50 and decreased time to death (TTD) of wild type and complement B. anthracis Sterne in the A/J mouse model. Following infection, anthrose mutant bacteria were more abundant in the spleen, indicating enhanced dissemination of Sterne anthrose mutant. At low sample sizes in the A/J mouse model, the mortality of ΔantC-infected mice challenged by intranasal or subcutaneous routes was 20% greater than wild type. Competitive index (CI) studies indicated that spores without anthrose disseminated to organs more extensively than a complemented mutant. Death process modeling using mouse mortality dynamics suggested that larger sample sizes would lead to significantly higher deaths in anthrose-negative infected animals. The model was tested by infecting Galleria mellonella with spores and confirmed the anthrose mutant was significantly more lethal. Vaccination studies in the A/J mouse model showed that the human vaccine protected against high-dose challenges of the nonencapsulated Sterne-based anthrose mutant. This work begins to identify the physiologic and pathogenic consequences of convergent anthrose mutations in B. anthracis.

Anthrax Toxin Detection: From In Vivo Studies to Diagnostic Applications

Anthrax toxins are produced by Bacillus anthracis throughout infection and shape the physiopathogenesis of the disease. They are produced in low quantities but are highly efficient. They have thus been long ignored, but recent biochemical methods have improved our knowledge in animal models. This article reviews the various methods that have been used and how they could be applied to clinical diagnosis.

Case Report of an Injectional Anthrax in France, 2012

(1) Background: Bacillus anthracis is a spore-forming, Gram-positive bacterium causing anthrax, a zoonosis affecting mainly livestock. When occasionally infecting humans, B. anthracis provokes three different clinical forms: cutaneous, digestive and inhalational anthrax. More recently, an injectional anthrax form has been described in intravenous drug users. (2) Case presentation: We report here the clinical and microbiological features, as well as the strain phylogenetic analysis, of the only injectional anthrax case observed in France so far. A 27-year-old patient presented a massive dermohypodermatitis with an extensive edema of the right arm, and the development of drug-resistant shocks. After three weeks in an intensive care unit, the patient recovered, but the microbiological identification of B. anthracis was achieved after a long delay. (3) Conclusions: Anthrax diagnostic may be difficult clinically and microbiologically. The phylogenetic analysis of the Bacillus anthracis strain PF1 confirmed its relatedness to the injectional anthrax European outbreak group-II.