Characterization of Bacillus cereus isolates associated with fatal pneumonias: strains are closely related to Bacillus anthracis and harbor B. anthracis virulence genes

Expression and contribution to virulence of each polysaccharide capsule of Bacillus cereus strain G9241

Bacillus cereus strain G9241 was isolated from a patient with pneumonia who had an anthrax-like illness. Like Bacillus anthracis, the virulence of G9241 is dependent on two large plasmids. In G9241 those plasmids are pBCXO1 and pBC210. There is a multi-gene capsule locus on each of these virulence plasmids, and both capsules are produced by G9241 in vitro and in mice. The hasACB operon on pBCXO1 is responsible for production of a hyaluronic acid (HA) capsule. The locus on pBC210 encodes a putative tetrasaccharide (TS) capsule that assembles in a Wzy-dependent manner. We found that the pBC210 capsule locus is transcribed as two operons and identified the promoter regions responsible for transcription. We constructed isogenic mutants to assess the role of genes in the two TS capsule operons in production of the capsule. Spores of strains deficient in production of either the HA or TS capsule were inoculated subcutaneously or intranasally into A/J and C57BL/6 mice to determine the lethal dose 50% of each bacterial mutant by each route of infection. The loss of the HA capsule attenuated G9241 more than the loss of the TS capsule for both infection routes in both mouse strains. Overall, our data further characterize the unique TS capsule on pBC210 and demonstrate that the two capsules do not have the same impact on virulence of G9241.

Genomic Characterization and Copy Number Variation of Bacillus anthracis Plasmids pXO1 and pXO2 in a Historical Collection of 412 Strains

Bacillus anthracis microorganisms are of historical and epidemiological importance and are among the most homogenous bacterial groups known, even though the B. anthracis genome is rich in mobile elements. Mobile elements can trigger the diversification of lineages; therefore, characterizing the extent of genomic variation in a large collection of strains is critical for a complete understanding of the diversity and evolution of the species. Here, we sequenced a large collection of B. anthracis strains (>400) that were recovered from human, animal, and environmental sources around the world. Our results confirmed the remarkable stability of gene content and synteny of the anthrax plasmids and revealed no signal of plasmid exchange between B. anthracis and pathogenic B. cereus isolates but rather predominantly vertical descent. These findings advance our understanding of the biology and pathogenomic evolution of B. anthracis and its plasmids.

Bacillus anthracis plasmids pXO1 and pXO2 carry the main virulence factors responsible for anthrax. However, the extent of copy number variation within the species and how the plasmids are related to pXO1/pXO2-like plasmids in other species of the Bacillus cereussensu lato group remain unclear. To gain new insights into these issues, we sequenced 412 B. anthracis strains representing the total phylogenetic and ecological diversity of the species. Our results revealed that B. anthracis genomes carried, on average, 3.86 and 2.29 copies of pXO1 and pXO2, respectively, and also revealed a positive linear correlation between the copy numbers of pXO1 and pXO2. No correlation between the plasmid copy number and the phylogenetic relatedness of the strains was observed. However, genomes of strains isolated from animal tissues generally maintained a higher plasmid copy number than genomes of strains from environmental sources (P < 0.05 [Welch two-sample t test]). Comparisons against B. cereus genomes carrying complete or partial pXO1-like and pXO2-like plasmids showed that the plasmid-based phylogeny recapitulated that of the main chromosome, indicating limited plasmid horizontal transfer between or within these species. Comparisons of gene content revealed a closed pXO1 and pXO2 pangenome; e.g., plasmids encode <8 unique genes, on average, and a single large fragment deletion of pXO1 in one B. anthracis strain (2000031682) was detected. Collectively, our results provide a more complete view of the genomic diversity of B. anthracis plasmids, their copy number variation, and the virulence potential of other Bacillus species carrying pXO1/pXO2-like plasmids.

IMPORTANCEBacillus anthracis microorganisms are of historical and epidemiological importance and are among the most homogenous bacterial groups known, even though the B. anthracis genome is rich in mobile elements. Mobile elements can trigger the diversification of lineages; therefore, characterizing the extent of genomic variation in a large collection of strains is critical for a complete understanding of the diversity and evolution of the species. Here, we sequenced a large collection of B. anthracis strains (>400) that were recovered from human, animal, and environmental sources around the world. Our results confirmed the remarkable stability of gene content and synteny of the anthrax plasmids and revealed no signal of plasmid exchange between B. anthracis and pathogenic B. cereus isolates but rather predominantly vertical descent. These findings advance our understanding of the biology and pathogenomic evolution of B. anthracis and its plasmids.

Genes under positive selection in the core genome of pathogenic Bacillus cereus group members

In this comparative genomics study our aim was to unravel genes under positive selection in the core genome of the Bacillus cereus group. Indeed, the members of this group share close genetic relationships but display a rather large phenotypic and ecological diversity, providing a unique opportunity for studying how genomic changes reflect ecological adaptation during the divergence of a bacterial group. For this purpose, we screened ten completely sequenced genomes of four pathogenic Bacillus species, finding that 254 out of 3093 genes have codon sites with d_N/d_S (ω) values above one. These results remained unchanged after having disentangled the confounding effects of recombination and selection signature in a Bayesian framework. The presumably adaptive nucleotide polymorphisms are distributed over a wide range of biological functions, such as antibiotic resistance, DNA repair, nutrient uptake, metabolism, cell wall assembly and spore structure. Our results indicate that adaptation to animal hosts, whether as pathogens, saprophytes or symbionts, is the major driving force in the evolution of the Bacillus cereus group. Future work should seek to understand the evolutionary dynamics of both core and accessory genes in an integrative framework to ultimately unravel the key networks involved in host adaptation.

Pathogenicity, population genetics and dissemination of Bacillus anthracis

Bacillus anthracis, the etiological agent of anthrax, procures its particular virulence by a capsule and two AB type toxins: the lethal factor LF and the edema factor EF. These toxins primarily disable immune cells. Both toxins are translocated to the host cell by the adhesin-internalin subunit called protective antigen PA. PA enables LF to reach intra-luminal vesicles, where it remains active for long periods. Subsequently, LF translocates to non-infected cells, leading to inefficient late therapy of anthrax. B. anthracis undergoes slow evolution because it alternates between vegetative and long spore phases. Full genome sequence analysis of a large number of worldwide strains resulted in a robust evolutionary reconstruction of this bacterium, showing that B. anthracis is split in three main clades: A, B and C. Clade A efficiently disseminated worldwide underpinned by human activities including heavy intercontinental trade of goat and sheep hair. Subclade A.Br.WNA, which is widespread in the Northern American continent, is estimated to have split from clade A reaching the Northern American continent in the late Pleistocene epoch via the former Bering Land Bridge and further spread from Northwest southwards. An alternative hypothesis is that subclade A.Br.WNA. evolved from clade A.Br.TEA tracing it back to strains from Northern France that were assumingly dispatched by European explorers that settled along the St. Lawrence River. Clade B established mostly in Europe along the alpine axis where it evolved in association with local cattle breeds and hence displays specific geographic subclusters. Sequencing technologies are also used for forensic applications to trace unintended or criminal acts of release of B. anthracis. Under natural conditions, B. anthracis generally affects domesticated and wild ruminants in arid ecosystems. The more recently discovered B. cereus biovar anthracis spreads in tropical forests, where it threatens particularly endangered primate populations.

Certhrax Is an Antivirulence Factor for the Anthrax-Like Organism Bacillus cereus Strain G9241

Bacillus cereus G9241 caused a life-threatening anthrax-like lung infection in a previously healthy human. This strain harbors two large virulence plasmids, pBCXO1 and pBC210, that are absent from typical B. cereus isolates. The pBCXO1 plasmid is nearly identical to pXO1 from Bacillus anthracis and carries genes (pagA1, lef, and cya) for anthrax toxin components (protective antigen [called PA1 in G9241], lethal factor [LF], and edema factor [EF], respectively). The plasmid also has an intact hyaluronic acid capsule locus. The pBC210 plasmid has a tetrasaccharide capsule locus, a gene for a PA1 homolog called PA2 (pagA2), and a gene (cer) for Certhrax, an ADP-ribosyltransferase toxin that inactivates vinculin. LF, EF, and Certhrax require PA for entry into cells. In this study, we asked what role PA1, PA2, LF, and Certhrax play in the pathogenicity of G9241. To answer this, we generated isogenic deletion mutations in the targeted toxin gene components and then assessed the strains for virulence in highly G9241-susceptible (A/J) and moderately G9241-sensitive (C57BL/6) mice. We found that full virulence of G9241 required PA1 and LF, while PA2 contributed minimally to pathogenesis of G9241 but could not functionally replace PA1 as a toxin-binding subunit in vivo Surprisingly, we discovered that Certhrax attenuated the virulence of G9241; i.e., a Δcer Δlef mutant strain was more virulent than a Δlef mutant strain following subcutaneous inoculation of A/J mice. Moreover, the enzymatic activity of Certhrax contributed to this phenotype. We concluded that Certhrax acts as an antivirulence factor in the anthrax-like organism B. cereus G9241.

Discovery and Biochemical Characterization of PlyP56, PlyN74, and PlyTB40-Bacillus Specific Endolysins

Three Bacillus bacteriophage-derived endolysins, designated PlyP56, PlyN74, and PlyTB40, were identified, cloned, purified, and characterized for their antimicrobial properties. Sequence alignment reveals these endolysins have an N-terminal enzymatically active domain (EAD) linked to a C-terminal cell wall binding domain (CBD). PlyP56 has a Peptidase_M15_4/VanY superfamily EAD with a conserved metal binding motif and displays biological dependence on divalent ions for activity. In contrast, PlyN74 and PlyTB40 have T7 lysozyme-type Amidase_2 and carboxypeptidase T-type Amidase_3 EADs, respectively, which are members of the MurNAc-LAA superfamily, but are not homologs and thus do not have a shared protein fold. All three endolysins contain similar SH3-family CBDs. Although minor host range differences were noted, all three endolysins show relatively broad antimicrobial activity against members of the Bacillus cereus sensu lato group with the highest lytic activity against B. cereus ATCC 4342. Characterization studies determined the optimal lytic activity for these enzymes was at physiological pH (pH 7.0–8.0), over a broad temperature range (4–55 °C), and at low concentrations of NaCl (<50 mM). Direct comparison of lytic activity shows the PlyP56 enzyme to be twice as effective at lysing the cell wall peptidoglycan as PlyN74 or PlyTB40, suggesting PlyP56 is a good candidate for further antimicrobial development as well as bioengineering studies.

Sensitive and Specific Recombinase Polymerase Amplification Assays for Fast Screening, Detection, and Identification of Bacillus anthracis in a Field Setting

Four isothermal recombinase polymerase amplification (RPA) assays were developed for fast in-field identification of Bacillus anthracis The RPA assays targeted three specific sequences (i.e., the BA_5345 chromosomal marker, the lethal factor lef [from pXO1], and the capsule-biosynthesis-related capA [from pXO2]) and a conserved sequence in the adenylate cyclase gene (adk) for the Bacillus cereus group. B. anthracis-specific RPA assays were tested first with purified genomic DNAs (n = 60), including 11 representatives of B. anthracis, and then with soil (n = 8) and white powder (n = 8) samples spiked with inactivated B. anthracis spores and/or other biological agents. The RPA assays were also tested in another laboratory facility, which blindly provided DNA and lysate samples (n = 30, including 20 B. anthracis strains). RPA assays displayed 100% specificity and sensitivity. The hands-off turnaround times at 42°C ranged from 5 to 6 min for 10² genomic copies. The analytical sensitivity of each RPA assay was ∼10 molecules per reaction. In addition, the BA_5345 and adk RPA assays were assessed under field conditions with a series of surface swabs (n = 13, including 11 swabs contaminated with B. thuringiensis spores) that were blindly brought to the field laboratory by a chemical, biological, radiological, and nuclear (CBRN) sampling team. None of the 13 samples, except the control, tested positive for B. anthracis, and all samples that had been harvested from spore-contaminated surfaces tested positive with the adk RPA assay. All three B. anthracis-specific RPA assays proved suitable for rapid and reliable identification of B. anthracis and therefore could easily be used by first responders under field conditions to quickly discriminate between a deliberate release of B. anthracis spores and a hoax attack involving white powder.IMPORTANCE In recent decades, particularly following the 11 September 2001 and Amerithrax attacks, the world has experienced attempts to sow panic and chaos in society through thousands of white-powder copycats using household powders to mimic real bioterrorism attacks. In such circumstances, field-deployable detection methods are particularly needed to screen samples collected from the scene. The aim is to test the samples directly using a fast and reliable assay for detection of the presence of B. anthracis While this would not preclude further confirmatory tests from being performed in reference laboratories, it would bring useful, timely, and relevant information to local crisis managers and help them make appropriate decisions without having to wait for quantitative PCR results (with turnaround times of a few hours) or phenotypic identification and sequencing (with turnaround times of a few days). In the current investigation, we developed a set of isothermal RPA assays for the rapid screening and identification of B. anthracis in powders and soil samples, with the purpose of discriminating a deliberate release of B. anthracis spores from a hoax attack involving white powder; this would also apply to dispersion by spraying of aerosolized forms of B. anthracis Further work is now ongoing to confirm the first observations and validate the on-site use of these assays by first responders.

Assembly and Function of the Bacillus anthracis S-Layer

Bacillus anthracis, the anthrax agent, is a member of the Bacillus cereus sensu lato group, which includes invasive pathogens of mammals or insects as well as nonpathogenic environmental strains. The genes for anthrax pathogenesis are located on two large virulence plasmids. Similar virulence plasmids have been acquired by other B. cereus strains and enable the pathogenesis of anthrax-like diseases. Among the virulence factors of B. anthracis is the S-layer-associated protein BslA, which endows bacilli with invasive attributes for mammalian hosts. BslA surface display and function are dependent on the bacterial S-layer, whose constituents assemble by binding to the secondary cell wall polysaccharide (SCWP) via S-layer homology (SLH) domains. B. anthracis and other pathogenic B. cereus isolates harbor genes for the secretion of S-layer proteins, for S-layer assembly, and for synthesis of the SCWP. We review here recent insights into the assembly and function of the S-layer and the SCWP.

Bacillus anthracis gamma phage lysis among soil bacteria: an update on test specificity

BACKGROUND

Bacillus anthracis, which causes anthrax in humans and animals, is enzootic in parts of the U.S. state of Texas where cases are typically reported in animals annually. The gamma phage lysis assay is a common diagnostic method for identification of B. anthracis and is based on the bacterium's susceptibility to lysis. This test has been shown to be 97% specific for B. anthracis, as a small number of strains of other Bacillus spp. are known to be susceptible. In this study, we evaluated the performance of a combination of B. anthracis diagnostic assays on 700 aerobic, spore-forming isolates recovered from soil collected in Texas. These assays include phenotypic descriptions, gamma phage susceptibility, and real-time polymerase chain reaction specific for B. anthracis. Gamma phage-susceptible isolates were also tested using cell wall and capsule direct fluorescent-antibody assays specific for B. anthracis. Gamma phage-susceptible isolates that were ruled out as B. anthracis were identified by 16S rRNA gene sequencing.

FINDINGS

We identified 29 gamma phage-susceptible isolates. One was confirmed as B. anthracis, while the other 28 isolates were ruled out for B. anthracis by the other diagnostic tests. Using 16S rRNA gene sequencing results, we identified these isolates as members of the B. cereus group, Bacillus sp. (not within B. cereus group), Lysinibacillus spp., and Solibacillus silvestris. Based on these results, we report a specificity of 96% for gamma phage lysis as a diagnostic test for B. anthracis, and identified susceptible isolates outside the Bacillus genus.

CONCLUSIONS

In this study we found gamma phage susceptibility to be consistent with previously reported results. However, we identified non-B. anthracis environmental isolates (including isolates from genera other than Bacillus) that are susceptible to gamma phage lysis. To date, susceptibility to gamma phage lysis has not been reported in genera other than Bacillus. Though these isolates are not of clinical origin, description of unexpected positives is important, especially as new diagnostic assays for B. anthracis are being developed based on gamma phage lysis or gamma phage proteins.

Incorporating germination-induction into decontamination strategies for bacterial spores

Bacterial spores resist environmental extremes and protect key spore macromolecules until more supportive conditions arise. Spores germinate upon sensing specific molecules, such as nutrients. Germination is regulated by specialized mechanisms or structural features of the spore that limit contact with germinants and enzymes that regulate germination. Importantly, germination renders spores more susceptible to inactivating processes such as heat, desiccation, and ultraviolet radiation, to which they are normally refractory. Thus, germination can be intentionally induced through a process called germination-induction and subsequent treatment of these germinated spores with common disinfectants or gentle heat will inactivate them. However, while the principle of germination-induction has been shown effective in the laboratory, this strategy has not yet been fully implemented in real-word scenarios. Here, we briefly review the mechanisms of bacterial spore germination and discuss the evolution of germination-induction as a decontamination strategy. Finally, we examine progress towards implementing germination-induction in three contexts: biodefense, hospital settings and food manufacture.

SIGNIFICANCE AND IMPACT

This article reviews implementation of germination-induction as part of a decontamination strategy for the cleanup of bacterial spores. To our knowledge this is the first time that germination-induction studies have been reviewed in this context. This article will provide a resource which summarizes the mechanisms of germination in Clostridia and Bacillus species, challenges and successes in germination-induction, and potential areas where this strategy may be implemented.

The use of loop-mediated isothermal DNA amplification for the detection and identification of the anthrax pathogen

The results of detection and identification of Bacillus anthracis strains in loop-mediated isothermal DNA amplification (LAMP) reaction performed under optimized conditions with original primers and thermostable DNA polymerase are presented. Reproducible LAMP-based detection of chromosomal and plasmid DNA targets specific for B. anthracis strains has been demonstrated. No cross reactions with DNA from bacterial strains of other species of the B. cereus group were detected. The development of tests for anthrax-pathogen detection based on the optimized reaction of loop isothermal DNA amplification is planned. These tests will be convenient for clinical studies and field diagnostics due to the absence of requirements for sophisticated equipment.

Structural and immunochemical relatedness suggests a conserved pathogenicity motif for secondary cell wall polysaccharides in Bacillus anthracis and infection-associated Bacillus cereus

Bacillus anthracis (Ba) and human infection-associated Bacillus cereus (Bc) strains Bc G9241 and Bc 03BB87 have secondary cell wall polysaccharides (SCWPs) comprising an aminoglycosyl trisaccharide repeat: →4)-β-d-ManpNAc-(1→4)-β-d-GlcpNAc-(1→6)-α-d-GlcpNAc-(1→, substituted at GlcNAc residues with both α- and β-Galp. In Bc G9241 and Bc 03BB87, an additional α-Galp is attached to O-3 of ManNAc. Using NMR spectroscopy, mass spectrometry and immunochemical methods, we compared these structures to SCWPs from Bc biovar anthracis strains isolated from great apes displaying “anthrax-like” symptoms in Cameroon (Bc CA) and Côte d’Ivoire (Bc CI). The SCWPs of Bc CA/CI contained the identical HexNAc trisaccharide backbone and Gal modifications found in Ba, together with the α-Gal-(1→3) substitution observed previously at ManNAc residues only in Bc G9241/03BB87. Interestingly, the great ape derived strains displayed a unique α-Gal-(1→3)-α-Gal-(1→3) disaccharide substitution at some ManNAc residues, a modification not found in any previously examined Ba or Bc strain. Immuno-analysis with specific polyclonal anti-Ba SCWP antiserum demonstrated a reactivity hierarchy: high reactivity with SCWPs from Ba 7702 and Ba Sterne 34F2, and Bc G9241 and Bc 03BB87; intermediate reactivity with SCWPs from Bc CI/CA; and low reactivity with the SCWPs from structurally distinct Ba CDC684 (a unique strain producing an SCWP lacking all Gal substitutions) and non-infection-associated Bc ATCC10987 and Bc 14579 SCWPs. Ba-specific monoclonal antibody EAII-6G6-2-3 demonstrated a 10–20 fold reduced reactivity to Bc G9241 and Bc 03BB87 SCWPs compared to Ba 7702/34F2, and low/undetectable reactivity to SCWPs from Bc CI, Bc CA, Ba CDC684, and non-infection-associated Bc strains. Our data indicate that the HexNAc motif is conserved among infection-associated Ba and Bc isolates (regardless of human or great ape origin), and that the number, positions and structures of Gal substitutions confer unique antigenic properties. The conservation of this structural motif could open a new diagnostic route in detection of pathogenic Bc strains.

Rapid Detection of Bacillus anthracis Bloodstream Infections by Use of a Novel Assay in the GeneXpert System

Bacillus anthracis is a tier 1 select agent with the potential to quickly cause severe disease. Rapid identification of this pathogen may accelerate treatment and reduce mortality in the event of a bioterrorism attack. We developed a rapid and sensitive assay to detect B. anthracis bacteremia using a system that is suitable for point-of-care testing. A filter-based cartridge that included both sample processing and PCR amplification functions was loaded with all reagents needed for sample processing and multiplex nested PCR. The assay limit of detection (LOD) and dynamic range were determined by spiking B. anthracis DNA into individual PCR mixtures and B. anthracis CFU into human blood. One-milliliter blood samples were added to the filter-based detection cartridge and tested for B. anthracis on a GeneXpert instrument. Assay specificity was determined by testing blood spiked with non-anthrax bacterial isolates or by testing blood samples drawn from patients with concurrent non-B. anthracis bacteremia or nonbacteremic controls. The assay LODs were 5 genome equivalents per reaction and 10 CFU/ml blood for both the B. anthracis Sterne and V1B strains. There was a 6-log₁₀ dynamic range. Assay specificity was 100% for tests of non-B. anthracis bacterial isolates and patient blood samples. Assay time was less than 90 min. This automated system suitable for point-of-care detection rapidly identifies B. anthracis directly from blood with high sensitivity. This assay might lead to early detection and more rapid therapy in the event of a bioterrorism attack.

Draft Genome Sequence of Bacillus cereus LA2007, a Human-Pathogenic Isolate Harboring Anthrax-Like Plasmids

We present the genome sequence of Bacillus cereus LA2007, a strain isolated in 2007 from a fatal pneumonia case in Louisiana. Sequence-based genome analysis revealed that LA2007 carries a plasmid highly similar to Bacillus anthracis pXO1, including the genes responsible for the production and regulation of anthrax toxin.

Identification of a Substrate-selective Exosite within the Metalloproteinase Anthrax Lethal Factor

The metalloproteinase anthrax lethal factor (LF) is secreted by Bacillus anthracis to promote disease virulence through disruption of host signaling pathways. LF is a highly specific protease, exclusively cleaving mitogen-activated protein kinase kinases (MKKs) and rodent NLRP1B (NACHT leucine-rich repeat and pyrin domain-containing protein 1B). How LF achieves such restricted substrate specificity is not understood. Previous studies have suggested the existence of an exosite interaction between LF and MKKs that promotes cleavage efficiency and specificity. Through a combination of in silico prediction and site-directed mutagenesis, we have mapped an exosite to a non-catalytic region of LF. Mutations within this site selectively impair proteolysis of full-length MKKs yet have no impact on cleavage of short peptide substrates. Although this region appears important for cleaving all LF protein substrates, we found that mutation of specific residues within the exosite differentially affects MKK and NLRP1B cleavage in vitro and in cultured cells. One residue in particular, Trp-271, is essential for cleavage of MKK3, MKK4, and MKK6 but dispensable for targeting of MEK1, MEK2, and NLRP1B. Analysis of chimeric substrates suggests that this residue interacts with the MKK catalytic domain. We found that LF-W271A blocked ERK phosphorylation and growth in a melanoma cell line, suggesting that it may provide a highly selective inhibitor of MEK1/2 for use as a cancer therapeutic. These findings provide insight into how a bacterial toxin functions to specifically impair host signaling pathways and suggest a general strategy for mapping protease exosite interactions.

Multi-functional nano silver: A novel disruptive and theranostic agent for pathogenic organisms in real-time

The present study was aimed at evaluating the fluorescence property, sporicidal potency against Bacillus and Clostridium endospores, and surface disinfecting ability of biogenic nano silver. The nano silver was synthesized using an actinobacterial cell-filtrate. The fluorescence property as well as imaging facilitator potency of this nano silver was verified adopting spectrofluorometer along with fluorescent and confocal laser scanning microscope wherein strong emission and bright green fluorescence, respectively, on the entire spore surface was observed. Subsequently, the endospores of B. subtilis, B. cereus, B. amyloliquefaciens, C. perfringens and C. difficile were treated with physical sporicides, chemical sporicides and nano silver, in which the nano silver brought about pronounced inhibition even at a very low concentration. Finally, the environmental surface-sanitizing potency of nano silver was investigated adopting cage co-contamination assay, wherein vital organs of mice exposed to the nano silver-treated cage did not show any signs of pathological lesions, thus signifying the ability of nano silver to completely disinfect the spore or reduce the count required for infection. Taken these observations together, we have shown the multi-functional biological properties of the nano silver, synthesized using an actinobacterial cell-filtrate, which could be of application in advanced diagnostics, biomedical engineering and therapeutics in the near future.

Bacillus cereus Biovar Anthracis Causing Anthrax in Sub-Saharan Africa-Chromosomal Monophyly and Broad Geographic Distribution

Through full genome analyses of four atypical Bacillus cereus isolates, designated B. cereus biovar anthracis, we describe a distinct clade within the B. cereus group that presents with anthrax-like disease, carrying virulence plasmids similar to those of classic Bacillus anthracis. We have isolated members of this clade from different mammals (wild chimpanzees, gorillas, an elephant and goats) in West and Central Africa (Côte d'Ivoire, Cameroon, Central African Republic and Democratic Republic of Congo). The isolates shared several phenotypic features of both B. anthracis and B. cereus, but differed amongst each other in motility and their resistance or sensitivity to penicillin. They all possessed the same mutation in the regulator gene plcR, different from the one found in B. anthracis, and in addition, carry genes which enable them to produce a second capsule composed of hyaluronic acid. Our findings show the existence of a discrete clade of the B. cereus group capable of causing anthrax-like disease, found in areas of high biodiversity, which are possibly also the origin of the worldwide distributed B. anthracis. Establishing the impact of these pathogenic bacteria on threatened wildlife species will require systematic investigation. Furthermore, the consumption of wildlife found dead by the local population and presence in a domestic animal reveal potential sources of exposure to humans.

Production of hemolysin BL by Bacillus cereus group isolates of dairy origin is associated with whole-genome phylogenetic clade

BACKGROUND

Bacillus cereus group isolates that produce diarrheal or emetic toxins are frequently isolated from raw milk and, in spore form, can survive pasteurization. Several species within the B. cereus group are closely related and cannot be reliably differentiated by established taxonomical criteria. While B. cereus is traditionally recognized as the principal causative agent of foodborne disease in this group, there is a need to better understand the distribution and expression of different toxin and virulence genes among B. cereus group food isolates to facilitate reliable characterization that allows for assessment of the likelihood of a given isolate to cause a foodborne disease.

RESULTS

We performed whole genome sequencing of 22 B. cereus group dairy isolates, which represented considerable genetic diversity not covered by other isolates characterized to date. Maximum likelihood analysis of these genomes along with 47 reference genomes representing eight validly published species revealed nine phylogenetic clades. Three of these clades were represented by a single species (B. toyonensis -clade V, B. weihenstephanensis - clade VI, B. cytotoxicus - VII), one by two dairy-associated isolates (clade II; representing a putative new species), one by two species (B. mycoides, B. pseudomycoides - clade I) and four by three species (B. cereus, B. thuringiensis, B. anthracis - clades III-a, b, c and IV). Homologues of genes encoding a principal diarrheal enterotoxin (hemolysin BL) were distributed across all, except the B. cytotoxicus clade. Using a lateral flow immunoassay, hemolysin BL was detected in 13 out of 18 isolates that carried hblACD genes. Isolates from clade III-c (which included B. cereus and B. thuringiensis) consistently did not carry hblACD and did not produce hemolysin BL. Isolates from clade IV (B. cereus, B. thuringiensis) consistently carried hblACD and produced hemolysin BL. Compared to others, clade IV was significantly (p = 0.0001) more likely to produce this toxin. Isolates from clade VI (B. weihenstephanensis) carried hblACD homologues, but did not produce hemolysin BL, possibly due to amino acid substitutions in different toxin-encoding genes.

CONCLUSIONS

Our results demonstrate that production of diarrheal enterotoxin hemolysin BL is neither inclusive nor exclusive to B. cereus sensu stricto, and that phylogenetic classification of isolates may be better than taxonomic identification for assessment of B. cereus group isolates risk for causing a diarrheal foodborne disease.

Discovery of a Unique Extracellular Polysaccharide in Members of the Pathogenic Bacillus That Can Co-form with Spores

An exopolysaccharide, produced during the late stage of stationary growth phase, was discovered and purified from the culture medium of Bacillus cereus, Bacillus anthracis, and Bacillus thuringiensis when strains were grown in a defined nutrient medium that induces biofilm. Two-dimensional NMR structural characterization of the polysaccharide, named pzX, revealed that it is composed of an unusual three amino-sugar sequence repeat of [-3)XylNAc4OAc(α1-3)GlcNAcA4OAc(α1-3)XylNAc(α1-]n The sugar residue XylNAc had never been described previously in any glycan structure. The XNAC operon that contains the genes for the assembly of pzX is also unique and so far has been identified only in members of the Bacillus cereus sensu lato group. Microscopic and biochemical analyses indicate that pzX co-forms during sporulation, so that upon the release of the spore to the extracellular milieu it becomes surrounded by pzX. The relative amounts of pzX produced can be manipulated by specific nutrients in the medium, but rich medium appears to suppress pzX formation. pzX has the following unique characteristics: a surfactant property that lowers surface tension, a cell/spore antiaggregant, and an adherence property that increases spores binding to surfaces. pzX in Bacillus could represent a trait shared by many spore-producing microorganisms. It suggests pzX is an active player in spore physiology and may provide new insights to the successful survival of the B. cereus species in natural environments or in the hosts.

Anthrax Toxin-Expressing Bacillus cereus Isolated from an Anthrax-Like Eschar

Bacillus cereus isolates have been described harboring Bacillus anthracis toxin genes, most notably B. cereus G9241, and capable of causing severe and fatal pneumonias. This report describes the characterization of a B. cereus isolate, BcFL2013, associated with a naturally occurring cutaneous lesion resembling an anthrax eschar. Similar to G9241, BcFL2013 is positive for the B. anthracis pXO1 toxin genes, has a multi-locus sequence type of 78, and a pagA sequence type of 9. Whole genome sequencing confirms the similarity to G9241. In addition to the chromosome having an average nucleotide identity of 99.98% when compared to G9241, BcFL2013 harbors three plasmids with varying homology to the G9241 plasmids (pBCXO1, pBC210 and pBFH_1). This is also the first report to include serologic testing of patient specimens associated with this type of B. cereus infection which resulted in the detection of anthrax lethal factor toxemia, a quantifiable serum antibody response to protective antigen (PA), and lethal toxin neutralization activity.

Animal Models for the Pathogenesis, Treatment, and Prevention of Infection by Bacillus anthracis

This article reviews the characteristics of the major animal models utilized for studies on Bacillus anthracis and highlights their contributions to understanding the pathogenesis and host responses to anthrax and its treatment and prevention. Advantages and drawbacks associated with each model, to include the major models (murine, guinea pig, rabbit, nonhuman primate, and rat), and other less frequently utilized models, are discussed. Although the three principal forms of anthrax are addressed, the main focus of this review is on models for inhalational anthrax. The selection of an animal model for study is often not straightforward and is dependent on the specific aims of the research or test. No single animal species provides complete equivalence to humans; however, each species, when used appropriately, can contribute to a more complete understanding of anthrax and its etiologic agent.

Plantazolicin is an ultra-narrow spectrum antibiotic that targets the Bacillus anthracis membrane

Plantazolicin (PZN) is a ribosomally synthesized and post-translationally modified natural product from Bacillus methylotrophicus FZB42 and Bacillus pumilus. Extensive tailoring to twelve of the fourteen amino acid residues in the mature natural product endows PZN with not only a rigid, polyheterocyclic structure, but also antibacterial activity. Here we report a remarkably discriminatory activity of PZN toward Bacillus anthracis, which rivals a previously-described gamma (γ) phage lysis assay in distinguishing B. anthracis from other members of the Bacillus cereus group. We evaluate the underlying cause of this selective activity by measuring the RNA expression profile of PZN-treated B. anthracis, which revealed significant upregulation of genes within the cell envelope stress response. PZN depolarizes the B. anthracis membrane like other cell envelope-acting compounds but uniquely localizes to distinct foci within the envelope. Selection and whole-genome sequencing of PZN-resistant mutants of B. anthracis implicate a relationship between the action of PZN and cardiolipin (CL) within the membrane. Exogenous CL increases the potency of PZN in wild type B. anthracis and promotes the incorporation of fluorescently tagged PZN in the cell envelope. We propose that PZN localizes to and exacerbates structurally compromised regions of the bacterial membrane, which ultimately results in cell lysis.

Cytotoxic Potential of Bacillus cereus Strains ATCC 11778 and 14579 Against Human Lung Epithelial Cells Under Microaerobic Growth Conditions

Bacillus cereus, a food poisoning bacterium closely related to Bacillus anthracis, secretes a multitude of virulence factors including enterotoxins, hemolysins, and phospholipases. However, the majority of the in vitro experiments evaluating the cytotoxic potential of B. cereus were carried out in the conditions of aeration, and the impact of the oxygen limitation in conditions encountered by the microbe in natural environment such as gastrointestinal tract remains poorly understood. This research reports comparative analysis of ATCC strains 11778 (BC1) and 14579 (BC2) in aerobic and microaerobic (static) cultures with regard to their toxicity for human lung epithelial cells. We showed that BC1 increased its toxicity upon oxygen limitation while BC2 was highly cytotoxic in both growth conditions. The combined effect of the pore-forming, cholesterol-dependent hemolysin, cereolysin O (CLO), and metabolic product(s) such as succinate produced in microaerobic conditions provided substantial contribution to the toxicity of BC1 but not BC2 which relied mainly on other toxins. This mechanism is shared between CB1 and B. anthracis. It involves the permeabilization of the cell membrane which facilitates transport of toxic bacterial metabolites into the cell. The toxicity of BC1 was potentiated in the presence of bovine serum albumin which appeared to serve as reservoir for bacteria-derived nitric oxide participating in the downstream production of reactive oxidizing species with the properties of peroxynitrite. In agreement with this the BC1 cultures demonstrated the increased oxidation of the indicator dye Amplex Red catalyzed by peroxidase as well as the increased toxicity in the presence of externally added ascorbic acid.

The Phylogeny of Bacillus cereus sensu lato

The three main species of the Bacillus cereus sensu lato , B. cereus , B. thuringiensis , and B. anthracis , were recognized and established by the early 1900s because they each exhibited distinct phenotypic traits. B. thuringiensis isolates and their parasporal crystal proteins have long been established as a natural pesticide and insect pathogen. B. anthracis , the etiological agent for anthrax, was used by Robert Koch in the 19th century as a model to develop the germ theory of disease, and B. cereus , a common soil organism, is also an occasional opportunistic pathogen of humans. In addition to these three historical species designations, are three less-recognized and -understood species: B. mycoides , B. weihenstephanensis , and B. pseudomycoides . All of these “species” combined comprise the Bacillus cereus sensu lato group. Despite these apparently clear phenotypic definitions, early molecular approaches to separate the first three by various DNA hybridization and 16S/23S ribosomal sequence analyses led to some “confusion” because there were limited differences to differentiate between these species. These and other results have led to frequent suggestions that a taxonomic change was warranted to reclassify this group to a single species. But the pathogenic properties of B. anthracis and the biopesticide applications of B. thuringiensis appear to “have outweighed pure taxonomic considerations” and the separate species categories are still being maintained. B. cereus sensu lato represents a classic example of a now common bacterial species taxonomic quandary.

Genomic insights into the taxonomic status of the Bacillus cereus group

The identification and phylogenetic relationships of bacteria within the Bacillus cereus group are controversial. This study aimed at determining the taxonomic affiliations of these strains using the whole-genome sequence-based Genome BLAST Distance Phylogeny (GBDP) approach. The GBDP analysis clearly separated 224 strains into 30 clusters, representing eleven known, partially merged species and accordingly 19–20 putative novel species. Additionally, 16S rRNA gene analysis, a novel variant of multi-locus sequence analysis (nMLSA) and screening of virulence genes were performed. The 16S rRNA gene sequence was not sufficient to differentiate the bacteria within this group due to its high conservation. The nMLSA results were consistent with GBDP. Moreover, a fast typing method was proposed using the pycA gene, and where necessary, the ccpA gene. The pXO plasmids and cry genes were widely distributed, suggesting little correlation with the phylogenetic positions of the host bacteria. This might explain why classifications based on virulence characteristics proved unsatisfactory in the past. In summary, this is the first large-scale and systematic study of the taxonomic status of the bacteria within the B. cereus group using whole-genome sequences, and is likely to contribute to further insights into their pathogenicity, phylogeny and adaptation to diverse environments.

Anthrax Pathogenesis

Anthrax is caused by the spore-forming, gram-positive bacterium Bacillus anthracis. The bacterium's major virulence factors are (a) the anthrax toxins and (b) an antiphagocytic polyglutamic capsule. These are encoded by two large plasmids, the former by pXO1 and the latter by pXO2. The expression of both is controlled by the bicarbonate-responsive transcriptional regulator, AtxA. The anthrax toxins are three polypeptides-protective antigen (PA), lethal factor (LF), and edema factor (EF)-that come together in binary combinations to form lethal toxin and edema toxin. PA binds to cellular receptors to translocate LF (a protease) and EF (an adenylate cyclase) into cells. The toxins alter cell signaling pathways in the host to interfere with innate immune responses in early stages of infection and to induce vascular collapse at late stages. This review focuses on the role of anthrax toxins in pathogenesis. Other virulence determinants, as well as vaccines and therapeutics, are briefly discussed.

Advances in Anthrax Detection: Overview of Bioprobes and Biosensors

Anthrax is an infectious disease caused by Bacillus anthracis. Although anthrax commonly affects domestic and wild animals, it causes a rare but lethal infection in humans. A variety of techniques have been introduced and evaluated to detect anthrax using cultures, polymerase chain reaction, and immunoassays to address the potential threat of anthrax being used as a bioweapon. The high-potential harm of anthrax in bioterrorism requires sensitive and specific detection systems that are rapid, field-ready, and real-time monitoring. Here, we provide a systematic overview of anthrax detection probes with their potential applications in various ultra-sensitive diagnostic systems.

Capsules, toxins and AtxA as virulence factors of emerging Bacillus cereus biovar anthracis

Emerging B. cereus strains that cause anthrax-like disease have been isolated in Cameroon (CA strain) and Côte d’Ivoire (CI strain). These strains are unusual, because their genomic characterisation shows that they belong to the B. cereus species, although they harbour two plasmids, pBCXO1 and pBCXO2, that are highly similar to the pXO1 and pXO2 plasmids of B. anthracis that encode the toxins and the polyglutamate capsule respectively. The virulence factors implicated in the pathogenicity of these B. cereus bv anthracis strains remain to be characterised. We tested their virulence by cutaneous and intranasal delivery in mice and guinea pigs; they were as virulent as wild-type B. anthracis. Unlike as described for pXO2-cured B. anthracis, the CA strain cured of the pBCXO2 plasmid was still highly virulent, showing the existence of other virulence factors. Indeed, these strains concomitantly expressed a hyaluronic acid (HA) capsule and the B. anthracis polyglutamate (PDGA) capsule. The HA capsule was encoded by the hasACB operon on pBCXO1, and its expression was regulated by the global transcription regulator AtxA, which controls anthrax toxins and PDGA capsule in B. anthracis. Thus, the HA and PDGA capsules and toxins were co-regulated by AtxA. We explored the respective effect of the virulence factors on colonisation and dissemination of CA within its host by constructing bioluminescent mutants. Expression of the HA capsule by itself led to local multiplication and, during intranasal infection, to local dissemination to the adjacent brain tissue. Co-expression of either toxins or PDGA capsule with HA capsule enabled systemic dissemination, thus providing a clear evolutionary advantage. Protection against infection by B. cereus bv anthracis required the same vaccination formulation as that used against B. anthracis. Thus, these strains, at the frontier between B. anthracis and B. cereus, provide insight into how the monomorphic B. anthracis may have emerged.

Anthrax is caused by the bacterium Bacillus anthracis that affects all mammals worldwide. It emerged more than 10,000 years ago from a Bacillus cereus precursor. In the past decade, B. cereus bacteria were isolated in the USA from anthrax-like pneumonia cases. They harbour one virulence plasmid very similar to the toxin–encoding plasmid of B. anthracis. Recently, an anthrax-like disease in great apes in Africa was caused by emerging B. cereus strains, named B. cereus biovar anthracis. These strains are atypical as they possess both plasmids coding for toxin and capsule similar to those so far found only in B. anthracis. These unusual pathogenic B. cereus are currently neglected. We explored the virulence of these pathogens and their colonisation and dissemination capacity within the murine host. We found that these toxinogenic strains harbour two capsules, the classical B. anthracis capsule and an additional polysaccharidic capsule. This latter capsule confers virulence alone or in combination with toxins. Both capsules are concomitantly expressed, under the control of a common global regulator and host signals. Our results show that acquisition of new genetic information by these B. cereus clearly gives them a selective advantage, favouring their dissemination within infected hosts and the environment.

Bacillus cereus from the environment is genetically related to the highly pathogenic B. cereus in Zambia

To follow-up anthrax in Zambia since the outbreak in 2011, we have collected samples from the environment and the carcasses of anthrax-suspected animals, and have tried to isolate Bacillus anthracis. In the process of identification of B. anthracis, we collected two isolates, of which colonies were similar to B. anthracis; however, from the results of identification using the molecular-based methods, two isolates were genetically related to the highly pathogenic B. cereus, of which clinical manifestation is severe and fatal (e.g., pneumonia). In this study, we showed the existence of bacteria suspected to be highly pathogenic B. cereus in Zambia, indicating the possibility of an outbreak caused by highly pathogenic B. cereus.

Multiplex PCR for species-level identification of Bacillus anthracis and detection of pXO1, pXO2, and related plasmids

The Bacillus anthracis virulence plasmids pXO1 and pXO2 have critical implications for biosafety and select agent status. The proper identification and characterization of B. anthracis and its plasmid profile is important to the biodefense research community. Multiplex PCR was used to simultaneously detect a B. anthracis-specific chromosomal mutation, 4 targets distributed across pXO1, 3 targets distributed across pXO2, and highly conserved regions of the 16S gene, allowing an internal positive control for each sample. The multiplex PCR can produce as many as 9 easily separable and distinguishable amplicons, ranging in size from 188 to 555 bp. The PCR results were used to characterize DNA samples extracted from B. anthracis, other Bacillus species, and other bacterial species from many different genera. With the exception of 2 novel putative plasmids discovered, testing against inclusion and extensive exclusion panels showed 100% correlation to previously published and expected results. Upon testing 29 previously unpublished B. anthracis strains, 10 (34.5%) were pXO1(+)/pXO2(+), 9 (31.0%) were pXO1(+)/pXO2(-), 7 (24.1%) were pXO1(-)/pXO2(+), and 3 (10.3%) were pXO1(-)/pXO2(-). The present work presents a novel 9-target multiplex PCR assay capable of species-level identification of B. anthracis via a unique chromosomal marker and the detection of pXO1 and pXO2 via multiply redundant targets on each.

A novel multiplex PCR discriminates Bacillus anthracis and its genetically related strains from other Bacillus cereus group species

Anthrax is an important zoonotic disease worldwide that is caused by Bacillus anthracis, a spore-forming pathogenic bacterium. A rapid and sensitive method to detect B. anthracis is important for anthrax risk management and control in animal cases to address public health issues. However, it has recently become difficult to identify B. anthracis by using previously reported molecular-based methods because of the emergence of B. cereus, which causes severe extra-intestinal infection, as well as the human pathogenic B. thuringiensis, both of which are genetically related to B. anthracis. The close genetic relation of chromosomal backgrounds has led to complexity of molecular-based diagnosis. In this study, we established a B. anthracis multiplex PCR that can screen for the presence of B. anthracis virulent plasmids and differentiate B. anthracis and its genetically related strains from other B. cereus group species. Six sets of primers targeting a chromosome of B. anthracis and B. anthracis-like strains, two virulent plasmids, pXO1 and pXO2, a bacterial gene, 16S rRNA gene, and a mammalian gene, actin-beta gene, were designed. The multiplex PCR detected approximately 3.0 CFU of B. anthracis DNA per PCR reaction and was sensitive to B. anthracis. The internal control primers also detected all bacterial and mammalian DNAs examined, indicating the practical applicability of this assay as it enables monitoring of appropriate amplification. The assay was also applied for detection of clinical strains genetically related to B. anthracis, which were B. cereus strains isolated from outbreaks of hospital infections in Japan, and field strains isolated in Zambia, and the assay differentiated B. anthracis and its genetically related strains from other B. cereus group strains. Taken together, the results indicate that the newly developed multiplex PCR is a sensitive and practical method for detecting B. anthracis.

Bacillus cereus in personal care products: risk to consumers

Bacillus cereus is ubiquitous in nature and thus occurs naturally in a wide range of raw materials and foodstuffs. B. cereus spores are resistant to desiccation and heat and able to survive dry storage and cooking. Vegetative cells produce several toxins which on ingestion in sufficient numbers can cause vomiting and/or diarrhoea depending on the toxins produced. Gastrointestinal disease is commonly associated with reheated or inadequately cooked foods. In addition to being a rare cause of several acute infections (e.g. pneumonia and septicaemia), B. cereus can also cause localized infection of post-surgical or trauma wounds and is a rare but significant pathogen of the eye where it may result in severe endophthalmitis often leading to loss of vision. Key risk factors in such cases are trauma to the eye and retained contaminated intraocular foreign bodies. In addition, rare cases of B. cereus-associated keratitis (inflammation of the cornea) have been linked to contact lens use. Bacillus cereus is therefore a microbial contaminant that could adversely affect product safety of cosmetic and facial toiletries and pose a threat to the user if other key risk factors are also present. The infective dose in the human eye is unknown, but as few as 100 cfu has been reported to initiate infection in a susceptible animal model. However, we are not aware of any reports in the literature of B. cereus infections in any body site linked with use of personal care products. Low levels of B. cereus spores may on occasion be present in near-eye cosmetics, and these products have been used by consumers for many years. In addition, exposure to B. cereus is more likely to occur through other routes (e.g. dustborne contamination) due to its ubiquity and resistance properties of spores. The organism has been recovered from the eyes of healthy individuals. Therefore, although there may be a perceived hazard, the risk of severe eye infections as a consequence of exposure through contaminated near-eye cosmetics is judged to be vanishingly small. It is unlikely that more stringent microbiological standards for near-eye cosmetics will have any impact on the risk of severe eye infections caused by B. cereus, as these are not linked to use of personal care products.

Anthrax: A disease of biowarfare and public health importance

Bioterrorism has received a lot of attention in the first decade of this century. Biological agents are considered attractive weapons for bioterrorism as these are easy to obtain, comparatively inexpensive to produce and exhibit widespread fear and panic than the actual potential of physical damage. Bacillus anthracis (B. anthracis), the etiologic agent of anthrax is a Gram positive, spore forming, non-motile bacterium. This is supposed to be one of the most potent BW agents because its spores are extremely resistant to natural conditions and can survive for several decades in the environment. B. anthracis spores enter the body through skin lesion (cutaneous anthrax), lungs (pulmonary anthrax), or gastrointestinal route (gastrointestinal anthrax) and germinate, giving rise to the vegetative form. Anthrax is a concern of public health also in many countries where agriculture is the main source of income including India. Anthrax has been associated with human history for a very long time and regained its popularity after Sept 2001 incidence in United States. The present review article describes the history, biology, life cycle, pathogenicity, virulence, epidemiology and potential of B. anthracis as biological weapon.

Finished Genome Sequence of Bacillus cereus Strain 03BB87, a Clinical Isolate with B. anthracis Virulence Genes

Bacillus cereus strain 03BB87, a blood culture isolate, originated in a 56-year-old male muller operator with a fatal case of pneumonia in 2003. Here we present the finished genome sequence of that pathogen, including a 5.46-Mb chromosome and two plasmids (209 and 52 Kb, respectively).

Characteristics and phylogeny of Bacillus cereus strains isolated from Maari, a traditional West African food condiment

Maari is a spontaneously fermented food condiment made from baobab tree seeds in West African countries. This type of product is considered to be safe, being consumed by millions of people on a daily basis. However, due to the spontaneous nature of the fermentation the human pathogen Bacillus cereus occasionally occurs in Maari. This study characterizes succession patterns and pathogenic potential of B. cereus isolated from the raw materials (ash, water from a drilled well (DW) and potash), seed mash throughout fermentation (0-96h), after steam cooking and sun drying (final product) from two production sites of Maari. Aerobic mesophilic bacterial (AMB) counts in raw materials were of 10(5)cfu/ml in DW, and ranged between 6.5×10(3) and 1.2×10(4)cfu/g in potash, 10(9)-10(10)cfu/g in seed mash during fermentation and 10(7) - 10(9) after sun drying. Fifty three out of total 290 AMB isolates were identified as B. cereus sensu lato by use of ITS-PCR and grouped into 3 groups using PCR fingerprinting based on Escherichia coli phage-M13 primer (M13-PCR). As determined by panC gene sequencing, the isolates of B. cereus belonged to PanC types III and IV with potential for high cytotoxicity. Phylogenetic analysis of concatenated sequences of glpF, gmk, ilvD, pta, pur, pycA and tpi revealed that the M13-PCR group 1 isolates were related to B. cereus biovar anthracis CI, while the M13-PCR group 2 isolates were identical to cereulide (emetic toxin) producing B. cereus strains. The M13-PCR group 1 isolates harboured poly-γ-D-glutamic acid capsule biosynthesis genes capA, capB and capC showing 99-100% identity with the environmental B. cereus isolate 03BB108. Presence of cesB of the cereulide synthetase gene cluster was confirmed by PCR in M13-PCR group 2 isolates. The B. cereus harbouring the cap genes were found in potash, DW, cooking water and at 8h fermentation. The "emetic" type B. cereus were present in DW, the seed mash at 48-72h of fermentation and in the final product, while the remaining isolates (PanC type IV) were detected in ash, at 48-72h fermentation and in the final product. This work sheds light on the succession and pathogenic potential of B. cereus species in traditional West African food condiment and clarifies their phylogenetic relatedness to B. cereus biovar anthracis. Future implementation of GMP and HACCP and development of starter cultures for controlled Maari fermentations will help to ensure a safe product.

Cytochrome c551 and the cytochrome c maturation pathway affect virulence gene expression in Bacillus cereus ATCC 14579

Loss of the cytochrome c maturation system in Bacillus cereus results in increased transcription of the major enterotoxin genes nhe, hbl, and cytK and the virulence regulator plcR. Increased virulence factor production occurs at 37°C under aerobic conditions, similar to previous findings in Bacillus anthracis. Unlike B. anthracis, much of the increased virulence gene expression can be attributed to loss of only c551, one of the two small c-type cytochromes. Additional virulence factor expression occurs with loss of resBC, encoding cytochrome c maturation proteins, independently of the presence of the c-type cytochrome genes. Hemolytic activity of strains missing either cccB or resBC is increased relative to that in the parental strain, while sporulation efficiency is unaffected in the mutants. Increased virulence gene expression in the ΔcccB and ΔresBC mutants occurs only in the presence of an intact plcR gene, indicating that this process is PlcR dependent. These findings suggest a new mode of regulation of B. cereus virulence and reveal intriguing similarities and differences in virulence regulation between B. cereus and B. anthracis.

Protein- and DNA-based anthrax toxin vaccines confer protection in guinea pigs against inhalational challenge with Bacillus cereus G9241

In the past decade, several Bacillus cereus strains have been isolated from otherwise healthy individuals who succumbed to bacterial pneumonia presenting symptoms resembling inhalational anthrax. One strain was indistinguishable from B. cereus G9241, previously cultured from an individual who survived a similar pneumonia-like illness and which was shown to possess a complete set of plasmid-borne anthrax toxin-encoding homologs. The finding that B. cereus G9241 pathogenesis in mice is dependent on pagA1-derived protective antigen (PA) synthesis suggests that an anthrax toxin-based vaccine may be effective against this toxin-encoding B. cereus strain. Dunkin Hartley guinea pigs were immunized with protein- and DNA-based anthrax toxin-based vaccines, immune responses were evaluated and survival rates were calculated after lethal aerosol exposure with B. cereus G9241 spores. Each vaccine induced seroconversion with the protein immunization regimen eliciting significantly higher serum levels of antigen-specific antibodies at the prechallenge time-point compared with the DNA-protein prime-boost immunization schedule. Complete protection against lethal challenge was observed in all groups with a detectable prechallenge serum titer of toxin neutralizing antibodies. For the first time, we demonstrated that the efficacy of fully defined anthrax toxin-based vaccines was protective against lethal B. cereus G9241 aerosol challenge in the guinea pig animal model.

Identification of pBC218/pBC210 Genes of Bacillus cereus G9241 in Five Florida Soils Using qPCR

The distribution of the virulent plasmid pBC210 of B. cereus that carries several B. anthracis genes and has been implicated in lethal anthrax-like pulmonary disease is unknown. We screened our collection of 103 B. cereus isolates and 256 soil samples using a quantitative PCR (qPCR) assay that targeted three open reading frames putatively unique to pBC210. When tested with DNA from 2 B. cereus strains carrying pBC210, and 64 Gram-positive and 55 Gram-negative bacterial species, the assay had 100% sensitivity and specificity. None of the DNA from the B. cereus isolates yielded positive amplicons but DNA extracted from five soils collected in Florida gave positive results for all three target sequences of pBC210. While screening confirms that pBC210 is uncommon in B. cereus, this study is the first to report that pBC210 is present in Florida soils. This study improves our knowledge of the distribution of pBC210 in soils and, of public health importance, the potential threat of B. cereus isolates carrying the toxin-carrying plasmid. We demonstrated that sequences of pBC210 can be found in a larger geographical area than previously thought and that finding more B. cereus carrying the virulent plasmid is a possibility in the future.

Bacillus anthracis-like bacteria and other B. cereus group members in a microbial community within the International Space Station: a challenge for rapid and easy molecular detection of virulent B. anthracis

For some microbial species, such as Bacillus anthracis, the etiologic agent of the disease anthrax, correct detection and identification by molecular methods can be problematic. The detection of virulent B. anthracis is challenging due to multiple virulence markers that need to be present in order for B. anthracis to be virulent and its close relationship to Bacillus cereus and other members of the B. cereus group. This is especially the case in environments where build-up of Bacillus spores can occur and several representatives of the B. cereus group may be present, which increases the chance for false-positives. In this study we show the presence of B. anthracis-like bacteria and other members of the B. cereus group in a microbial community within the human environment of the International Space Station and their preliminary identification by using conventional culturing as well as molecular techniques including 16S rDNA sequencing, PCR and real-time PCR. Our study shows that when monitoring the microbial hygiene in a given human environment, health risk assessment is troublesome in the case of virulent B. anthracis, especially if this should be done with rapid, easy to apply and on-site molecular methods.

Draft Genome Sequence of Bacillus cereus Strain BcFL2013, a Clinical Isolate Similar to G9241

Bacillus cereus strains, such as G9241, causing anthrax-like illnesses have recently been discovered. We report the genome sequence of a clinical strain, B. cereus BcFL2013, which is similar to G9241, recovered from a patient in Florida.

Transcriptome analysis identifies Bacillus anthracis genes that respond to CO2 through an AtxA-dependent mechanism

Background

Upon infection of a mammalian host, Bacillus anthracis responds to host cues, and particularly to elevated temperature (37°C) and bicarbonate/CO₂ concentrations, with increased expression of virulence factors that include the anthrax toxins and extracellular capsular layer. This response requires the presence of the pXO1 virulence plasmid-encoded pleiotropic regulator AtxA. To better understand the genetic basis of this response, we utilized a controlled in vitro system and Next Generation sequencing to determine and compare RNA expression profiles of the parental strain and an isogenic AtxA-deficient strain in a 2 × 2 factorial design with growth environments containing or lacking carbon dioxide.

Results

We found 15 pXO1-encoded genes and 3 chromosomal genes that were strongly regulated by the separate or synergistic actions of AtxA and carbon dioxide. The majority of the regulated genes responded to both AtxA and carbon dioxide rather than to just one of these factors. Interestingly, we identified two previously unrecognized small RNAs that are highly expressed under physiological carbon dioxide concentrations in an AtxA-dependent manner. Expression levels of the two small RNAs were found to be higher than that of any other gene differentially expressed in response to these conditions. Secondary structure and small RNA-mRNA binding predictions for the two small RNAs suggest that they may perform important functions in regulating B. anthracis virulence.

Conclusions

A majority of genes on the virulence plasmid pXO1 that are regulated by the presence of either CO₂ or AtxA separately are also regulated synergistically in the presence of both. These results also elucidate novel pXO1-encoded small RNAs that are associated with virulence conditions.

Bacillus cereus Certhrax ADP-ribosylates vinculin to disrupt focal adhesion complexes and cell adhesion

Bacillus cereus is often associated with mild to moderate gastroenteritis; however, some recent isolates cause inhalational anthrax-like diseases and death. These potential emerging human pathogens express multiple virulence factors. B. cereus strain G9241 expresses anthrax toxin, several polysaccharide capsules, and the novel ADP-ribosyltransferase, Certhrax. In this study, we show that Certhrax ADP-ribosylates Arg-433 of vinculin, a protein that coordinates actin cytoskeleton and extracellular matrix interactions. ADP-ribosylation of vinculin disrupted focal adhesion complexes and redistributed vinculin to the cytoplasm. Exogenous vinculin rescued these phenotypes. This provides a mechanism for strain G9241 to breach host barrier defenses and promote bacterial growth and spread. Certhrax is the first bacterial toxin to add a post-translational modification to vinculin to disrupt the actin cytoskeleton.

Exoproteome analysis of a novel strain of Bacillus cereus implicated in disease resembling cutaneous anthrax

Bacillus cereus belongs to B. cereus sensu lato group, shared by six other related species including Bacillus anthracis. B. anthracis is the causative agent for serious illness affecting a wide range of animals as well as humans and is a category A Biological and Toxin Warfare (BTW) agent. Recent studies indicate that a Bacillus species other than B. anthracis can cause anthrax-like disease and role of anthrax virulence plasmids (pXO1 and pXO2) on the pathogenicity of B. cereus has been documented. B. cereus strain TF5 was isolated from the tissue fluid of cutaneous anthrax-like skin lesions of a human patient from an anthrax endemic area in India. The strain harboured a PA gene, however, presence of pXO1 or pXO2-like plasmids could not be ascertained using reported primers. Abundant exoproteome of the strain in the early stationary phase was elucidated using a 2-DE MS approach and compared with that from a reference B. cereus strain. Analysis of proteins showing qualitative and quantitative differences between the two strains indicated an altered regulatory mechanism and putative role of S-layer protein and sphingomyelinase in the pathogenesis of strain TF5. Phylogenetic analysis of the S-layer protein indicated close affiliation of the strain with anthracis-like B. cereus strains such as B. cereus var. anthracis strain CI; whereas sphingomyelinase exhibited specific relationship with all the strains of B. anthracis apart from that with anthracis-like B. cereus strains.