Bacillus cereus and related species

Microbial based assay for specific detection of β-lactam group of antibiotics in milk

The spore forming Bacillus cereus (66) was screened for the induction of β-lactamase in presence of an inducer using iodometric assay. A significant induction in marker enzyme was observed in B. cereus 66 at maximum residual limit (MRL) of penicillin, ampicillin, cloxacillin, amoxicillin, cefalexin, and cephazolin belonging to β-lactam group of antibiotics. A microbial based assay, where enzyme induction was optimized at pH 7.0, temperature 30°C, and whey powder (0.25%) after 4 h of incubation. The spore based assay was tested with milk samples spiked with 6 different β-lactam antibiotics. The results were 100 and 83.33% in correlation with microbial receptor and inhibition based assay, respectively. Overall, spore based assay can be a useful and cost effective tool for the specific detection of β-lactam group of antibiotics in milk.

The pore-forming protein Cry5B elicits the pathogenicity of Bacillus sp. against Caenorhabditis elegans

The soil bacterium Bacillus thuringiensis is a pathogen of insects and nematodes and is very closely related to, if not the same species as, Bacillus cereus and Bacillus anthracis. The defining characteristic of B. thuringiensis that sets it apart from B. cereus and B. anthracis is the production of crystal (Cry) proteins, which are pore-forming toxins or pore-forming proteins (PFPs). Although it is known that PFPs are important virulence factors since their elimination results in reduced virulence of many pathogenic bacteria, the functions by which PFPs promote virulence are incompletely understood. Here we study the effect of Cry proteins in B. thuringiensis pathogenesis of the nematode Caenorhabditis elegans. We find that whereas B. thuringiensis on its own is not able to infect C. elegans, the addition of the PFP Cry protein, Cry5B, results in a robust lethal infection that consumes the nematode host in 1–2 days, leading to a “Bob” or bag-of-bacteria phenotype. Unlike other infections of C. elegans characterized to date, the infection by B. thuringiensis shows dose-dependency based on bacterial inoculum size and based on PFP concentration. Although the infection process takes 1–2 days, the PFP-instigated infection process is irreversibly established within 15 minutes of initial exposure. Remarkably, treatment of C. elegans with Cry5B PFP is able to instigate many other Bacillus species, including B. anthracis and even “non-pathogenic” Bacillus subtilis, to become lethal and infectious agents to C. elegans. Co-culturing of Cry5B-expressing B. thuringiensis with B. anthracis can result in lethal infection of C. elegans by B. anthracis. Our data demonstrate that one potential property of PFPs is to sensitize the host to bacterial infection and further that C. elegans and probably other roundworms can be common hosts for B. cereus-group bacteria, findings with important ecological and research implications.

Developing an integrated proteo-genomic approach for the characterisation of biomarkers for the identification of Bacillus anthracis

Bacillus anthracis is the causative agent of anthrax, an acute and often fatal disease in humans. Due to the high genomic relatedness within the Bacillus cereus group of species it is a challenge to identify B. anthracis consistently. Alternative strategies such as proteomics coupled with mass spectrometry (MS) provide a powerful approach for biomarker discovery. However, validating and evaluating these markers, particularly for genetically homogeneous species such as B. anthracis are challenging. The objective of this study is to develop a robust biomarker discovery and validation pipeline, using proteomic methodology combined with in silico and molecular approaches, to determine a biomarker list, using B. anthracis as a model. In this exploratory study we profiled the proteome of B. anthracis and genetically related species using GeLC-Liquid Chromatography MS/MS (GeLC-LC MS/MS), identifying peptides that could be used to detect B. anthracis. Peptides were filtered to remove low quality identifications. Using comparative bioinformatic approaches, matching and searching against genomic sequence data a shortlist of peptide biomarkers was determined and validated using DNA sequencing, against a panel of closely related strains, to determine marker specificity. Further validation was performed using MS quantitation methods to assess sensitivity and specificity. A biomarker discovery pipeline was successfully developed in this study, comprising four distinct stages: proteome profiling, comparative bioinformatic validation, DNA sequencing and MS validation. Using the pipeline, 5379 peptides specific for Bacillus species and 36 peptides specific for B. anthracis were identified and validated. The 36 peptides, representing 30 proteins were derived from over 15 different clusters of orthologous group categories, including proteins involved in transcription, energy production/conservation as well as multifunctional proteins. We demonstrated that the peptide biomarkers identified in this study could be detected in a complex background, in which 0.1 μg of protein extract from B. anthracis was spiked into 9.90 μg of B. cereus protein extracts. The integration of both stable non-redundant peptides with molecular methodology for marker discovery and validation, improves the robustness of identifying and characterising candidate biomarkers for the identification of bacteria such as B. anthracis.

Native valve Bacillus cereus endocarditis in a non-intravenous-drug-abusing patient

Bacillus cereus is a rare cause of endocarditis, typically associated with intravenous drug abuse, rheumatic heart disease, prosthetic heart valves, pacemakers, or immunodeficiency. We present the first case of native valve Bacillus cereus endocarditis with no apparent risk factors. The patient had a fulminant course requiring emergent valve replacement.

Monoclonal antibodies neutralize Bacillus cereus Nhe enterotoxin by inhibiting ordered binding of its three exoprotein components

The Nhe enterotoxin from Bacillus cereus is known to induce cytotoxicity on Vero and CaCo-2 cells by ordered binding of its single components NheA, NheB, and NheC. This study aimed to elucidate functional sites on NheB by identifying the epitopes of the neutralizing monoclonal antibodies 1E11 and 2B11. The binding regions of both antibodies were determined by using recombinant NheB fragments and synthetic peptides. The antigenic site of antibody 1E11 was located within the amino acids 321 to 341 of NheB, whereas reactivity of antibody 2B11 was dependent on the presence of amino acids 122 to 150 and on conformation. Both antibodies were able to bind simultaneously to NheB and did not interfere with target cell binding as shown by immunofluorescence microscopy. A set of neutralization assays revealed that antibody 2B11 most likely interfered with the interaction between NheB and NheC both on the epithelium cell surface and in solution. In contrast, antibody 1E11 inhibited association between NheA and cell-bound NheB in a competitive manner, and effectively neutralized Nhe cytotoxicity on a variety of human cell lines. This distinct mechanism further supports that NheA is the key component during the Nhe mode of action and the C-terminal epitope recognized by antibody 1E11 points to an important functional region of NheB.

Identification of a Bacillus anthracis specific indel in the yeaC gene and development of a rapid pyrosequencing assay for distinguishing B. anthracis from the B. cereus group

Bacillus anthracis, the causative agent of anthrax, is a potential source of bioterrorism. The existing assays for its identification lack specificity due to the close genetic relationship it exhibits to other members of the B. cereus group. Our comparative analyses of protein sequences from Bacillus species have identified a 24 amino acid deletion in a conserved region of the YeaC protein that is uniquely present in B. anthracis. PCR primers based on conserved regions flanking this indel in the Bacillus cereus group of species (viz. Bacillus cereus, B. anthracis, B. thuringiensis, B. mycoides, B. weihenstephnensis and B. pseudomycoides) specifically amplified a 282 bp fragment from all six reference B. anthracis strains, whereas a 354 bp fragment was amplified from 15 other B. cereus group of species/strains. These fragments, due to large size difference, are readily distinguished by means of agarose gel electrophoresis. In contrast to the B. cereus group, no PCR amplification was observed with any of the non-B. cereus group of species/strains. This indel was also used for developing a rapid pyrosequencing assay for the identification of B. anthracis. Its performance was evaluated by examining the presence or absence of this indel in a panel of 81 B. cereus-like isolates from various sources that included 39 B. anthracis strains. Based upon the sequence data from the pyrograms, the yeaC indel was found to be a distinctive characteristic of various B. anthracis strains tested and not found in any other species/strains from these samples. Therefore, this B. anthracis specific indel provides a robust and highly-specific chromosomal marker for the identification of this high-risk pathogen from other members of the B. cereus group independent of a strain's virulence. The pyrosequencing platform also allows for the rapid and simultaneous screening of multiple samples for the presence of this B. anthracis-specific marker.

Evolutionary history and functional characterization of three large genes involved in sporulation in Bacillus cereus group bacteria

The Bacillus cereus group of bacteria is a group of closely related species that are of medical and economic relevance, including B. anthracis, B. cereus, and B. thuringiensis. Bacteria from the Bacillus cereus group encode three large, highly conserved genes of unknown function (named crdA, crdB, and crdC) that are composed of 16 to 35 copies of a repeated domain of 132 amino acids at the protein level. Bioinformatic analysis revealed that there is a phylogenetic bias in the genomic distribution of these genes and that strains harboring all three large genes mainly belong to cluster III of the B. cereus group phylogenetic tree. The evolutionary history of the three large genes implicates gain, loss, duplication, internal deletion, and lateral transfer. Furthermore, we show that the transcription of previously identified antisense open reading frames in crdB is simultaneously regulated with its host gene throughout the life cycle in vitro, with the highest expression being at the onset of sporulation. In B. anthracis, different combinations of double- and triple-knockout mutants of the three large genes displayed slower and less efficient sporulation processes than the parental strain. Altogether, the functional studies suggest an involvement of these three large genes in the sporulation process.

Narrow antagonistic activity of antimicrobial peptide from Bacillus subtilis SCK-2 against Bacillus cereus

Bacillus subtilis SCK-2, producing an antimicrobial peptide of this study, was isolated from Kyeopjang, the Korean traditional fermented-soybean paste. This strain showed a narrow antagonistic activity as it inhibited Bacillus cereus causing food poisoning in human. The antimicrobial peptide, tentatively named AMP IC-1, was purified, characterized, and compared to BSAP-254, another peptide which was previously recovered from traditionally fermented-soybean paste. AMP IC-1 was found to be more thermally stable than BSAP-254, retained inhibitory activity similar to that of BSAP-254 over wide range of pH values, and was also destroyed by proteolytic enzymes. Two compounds were detected by anti-BSAP-254 polyclonal antibody and showed to contain peptide moieties and aliphatic hydrocarbons by Fourier transform infrared analysis. AMP IC-1 had an identical R(f) value (0.69) on TLC plate and a molecular weight similar to that of BSAP-254 (AMP IC-1, m/z 3401; BSAP-254, m/z 3400 to 3473). AMP IC-1 was found to contain about 33 residues and 13 types of amino acids: Cys, Asp or Asn, Glu or Gln, Ser, Gly, Arg, Thr, Ala, Pro, Val, Ile, Leu, and Lys. Compared to BSAP-254, the molar ratios of Asp or Asn, Ser, Val, and Leu were different and only AMP IC-1 contained Arg, but not Trp. Both compounds showed non-hemolytic activity. A partial synergistic effect against B. cereus was observed in response to treatment when AMP IC-1 and BSAP-254 were administered in combination. Therefore, AMP IC-1 is a possible candidate as an antimicrobial agent to prevent food-borne infectious disease in human caused by B. cereus.

Prevalence of Bacillus cereus bacteriophages in fermented foods and characterization of phage JBP901

Bacillus cereus is widely distributed in the environment and is responsible for foodborne illnesses, causing diarrhea and vomiting. In this study, the prevalence of B. cereus bacteriophages in Korean fermented foods was studied using 6 reference strains, and JBP901 was further characterized. In a total of 47 samples, 19 (40.4%) contained more than one kind of B. cereus phage. Fourteen phages were purified and determined for host lysis profile. Among them, JBP901 was specific to B. cereus group strains (forming plaques in 13 of 14 isolates) and not able to lyse other tested Gram-positive and Gram-negative strains including Bacillus subtilis. Transmission electron microscopy analysis suggested that JBP901 is a member of the family Myoviridae. Restriction enzyme digestion pattern analysis and one-step growth study indicated a genome size of approximately 150 kbp and a burst size of 100. Furthermore, bacterial lysis studies revealed that JBP901 could be used to control the growth of B. cereus in liquid culture and in food. This is the first report to examine the prevalence of phages in fermented foods in Korea, and suggests that fermented foods are useful sources of B. cereus phage isolation; moreover, B. cereus phages could provide an additional tool to tackle problems associated with B. cereus contamination.

Pathogenicity of Bacteria Contaminating Blood Products

SUMMARY: Bacterial contaminations of blood products often originate from the flora of the donor. Normally, components of the skin flora less frequently give rise to severe or complicated infections, although their participation in such conditions has been described. In contrast, bacteria that can cause infections in immunocompetent persons may give rise to life-threatening infections when present in blood products. The latter microorganisms are well-equipped with a variety of virulence factors that contribute to their pathogenicity.

A subset of naturally isolated Bacillus strains show extreme virulence to the free-living nematodes Caenorhabditis elegans and Pristionchus pacificus

The main food source of free-living nematodes in the soil environment is bacteria, which can affect nematode development, fecundity and survival. In order to occupy a reliable source of bacterial food, some nematodes have formed specific relationships with an array of invertebrate hosts (where bacteria proliferate once the hosts dies), thus forming a tritrophic system of nematode, bacteria and insect or other invertebrates. We isolated 768 Bacillus strains from soil (from Germany and the UK), horse dung and dung beetles and fed them to the genetically tractable free-living nematodes Caenorhabditis elegans and Pristionchus pacificus to isolate nematocidal strains. While C. elegans is a bacteriovorous soil nematode, P. pacificus is an omnivorous worm that is often found in association with scarab beetles. We found 20 Bacillus strains (consisting of B. cereus, B. weihenstephanensis, B. mycoides and Bacillus sp.) that were pathogenic to C. elegans and P. pacificus causing 70% to 100% mortality over 5 days and significantly affect development and brood size. The most pathogenic strains are three B. cereus-like strains isolated from dung beetles, which exhibit extreme virulence to C. elegans in less than 24 h, but P. pacificus remains resistant. C. elegans Bre mutants were also highly susceptible to the B. cereus-like strains indicating that their toxins use a different virulence mechanism than B. thuringiensis Cry 5B toxin. Also, mutations in the daf-2/daf-16 insulin signaling pathway do not rescue survival. We profiled the toxin genes (bcet, nhe complex, hbl complex, pcpl, sph, cytK, piplc, hly2, hly3, entFM and entS) of these three B. cereus-like strains and showed presence of most toxin genes but absence of the hbl complex. Taken together, this study shows that the majority of naturally isolated Bacillus from soil, horse dung and Geotrupes beetles are benign to both C. elegans and P. pacificus. Among 20 pathogenic strains with distinct virulence patterns against the two nematodes, we selected three B. cereus-like strains to investigate resistance and susceptibility immune responses in nematodes.

Characterization of Bacilli isolated from the confined environments of the Antarctic Concordia station and the International Space Station

Bacillus and related genera comprise opportunist and pathogen species that can threaten the health of a crew in confined stations required for long-term missions. In this study, 43 Bacilli from confined environments, that is, the Antarctic Concordia station and the International Space Station, were characterized in terms of virulence and plasmid exchange potentials. No specific virulence feature, such as the production of toxins or unusual antibiotic resistance, was detected. Most of the strains exhibited small or large plasmids, or both, some of which were related to the replicons of the Bacillus anthracis pXO1 and pXO2 virulence elements. One conjugative element, the capacity to mobilize and retromobilize small plasmids, was detected in a Bacillus cereus sensu lato isolate. Six out of 25 tested strains acquired foreign DNA by conjugation. Extremophilic bacteria were identified and exhibited the ability to grow at high pH and salt concentrations or at low temperatures. Finally, the clonal dispersion of an opportunist isolate was demonstrated in the Concordia station. Taken together, these results suggest that the virulence potential of the Bacillus isolates in confined environments tends to be low but genetic transfers could contribute to its capacity to spread.

Investigating the genome diversity of B. cereus and evolutionary aspects of B. anthracis emergence

Here we report the use of a multi-genome DNA microarray to investigate the genome diversity of Bacillus cereus group members and elucidate the events associated with the emergence of Bacillus anthracis the causative agent of anthrax-a lethal zoonotic disease. We initially performed directed genome sequencing of seven diverse B. cereus strains to identify novel sequences encoded in those genomes. The novel genes identified, combined with those publicly available, allowed the design of a "species" DNA microarray. Comparative genomic hybridization analyses of 41 strains indicate that substantial heterogeneity exists with respect to the genes comprising functional role categories. While the acquisition of the plasmid-encoded pathogenicity island (pXO1) and capsule genes (pXO2) represents a crucial landmark dictating the emergence of B. anthracis, the evolution of this species and its close relatives was associated with an overall shift in the fraction of genes devoted to energy metabolism, cellular processes, transport, as well as virulence.

Two capsular polysaccharides enable Bacillus cereus G9241 to cause anthrax-like disease

Bacillus cereus G9241 causes an anthrax-like respiratory illness in humans; however, the molecular mechanisms of disease pathogenesis are not known. Genome sequencing identified two putative virulence plasmids proposed to provide for anthrax toxin (pBCXO1) and/or capsule expression (pBC218). We report here that B. cereus G9241 causes anthrax-like disease in immune-competent mice, which is dependent on each of the two virulence plasmids. pBCXO1 encodes pagA1, the homologue of anthrax protective antigen, as well as hasACB, providing for hyaluronic acid capsule formation, two traits that each contribute to disease pathogenesis. pBC218 harbours bpsX-H, B. cereus exo-polysaccharide, which produce a second capsule. During infection, B. cereus G9241 elaborates both hasACB and bpsX-H capsules, which together are essential for the establishment of anthrax-like disease and the resistance of bacilli to phagocytosis. A single nucleotide deletion causes premature termination of hasA translation in Bacillus anthracis, which is known to escape phagocytic killing by its pXO2 encoded poly-d-γ-glutamic acid (PDGA) capsule. Thus, multiple different gene clusters endow pathogenic bacilli with capsular material, provide for escape from innate host immune responses and aid in establishing the pathogenesis of anthrax-like disease.

Bacillus species infective arthritis after knee arthroscopy

BACKGROUND

Bacillus species infection of the joints is a very rare occurrence, with sporadic reports in the medical literature.

CASE REPORT

A 67-year-old woman with osteoarthritis developed infection in the knee joint after arthroscopy. Percutaneous needle aspiration of articular fluid performed post-operatively showed a positive culture for Bacillus species. The diagnosis of septic arthritis was, however, not confirmed as the results were considered contamination. Failure of treatment with beta-lactam antibiotics on two occasions and successful cure of infective arthritis by long-term administration of a fluoroquinolone confirmed iatrogenic clinical joint infection with Bacillus species.

CONCLUSION

Any clinically suspected joint infection must be treated as septic arthritis until proved otherwise.

Selection of Biocontrol Agents of Pink Rot Based on Efficacy and Growth Kinetics Index Rankings

The microbiota of 84 different agricultural soils were transferred to separate samples of a γ irradiation-sterilized field soil enriched with potato periderm, and the resulting soils were assayed for biological suppressiveness to Phytophthora erythroseptica and their effect on zoospore production. The 13 most suppressive soil samples, which reduced zoospore production by 14 to 93% and disease severity on tubers by 6 to 21%, were used to isolate 279 organisms. Fourteen strains that reduce pink rot infections in preliminary tests were selected for further study. Six bacterial strains that reduced the severity of disease (P ≤ 0.05, Fischer's protected least significant difference) in subsequent tests were identified as Bacillus simplex (three strains), Pantoea agglomerans, Pseudomonas koreensis, and P. lini. Relative performance indices (RPIs) for biocontrol efficacy and for each of four kinetic parameters, including total colony-forming units (CFU_max), biomass production values (DW_max), cell production after 8 h (OD₈), and time of recovery from oxygen depletion (DT) were calculated for each strain. Overall RPI_Eff,Kin values for each strain then were calculated using strain RPI values for both efficacy (RPI_Eff) and kinetics (RPI_Kin). Strains with the highest RPI_Eff,Kin possess the best biocontrol efficacy of the strains tested and liquid culture growth characteristics that suggest commercial development potential.

Bacillus anthracis sin locus and regulation of secreted proteases

Bacillus anthracis shares many regulatory loci with the nonpathogenic Bacillus species Bacillus subtilis. One such locus is sinIR, which in B. subtilis controls sporulation, biofilm formation, motility, and competency. As B. anthracis is not known to be motile, to be naturally competent, or to readily form biofilms, we hypothesized that the B. anthracis sinIR regulon is distinct from that of B. subtilis. A genome-wide expression microarray analysis of B. anthracis parental and sinR mutant strains indicated limited convergence of the B. anthracis and B. subtilis SinR regulons. The B. anthracis regulon includes homologues of some B. subtilis SinR-regulated genes, including the signal peptidase gene sipW near the sinIR locus and the sporulation gene spoIIE. The B. anthracis SinR protein also negatively regulates transcription of genes adjacent to the sinIR locus that are unique to the Bacillus cereus group species. These include calY and inhA1, structural genes for the metalloproteases camelysin and immune inhibitor A1 (InhA1), which have been suggested to be associated with virulence in B. cereus and B. anthracis, respectively. Electrophoretic mobility shift assays revealed direct binding of B. anthracis SinR to promoter DNA from strongly regulated genes, such as calY and sipW, but not to the weakly regulated inhA1 gene. Assessment of camelysin and InhA1 levels in culture supernates from sinR-, inhA1-, and calY-null mutants showed that the concentration of InhA1 in the culture supernatant is inversely proportional to the concentration of camelysin. Our data are consistent with a model in which InhA1 protease levels are controlled at the transcriptional level by SinR and at the posttranslational level by camelysin.

Catheter-related bloodstream infections: catheter management according to pathogen

Central-line access is an essential part of modern healthcare practice; however, catheter-related bloodstream infection is a major problem that causes substantial morbidity and mortality, and excess length of stay and cost. The risk of infection depends on the type of device, the site of insertion, the underlying conditions and the appropriate prevention measures taken during catheter insertion. Management of catheter-related bloodstream infection involves deciding on catheter removal, antimicrobial catheter lock solution and the type and duration of systemic antimicrobial therapy. Systemic antimicrobial use is essential but, although generally effective in controlling sepsis, it often fails to sterilise the line, increasing the incidence of complications or recurrence. The decision regarding whether the catheter should be removed or retained is therefore crucial. One of the major factors to be considered is the type of organism involved in the catheter-related infection. This review outlines the epidemiology, pathogenesis, diagnosis, microbiology and management of catheter-related infections, mainly focusing on the management of the intravascular device according to the pathogen.

Etiology and antibacterial susceptibility pattern of community-acquired bacterial ocular infections in a tertiary eye care hospital in south India

AIMS

To identify the etiology, incidence and prevalence of ocular bacterial infections, and to assess the in vitro susceptibility of these ocular bacterial isolates to commonly used antibiotics.

MATERIALS AND METHODS

Retrospective analysis of consecutive samples submitted for microbiological evaluation from patients who were clinically diagnosed with ocular infections and were treated at a tertiary eye care referral center in South India between January 2002 and December 2007.

RESULTS

A total of 4417 ocular samples was submitted for microbiological evaluation, of which 2599 (58.8%) had bacterial growth, 456 (10.3%) had fungal growth, 15 (0.34%) had acanthamoebic growth, 14 (0.32%) had mixed microbial growth and the remaining 1333 (30.2%) had negative growth. The rate of culture-positivity was found to be 88% (P < 0.001) in eyelids' infection, 70% in conjunctival, 69% in lacrimal apparatus, 67.4% in corneal, 51.6% in intraocular tissues, 42.9% in orbital and 39.2% in scleral infections. The most common bacterial species isolated were Staphylococcus aureus (26.69%) followed by Streptococcus pneumoniae (22.14%). Sta. aureus was more prevalent more in eyelid infections (51.22%; P = 0.001) coagulase-negative staphylococci in endophthalmitis (53.1%; P = 0.001), Str. pneumoniae in lacrimal apparatus and corneal infections (64.19%; P = 0.001), Corynebacterium species in blepharitis and conjunctivitis (71%; P = 0.001), Pseudomonas aeruginosa in keratitis and dacryocystitis (66.5%; P = 0.001), Haemophilus species in dacryocystitis and conjunctivitis (66.7%; P = 0.001), Moraxella lacunata in blepharitis (54.17%; P = 0.001) and Moraxella catarrhalis in dacryocystitis (63.83%; P = 0.001). The largest number of gram-positive isolates was susceptible to moxifloxacin (98.7%) and vancomycin (97.9%), and gram-negative isolates to amikacin (93.5%) and gatifloxacin (92.7%).

CONCLUSIONS

Gram-positive cocci were the most frequent bacteria isolated from ocular infections and were sensitive to moxifloxacin and vancomycin, while gram-negative isolates were more sensitive to amikacin and gatifloxacin.

Features of Bacillus cereus swarm cells

When propagated on solid surfaces, Bacillus cereus can produce differentiated swarm cells under a wide range of growth conditions. This behavioural versatility is ecologically relevant, since it allows this bacterium to adapt swarming to environmental changes. Swarming by B. cereus is medically important: swarm cells are more virulent and particularly prone to invade host tissues. Characterisation of swarming-deficient mutants highlights that flagellar genes as well as genes governing different metabolic pathways are involved in swarm-cell differentiation. In this review, the environmental and genetic requirements for swarming and the role played by swarm cells in the virulence this pathogen exerts will be outlined.

Interspersed DNA repeats bcr1-bcr18 of Bacillus cereus group bacteria form three distinct groups with different evolutionary and functional patterns

Many short (<400 bp) interspersed sequence repeats exist in bacteria, yet little is known about their origins, mode of generation, or possible function. Here, we present a comprehensive analysis of 18 different previously identified repeated DNA elements, bcr1-bcr18 (Økstad OA, Hegna I, Lindback T, Rishovd AL, Kolstø AB. 1999. Genome organization is not conserved between Bacillus cereus and Bacillus subtilis. Microbiology. 145:621-631.; Tourasse NJ, Helgason E, Økstad OA, Hegna IK, Kolstø AB. 2006. The Bacillus cereus group: novel aspects of population structure and genome dynamics. J Appl Microbiol. 101:579-593.), in 36 sequenced genomes from the Bacillus cereus group of bacteria. This group consists of genetically closely related species with variable pathogenic specificity toward different hosts and includes among others B. anthracis, B. cereus, and B. thuringiensis. The B. cereus group repeat elements could be classified into three categories with different properties: Group A elements (bcr1-bcr3) exhibited highly variable copy numbers ranging from 4 to 116 copies per strain, showed a nonconserved chromosomal distribution pattern between strains, and displayed several features characteristic of mobile elements. Group B repeats (bcr4-bcr6) were present in 0-10 copies per strain and were associated with strain-specific genes and disruptions of genome synteny, implying a possible contribution to genome rearrangements and/or horizontal gene transfer events. bcr5, in particular, was associated with large gene clusters showing resemblance to integrons. In agreement with their potentially mobile nature or involvement in horizontal transfers, the sequences of the repeats from Groups A and B (bcr1-bcr6) followed a phylogeny different from that of the host strains. Conversely, repeats from Group C (bcr7-bcr18) had a conserved chromosomal location and orthologous gene neighbors in the investigated B. cereus group genomes, and their phylogeny matched that of the host chromosome. Several of the group C repeats exhibited a conserved secondary structure or had parts of the structure conserved, possibly indicating functional RNAs. Accordingly, five of the repeats in group C overlapped regions encoding previously characterized riboswitches. Similarly, other group C repeats could represent novel riboswitches, encode small RNAs, and/or constitute other types of regulatory elements with specific biological functions. The current analysis suggests that the multitude of repeat elements identified in the B. cereus group promote genome dynamics and plasticity and could contribute to the flexible and adaptive life style of these bacteria.

Sub-chronic lung inflammation after airway exposures to Bacillus thuringiensis biopesticides in mice

BACKGROUND

The aim of the present study was to assess possible health effects of airway exposures to Bacillus thuringiensis (Bt) based biopesticides in mice. Endpoints were lung inflammation evaluated by presence of inflammatory cells in bronchoalveolar lavage fluid (BALF), clearance of bacteria from the lung lumen and histological alterations of the lungs. Hazard identifications of the biopesticides were carried out using intratracheal (i.t.) instillation, followed by an inhalation study. The two commercial biopesticides used were based on the Bt. subspecies kurstaki and israelensis, respectively. Groups of BALB/c mice were i.t instilled with one bolus (3.5 × 105 or 3.4 × 106 colony forming units (CFU) per mouse) of either biopesticide. Control mice were instilled with sterile water. BALFs were collected and the inflammatory cells were counted and differentiated. The BALFs were also subjected to CFU counts.

RESULTS

BALF cytology showed an acute inflammatory response dominated by neutrophils 24 hours after instillation of biopesticide. Four days after instillation, the neutrophil number was normalised and inflammation was dominated by lymphocytes and eosinophils, whereas 70 days after instillation, the inflammation was interstitially located with few inflammatory cells present in the lung lumen.Half of the instilled mice had remaining CFU recovered from BALF 70 days after exposure. To gain further knowledge with relevance for risk assessment, mice were exposed to aerosols of biopesticide one hour per day for 2 × 5 days. Each mouse received 1.9 × 104 CFU Bt israelensis or 2.3 × 103 CFU Bt kurstaki per exposure. Seventy days after end of the aerosol exposures, 3 out of 17 mice had interstitial lung inflammation. CFU could be recovered from 1 out of 10 mice 70 days after exposure to aerosolised Bt kurstaki. Plethysmography showed that inhalation of Bt aerosol did not induce airway irritation.

CONCLUSIONS

Repeated low dose aerosol exposures to commercial Bt based biopesticides can induce sub-chronic lung inflammation in mice, which may be the first step in the development of chronic lung diseases. Inhalation of Bt aerosols does not induce airway irritation, which could explain why workers may be less inclined to use a filter mask during the application process, and are thereby less protected from exposure to Bt spores.

Identifying experimental surrogates for Bacillus anthracis spores: a review

Bacillus anthracis, the causative agent of anthrax, is a proven biological weapon. In order to study this threat, a number of experimental surrogates have been used over the past 70 years. However, not all surrogates are appropriate for B. anthracis, especially when investigating transport, fate and survival. Although B. atrophaeus has been widely used as a B. anthracis surrogate, the two species do not always behave identically in transport and survival models. Therefore, we devised a scheme to identify a more appropriate surrogate for B. anthracis. Our selection criteria included risk of use (pathogenicity), phylogenetic relationship, morphology and comparative survivability when challenged with biocides. Although our knowledge of certain parameters remains incomplete, especially with regards to comparisons of spore longevity under natural conditions, we found that B. thuringiensis provided the best overall fit as a non-pathogenic surrogate for B. anthracis. Thus, we suggest focusing on this surrogate in future experiments of spore fate and transport modelling.

Characterization of an environmental strain of Bacillus thuringiensis from a hot spring in Western Himalayas

Bacillus anthracis, the etiological agent of anthrax, is responsible for a serious and often fatal disease of mammalian livestock and humans and is an important biological warfare agent. Bacillus sp. AKG was isolated from a hot spring in western Himalayas and species-specific primers targeting gyrB gene identified the strain as B. anthracis within cereus-group. Cloning, sequencing, and phylogenetic analysis of the partial gyrB sequence from strain AKG indicated a close affiliation with B. anthracis and a few recently isolated strains of B. thuringiensis (e.g., strain Al Hakam and serovar konkukian). Phylogenetic analysis of two other housekeeping genes, clpC and gdpD yielded similar results. This observation is further substantiated by phylogenetic reconstruction using concatenated sequences (1680 bases) of the three genes (gyrB, clpC, and gdpD). Phenotypic features indicated a non-anthracis affiliation for the strain AKG. A novel strategy to distinguish among strains of B. anthracis, B. cereus, and B. thuringiensis based on whole proteome comparison was developed and tested for the identification of this environmental strain. Proteome comparison was used to establish the identity of this unknown environmental strain. Group of replicate 2DE gels for whole cell proteome were generated for each of the three species and strain AKG. Protein spots unique to each group and those showing match between the groups, in a pair-wise comparison, indicated strain AKG as a member of B. thuringiensis. This strategy can be used to assign strains of B. cereus group to their respective species.

Activation of the latent PlcR regulon in Bacillus anthracis

Many genes in Bacillus cereus and Bacillus thuringiensis are under the control of the transcriptional regulator PlcR and its regulatory peptide, PapR. In Bacillus anthracis, the causative agent of anthrax, PlcR is inactivated by truncation, and consequently genes having PlcR binding sites are expressed at very low levels when compared with B. cereus. We found that activation of the PlcR regulon in B. anthracis by expression of a PlcR–PapR fusion protein does not alter sporulation in strains containing the virulence plasmid pXO1 and thereby the global regulator AtxA. Using comparative 2D gel electrophoresis, we showed that activation of the PlcR regulon in B. anthracis leads to upregulation of many proteins found in the secretome of B. cereus, including phospholipases and proteases, such as the putative protease BA1995. Transcriptional analysis demonstrated expression of BA1995 to be dependent on PlcR–PapR, even though the putative PlcR recognition site of the BA1995 gene does not exactly match the PlcR consensus sequence, explaining why this protein had escaped recognition as belonging to the PlcR regulon. Additionally, while transcription of major PlcR-dependent haemolysins, sphingomyelinase and anthrolysin O is enhanced in response to PlcR activation in B. anthracis, only anthrolysin O contributes significantly to lysis of human erythrocytes. In contrast, the toxicity of bacterial culture supernatants from a PlcR-positive strain towards murine macrophages occurred independently of anthrolysin O expression in vitro and in vivo.

Extended and global phylogenetic view of the Bacillus cereus group population by combination of MLST, AFLP, and MLEE genotyping data

The Bacillus cereus group of bacteria includes species that can cause food-poisoning or spoilage, such as B. cereus, as well as Bacillus anthracis, the cause of anthrax. In the present report we have conducted a multi-datatype analysis using tools from the HyperCAT database (http://mlstoslo.uio.no/) that we recently developed, combining data from multilocus sequence typing (Tourasse et al., 2010), amplified fragment length polymorphism, and multilocus enzyme electrophoresis typing techniques. We provide a comprehensive snapshot of the B. cereus group population, incorporating 2213 isolates including 450 from food and dairy products, in the form of both phylogenetic supertrees and superclusters of genetically closely related isolates. Our main findings include the detection of phylogenetically separated groups of isolates possibly representing novel evolutionary lineages within the B. cereus group, a putative new branch of B. anthracis, as well as new groups of related strains containing both environmental and clinical isolates. In addition, the multi-datatype analysis revealed to a larger extent than previously recognized that food-borne isolates can share identical genotyping profiles with strains from various other origins. Altogether, the global analysis confirms and extends the results underlining the opportunistic nature of B. cereus group organisms, and the fact that isolates responsible for disease outbreaks and contamination of foodstuffs can originate from various genetic backgrounds.

Polymyxin-direct hemoperfusion for sepsis-induced multiple organ failure

We report a case of multiple organ failure caused by the Bacillus cereus infection during acute lymphoblastic leukemia therapy, who was treated successfully. A 15-year-old male developed (B. cereus) sepsis on the 19th day after chemotherapy initiation. Polymyxin-direct hemoperfusion for septic shock was started, followed by continuous hemodiafiltration. His condition improved after starting the hemoperfusion. At the onset of sepsis, elevated levels of serum inflammatory cytokines, anti-inflammatory cytokines, and plasminogen-activator inhibitor complex-1 were observed. Serum levels of these cytokines and bioactive substances decreased after blood purification therapy, which correlated with the improvement of clinical symptoms.

The genome of a Bacillus isolate causing anthrax in chimpanzees combines chromosomal properties of B. cereus with B. anthracis virulence plasmids

Anthrax is a fatal disease caused by strains of Bacillus anthracis. Members of this monophyletic species are non motile and are all characterized by the presence of four prophages and a nonsense mutation in the plcR regulator gene. Here we report the complete genome sequence of a Bacillus strain isolated from a chimpanzee that had died with clinical symptoms of anthrax. Unlike classic B. anthracis, this strain was motile and lacked the four prohages and the nonsense mutation. Four replicons were identified, a chromosome and three plasmids. Comparative genome analysis revealed that the chromosome resembles those of non-B. anthracis members of the Bacillus cereus group, whereas two plasmids were identical to the anthrax virulence plasmids pXO1 and pXO2. The function of the newly discovered third plasmid with a length of 14 kbp is unknown. A detailed comparison of genomic loci encoding key features confirmed a higher similarity to B. thuringiensis serovar konkukian strain 97-27 and B. cereus E33L than to B. anthracis strains. For the first time we describe the sequence of an anthrax causing bacterium possessing both anthrax plasmids that apparently does not belong to the monophyletic group of all so far known B. anthracis strains and that differs in important diagnostic features. The data suggest that this bacterium has evolved from a B. cereus strain independently from the classic B. anthracis strains and established a B. anthracis lifestyle. Therefore we suggest to designate this isolate as "B. cereus variety (var.) anthracis".

Spore-forming Bacilli and Clostridia in human disease

Many Gram-positive spore-forming bacteria in the Firmicute phylum are important members of the human commensal microbiota, which, in rare cases, cause opportunistic infections. Other spore-formers, however, have evolved to become dedicated pathogens that can cause a striking variety of diseases. Despite variations in disease presentation, the etiologic agent is often the spore, with bacterially produced toxins playing a central role in the pathophysiology of infection. This review will focus on the specific diseases caused by spores of the Clostridia and Bacilli.

Production, secretion and biological activity of Bacillus cereus enterotoxins

Bacillus cereus behaves as an opportunistic pathogen frequently causing gastrointestinal diseases, and it is increasingly recognized to be responsible for severe local or systemic infections. Pathogenicity of B. cereus mainly relies on the secretion of a wide array of toxins and enzymes and also on the ability to undergo swarming differentiation in response to surface-sensing. In this report, the pathogenicity exerted by B. cereus toxins is described with particular attention to the regulatory mechanisms of production and secretion of HBL, Nhe and CytK enterotoxins.

A novel spore protein, ExsM, regulates formation of the exosporium in Bacillus cereus and Bacillus anthracis and affects spore size and shape

Bacillus cereus spores are assembled with a series of concentric layers that protect them from a wide range of environmental stresses. The outermost layer, or exosporium, is a bag-like structure that interacts with the environment and is composed of more than 20 proteins and glycoproteins. Here, we identified a new spore protein, ExsM, from a beta-mercaptoethanol extract of B. cereus ATCC 4342 spores. Subcellular localization of an ExsM-green fluorescent protein (GFP) protein revealed a dynamic pattern of fluorescence that follows the site of formation of the exosporium around the forespore. Under scanning electron microscopy, exsM null mutant spores were smaller and rounder than wild-type spores, which had an extended exosporium (spore length for the wt, 2.40 +/- 0.56 microm, versus that for the exsM mutant, 1.66 +/- 0.38 microm [P < 0.001]). Thin-section electron microscopy revealed that exsM mutant spores were encased by a double-layer exosporium, both layers of which were composed of a basal layer and a hair-like nap. Mutant exsM spores were more resistant to lysozyme treatment and germinated with higher efficiency than wild-type spores, and they had a delay in outgrowth. Insertional mutagenesis of exsM in Bacillus anthracis DeltaSterne resulted in a partial second exosporium and in smaller spores. In all, these findings suggest that ExsM plays a critical role in the formation of the exosporium.

Germination and outgrowth of spores of Bacillus cereus group members: diversity and role of germinant receptors

Bacillus cereus is a gram-positive, facultative anaerobic, endospore-forming toxicogenic human pathogen. Endospores are highly specialized, metabolically dormant cell types that are resistant to extreme environmental conditions, including heat, dehydration and other physical stresses. B. cereus can enter a range of environments, and can in its spore form, survive harsh conditions. If these conditions become favorable, spores can germinate and grow out and reach considerable numbers in a range of environments including processed foods. Certainly the last decade, when consumer preferences have shifted to mildly processed food, new opportunities arose for spore-forming spoilage and pathogenic organisms. Only rigorous methods have been shown to be capable of destroying all spores present in food, thus a shift toward e.g., milder heat preservation strategies, may result in low but significant amounts of viable spores in food products. Hence, the need for a mild spore destruction strategy is eminent including control of spore outgrowth. Consequently, there is a large interest in triggering spore germination in foodstuffs, since germinated spores have lost the extreme resistance of dormant spores and are relatively easy to kill. Another option could be to prevent germination so that no dangerous levels can be reached. This contribution will focus on germination and outgrowth characteristics of B. cereus and other members of the B. cereus group, providing an overview of the niches these spore-formers can occupy, the signals that trigger germination, and how B. cereus copes with these wake-up calls in different environments including foods, during food processing and upon interaction with the human host.