Bacillus cereus and related species

Bacillus cereus, a volatile human pathogen

Bacillus cereus is a Gram-positive aerobic or facultatively anaerobic, motile, spore-forming, rod-shaped bacterium that is widely distributed environmentally. While B. cereus is associated mainly with food poisoning, it is being increasingly reported to be a cause of serious and potentially fatal non-gastrointestinal-tract infections. The pathogenicity of B. cereus, whether intestinal or nonintestinal, is intimately associated with the production of tissue-destructive exoenzymes. Among these secreted toxins are four hemolysins, three distinct phospholipases, an emesis-inducing toxin, and proteases. The major hurdle in evaluating B. cereus when isolated from a clinical specimen is overcoming its stigma as an insignificant contaminant. Outside its notoriety in association with food poisoning and severe eye infections, this bacterium has been incriminated in a multitude of other clinical conditions such as anthrax-like progressive pneumonia, fulminant sepsis, and devastating central nervous system infections, particularly in immunosuppressed individuals, intravenous drug abusers, and neonates. Its role in nosocomial acquired bacteremia and wound infections in postsurgical patients has also been well defined, especially when intravascular devices such as catheters are inserted. Primary cutaneous infections mimicking clostridial gas gangrene induced subsequent to trauma have also been well documented. B. cereus produces a potent beta-lactamase conferring marked resistance to beta-lactam antibiotics. Antimicrobials noted to be effective in the empirical management of a B. cereus infection while awaiting antimicrobial susceptibility results for the isolate include ciprofloxacin and vancomycin.

Multiplex PCR assay for the detection of enterotoxic Bacillus cereus group strains and its application in food matrices

Bacillus cereus, Bacillus thuringiensis and Bacillus anthracis are the major concerns for the food safety in terms of frequency and/or seriousness of the disease. Being members of the same group and sharing DNA homology to a larger extent, they do create problems when their specific detection/identification is attempted from different food and environmental sources. Numerous individual polymerase chain reaction (PCR) and few multiplex PCR (mPCR) methods have been employed to detect these organisms by targeting toxin genes but with lack of internal amplification control (IAC). Therefore, we attempted a mPCR with IAC for the detection of enterotoxic B. cereus group strains by selecting hbl A, nhe A and cyt K genes from B. cereus, indicative of the diarrheal potential and cry I A and pag genes, the plasmid borne phenotypic markers specific to B. thuringiensis and B. anthracis strains, respectively. Multiplex PCR assay validation was performed by simultaneous comparison with the results of single-target PCR assays and correlated to the classical conventional and biochemical identification of the organisms. The mPCR was able to detect as low as 10(1)-10(2) organisms per ml following overnight enrichment of spiked food samples (vegetable biriyani and milk) in buffered peptone water (BPW). The presence of these organisms could also be detected by mPCR in naturally contaminated samples of rice based dishes and milk. The high throughput and cost-effective mPCR method described could provide a powerful tool for simultaneous, rapid and reliable detection of enterotoxic B. cereus group organisms.

The role of anthrolysin O in gut epithelial barrier disruption during Bacillus anthracis infection

Gastrointestinal (GI) anthrax, caused by the bacterial infection of Bacillus anthracis, posts a significant bioterrorism threat by its relatively high mortality rate in humans. Different from inhalational anthrax by the route of infection, accumulating evidence indicates the bypass of vegetative bacteria across GI epithelium is required to initiate GI anthrax. Previously, we reported that purified anthrolysin O (ALO), instead of tripartite anthrax edema and lethal toxins, is capable of disrupting gut epithelial tight junctions and barrier function in cultured cells. Here, we show that ALO can disrupt intestinal tissue barrier function in an ex vivo mouse model. To explore the effects of ALO in a cell culture model of B. anthracis infection, we showed that anthrax bacteria can effectively reduce the monolayer integrity of human Caco-2 brush-border expressor (C2BBE) cells based on the reduced transepithelial resistance and the increased leakage of fluorescent dye. This disruption is likely caused by tight junction dysfunction observed by the reorganization of the tight junction protein occludin. Consequently, we observe significant passage of vegetative anthrax bacteria across C2BBE cells. This barrier disruption and bacterial crossover requires ALO since ALO-deficient B. anthracis strains fail to induce monolayer dysfunction and allow the passage of anthrax bacteria. Together these findings point to a pivotal role for ALO within the establishment of GI anthrax infection and the initial bypass of the epithelial barrier.

Safety assessment of recalled Haemophilus influenzae type b (Hib) conjugate vaccines--United States, 2007-2008

PURPOSE

On 13 December 2007, Merck & Co., Inc. voluntarily recalled 1.2 million doses of Haemophilus influenzae type b (Hib) vaccines that had been distributed since April 2007 for concerns regarding potential Bacillus cereus contamination. Enhanced postrecall surveillance was conducted to detect vaccine-associated B. cereus infections.

METHODS

We reviewed reports involving recalled Hib vaccines received by the Vaccine Adverse Event Reporting System (VAERS) during 1 April 2007-29 February 2008. For each reported death, autopsy review sought evidence of B. cereus infections. For each specified outcome, the proportional reporting ratios (PRRs) were calculated to compare the recalled Hib vaccines with the manufacturer's nonrecalled Hib vaccines in the VAERS databases. On 20 December 2007, we used the Epidemic Information Exchange (Epi-X) to solicit nongastrointestinal vaccine-associated B. cereus infections, and requested B. cereus isolates for genotyping to compare with the manufacturing facility isolate.

RESULTS

VAERS received 75 reports involving recalled Hib vaccines; none described a confirmed B. cereus infection. Comparative analyses did not reveal disproportionate reporting of specified outcomes for recalled Hib vaccines. The Epi-X posting triggered one report of vaccine-associated B. cereus bacteremia from a child who received a nonrecalled Hib vaccine manufactured by Merck; the genotypes of isolates from the patient and the manufacturing facility differed.

CONCLUSIONS

No evidence of vaccine-associated B. cereus infection had been found in recipients of recalled Hib vaccines. Conducting laboratory surveillance through Epi-X was feasible and may enhance public health response capacities for future vaccine safety emergencies.

Successful surgical drainage and aggressive medical therapy in a preterm neonate with Bacillus cereus meningitis

Bacillus cereus meningitis is a rare disease with a very high mortality rate in neonates. The authors present the rare case of a premature infant with B. cereus bacteremia and subsequent intracranial abscesses. In addition to aggressive medical therapy, surgical drainage was performed via a left frontal mini-craniotomy. At 15 months of age, the patient had mild developmental delay, cortical blindness, and sensorineural hearing loss. The clinical case is described and difficulties in the management of B. cereus meningoencephalitis in infants are discussed.

Optimal sterilization method for the zirconia/alumina composites used for total hip replacements

Zirconia/alumina composite ceramics have been recently developed for total hip arthroplasty because of their excellent mechanical properties and tribologic characteristics. All such materials used clinically must be easily sterilized, but no report has been issued concerning methods for sterilizing zirconia/alumina composite hip prostheses. Here, we show that 50 kGy of gamma irradiation effectively sterilizes both the surfaces and interiors of these materials. In addition, it was found that the commonly used ethylene oxide and 25-kGy gamma irradiation sterilization methods inadequately sterilize deep inside the femoral head. Moreover, no changes in the chemical or mechanical properties of the composites were noted after exposure to 50-kGy gamma irradiation. We suggest that 50-kGy gamma irradiation is an optimal sterilization method for zirconia/alumina composite total hip replacements.

Antifungal activity of selected indigenous pseudomonas and bacillus from the soybean rhizosphere

The purpose of this study was to isolate and select indigenous soil Pseudomonas and Bacillus bacteria capable of developing multiple mechanisms of action related to the biocontrol of phytopathogenic fungi affecting soybean crops. The screening procedure consisted of antagonism tests against a panel of phytopathogenic fungi, taxonomic identification, detection by PCR of several genes related to antifungal activity, in vitro detection of the antifungal products, and root colonization assays. Two isolates, identified and designated as Pseudomonas fluorescens BNM296 and Bacillus amyloliquefaciens BNM340, were selected for further studies. These isolates protected plants against the damping-off caused by Pythium ultimum and were able to increase the seedling emergence rate after inoculation of soybean seeds with each bacterium. Also, the shoot nitrogen content was higher in plants when seeds were inoculated with BNM296. The polyphasic approach of this work allowed us to select two indigenous bacterial strains that promoted the early development of soybean plants.

Liver abscess and sepsis with Bacillus pantothenticus in an immunocompetent patient: A first case report

Bacillus species are aerobic, gram-positive, spore forming rods that are usually found in the soil, dust, streams, and other environmental sources. Except for Bacillus. anthracis (B. anthracis), most species display low virulence, and only rarely cause infections in hosts with weak or damaged immune systems. There are two case reports of B. cereus as a potentially serious bacterial pathogen causing a liver abscess in an immunologically competent patient. We herein report a case of liver abscess and sepsis caused by B. pantothenticus in an immunocompetent patient. Until now, no case of liver abscess due to B. pantothenticus has been reported.

What sets Bacillus anthracis apart from other Bacillus species?

Bacillus anthracis is the cause of anthrax, and two large plasmids are essential for toxicity: pXO1, which contains the toxin genes, and pXO2, which encodes a capsule. B. anthracis forms a highly monomorphic lineage within the B. cereus group, but strains of Bacillus thuringiensis and B. cereus exist that are genetically closely related to the B. anthracis cluster. During the past five years B. cereus strains that contain the pXO1 virulence plasmid were discovered, and strains with both pXO1 and pXO2 have been isolated from great apes in Africa. Therefore, the presence of pXO1 and pXO2 no longer principally separates B. anthracis from other Bacilli. The B. anthracis lineage carries a specific mutation in the global regulator PlcR, which controls the transcription of secreted virulence factors in B. cereus and B. thuringiensis. Coevolution of the B. anthracis chromosome with its plasmids may be the basis for the successful development and uniqueness of the B. anthracis lineage.

Novel and unique diagnostic biomarkers for Bacillus anthracis infection

A search for bacterium-specific biomarkers in peripheral blood following infection with Bacillus anthracis was carried out with rabbits, using a battery of specific antibodies generated by DNA vaccination against 10 preselected highly immunogenic bacterial antigens which were identified previously by a genomic/proteomic/serologic screen of the B. anthracis secretome. Detection of infection biomarkers in the circulation of infected rabbits could be achieved only after removal of highly abundant serum proteins by chromatography using a random-ligand affinity column. Besides the toxin component protective antigen, the following three secreted proteins were detected in the circulation of infected animals: the chaperone and protease HtrA (BA3660), an NlpC/P60 endopeptidase (BA1952), and a protein of unknown function harboring two SH3 (Src homology 3) domains (BA0796). The three proteins could be detected in plasma samples from infected animals exhibiting 10(3) to 10(5) CFU/ml blood and also in standard blood cultures at 3 to 6 h post-bacterial inoculation at a bacteremic level as low as 10(3) CFU/ml. Furthermore, the three biomarkers appear to be present only in the secretome of B. anthracis, not in those of the related pathogens B. thuringiensis and B. cereus. To the best of our knowledge, this is the first report of direct detection of B. anthracis-specific proteins, other than the toxin components, in the circulation of infected animals.

Identification and classification of bcl genes and proteins of Bacillus cereus group organisms and their application in Bacillus anthracis detection and fingerprinting

The Bacillus cereus group includes three closely related species, B. anthracis, B. cereus, and B. thuringiensis, which form a highly homogeneous subdivision of the genus Bacillus. One of these species, B. anthracis, has been identified as one of the most probable bacterial biowarfare agents. Here, we evaluate the sequence and length polymorphisms of the Bacillus collagen-like protein bcl genes as a basis for B. anthracis detection and fingerprinting. Five genes, designated bclA to bclE, are present in B. anthracis strains. Examination of bclABCDE sequences identified polymorphisms in bclB alleles of the B. cereus group organisms. These sequence polymorphisms allowed specific detection of B. anthracis strains by PCR using both genomic DNA and purified Bacillus spores in reactions. By exploiting the length variation of the bcl alleles it was demonstrated that the combined bclABCDE PCR products generate markedly different fingerprints for the B. anthracis Ames and Sterne strains. Moreover, we predict that bclABCDE length polymorphism creates unique signatures for B. anthracis strains, which facilitates identification of strains with specificity and confidence. Thus, we present a new diagnostic concept for B. anthracis detection and fingerprinting, which can be used alone or in combination with previously established typing platforms.

Management of Bacillus bacteremia: the need for catheter removal

Bacillus species are biofilm-forming organisms that are associated with Bacillus catheter-related bloodstream infections (CRBSIs). The optimal treatment of Bacillus CRBSIs is not known. Therefore, in the current study, we determined the role of long-term central venous catheter (CVC) removal and treatment with vancomycin compared with other agents in Bacillus CRBSIs by retrospectively reviewing the medical records of cancer patients with Bacillus bacteremia who had been treated at our institution from December 1990 to March 2008. True bacteremia was defined as a positive blood culture (>15 colony-forming units/mL) with signs and symptoms of infection (such as fever and chills). Bacillus CRBSI was defined in accordance with the Infectious Diseases Society of America guidelines as probable or definite. There were 94 Bacillus bacteremia episodes, 93 of which (99%) were Bacillus CRBSIs (28% definite and 71% probable). Neutropenia during bacteremia occurred in 29%. Almost all bacteremia patients (99%) had been treated with antibiotics; 63% had received vancomycin. Sepsis with hypotension occurred in 6%, and endocarditis in 1%. Bacillus isolates were susceptible to linezolid (100%), vancomycin (98%), tetracycline (77%), and rifampin (67%). All 4 recurrences occurred in patients in whom the CVC had not been removed (12%), whereas no recurrences occurred in patients whose CVC had been removed (p = 0.028). Patient outcome, in terms of fever and hospitalization duration after the infection, was similar in patients who had received < or =10 days of systemic antibiotics compared with patients who had received >10 days. In conclusion, catheter retention in patients with Bacillus CRBSIs is associated with a significantly higher recurrence rate. If the CVC is retained, treatment with non-vancomycin antibiotics is associated with significantly shorter hospitalization duration after the infection, which may be because glycopeptide antibiotics have poor activity against bacilli embedded in biofilm.

Bacillus cereus meningitis in a term neonate

A case of Bacillus cereus meningitis in a term neonate without identifiable risk factors or source of the organism is presented. Prompt identification of the organism and treatment resulted in a favourable outcome.

Burn wounds infected by contaminated water: case reports, review of the literature and recommendations for treatment

First-aid education for the management of burns advocates cool running water over burnt skin to limit soft tissue damage. However, the water used may itself constitute a risk. We report three cases of severe invasive and necrotizing infection in patients who used or immersed themselves in contaminated water in an attempt to extinguish the fire following acute major burns. Wound cultures from all patients yielded Aeromonas hydrophila and two yielded Bacillus cereus. One patient had a complex polymicrobial infection, including zygomycosis with Rhizomucor variabilis. All patients were treated aggressively with wound débridement, including one patient who required bilateral lower limb amputations to control progressive infection. All infections were successfully treated and all patients survived their burn injuries. We review the management of burns complicated by exposure to contaminated water leading to burn wound infections. We describe commonly reported organisms from various water sources, the appropriate initial empirical antimicrobial chemotherapy and present the clinician with a proposed algorithm for managing these serious infections.

Improving the enrichment procedure for Enterobacteriaceae detection

The current ISO standard method for detection of Enterobacteriaceae (21528-1:2004) includes enrichment in EE broth which has been shown to be inhibitory to some members of this family, notably Cronobacter spp. A shortened procedure omitting the EE broth has been proposed, however competition from Gram-positive flora may be detrimental to the effective recovery of low levels of target organisms in some sample matrices. In this study we investigated novel cost effective modifications, designed to improve ISO 21528-1:2004 for the detection of Enterobacteriaceae. Initial experiments used a worse-case scenario involving stressed Enterobacteriaceae strains known to grow poorly in laboratory media as well as representative background competitors from powdered milk. The interaction between the Enterobacteriaceae and their competitors was characterised and additives to enhance the growth of target strains over non-target strains were investigated. Supplementation of BPW with 40 microM 8-hydroxyquinoline, 0.5 gL(-1) ammonium iron(III) citrate, 0.1 gL(-1) sodium deoxycholate and 0.1 gL(-1) sodium pyruvate (BPW-S) improved the recovery of Enterobacteriaceae from artificially and naturally contaminated samples. This improvement of the pre-enrichment broth may also be of interest for methods designed to detect specific foodborne pathogens belonging to the Enterobacteriaceae (e.g. Salmonella spp., Cronobacter spp.) that require a pre-enrichment step in BPW.

A new rapid and sensitive detection method for cereulide-producing Bacillus cereus using a cycleave real-time PCR

AIMS

To develop a rapid and sensitive detection method for cereulide-producing Bacillus cereus using a real-time PCR based on the sequence of the cereulide synthesis gene.

METHODS AND RESULTS

A total of 56 cereulide-producing B. cereus and 15 cereulide-negative strains were tested. We designed specific primers and probes for the detection of cereulide-producing B. cereus. The new cycleave real-time PCR assay gave positive detections for all of 56 cereulide-producing B. cereus strains, whereas all other strains including 10 systemic infectious disease strains were negative. No cross-reaction was observed and the internal control showed positive for all samples.

CONCLUSIONS

The performance of the assay was highly reproducible and specific for cereulide-producing B. cereus. The positive detection was obtained within only 2 h for cereulide-producing strains. The detection limit of this assay was evaluated as 10(4) CFU g(-1) food sample. The assay also confirmed that strains from systemic infectious cases were cereulide-negative.

SIGNIFICANCE AND IMPACT OF THE STUDY

This assay is applicable for contaminated foods as well as specimens from infectious disease cases. We recommend this assay for routine examination of suspected B. cereus food poisonings.

Cellular functions and X-ray structure of anthrolysin O, a cholesterol-dependent cytolysin secreted by Bacillus anthracis

Anthrolysin O (ALO) is a pore-forming, cholesterol-dependent cytolysin (CDC) secreted by Bacillus anthracis, the etiologic agent for anthrax. Growing evidence suggests the involvement of ALO in anthrax pathogenesis. Here, we show that the apical application of ALO decreases the barrier function of human polarized epithelial cells as well as increases intracellular calcium and the internalization of the tight junction protein occludin. Using pharmacological agents, we also found that barrier function disruption requires increased intracellular calcium and protein degradation. We also report a crystal structure of the soluble state of ALO. Based on our analytical ultracentrifugation and light scattering studies, ALO exists as a monomer. Our ALO structure provides the molecular basis as to how ALO is locked in a monomeric state, in contrast to other CDCs that undergo antiparallel dimerization or higher order oligomerization in solution. ALO has four domains and is globally similar to perfringolysin O (PFO) and intermedilysin (ILY), yet the highly conserved undecapeptide region in domain 4 (D4) adopts a completely different conformation in all three CDCs. Consistent with the differences within D4 and at the D2-D4 interface, we found that ALO D4 plays a key role in affecting the barrier function of C2BBE cells, whereas PFO domain 4 cannot substitute for this role. Novel structural elements and unique cellular functions of ALO revealed by our studies provide new insight into the molecular basis for the diverse nature of the CDC family.

Fructose and glucose mediates enterotoxin production and anaerobic metabolism of Bacillus cereus ATCC14579(T)

AIMS

To determine the effects of carbohydrates on Bacillus cereus ATCC14579(T) anaerobic metabolism and enterotoxin production in amino acids rich medium.

METHODS AND RESULTS

Bacillus cereus anaerobic growth on different carbohydrates (glucose, fructose, sucrose or glucose-fructose mixture) was examined in synthetic mMOD medium under continuous cultures (mu = 0.2 h(-1)). Fermentation end-products, flux partitioning at each key branch points of the mixed acid pathway and consumption or production of amino acids were determined. On both fructose and sucrose, ATP production was favoured via acetate production from acetyl-CoA. In addition, amino acids present in the growth medium showed significant variations with high consumption of serine and net production of glutamate and alanine on some or all sugars. Enterotoxins Hbl and Nhe production was high during growth on fructose (or mixtures involving a fructose moiety).

CONCLUSIONS

Fructose was identified as a key sugar influencing anaerobic metabolism and toxin production of B. cereus.

SIGNIFICANCE AND IMPACT OF THE STUDY

The physiological differences associated with the fermentation of the various carbohydrates clearly modify toxinogenesis indicating that the risk of foodborne pathogens is to some extent dependent upon the prevailing nutritional environment.

Prevalence and toxigenic profiles of Bacillus cereus isolated from dried red peppers, rice, and Sunsik in Korea

Bacillus cereus is a spore-forming foodborne pathogen responsible for diarrheal and emetic types of food poisoning. Intoxication is caused by various enterotoxins or by emetic toxin. Because of its widespread presence and the ability to form heat-stable endospores in a relatively short time, B. cereus has been difficult to control. In this study, 21 rice and 36 Sunsik (a mixture of powdered raw grains) samples were examined for the prevalence of B. cereus. A multiplex PCR assay was used to evaluate the distribution of 10 different toxigenicity-related genes among 1,082 B. cereus strains isolated from dried red peppers (919 isolates), rice (98 isolates), and Sunsik (65 isolates). The results suggest that (i) the examined foods were free of the emetic toxin but not free of enterotoxins and (ii) the distribution of enterotoxigenic genes was significantly different among the B. cereus isolates from various sources.

Phylogeny in aid of the present and novel microbial lineages: diversity in Bacillus

Bacillus represents microbes of high economic, medical and biodefense importance. Bacillus strain identification based on 16S rRNA sequence analyses is invariably limited to species level. Secondly, certain discrepancies exist in the segregation of Bacillus subtilis strains. In the RDP/NCBI databases, out of a total of 2611 individual 16S rDNA sequences belonging to the 175 different species of the genus Bacillus, only 1586 have been identified up to species level. 16S rRNA sequences of Bacillus anthracis (153 strains), B. cereus (211 strains), B. thuringiensis (108 strains), B. subtilis (271 strains), B. licheniformis (131 strains), B. pumilus (83 strains), B. megaterium (47 strains), B. sphaericus (42 strains), B. clausii (39 strains) and B. halodurans (36 strains) were considered for generating species-specific framework and probes as tools for their rapid identification. Phylogenetic segregation of 1121, 16S rDNA sequences of 10 different Bacillus species in to 89 clusters enabled us to develop a phylogenetic frame work of 34 representative sequences. Using this phylogenetic framework, 305 out of 1025, 16S rDNA sequences presently classified as Bacillus sp. could be identified up to species level. This identification was supported by 20 to 30 nucleotides long signature sequences and in silico restriction enzyme analysis specific to the 10 Bacillus species. This integrated approach resulted in identifying around 30% of Bacillus sp. up to species level and revealed that B. subtilis strains can be segregated into two phylogenetically distinct groups, such that one of them may be renamed.

PapR peptide maturation: role of the NprB protease in Bacillus cereus 569 PlcR/PapR global gene regulation

The global transcriptional regulator PlcR controls gene expression in Bacillus cereus and Bacillus thuringiensis. Activity of PlcR is regulated by PapR, the product of an ORF located immediately downstream of plcR. To be active in B. cereus, PapR must be secreted and then processed to the mature peptide by an unknown protease. This peptide is transported by an oligopeptide permease into the cell, where it activates PlcR. In this study, we show that the neutral protease B (NprB) secreted by B. cereus 569 is required for extracellular PapR maturation. Purified recombinant NprB processed the synthetic PapR propeptide to produce a set of peptides derived from the C-terminal domain of PapR. Supplementation of growth media with synthetic PapR-derived C-terminal 5-, 7-, 8- and 27-amino acid (aa) peptides caused activation of intracellular PlcR in a PapR-deficient strain of B. cereus 569 while only the 5- and 7-aa peptides activated PlcR in a nprB mutant. The maximum activity was found for the 7-mer peptide. However, even the 7-mer peptide could not activate PlcR with a C-terminal truncation of as few as 6 aa. This indicates that interactions of the C-terminal regions of both PlcR and PapR are important in transcriptional activation of the B. cereus 569 PlcR regulon.

Role of visible light-activated photocatalyst on the reduction of anthrax spore-induced mortality in mice

Background

Photocatalysis of titanium dioxide (TiO₂) substrates is primarily induced by ultraviolet light irradiation. Anion-doped TiO₂ substrates were shown to exhibit photocatalytic activities under visible-light illumination, relative environmentally-friendly materials. Their anti-spore activity against Bacillus anthracis, however, remains to be investigated. We evaluated these visible-light activated photocatalysts on the reduction of anthrax spore-induced pathogenesis.

Methodology/Principal Findings

Standard plating method was used to determine the inactivation of anthrax spore by visible light-induced photocatalysis. Mouse models were further employed to investigate the suppressive effects of the photocatalysis on anthrax toxin- and spore-mediated mortality. We found that anti-spore activities of visible light illuminated nitrogen- or carbon-doped titania thin films significantly reduced viability of anthrax spores. Even though the spore-killing efficiency is only approximately 25%, our data indicate that spores from photocatalyzed groups but not untreated groups have a less survival rate after macrophage clearance. In addition, the photocatalysis could directly inactivate lethal toxin, the major virulence factor of B. anthracis. In agreement with these results, we found that the photocatalyzed spores have tenfold less potency to induce mortality in mice. These data suggest that the photocatalysis might injury the spores through inactivating spore components.

Conclusion/Significance

Photocatalysis induced injuries of the spores might be more important than direct killing of spores to reduce pathogenicity in the host.

Nosocomial bacteremia caused by biofilm-forming Bacillus cereus and Bacillus thuringiensis

OBJECTIVE

Bacterial biofilms cause serious problems, such as antibiotic resistance and medical device-related infections. Recent reports indicate that Bacillus species potentially form biofilms and cause nosocomial bacteremia via catheter infection. Our objective was to investigate the relationship between nosocomial bacteremia caused by Bacillus species and biofilm formations.

METHODS

Between 2001 and 2006, Bacillus cereus and Bacillus thuringiensis were isolated from blood samples of 21 patients with nosocomial bacteremia in two hospitals. The patients had underlying diseases such as cerebrovascular damage, malignant disease, or chronic obstructive lung disease and had high fever at the onset of bacteremia. After investigation, B. cereus and B. thuringiensis were isolated from patient's catheter tip, gauze, and hospital environment. Pulsed-field gel electrophoresis (PFGE) on 32 B. cereus and 7 B. thuringiensis isolates, microtiter biofilm assay and scanning electron microscopy (SEM) on 22 B. cereus isolates from patient's blood were performed.

RESULTS

Molecular analysis by PFGE showed that 32 B. cereus strains had 21 patterns and 7 B. thuringiensis strains had 3 patterns. The PFGE patterns of B. thuringiensis and B. cereus in blood samples from 2 patients blood were similar to those from the same patient's catheter tip. The PFGE pattern of B. cereus from a hospital environment was similar to that from 2 patients' blood samples, and the PFGE pattern of B. thuringiensis from 2 hospital environments was similar to that from 2 patients' blood. The biofilm formations by 22 B. cereus isolates from patients' blood were confirmed by microtiter biofilm assay and SEM even at 24 hours.

CONCLUSION

Our data indicate that various types of Bacillus species exist in hospital environments and the biofilm-forming strains potentially cause nosocomial bacteremia by catheter infection.

Modelling the number of viable vegetative cells of Bacillus cereus passing through the stomach

AIMS

Model the number of viable vegetative cells of B. cereus surviving the gastric passage after experiments in simulated gastric conditions.

MATERIALS AND METHODS

The inactivation of stationary and exponential phase vegetative cells of twelve different strains of Bacillus cereus, both mesophilic and psychrotrophic strains isolated from food and faeces from healthy and ill individuals, in simulated gastric conditions was determined using decimal reduction times at low pH (D(pH)). Subsequently inactivation rates were calculated. Inclusion of the inactivation rates into models describing the course of the gastric pH after the consumption of meal of solid food and the transfer of food from the stomach to the small intestine resulted in numbers of viable Bacillus cereus vegetative cells able to pass the stomach.

CONCLUSIONS

According to the model, 3-26% of the ingested vegetative cells from Bacillus cereus may survive the gastric passage, dependent on the growth phase of the vegetative cells, the type of strains, and the age of the consumer.

SIGNIFICANCE AND IMPACT OF THE STUDY

Vegetative cells of Bacillus cereus may be involved in the onset of diarrhoeal disease to a greater extent than expected since up to 26% of the ingested cells survive simulated gastric conditions.

Role of germinant receptors in Caco-2 cell-initiated germination of Bacillus cereus ATCC 14579 endospores

Spores obtained from Bacillus cereus ATCC 14579 and mutant strains lacking each of seven germinant receptor operons were exposed to differentiated Caco-2 cells and monitored for germination. Spores of the gerI and gerL mutants showed a reduced germination response, pointing to a role for these receptors in Caco-2-induced germination.

Genetic diversity of clinical isolates of Bacillus cereus using multilocus sequence typing

Background

Bacillus cereus is most commonly associated with foodborne illness (diarrheal and emetic) but is also an opportunistic pathogen that can cause severe and fatal infections. Several multilocus sequence typing (MLST) schemes have recently been developed to genotype B. cereus and analysis has suggested a clonal or weakly clonal population structure for B. cereus and its close relatives B. anthracis and B. thuringiensis. In this study we used MLST to determine if B. cereus isolates associated with illnesses of varying severity (e.g., severe, systemic vs. gastrointestinal (GI) illness) were clonal or formed clonal complexes.

Results

A retrospective analysis of 55 clinical B. cereus isolates submitted to the Centers for Disease Control and Prevention between 1954 and 2004 was conducted. Clinical isolates from severe infections (n = 27), gastrointestinal (GI) illness (n = 18), and associated isolates from food (n = 10) were selected for analysis using MLST. The 55 isolates were diverse and comprised 38 sequence types (ST) in two distinct clades. Of the 27 isolates associated with serious illness, 13 clustered in clade 1 while 14 were in clade 2. Isolates associated with GI illness were also found throughout clades 1 and 2, while no isolates in this study belonged to clade 3. All the isolates from this study belonging to the clade 1/cereus III lineage were associated with severe disease while isolates belonging to clade1/cereus II contained isolates primarily associated with severe disease and emetic illness. Only three STs were observed more than once for epidemiologically distinct isolates.

Conclusion

STs of clinical B. cereus isolates were phylogenetically diverse and distributed among two of three previously described clades. Greater numbers of strains will need to be analyzed to confirm if specific lineages or clonal complexes are more likely to contain clinical isolates or be associated with specific illness, similar to B. anthracis and emetic B. cereus isolates.

Neonatal meningoencephalitis caused by Bacillus cereus

The classic organisms associated with central nervous system infection in the neonate are herpes simplex, Listeria monocytogenes, Escherichia coli, and Streptococcus agalactiae; we describe an unusual case of neonatal meningoencephalitis caused by Bacillus cereus.

Bacillus Cereus Endocarditis in a permanent pacemaker: a case report

Introduction

Bacillus Cereus endocarditis is a rare condition which has been implicated in intravenous drug users, and in patients with prosthetic heart valves. We report a rare case of Bacillus Cereus infecting a permanent pacing wire.

Case presentation

A 69 year old female with a permanent pacemaker presented with rigors, sweats and weight loss. Blood cultures grew Bacillus Cereus; Transesophageal echocardiogram demonstrated a mobile lesion attached to the pacing wire. She was treated with appropriate intravenous antibiotics for 6 weeks with a good clinical recovery at 6 months follow up.

Conclusion

This case reminds the clinician to have a high index of suspicion for endocarditis in any patient with cardiac prosthesis and to pursue the blood culture results even for rare and unexpected organisms. It also suggests the possibility of a trial of antibiotic therapy prior to prosthesis removal in select patients who are not in heart failure and hemodynamically stable.

Bacillus cereus nosocomial infection from reused towels in Japan

It was noticed that there was an increase in Bacillus cereus nosocomial infections in the summer from 2000 to 2005. In 2005, five bloodstream infections occurred in five patients related to catheter use. The causative strains were distinct from each other and belonged to novel multilocus sequence types (ST): ST365, ST366, ST367 and ST368. Two ST365 strains from two patients were further distinguished by pulsed-field gel electrophoresis. B. cereus contamination was observed with reused (dried and steamed) towels (>10(6)cfu/towel) and washing machines in hospital linen rooms. B. cereus strains from towels belonged to ST167, ST365, ST380 and ST382, and a proportion of these were the same, or similar, to strains from patients. All the hospital strains of B. cereus were distinct from those from food-poisoning strains (ST26, ST142, ST381). Ciprofloxacin resistance was observed only in hospital strains. Neither emetic toxin nor cytotoxin K gene, usually present in food poisoning strains, were found in the hospital strains, except for one patient isolate. The data suggest that specific B. cereus strains are circulating within a hospital, with genotypes, antibiotic susceptibilities and virulence gene patterns generally distinct from those of food poisoning, and that in Japan, towels are an important source of contamination, especially in summer.

Extracellular proteolytic activities expressed by Bacillus pumilus isolated from endodontic and periodontal lesions

The purpose of the present study was to identify 12 Bacillus isolates that had been obtained from root canals of teeth requiring endodontic therapy and from periodontal pockets in severe marginal periodontitis, and to determine whether these isolates exhibited extracellular proteolytic activity and, using in vitro assays, whether any such activity could degrade substrates that would be pathophysiologically relevant with regard to the production of endodontic and periodontal lesions. Biochemical and carbohydrate fermentation patterns were used in the identification of all strains, which was confirmed by determination of the16S rRNA gene sequence for strain BJ0055. Screening for production of extracellular proteolytic activity by all strains was done with a general proteinase substrate. All isolates were identified as representing Bacillus pumilus and all exhibited extracellular proteolytic activity. The putative pathophysiological relevance of extracellular proteinase production in strain BJ0055 was assessed using fluorophore-labelled elastin and collagen and several chromogenic peptides. Probable classes of proteinases acting on each substrate were investigated using class-specific inhibitors. Activity-pH profiles were determined in buffers at different pH values. Extracellular activities that were caseinolytic, elastinolytic, collagenolytic, glutamyl endopeptidase-like, and alanyl tripeptidyl peptidase-like were observed. No trypsin-like activities were detected. Serine- and chymotrypsin-like serine proteinase activities were detected, with activity observed at neutral and alkaline, but not acidic, pH. B. pumilus strains isolated from endodontic and periodontal lesions exhibited extracellular activities that degrade elastin, collagen and other substrates. These activities may be virulence factors that contribute to tissue damage in apical periodontitis and severe marginal periodontitis.

Identification of proteolytic bacteria from thai traditional fermented foods and their allergenic reducing potentials

This study aimed to identify proteolytic bacteria from Thai traditional fermented foods and investigate their allergenic reducing potentials to wheat and milk allergens. Nine bacteria were isolated from fermented foods as follows: fermented soybean seeds (Thua Nao), fermented soybean paste (Thua Nao), wheat flour dough of steamed stuffed bun (Sa La Pao), and soaked rice from Thai fermented rice-noodle (Kha Nhom Jeen) processing. Both phenotypic and genotypic identifications were used in this study. It was found that all isolates were Gram-positive rods. Seven isolates were matched and identified as Bacillus subtilis by both techniques, and the remaining 2 isolates were phenotypically and genotypically identified as B. licheniformis and B. subtilis, respectively. The concentrated crude enzyme of B. subtilis DB and SR could reduce allergenicity of gliadin by hydrolyzing the allergenic gliadin fragments detected by immunoblotting. Furthermore, the enzyme of B. subtilis DB could also reduce allergenicity of beta-lactoglobulin (beta-LG) detected by hydrolyzing the major allergenic epitope of beta-LG at Gln(35)-Ser(36) position. B. subtilis DB and SR can be applied for the production of hypoallergenic wheat flour or milk food products.

Levels and toxigenicity of Bacillus cereus and Clostridium perfringens from retail seafood

For the period 1990 through 2003, seafood was the most commonly identified food linked to foodborne outbreaks in the United States. Fish as a commodity has rarely been examined for the presence of Bacillus cereus in particular. For the present study, 347 fresh and processed retail seafood samples were examined for the presence of Clostridium botulinum, Clostridium perfringens, and B. cereus. The presence of C. botulinum was not confirmed in any of the isolates, but C. perfringens was confirmed in 17 samples. One of the C. perfringens isolates possessed the enterotoxin gene, as determined by PCR. In contrast, 62 confirmed B. cereus isolates were obtained from separate samples at levels ranging from 3.6 to > 1,100 CFU/g. Thirty (48%) of 62 isolates produced both the hemolysin BL (HBL) and nonhemolytic (NHE) enterotoxins, and 58 (94%) and 31 (50%) produced NHE or HBL toxins, respectively. The presence of at least one of the three genes of the NHE complex was detected in 99% of the isolates; 69% of the isolates possessed all three genes. In contrast, 71% of the isolates possessed at least one of the three genes of the HBL complex, and 37% possessed all three HBL gene components. Fifty of the 62 B. cereus isolates were from imported seafood, and 19 (38%) of these samples were at levels > 100 CFU/g. Twelve of the 14 highest enterotoxin assay results were from isolates from imported food. Only one B. cereus isolate possessed the cereulide synthetase gene, ces; this isolate also possessed the genes for the three-component HBL and NHE complexes. A majority of enterotoxin-producing isolates were resistant to 2 of 10 antibiotics tested, ceftriaxone and clindamycin. Our results demonstrate the potential of seafood as a vehicle for foodborne illness caused by B. cereus, in particular the enterotoxin-producing genotype.

Petrobactin is produced by both pathogenic and non-pathogenic isolates of the Bacillus cereus group of bacteria

Petrobactin is the primary siderophore synthesized by Bacillus anthracis str Sterne and is required for virulence of this organism in a mouse model. The siderophore's biosynthetic machinery was recently defined and gene homologues of this operon exist in several other Bacillus strains known to be mammalian pathogens, but are absent in several known to be harmless such as B. subtilis and B. lichenformis. Thus, a common hypothesis regarding siderophore production in Bacillus species is that petrobactin production is exclusive to pathogenic isolates. In order to test this hypothesis, siderophores produced by 106 strains of an in-house library of the Bacillus cereus sensu lato group were isolated and identified using a MALDI-TOF-MS assay. Strains were selected from a previously defined phylogenetic tree of this group in order to include both known pathogens and innocuous strains. Petrobactin is produced by pathogenic strains and innocuous isolates alike, and thus is not itself indicative of virulence.