An emetic Bacillus cereus outbreak in a kindergarten: detection and quantification of critical levels of cereulide toxin

A poisonous cocktail: interplay of cereulide toxin and its structural isomers in emetic Bacillus cereus

Food intoxications evoked by emetic Bacillus cereus strains constitute a serious threat to public health, leading to emesis and severe organ failure. The emetic peptide toxin cereulide, assembled by the non-ribosomal peptide synthetase CesNRPS, cannot be eradicated from contaminated food by usual hygienic measures due to its molecular size and structural stability. Next to cereulide, diverse chemical variants have been described recently that are produced concurrently with cereulide by CesNRPS. However, the contribution of these isocereulides to the actual toxicity of emetic B. cereus, which produces a cocktail of these toxins in a certain ratio, is still elusive. Since cereulide isoforms have already been detected in food remnants from foodborne outbreaks, we aimed to gain insights into the composition of isocereulides and their impact on the overall toxicity of emetic B. cereus. The amounts and ratios of cereulide and isocereulides were determined in B. cereus grown under standard laboratory conditions and in a contaminated sample of fried rice balls responsible for one of the most severe food outbreaks caused by emetic B. cereus in recent years. The ratios of variants were determined as robust, produced either under laboratory or natural, food-poisoning conditions. Examination of their actual toxicity in human epithelial HEp2-cells revealed that isocereulides A-N, although accounting for only 10% of the total cereulide toxins, were responsible for about 40% of the total cytotoxicity. An this despite the fact that some of the isocereulides were less cytotoxic than cereulide when tested individually for cytotoxicity. To estimate the additive, synergistic or antagonistic effects of the single variants, each cereulide variant was mixed with cereulide in a 1:9 and 1:1 binary blend, respectively, and tested on human cells. The results showed additive and synergistic impacts of single variants, highlighting the importance of including not only cereulide but also the isocereulides in routine food and clinical diagnostics to achieve a realistic toxicity evaluation of emetic B. cereus in contaminated food as well as in patient samples linked to foodborne outbreaks. Since the individual isoforms confer different cell toxicity both alone and in association with cereulide, further investigations are needed to fully understand their cocktail effect.

Development of a simple screening method for analyzing cereulide toxin in fried rice using liquid chromatography-tandem mass spectrometry

PURPOSE

The presence of cereulide, an emetic toxin produced by Bacillus cereus, in fried rice samples is critical evidence of food poisoning even in situations where B. cereus could not be detected. This study aims to develop a screening method for analyzing cereulide in fried rice using the QuEChERS procedure and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

METHODS

Cereulide was identified and quantified in fried rice samples using the QuEChERS extraction method and LC-MS/MS. The accuracies of the methods were determined by analyzing fortified blank samples at two concentrations (10 and 50 µg/kg) conducted on three samples daily for five days.

RESULTS

The QuEChERS procedure removed matrix compounds from fried rice. Characteristic MS/MS spectra enabled the identification of cereulide. As the matrix effects in seven fried rice samples were within ± 6%, an external solvent calibration curve could be used for quantification. This method exhibited good accuracy ranging from 88 to 89%. The relative standard deviations for both repeatability and intra-laboratory reproducibility were < 4%. These standard deviations satisfied the criteria of the Japanese validation guidelines for residues (MHLW 2010, Director Notice, Syoku-An No. 1224-1). The limit of quantification was 2 μg/kg. The applicability of this method was confirmed using the analysis of cereulide in fried rice samples incubated with emetic Bacillus cereus.

CONCLUSIONS

The QuEChERS extraction procedure described herein showed substantial promise as a reliable screening tool for cereulide in fried rice sample.

Validation of a Targeted LC-MS/MS Method for Cereulide and Application in Food and Faeces

Cereulide is an emetic toxin produced by some strains of Bacillus cereus. This bacterial toxin, a cyclic 1.2 kDa dodecadepsipeptide, is stable to heat and acids and causes nausea and vomiting when ingested via contaminated food. This work aimed to develop and validate a targeted analytical method applying liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantify this toxin in food and human faeces. Samples were extracted with acetonitrile in the presence of 13C6-cereulide, a labelled internal standard, and purified by centrifugation and filtration. The limits of quantification were 0.5 and 0.3 µg kg-1 for food and faeces, respectively. The linearity of the method was very good, with calculated R2 values above 0.995. The mean recovery of the method was within the acceptable range of 70.0%-120.0%, the repeatability was not higher than 7.3%, and the highest intra-laboratory reproducibility was 8.9%. The estimated range for the expanded measurement uncertainty was between 5.1% and 18.0%. The LC-MS/MS method was used to analyse one food sample (rice) from a Belgian foodborne outbreak and five faecal samples from patients with clinical symptoms after consumption of the contaminated rice. The levels of cereulide were 12.22 µg g-1 for food and between 6.32 and 773.37 ng g-1 for faecal samples.

Portable dual-aptamer microfluidic chip biosensor for Bacillus cereus based on aptamer tailoring and dumbbell-shaped probes

As food-borne pathogens, Bacillus cereus not only produce toxins that contaminate food and threaten human health, but also rely on spores to resist extreme environments. At present, the detection of B. cereus is still at the genome level and it is not easily distinguished from other Bacilli of the same group. Herein, we obtained the aptamers of B. cereus in different phases through Cell-SELEX technology. Then, through step-by-step tailoring and molecular docking, the two best performing aptamers were ascertained and the interaction revealed between the repeated G bases in the aptamer and the polar amino acids in the α-helix of the epiprotein. Based on these aptamers, a multifunctional dumbbell-shaped probe and an ultrasensitive microfluidic chip biosensor were designed. Tests showed that the novel sensor is able to complete detection within 1 h with a limit of detection (LOD) of 9.27 CFU/mL. Moreover, the sensor can be used in complex food environments, such as milk and rice, is able to detect both vegetative cells and spores, and it can also distinguish B. thuringiensis from the same flora. This study can provide a reference for the future development of food-borne pathogenic bacteria aptamer selecting, target interaction analysis, detection methods and equipment.

Cereulide and Emetic Bacillus cereus: Characterizations, Impacts and Public Precautions

Cereulide, which can be produced by Bacillus cereus, is strongly associated with emetic-type food poisoning outbreaks. It is an extremely stable emetic toxin, which is unlikely to be inactivated by food processing. Considering the high toxicity of cereulide, its related hazards raise public concerns. A better understanding of the impact of B. cereus and cereulide is urgently needed to prevent contamination and toxin production, thereby protecting public health. Over the last decade, a wide range of research has been conducted regarding B. cereus and cereulide. Despite this, summarized information highlighting precautions at the public level involving the food industry, consumers and regulators is lacking. Therefore, the aim of the current review is to summarize the available data describing the characterizations and impacts of emetic B. cereus and cereulide; based on this information, precautions at the public level are proposed.

Rapid, Sensitive, and Selective Quantification of Bacillus cereus Spores Using xMAP Technology

Bacillus cereus is a spore-forming ubiquitous bacterium notable as a food poisoning agent. Detection of B. cereus spores using selective media is laborious and non-specific. Herein, the quantitative detection of B. cereus spores was investigated with commercial antibodies and published aptamer sequences. Several detection reagents were screened for affinity to Bacillus collagen-like protein A (BclA), an abundant exosporium glycoprotein. Sensitivity and selectivity toward B. cereus spores were tested using immunoassays and multi-analyte profiling (xMAP). A recombinant antibody developed in llama against BclA protein showed B. cereus spore selectivity and sensitivity between 10² and 10⁵ spores/mL using xMAP. DNA aptamer sequences demonstrated sensitivity from 10³ to 10⁷ spores/mL and no cross-reaction to B. megaterium and B. subtilis. Selectivity for B. cereus spores was also demonstrated in a mixture of several diverse microorganisms and within a food sample with no compromise of sensitivity. As proof of concept for multiplexed measurement of human pathogens, B. cereus and three other microorganisms, E. coli, P. aeruginosa, and S. cerevisiae, were simultaneously detected using xMAP. These data support the development of a rapid, sensitive, and selective system for quantitation of B. cereus spores and multiplexed monitoring of human pathogens in complex matrices.

Insight into Bacillus cereus Associated with Infant Foods in Beijing

This study was undertaken to investigate the prevalence, antimicrobial resistance, and virulence gene profiles of Bacillus cereus in different brands of infant formula in Beijing supermarkets. Eighty-eight Bacillus cereus isolates were recovered in sixty-eight infant formulas of five domestic brands and fourteen imported brands. The prevalence rate in domestic and imported samples were 70.6% and 52.9%, respectively. Lower mean prevalence level was found in domestic samples (1.17 MPN/g) compared with the imported samples (3.52 MPN/g). Twenty-four virulence gene profiles were found, and most strains carried at least one virulence gene. The prevalence of nheA, nheB, nheC, cytK, bceT, and entFM in domestic and imported brand samples was similar. The occurrence of enterotoxin genes hblA, hblC, and hblD in domestic samples were 22.2%, 27.8%, and 22.2%, respectively, which was significantly higher than imported samples. Antimicrobial drugs-susceptibility analysis showed that all isolates were susceptible to gentamincin, amikacin, and ciprofloxacin; 38%, 7%, and 2.3% were resistant to rifampin, tetracycline, and chloramphenicol, respectively; and only one isolate was resistant to trimethoprim-sulfamethoxazole. Moreover, the cell numbers of Bacillus cereus in prepared infant formula increased rapidly at room temperature. Thus, monitoring guidelines are needed for accepted levels of Bacillus cereus in infant formula.

Cereulide Exposure Caused Cytopathogenic Damages of Liver and Kidney in Mice

Cereulide is one of the main food-borne toxins for vomiting synthesized by Bacillus cereus, and it widely contaminates meat, eggs, milk, and starchy foods. However, the toxicological effects and mechanisms of the long-time exposure of cereulide in vivo remain unknown. In this study, oral administration of 50 and 200 μg/kg body weight cereulide in the mice for 28 days caused oxidative stress in liver and kidney tissues and induce abnormal expression of inflammatory factors. In pathogenesis, cereulide exposure activated endoplasmic reticulum stress (ER stress) via the pathways of inositol-requiring enzyme 1α (IRE1α)/Xbox binding protein (XBP1) and PRKR-like ER kinase (PERK)/eukaryotic translation initiation factor 2α (eIF2α), and consequently led to the apoptosis and tissue damages in mouse liver and kidney. In vitro, we confirmed that the accumulation of reactive oxygen species (ROS) caused by cereulide is the main factor leading to ER stress in HepaRG and HEK293T cells. Supplementation of sodium butyrate (NaB) inhibited the activations of IRE1α/XBP1 and PERK/eIF2α pathways caused by cereulide exposure in mice, and reduced the cell apoptosis in liver and kidney. In conclusion, this study provides a new insight in understanding the toxicological mechanism and prevention of cereulide exposure.

Bacillus cereus food intoxication and toxicoinfection

Bacillus cereus is one of the leading etiological agents of toxin-induced foodborne diseases. Its omnipresence in different environments, spore formation, and its ability to adapt to varying conditions and produce harmful toxins make this pathogen a health hazard that should not be underestimated. Food poisoning by B. cereus can manifest itself as an emetic or diarrheal syndrome. The former is caused by the release of the potent peptide toxin cereulide, whereas the latter is the result of proteinaceous enterotoxins (e.g., hemolysin BL, nonhemolytic enterotoxin, and cytotoxin K). The final harmful effect is not only toxin and strain dependent, but is also affected by the stress responses, accessory virulence factors, and phenotypic properties under extrinsic, intrinsic, and explicit food conditions and host-related environment. Infamous portrait of B. cereus as a foodborne pathogen, as well as a causative agent of nongastrointestinal infections and even nosocomial complications, has inspired vast volumes of multidisciplinary research in food and clinical domains. As a result, extensive original data became available asking for a new, both broad and deep, multifaceted look into the current state-of-the art regarding the role of B. cereus in food safety. In this review, we first provide an overview of the latest knowledge on B. cereus toxins and accessory virulence factors. Second, we describe the novel taxonomy and some of the most pertinent phenotypic characteristics of B. cereus related to food safety. We link these aspects to toxin production, overall pathogenesis, and interactions with its human host. Then we reflect on the prevalence of different toxinotypes in foods opening the scene for epidemiological aspects of B. cereus foodborne diseases and methods available to prevent food poisoning including overview of the different available methods to detect B. cereus and its toxins.

Traditional and Artisanal Beverages in Nigeria: Microbial Diversity and Safety Issues

A review of up to 90 articles on the microorganisms associated with important artisanal or traditional beverages in Nigeria was carried out. This resulted in an overview of the prevalent microorganisms associated with soymilk, nono (fermented cow milk), tiger nut milk, yoghurt, kunu, zobo, palm wine and the local beers pito and brukutu. The bacteria genera, namely Bacillus, Escherichia, Lactobacillus, Staphylococcus, and Streptococcus, were detected in all nine beverages. On the contrary, this survey resulted in finding that the genera Saccharomyces, Aspergillus, Candida, and Penicillium were the eukaryotic microorganisms isolated in all beverages. The occurrence of fungal isolates, which can be responsible for producing mycotoxins, is a concern and shows the need for post-production tests. Overall, there is a low prevalence of bacteria associated with hygiene, especially the Escherichia genus in alcoholic beverages such as palm wine, pito and burukutu, which may be due both to a low acidity and high ethanol content. However, the prevalence of hygiene indicator genera was higher in nonalcoholic drinks, probably because of incorrect practices during processing. The magnitude of the production and sales of unregulated local beverages in Nigeria has reached the stage where significant regulation and food safety standards are required to safeguard public health. An opportunity exists to monitor and characterize the microbial flora of the artisanal beverages using molecular methods at all stages of production and storage.

Enterotoxin and Emetic Toxin Genes Profiles and Genetic Diversity of Bacillus cereus Isolated from Food, Environmental and Clinical Samples in Serbia

Bacillus cereus, usually ingested by food, can cause two types of disease due to the presence of toxins: vomiting and diarrhea syndrome. Systemic infections can also occur. The aim was to detect genes for enterotoxins (hblA, entFM) and emetic toxin (cer) and to investigate the genetic heterogeneity of B. cereus isolates from food, environment and human stool. Identification of B. cereus was performed by means of selective medium, classical biochemical test and polymerase chain reaction (PCR). Toxin genes were detected by PCR. Typing was performed by random amplified polymorphic DNA (RAPD). EntFM gene was present in all stool and food samples and in 28/30 environmental isolates. HblA gene was present in 29/30 stool, 23/30 food and 24/30 environmental isolates. Cer gene was present in 30/30 stool, 28/30 food and 25/30 environmental isolates. The RAPD results show high heterogeneity among the isolates from each group. In the cumulative dendrogram, representative isolates from all three groups formed two clusters with a difference of 53%. The detection of toxin genes in all B. cereus isolates indicated these bacteria as potentially pathogenic and a serious threat for human health. The presence of isolates from all three groups in the same cluster suggests the existence of similar strains in the environment, food and patients, which is in line with the circulation of strains in nature through the food chain.

Advanced Methods for Detection of Bacillus cereus and Its Pathogenic Factors

Bacillus cereus is an opportunistic foodborne pathogen causing food intoxication and infectious diseases. Different toxins and pathogenic factors are responsible for diarrheal syndrome, like nonhemolytic enterotoxin Nhe, hemolytic enterotoxin Hbl, enterotoxin FM and cytotoxin K, while emetic syndrome is caused by the depsipeptide cereulide toxin. The traditional method of B. cereus detection is based on the bacterial culturing onto selective agars and cells enumeration. In addition, molecular and chemical methods are proposed for toxin gene profiling, toxin quantification and strain screening for defined virulence factors. Finally, some advanced biosensors such as phage-based, cell-based, immunosensors and DNA biosensors have been elaborated to enable affordable, sensitive, user-friendly and rapid detection of specific B. cereus strains. This review intends to both illustrate the state of the B. cereus diagnostic field and to highlight additional research that is still at the development level.

Monitoring of Hygiene in Institutional Kitchens in Belgium

ABSTRACT

Microbiological contamination of food during preparation and storage is a risk factor in institutional kitchens. In this Belgian study, hygiene practices in 40 institutional kitchens from four public sectors (10 hospitals, 10 schools, 10 retirement homes, and 10 child care centers) were evaluated to determine whether differences in these practices exist between these sectors. Contamination levels were also analyzed at several critical contact points. A data collection instrument and microbiological analysis of hand contact surfaces, food contact surfaces, and kitchen utensils were used. Hand washing resulted in only a slight reduction in total aerobic bacteria counts (TACs), and all microorganisms evaluated except E. coli were still present at countable levels. Enterobacteriaceae were found on one-third of the cleaned cutting boards. Cleaned work surfaces had the highest average TAC of all cleaned surfaces. Only slight improvements in TACs and Enterobacteriaceae and B. cereus counts were observed between used and cleaned work surfaces. The results from the data collection instrument revealed that child care centers had the lowest hygiene scores, whereas the other three sectors were fairly similar, with hospitals scoring highest. The low hygiene score for the child care centers was verified by comparing the results for cleaned surfaces among the sectors. The average TAC on surfaces was highest for child care centers and lowest for hospitals. Child care centers also had the second highest total mean counts and the highest number of total surface samples positive for Enterobacteriaceae. The highest number of surface samples positive for Staphylococcus aureus was also found in child care centers. This study highlights some areas of concern for hygiene improvement in institutional kitchens, differences between public sectors, and similarities in conclusions about hygiene based on the scores from the survey instrument and the results of the microbiological analyses.

HIGHLIGHTS

A Study on Prevalence and Characterization of Bacillus cereus in Ready-to-Eat Foods in China

Bacillus cereus is widely distributed in different food products and can cause a variety of symptoms associated with food poisoning. Since ready-to-eat (RTE) foods are not commonly sterilized by heat treatment before consumption, B. cereus contamination may cause severe food safety problems. In this study, we investigated the prevalence of B. cereus in RTE food samples from different regions of China and evaluated the levels of bacterial contamination, antibiotic resistance, virulence gene distribution, and genetic polymorphisms of these isolates. Of the tested retail RTE foods, 35% were positive for B. cereus, with 39 and 83% of the isolated strains harboring the enterotoxin-encoding hblACD and nheABC gene clusters, respectively. The entFM gene was detected in all B. cereus strains. The cytK gene was present in 68% of isolates, but only 7% harbored the emetic toxin-encoding gene cesB. Antimicrobial susceptibility testing revealed that the majority of the isolates were resistant not only to most β-lactam antibiotics, but also to rifamycin. Multilocus sequence typing (MLST) revealed that the 368 isolates belonged to 192 different sequence types (STs) including 93 new STs, the most prevalent of which was ST26. Collectively, our study indicates the prevalence, bacterial contamination levels, and biological characteristics of B. cereus isolated from RTE foods in China and demonstrates the potential hazards of B. cereus in RTE foods.

Review of Electrochemical DNA Biosensors for Detecting Food Borne Pathogens

The vital importance of rapid and accurate detection of food borne pathogens has driven the development of biosensor to prevent food borne illness outbreaks. Electrochemical DNA biosensors offer such merits as rapid response, high sensitivity, low cost, and ease of use. This review covers the following three aspects: food borne pathogens and conventional detection methods, the design and fabrication of electrochemical DNA biosensors and several techniques for improving sensitivity of biosensors. We highlight the main bioreceptors and immobilizing methods on sensing interface, electrochemical techniques, electrochemical indicators, nanotechnology, and nucleic acid-based amplification. Finally, in view of the existing shortcomings of electrochemical DNA biosensors in the field of food borne pathogen detection, we also predict and prospect future research focuses from the following five aspects: specific bioreceptors (improving specificity), nanomaterials (enhancing sensitivity), microfluidic chip technology (realizing automate operation), paper-based biosensors (reducing detection cost), and smartphones or other mobile devices (simplifying signal reading devices).

Why be serious about emetic Bacillus cereus: Cereulide production and industrial challenges

Cereulide, a potent toxin produced by Bacillus cereus, is a small, highly heat- and acid-resistant depsipeptide toxin, which confronts food industry with several challenges. Due to the ubiquitous presence of B. cereus in the environment, this opportunistic pathogen can enter food production and processing at almost any stage. Although the bacteria itself might be removed during food processing, the cereulide toxin will most likely not be destroyed or inactivated by these processes. Because of the high toxicity of cereulide and the high incidence rates often observed in connection with foodborne outbreaks, the understanding of the mechanisms of toxin production as well as accurate data on contamination sources and factors promoting toxin formation are urgently needed to prevent contamination and toxin production in food production processes. Over the last decade, considerable progress had been made on the understanding of cereulide toxin biosynthesis in emetic B. cereus, but an overview of current knowledge on this toxin with regards to food industry perspective is lacking. Thus, we aim in this work to summarize data available on extrinsic parameters acting on cereulide toxin synthesis in emetic B. cereus and to discuss the food industry specific challenges related to this toxin. Furthermore, we emphasize how identification of the cardinals in food production processes can lead to novel effective strategies for prevention of toxin formation in the food processing chain and could contribute to the improvement of existing HACCP studies.

Multifaceted toxin profile, an approach toward a better understanding of probiotic Bacillus cereus

Strains of the Bacillus cereus group have been widely used as probiotics for human beings, food animals, plants, and environmental remediation. Paradoxically, B. cereus is responsible for both gastrointestinal and nongastrointestinal syndromes and represents an important opportunistic food-borne pathogen. Toxicity assessment is a fundamental issue to evaluate safety of probiotics. Here, we summarize the state of our current knowledge about the toxins of B. cereus sensu lato to be considered for safety assessment of probiotic candidates. Surfactin-like emetic toxin (cereulide) and various enterotoxins including nonhemolytic enterotoxin, hemolysin BL, and cytotoxin K are responsible for food poisoning outbreaks characterized by emesis and diarrhea. In addition, other factors, such as hemolysin II, Certhrax, immune inhibitor A1, and sphingomyelinase, contribute to toxicity and overall virulence of B. cereus.

Removal of B. cereus cereulide toxin from monoclonal antibody bioprocess feed via two-step Protein A affinity and multimodal chromatography

A rapid and sensitive liquid chromatography-mass spectrometry assay was developed and used to quantify emetic cereulide peptide exotoxin, which can be related to possible Bacillus cereus contamination in monoclonal antibody (mAb) bioprocess feeds. The assay limit of detection was 0.05 ng/mL (~1 fmol injected) and limit of quantification 0.16 ng/mL (~3 fmol injected) over a standard curve with >3 orders of magnitude linear dynamic range. The assay allowed quantification of toxin removal in an established two-step mAb purification process consisting of Protein A affinity chromatography followed by multi-modal anion exchange chromatography. Toxin content was ascertained in process stream sample fractions as well as on the Protein A affinity column. An optimized analytical method allowed separation of cereulide toxin from other mAb cell culture components within 6 min. Spiking experiments showed that samples should be collected in high (80% v/v) content acetonitrile to reduce nonspecific losses of the cereulide. The majority of mAb purification process-associated cereulide was detected in the Protein A flow through fraction, whereas only residual amounts were found in wash, strip, and elution fractions. Column cleaning-in-place (CIP) procedures were evaluated to prevent carryover between affinity capture cycles. No carryover was detected between cycles, however trace amounts of cereulide were extracted from the Protein A resin. Increasing the CIP NaOH concentration from 0.1 M to 0.5 M, and contact time from 15 min to 1 h, improved removal of residual cereulide from the resin. Applicability of CIP clearance of cereulide during Protein A chromatography was confirmed with three different mAb feeds. Post Protein A polishing, via target flow through on a multi-modal anion exchange chromatography column, resulted in a product pool with no detectable cereulide. Approximately 5 logs of reduction in cereulide concentration was obtained over the two-step chromatography process. Cereulide contamination is well known and of concern in food processing, however this research may be the first LC-MS quantification of cereulide contamination, and its clearance, in biopharmaceutical mAb processing. The analytical method may also be used to rapidly screen for cereulide contamination in upstream cell culture process streams, prior to downstream product purification. This will allow appropriate measures to be taken to reduce toxin exposure to downstream bioprocess raw materials, consumables and equipment.

First Insights Into Within Host Translocation of the Bacillus cereus Toxin Cereulide Using a Porcine Model

Bacillus cereus is a gram-positive pathogen mainly known to evoke two types of foodborne poisonings. The diarrheal syndrome is caused by enterotoxins produced during growth in the intestine. In contrast, the emetic type is caused by the dodecadepsipeptide cereulide pre-formed in food. Usually, both diseases are self-limiting but occasionally more severe forms, including fatal ones, are reported. Since the mechanisms of cereulide toxin uptake and translocation within the body as well as the mechanism of its toxic action are still unknown, we used a porcine model to investigate the uptake, routes of excretion and distribution of cereulide within the host. Pigs were orally challenged with cereulide using single doses of 10-150 μg cereulide kg^-1 body weight to study acute effects or using daily doses of 10 μg cereulide kg^-1 body weight administered for 7 days to investigate effects of longtime, chronic exposure. Our study showed that part of cereulide ingested with food is rapidly excreted with feces while part of the cereulide toxin is absorbed, passes through membranes and is distributed within the body. Results from the chronic trial indicate bioaccumulation of cereulide in certain tissues and organs, such as kidney, liver, muscles and fat tissues. Beside its detection in various tissues and organs, our study also demonstrated that cereulide is able to cross the blood-brain-barrier, which may partially explain the cerebral effects reported from human intoxication cases. The neurobehavioral symptoms, such as seizures and lethargy, observed in our porcine model resemble those reported from human food borne intoxications. The rapid onset of these symptoms indicates direct effects of cereulide on the central nervous system (CNS), which warrant further research. The porcine model presented here might be useful to study the specific neurobiological effect in detail. Furthermore, our study revealed that typical diagnostic specimens used in human medicine, such as blood samples and urine, are not suitable for diagnostics of food borne cereulide intoxications. Instead, screening of fecal samples by SIDA-LC-MS may represent a simple and non-invasive method for detection of cereulide intoxications in clinical settings as well as in foodborne outbreak situations.

Characterization of Enterotoxigenic Bacillus cereus sensu lato and Staphylococcus aureus Isolates and Associated Enterotoxin Production Dynamics in Milk or Meat-Based Broth

Bacillus cereus sensu lato species, as well as Staphylococcus aureus, are important pathogenic bacteria which can cause foodborne illness through the production of enterotoxins. This study characterised enterotoxin genes of these species and examined growth and enterotoxin production dynamics of isolates when grown in milk or meat-based broth. All B. cereus s. l. isolates harboured nheA, hblA and entFM toxin genes, with lower prevalence of bceT and hlyII. When grown at 16 °C, toxin production by individual B. cereus s. l. isolates varied depending on the food matrix; toxin was detected at cell densities below 5 log₁₀(CFU/mL). At 16 °C no staphylococcal enterotoxin C (SEC) production was detected by S. aureus isolates, although low levels of SED production was noted. At 30 °C all S. aureus isolates produced detectable enterotoxin in the simulated meat matrix, whereas SEC production was significantly reduced in milk. Relative to B. cereus s. l. toxin production, S. aureus typically required reaching higher cell numbers to produce detectable levels of enterotoxin. Phylogenetic analysis of the sec and sel genes suggested population evolution which correlated with animal host adaptation, with subgroups of bovine isolates or caprine/ovine isolates noted, which were distinct from human isolates. Taken together, this study highlights the marked differences in the production of enterotoxins both associated with different growth matrices themselves, but also in the behaviour of individual strains when exposed to different food matrices.

Development and validation of ultra-high-performance liquid chromatography-tandem mass spectrometry methods for the simultaneous determination of beauvericin, enniatins (A, A1, B, B1) and cereulide in maize, wheat, pasta and rice

Rapid and accurate UPLC-MS/MS methods for the simultaneous determination of beauvericin and the related enniatins (A, A1, B, B1), together with cereulide were successfully developed and validated in cereal and cereal-based food matrices such as wheat, maize, rice and pasta. Although these emerging foodborne toxins are of different microbial origin, the similar structural, toxicological and food safety features provided rationale for their concurrent detection in relevant food matrices. A Waters Acquity UPLC system coupled to a Waters Quattro Premier XE™ Mass Spectrometer operating in ESI+ mode was employed. Sample pretreatment involved a fast and simple liquid extraction of the target toxins without any further clean-up step. For all toxins the sample preparation resulted in acceptable extraction recoveries with values of 85-105% for wheat, 87-106% for maize, 84-106% for rice and 85-105% for pasta. The efficient extraction protocol, together with a fast chromatographic separation of 7min allowed substantial saving costs and time showing its robustness and performance. The validation of the developed method was performed based on Commission Decision 2002/657/EC. The obtained limits of detection ranged from 0.1 to 1.0μgkg^-1 and the limits of quantification from 0.3 to 2.9μgkg^-1 for the targeted toxins in the selected matrices. The obtained sensitivities allow detection of relevant toxicological concentrations. All relative standard deviations for repeatability (intra-day) and intermediate precision (inter-day) were lower than 20%. Trueness, expressed as the apparent recovery varied from 80 to 107%. The highly sensitive and repeatable validated method was applied to 57 naturally contaminated samples allowing detection of sub-clinical doses of the toxins.

Characterization and Exposure Assessment of Emetic Bacillus cereus and Cereulide Production in Food Products on the Dutch Market

The emetic toxin cereulide, which can be produced by Bacillus cereus, can be the cause of food poisoning upon ingestion by the consumer. The toxin causes vomiting and is mainly produced in farinaceous food products. This article includes the prevalence of B. cereus and of cereulide in food products in The Netherlands, a characterization of B. cereus isolates obtained, cereulide production conditions, and a comparison of consumer exposure estimates with those of a previous exposure assessment. Food samples (n = 1,489) were tested for the presence of B. cereus; 5.4% of the samples contained detectable levels (>10(2) CFU/g), and 0.7% contained levels above 10(5) CFU/g. Samples (n = 3,008) also were tested for the presence of cereulide. Two samples (0.067%) contained detectable levels of cereulide at 3.2 and 5.4 μg/kg of food product. Of the 481 tested isolates, 81 produced cereulide and/or contained the ces gene. None of the starch-positive and hbl-containing isolates possessed the ces gene, whereas all strains contained the nhe genes. Culture of emetic B. cereus under nonoptimal conditions revealed a delay in onset of cereulide production compared with culture under optimal conditions, and cereulide was produced in all cases when B. cereus cells had been in the stationary phase for some time. The prevalence of cereulide-contaminated food approached the prevalence of contaminated products estimated in an exposure assessment. The main food safety focus associated with this pathogen should be to prevent germination and growth of any B. cereus present in food products and thus prevent cereulide production in foods.

Cereulide food toxin, beta cell function and diabetes: Facts and hypotheses

The incidence of both type 1 and type 2 diabetes is increasing and although environmental pollutants are believed to be potential culprits, the extent to which they can be held responsible remains uncertain. Some bacterial strains of the Bacillus cereus produce a toxin, cereulide, which is frequently found in starchy meals and which is difficult to eradicate from the food chain as it is highly resistant to heat, acidity and proteolysis. While cereulide is well known to cause acute emetic toxicity when ingested at high doses, several in vitro studies have shown that also extremely low doses of cereulide can be toxic, with beta cells being particularly sensitive. Mechanistically, such low doses impair the mitochondrial activity of the beta cells thereby leading to hampered insulin secretion and cell death, both key traits in the pathophysiology of diabetes. In vivo studies of chronic or repeated low dose exposure to cereulide are currently lacking, but should be performed to further clarify the true relevance of cereulide as a potential environmental contributor to the ongoing diabetes epidemic.