Analytical methods for Bacillus cereus and other Bacillus species

Genetic Characterization, Antibiotic Resistance, and Virulence Genes Profiling of Bacillus cereus Strains from Various Foods in Japan

Bacillus cereus sensu stricto is a foodborne pathogen that causes food poisoning. Their spore and biofilm-forming abilities persist in various environments and foods. This study investigated the prevalence, virulence, antibiotic resistance, and genetic diversity of B. cereus s. s. strains isolated from various food samples. Of 179 samples, 22.34% were positive for B. cereus s. s., with significantly high detection rates in milk products and raw chicken meat. Forty strains were isolated from positive samples. Matrix-assisted laser desorption ionization/time of flight mass spectrometry analysis revealed nine distinct clusters and multi-locus sequence typing revealed 34 sequence types including 23 novel sequences, demonstrating high genetic diversity among the isolates. PCR analysis revealed that all the strains contained at least one toxin gene, but none contained the cytK gene. Antibiotic resistance tests revealed that all isolates were classified as multidrug-resistant, with high resistance levels, particularly to β-lactam antibiotics and vancomycin, but were susceptible to gentamicin. All isolates showed variations in biofilm formation. This study highlights the significant public health risk due to B. cereus s. s. and underscores the need for stringent monitoring and control measures in food production to manage antimicrobial resistance and ensure food safety.

Evaluation of Ceftazidime as an Antibiotic Supplement in Mannitol-Yolk-Polymyxin B Agar Used for Enumeration of Bacillus cereus in Ready-to-Eat Vegetables

ABSTRACT

The Bacillus cereus group of bacteria, which causes foodborne diseases, can be detected by culture on selective media. However, the presence of competing flora is the most common factor preventing the accurate enumeration of B. cereus on selective agars. In this study, we improved the selectivity of mannitol-yolk-polymyxin B agar (MYPA) and its modified version containing trimethoprim (mMYPA) developed in our previous study by supplementation with ceftazidime (16 μg/mL). Ceftazidime-supplemented MYPA (C-MYPA16) and mMYPA (C-mMYPA16) were evaluated for bacteria recovery and selectivity with three types of ready-to-eat vegetables. Four B. cereus and one Bacillus thuringiensis strains were mixed and artificially inoculated into vegetable salad, radish sprouts, and sprout mix and then recovered on MYPA, mMYPA, C-MYPA16, and C-mMYPA16. In all tested vegetables, mMYPA, C-MYPA16, and C-mMYPA16 culture resulted in similar recovery of B. cereus and B. thuringiensis (P > 0.05), whereas radish sprout and sprout mix colonies grown on MYPA were undistinguishable. C-mMYPA16 was the most selective medium because it eliminated most of the competing flora, especially that in sprouts, without negatively affecting the recovery of B. cereus and B. thuringiensis. Our results indicate that supplementation of mMYPA with ceftazidime may improve the selectivity of this medium for B. cereus and B. thuringiensis in food testing.

HIGHLIGHTS

The divergent roles of sortase in the biology of Gram-positive bacteria

The bacterial cell wall contains numerous surface-exposed proteins, which are covalently anchored and assembled by a sortase family of transpeptidase enzymes. The sortase are cysteine transpeptidases that catalyzes the covalent attachment of surface protein to the cell wall peptidoglycan. Among the reported six classes of sortases, each distinct class of sortase plays a unique biological role in anchoring a variety of surface proteins to the peptidoglycan of both pathogenic and non-pathogenic Gram-positive bacteria. Sortases not only exhibit virulence and pathogenesis properties to host cells, but also possess a significant role in gut retention and immunomodulation in probiotic microbes. The two main distinct functions are to attach proteins directly to the cell wall or assemble pili on the microbial surface. This review provides a compendium of the distribution of different classes of sortases present in both pathogenic and non-pathogenic Gram-positive bacteria and also the noteworthy role played by them in bacterial cell wall assembly which enables each microbe to effectively interact with its environment.

The Bacillus cereus Food Infection as Multifactorial Process

The ubiquitous soil bacterium Bacillus cereus presents major challenges to food safety. It is responsible for two types of food poisoning, the emetic form due to food intoxication and the diarrheal form emerging from food infections with enteropathogenic strains, also known as toxico-infections, which are the subject of this review. The diarrheal type of food poisoning emerges after production of enterotoxins by viable bacteria in the human intestine. Basically, the manifestation of the disease is, however, the result of a multifactorial process, including B. cereus prevalence and survival in different foods, survival of the stomach passage, spore germination, motility, adhesion, and finally enterotoxin production in the intestine. Moreover, all of these processes are influenced by the consumed foodstuffs as well as the intestinal microbiota which have, therefore, to be considered for a reliable prediction of the hazardous potential of contaminated foods. Current knowledge regarding these single aspects is summarized in this review aiming for risk-oriented diagnostics for enteropathogenic B. cereus.

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.

Food Sensing: Detection of Bacillus cereus Spores in Dairy Products

Milk is a source of essential nutrients for infants and adults, and its production has increased worldwide over the past years. Despite developments in the dairy industry, premature spoilage of milk due to the contamination by Bacillus cereus continues to be a problem and causes considerable economic losses. B. cereus is ubiquitously present in nature and can contaminate milk through a variety of means from the farm to the processing plant, during transport or distribution. There is a need to detect and quantify spores directly in food samples, because B. cereus might be present in food only in the sporulated form. Traditional microbiological detection methods used in dairy industries to detect spores show limits of time (they are time consuming), efficiency and sensitivity. The low level of B. cereus spores in milk implies that highly sensitive detection methods should be applied for dairy products screening for spore contamination. This review describes the advantages and disadvantages of classical microbiological methods used to detect B. cereus spores in milk and milk products, related to novel methods based on molecular biology, biosensors and nanotechnology.

Case Report: Bacillus pumilus-Caused Bacteremia in a Patient with Food Poisoning

Bacillus pumilus has rarely been reported as a cause of human infections. We report a case of a B. pumilus causing food poisoning in an adult male. A 51-year-old Japanese man complained of severe abdominal cramps, fever with chills, diarrhea, dizziness, and loss of appetite after eating reheated rice with stewed minced meat purchased from a Kenyan restaurant. Bacillus pumilus was isolated from blood culture and was identified using a biochemical test and 16S rRNA gene sequencing analysis. The patient was treated with probiotics and ciprofloxacin and recovered after 3 days. To our knowledge, this is the first report describing the potential role of B. pumilus as a foodborne pathogen in Kenya and highlights the importance of good hygiene and food preparation practices.

Comparative Evaluation of Selective Media for the Detection of Bacillus cereus

The commercially available 3 types of selective media in Japan were compared for the detection of Bacillus cereus. When assessed inclusivity using 25 B. cereus strains, MYP agar, NGKG agar, and chromogenic X-BC agar demonstrated excellent inclusivity. For exclusivity study using 50 non-B. cereus strains, MYP, NGKG, and X-BC allowed to grow 11, 7, and 3 strains, respectively. Of the grown bacteria on each strains tested, only 2 strains of B. thuringiensis formed typical B. cereus colonies on all selective media tested. The NGKG and X-BC were compared with MYP as a reference using artificially contaminated food (fried rice, plain rice, fried noodle, and potato salad ), since MYP is recommended in ISO 7932: 2004. The both correlation coefficients between NGKG and MYP, and X-BC and MYP were 0.999. Therefore, we demonstrated that NGKG and X-BC can be adapted to ISO 7932: 2004 method for selected food as well as MYP.

Supplementation of Modified Mannitol-Yolk-Polymyxin B Agar with Cefuroxime for Quantitative Detection of Bacillus cereus in Food

The presence of unwanted competing flora has been the most common confounding factor in the enumeration of Bacillus cereus (B. cereus) using selective media such as mannitol-yolk-polymyxin B agar (MYPA). The objective of this study was to improve MYPA selectivity for B. cereus by supplementation with a second-generation cephalosporin, cefuroxime. The performance of cefuroxime-supplemented MYPA (cefu-MYPA) was evaluated by comparison with original MYPA in 60 food products with established microbiological standards for B. cereus contamination. Cefu-MYPA demonstrated superior recoverability and selectivity for B. cereus compared with original MYPA in most tested foods. B. cereus numbers on MYPA and cefu-MYPA were 363.5 and 462.0 CFU/g, respectively. Competing flora on cefu-MYPA was detected in significantly less samples (70%) compared to original MYPA (93%). In addition, the detection and isolation of suspected colonies were significantly improved in cefu-MYPA because of the reduction or elimination of competing flora in all tested foods except fruit juice, indicating superior selectivity of the modified medium. Our findings suggest that cefuroxime supplementation of MYPA would markedly improve the detection rate of B. cereus, particularly in foods with high levels of indigenous flora.

Novel Bacillus cereus strain from electrokinetically remediated saline soil towards the remediation of crude oil

A new strain SWH-15 was successfully isolated after initial electrokinetic remediation experiment using the same saline soil sampled from Shengli Oilfield, China. Four methods (morphological and biochemical characteristics, whole-cell fatty acid methyl esters (FAMEs) analysis, 16S rRNA sequence analysis and DNA G + C content and DNA-DNA hybridization analysis) were used to identify the taxonomic status of SWH-15 and confirmed that SWH-15 was a novel species of the Bacillus (B.) cereus group. Then, we assessed the degrading ability of the novel strain SWH-15 to crude oil through a microcosm experiment with four treatments, including control (CK), bioremediation using SWH-15 (Bio), electrokinetic remediation (EK), and combined bioremediation and electrokinetic remediation (Bio + EK). The results showed that the Bio + EK combined remediation treatment was more effective than the CK, Bio, and EK treatments in degrading crude oil contaminants. Bioaugmentation, by addition of the strain SWH-15 had synergistic effect with EK in Bio + EK treatment. Bacterial community analysis showed that electrokinetic remediation alone significantly altered the bacterial community of the saline soil. The addition of the strain SWH-15 alone had a weak effect on the bacterial community. However, the strain SWH-15 boosted the growth of other bacterial species in the metabolic network and weakened the impact of electrical field on the whole bacterial community structure in the Bio + EK treatment.

Consumed Foodstuffs Have a Crucial Impact on the Toxic Activity of Enteropathogenic Bacillus cereus

Enteropathogenic Bacillus cereus cause diarrhea due to the production of enterotoxins in the intestine. To start this process, spores have to be ingested together with contaminated food and survive the stomach passage. In this study, the influence of consumed foodstuffs on spore survival as well as on cytotoxicity toward colon epithelial cells was investigated. Spore survival of 20 enteropathogenic and apathogenic B. cereus strains during simulated stomach passage was highly strain-specific and did not correlate with the toxic potential. Survival of three tested strains was strain-specifically altered by milk products. Whereas milk, a follow-on formula and rice pudding had only little influence, spores seemed to be protected by milk products with high fat content such as whipped cream and mascarpone. Furthermore, tested milk products decreased the toxic activity of three B. cereus strains toward CaCo-2 cells. Investigating the individual components, lactoferrin, a skim milk powder and vitamins C, B5 and A showed the most inhibiting effects. On the other hand, biotin, vitamin B3 and another skim milk powder even enhanced cytotoxicity. Further studies suggested that these inhibiting effects result only partially from inhibiting cell binding, but rather from blocking the interaction between the single enterotoxin components.

Comparative Bioinformatics and Experimental Analysis of the Intergenic Regulatory Regions of Bacillus cereus hbl and nhe Enterotoxin Operons and the Impact of CodY on Virulence Heterogeneity

Bacillus cereus is a food contaminant with greatly varying enteropathogenic potential. Almost all known strains harbor the genes for at least one of the three enterotoxins Nhe, Hbl, and CytK. While some strains show no cytotoxicity, others have caused outbreaks, in rare cases even with lethal outcome. The reason for these differences in cytotoxicity is unknown. To gain insight into the origin of enterotoxin expression heterogeneity in different strains, the architecture and role of 5′ intergenic regions (5′ IGRs) upstream of the nhe and hbl operons was investigated. In silico comparison of 142 strains of all seven phylogenetic groups of B. cereus sensu lato proved the presence of long 5′ IGRs upstream of the nheABC and hblCDAB operons, which harbor recognition sites for several transcriptional regulators, including the virulence regulator PlcR, redox regulators ResD and Fnr, the nutrient-sensitive regulator CodY as well as the master regulator for biofilm formation SinR. By determining transcription start sites, unusually long 5′ untranslated regions (5′ UTRs) upstream of the nhe and hbl start codons were identified, which are not present upstream of cytK-1 and cytK-2. Promoter fusions lacking various parts of the nhe and hbl 5′ UTR in B. cereus INRA C3 showed that the entire 331 bp 5′ UTR of nhe is necessary for full promoter activity, while the presence of the complete 606 bp hbl 5′ UTR lowers promoter activity. Repression was caused by a 268 bp sequence directly upstream of the hbl transcription start. Luciferase activity of reporter strains containing nhe and hbl 5′ IGR lux fusions provided evidence that toxin gene transcription is upregulated by the depletion of free amino acids. Electrophoretic mobility shift assays showed that the branched-chain amino acid sensing regulator CodY binds to both nhe and hbl 5′ UTR downstream of the promoter, potentially acting as a nutrient-responsive roadblock repressor of toxin gene transcription. PlcR binding sites are highly conserved among all B. cereus sensu lato strains, indicating that this regulator does not significantly contribute to the heterogeneity in virulence potentials. The CodY recognition sites are far less conserved, perhaps conferring varying strengths of CodY binding, which might modulate toxin synthesis in a strain-specific manner.

Applying standard epidemiological methods for investigating foodborne disease outbreak in resource-poor settings: lessons from Vietnam

An outbreak of gastroenteritis occurred among workers of company X after eating lunch prepared by a catering service. Of 430 workers attending the meal, 56 were hospitalized with abdominal pain, diarrhea, vomiting, and nausea, according to the initial report. We conducted an investigation to identify the extent, vehicle, and source of the outbreak. In our case-control study, a case was a worker who attended the meal and who was hospitalized with acute gastroenteritis; controls were randomly selected from non-ill workers. Cases and controls were interviewed using a standard questionnaire. We used logistic regression to calculate adjusted odds ratios for the consumption of food items. Catering service facilities and food handlers working for the service were inspected. Food samples from the catering service were tested at reference laboratories. Of hospitalized cases, 54 fulfilled the case definition, but no stool specimens were collected for laboratory testing. Of four food items served during lunch, only "squash and pork soup" was significantly associated with gastroenteritis, with an adjusted odds ratio of 9.5 (95 % CI 3.2, 27.7). The caterer did not separate cooked from raw foods but used the same counter for both. Cooked foods were kept at room temperature for about 4 h before serving. Four of 14 food handlers were not trained on basic food safety principles and did not have health certificates. Although no microbiological confirmation was obtained, our epidemiological investigation suggested that squash and pork soup caused the outbreak. Hospitals should be instructed to obtain stool specimens from patients with gastroenteritis. Food catering services should be educated in basic food safety measures.

Development of blood-yolk-polymyxin B-trimethoprim agar for the enumeration of Bacillus cereus in various foods

Blood-yolk-polymyxin B-trimethoprim agar (BYPTA) was developed by the addition of egg yolk, laked horse blood, sodium pyruvate, polymyxin B, and trimethoprim, and compared with mannitol-yolk-polymyxin B agar (MYPA) for the isolation and enumeration of Bacillus cereus (B. cereus) in pure culture and various food samples. In pure culture, there was no statistical difference (p>0.05) between the recoverability and sensitivity of MYPA and BYPTA, whereas BYPTA exhibited higher specificity (p<0.05). To evaluate BYPTA agar with food samples, B. cereus was experimentally spiked into six types of foods, triangle kimbab, sandwich, misugaru, Saengsik, red pepper powder, and soybean paste. No statistical difference was observed in recoverability (p>0.05) between MYPA and BYPTA in all tested foods, whereas BYPTA exhibited higher selectivity than MYPA, especially in foods with high background microflora, such as Saengsik, red pepper powder, and soybean paste. The newly developed selective medium BYPTA could be a useful enumeration tool to assess the level of B. cereus in foods, particularly with high background microflora.

Prevalence and levels of Bacillus cereus emetic toxin in rice dishes randomly collected from restaurants and comparison with the levels measured in a recent foodborne outbreak

Whereas the prevalence of Bacillus cereus emetic strains in the environment has been shown to be very low, there is a lack of information on the prevalence of its toxin, cereulide, in food. Yet, the rice leftovers of a family outbreak which occurred after the consumption of dishes taken away from an Asian restaurant revealed significant amounts of cereulide, reaching up to 13,200 ng/g of food. The occurrence of cereulide in rice dishes collected from various restaurants was therefore evaluated using the liquid chromatography coupled with tandem mass spectrometry method, which allows for the direct quantification of the toxin in food. The cereulide prevalence was found to be 7.4% when samples were analyzed at the day of sampling, but reached 12.9% when exposed to temperature abuse conditions (25°C). The cereulide concentrations observed in cooked rice dishes were low (approximately 4 ng/g of food). However, since little is known yet about the potential chronic toxicity of cereulide, one needs to be very careful and vigilant.

Improvement of mannitol-yolk-polymyxin B agar by supplementing with trimethoprim for quantitative detection of Bacillus cereus in foods

Mannitol-yolk-polymyxin B agar (MYPA) was modified by supplementation with trimethoprim. The ability of the supplemented medium to select for and recover Bacillus cereus from pure cultures and food samples with high background microflora was compared with MYPA. For evaluation of the modified MYPA (mMYPA) in food samples with high background microflora, B. cereus was experimentally spiked into red pepper powder, fermented soybean paste, vegetable salad, and radish sprouts, and then it was recovered on MYPA and mMYPA for comparison. In all food samples, there was no difference in recoverability (P > 0.05) between mMYPA (red pepper powder, 3.34 ± 0.24 log CFU/g; fermented soybean paste, 3.52 ± 0.47 log CFU/g; vegetable salad, 3.51 ± 0.23 log CFU/g; radish sprouts, 3.32 ± 0.40 log CFU/g) and MYPA (red pepper powder, 3.18 ± 0.20 log CFU/g; fermented soybean paste, 3.33 ± 0.43 log CFU/g; vegetable salad, 3.36 ± 0.19 log CFU/g; radish sprouts, 3.33 ± 0.31 log CFU/g). However, mMYPA exhibited better selectivity than MYPA, because additional trimethoprim made the differentiation of suspected colonies easier by inhibiting competing flora. The addition of trimethoprim to conventional media could be a useful option to improve selectivity in foods with high background microflora.

Genetic diversity, antimicrobial resistance, and toxigenic profiles of Bacillus cereus strains isolated from Sunsik

Bacillus cereus can cause emetic and diarrheal types of food poisoning, but little study has been done on the toxins and toxin-encoding genes of B. cereus strains isolated from Sunsik, a Korean ready-to-eat food prepared from grains, fruits, and vegetables. In this study, 39 unique B. cereus strains were isolated and identified from Sunsik samples, with an average contamination level of 10 to 200 CFU/g. The detection rates of the hblACD, cytK, and bceT genes among all the strains were 48.7, 66.7, and 87.1%, respectively. All 39 B. cereus strains carried nheABC and entFM genes, and 36 strains also had the ces gene, which encodes an emetic toxin. Nonhemolytic enterotoxin and hemolysin BL enterotoxin were produced by 39 and 26 strains, respectively. The strains were separated into 13 profiles based on the presence or absence of toxins and their genes, as determined by antibody tests and PCR analysis. Profile 1 was the largest group, comprising 30.7% (12 of 39) of the B. cereus strains tested; these strains harbored all toxins and their genes. The B. cereus strains were susceptible to most of the antibiotics tested but were highly resistant to b -lactam antibiotics. The repetitive element sequence polymorphism PCR fingerprints of the B. cereus strains were not influenced by the presence of toxin genes or antibiotic resistance profiles. Our results suggest that B. cereus strains from Sunsik could cause either the diarrheal or emetic types of food poisoning because all strains isolated contained at least one toxin and its gene, although the level of B. cereus contamination in Sunsik was low.

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.

Assembly of pili on the surface of Bacillus cereus vegetative cells

Vegetative forms of Bacillus cereus are reported to form pili, thin protein filaments that protrude up to 1 mum from the bacterial surface. Pili are assembled from two precursor proteins, BcpA and BcpB, in a manner requiring a pilus-associated sortase enzyme (SrtD). Pili are also formed on the surface of Bacillus anthracis expressing bcpA-srtD-bcpB. BcpA is distributed throughout the entire pilus, whereas BcpB appears positioned at its tip. In agreement with the hypothesis for pilus assembly in Gram-positive bacteria, BcpA encompasses the YPK pilin motif and the LPXTG sorting signal, each of which is absolutely required for the incorporation of BcpA and BcpB into pili. In contrast to BcpB, which relies on the presence of BcpA for incorporation into pili, BcpA fibre assembly occurs even in the absence of BcpB. B. anthracis sortase A (srtA), but not sortase B (srtB) or C (srtC), is required for proper anchoring of pili to the bacterial envelope, suggesting that BcpA/BcpB pili are linked to peptidoglycan cross-bridges.

O, Vidal-Martins A, Amaral L. Ocorrência de Bacillus cereus em leite integral e capacidade enterotoxigênica das cepas isoladas

Pesquisaram-se a presença de Bacillus cereus e a produção de enterotoxinas produzidas por esses microrganismos em 120 amostras de diversos tipos de leite. Bacillus cereus foi isolado e identificado em 22 (73,3%), 15 (50,0%), 29 (96,7%) e quatro (13,3%) amostras de leite em pó, cru, pasteurizado e UAT (longa vida), respectivamente. Para a detecção de enterotoxinas pela técnica da alça ligada de coelho, foram positivos, respectivamente, três (13,6%), um (7,1%) e 10 (35,7%) microrganismos isolados das amostras de leite em pó, leite cru e leite pasteurizado. Pelo teste de aumento de permeabilidade vascular, dois (9,1%), um (7,1%), um (3,6%) e um (4,0%) microrganismos isolados de leite em pó, cru, pasteurizado e UAT apresentaram-se enterotoxigênicos, respectivamente. O uso da técnica de aglutinação passiva em látex demonstrou a produção da toxina diarréica por três (33,3%), sete (63,6%), quatro (30,8%) e oito (80,0%) microrganismos isolados, respectivamente, de leite em pó, cru, pasteurizado e UAT. Os resultados indicam um risco potencial, podendo colocar em risco a saúde dos consumidores desses produtos.

Food poisoning associated with pumilacidin-producing Bacillus pumilus in rice

Food poisoning caused by other Bacillus species than B. cereus has been described, but the toxins involved have rarely been isolated. Endospores will survive heat treatment and will germinate and multiply in cooked foods producing toxins under appropriate conditions. We describe a small food poisoning outbreak where three people became ill after a dinner in a Chinese restaurant. Acute symptoms including dizziness, headache, chills and back pain developed during the meal, and a few hours later they got stomach cramps and diarrhoea which lasted for several days. Cooked, reheated rice was the prime suspect of the food poisoning, and from the rice large numbers of Bacillus pumilus were isolated. The isolated B. pumilus strain was found to produce a complex of lipopeptides known as pumilacidins with the highest amounts produced at 15 degrees C. This is the first report on isolation of a pumilacidin-producing B. pumilus strain from food implicated in food poisoning and characterization of the organism and the toxin complex involved.

Thermal inactivation of Bacillus cereus and Clostridium perfringens vegetative cells and spores in pork luncheon roll

The aim of this study was to design a thermal treatment(s) for pork luncheon roll, which would destroy Bacillus cereus and Clostridium perfringens vegetative cells and spores. B. cereus and C. perfringens vegetative and spore cocktails were used to inoculate luncheon meat. Samples were subjected to different temperatures and removal times. The decimal-reduction times (D-values) were calculated by linear regression analysis (D = -1/slope of a plot of log surviving cells versus time). The log(10) of the resulting D-values were plotted against their corresponding temperatures to calculate (-1/slope of the curve) the thermal resistance (z-values) of each cocktail. The D-values for vegetative cells ranged from 1 min (60 degrees C) to 33.2 min (50 degrees C) for B. cereus and from 0.9 min (65 degrees C) to 16.3 min (55 degrees C) for C. perfringens. The D-values for B. cereus spores ranged from 2.0 min (95 degrees C) to 32.1 min (85 degrees C) and from 2.2 min (100 degrees C) to 34.2 min (90 degrees C) for C. perfringens. The z-values were calculated to be 6.6 and 8.5 degrees C for B. cereus vegetative and spores, respectively, and 7.8 and 8.4 degrees C for C. perfringens vegetative cells and spores, respectively. The D-values of B. cereus and C. perfringens suggest that a mild cook of 70 degrees C for 12s and 1.3 min would achieve a 6 log reduction of B. cereus and C. perfringens vegetative cells, respectively. The equivalent reduction of B. cereus and C. perfringens spores would require the pork luncheon meat to be heated for 36 s at 105 and 110 degrees C, respectively. The results of this study provide the thermal inactivation data necessary to design a cooking protocol for pork luncheon roll that would inactivate B. cereus and C. perfringens vegetative cells and spores. The data may also be used in future risk assessment studies.

Detection ofBacillus thuringiensis kurstakiHD1 on cabbage for human consumption

The objectives of the study were to develop a specific procedure for quantification and identification of Bacillus thuringiensis kurstaki HD1, which is used as a biopesticide, and to quantify its presence in different kinds of cabbage for human consumption. We found that B. thuringiensis kurstaki HD1 can be distinguished from other B. thuringiensis strains by its unique random amplification of polymophic DNA-PCR pattern with the OPA9 primer and the presence of the flagellin genes, as detected by the primers FLAB1 and FLAB2. We detected from one to 100 Bacillus cereus-like bacteria in 10 batches of five different cabbage products for consumption. As many as 73 out of 134 isolates (53.7%) were identical with B. thuringiensis kurstaki HD1. The results show that B. thuringiensis kurstaki HD1 from biopesticides can be found in vegetables for human consumption.

Bacillus cereus food poisoning and its toxins

The genus Bacillus includes members that demonstrate a wide range of diversity from physiology and ecological niche to DNA sequence and gene regulation. The species of most interest tend to be known for their pathogenicity and are closely linked genetically. Bacillus anthracis causes anthrax, and Bacillus thuringiensis is widely used for its insecticidal properties but has also been associated with foodborne disease. Bacillus cereus causes two types of food poisoning, the emetic and diarrheal syndromes, and a variety of local and systemic infections. Although in this review we provide information on the genus and a variety of species, the primary focus is on the B. cereus strains and toxins that are involved in foodborne illness. B. cereus produces a large number of potential virulence factors, but for the majority of these factors their roles in specific infections have not been established. To date, only cereulide and the tripartite hemolysin BL have been identified specifically as emetic and diarrheal toxins, respectively. Nonhemolytic enterotoxin, a homolog of hemolysin BL, also has been associated with the diarrheal syndrome. Recent findings regarding these and other putative enterotoxins are discussed.

Bacillus cereus, the causative agent of an emetic type of food-borne illness

Bacillus cereus is the causative agent of two distinct forms of gastroenteritic disease connected to food-poisoning. It produces one emesis-causing toxin and three enterotoxins that elicit diarrhea. Due to changing lifestyles and eating habits, B. cereus is responsible for an increasing number of food-borne diseases in the industrial world. In the past, most studies concentrated on the diarrhoeal type of food-borne disease, while less attention has been given to the emetic type of the disease. The toxins involved in the diarrhoeal syndrome are well-known and detection methods are commercially available, whereas diagnostic methods for the emetic type of disease have been limited. Only recently, progress has been made in developing identification methods for emetic B. cereus and its corresponding toxin. We will summarize the data available for the emetic type of the disease and discuss some new insights in emetic strain characteristics, diagnosis, and toxin synthesis.

Cereulide, the emetic toxin of Bacillus cereus, is putatively a product of nonribosomal peptide synthesis

AIMS

To determine if cereulide, the emetic toxin produced by Bacillus cereus, is produced by a nonribosomal peptide synthetase (NRPS).

METHODS AND RESULTS

NC Y, an emetic strain of Bacillus cereus, was examined for a NRPS gene using PCR with primers recognizing a fragment of a NRPS gene from the cyanobacterium Microcystis. The amplicon was sequenced and compared with other gene sequences using BLAST analysis, which showed that the amplicon from strain NC Y was similar in sequence to peptide synthetase genes in other micro-organisms, including Bacillus subtilis and B. brevis, while no such sequence was found in the complete genome sequence of a nonemetic strain of B. cereus. Specific PCR primers were then designed and used to screen 40 B. cereus isolates previously implicated in outbreaks of foodborne illness. The isolates were also screened for toxin production using the MTT cell cytotoxicity assay. PCR and MTT assay screening of the B. cereus isolates revealed a high correlation between the presence of the NRPS gene and cereulide production.

CONCLUSIONS

The results indicate that cereulide is produced by a NRPS complex.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to provide evidence identifying the mechanism of production of cereulide, the emetic toxin of B. cereus. The PCR primers developed in the study allow determination of the potential for cereulide production among isolates of B. cereus.

Bacillus thuringiensis in fecal samples from greenhouse workers after exposure to B. thuringiensis-based pesticides

In a study of occupational exposure to Bacillus thuringiensis, 20 exposed greenhouse workers were examined for Bacillus cereus-like bacteria in fecal samples and on biomonitoring filters. Bacteria with the following characteristics were isolated from eight individuals: intracellular crystalline inclusions characteristic of B. thuringiensis, genes for and production of B. cereus enterotoxins, and positivity for cry11 as determined by PCR. DNA fingerprints of the fecal isolates were identical to those of strains isolated from the commercial products used. Work processes (i.e., spraying) correlated with the presence of B. thuringiensis in the fecal samples (10(2) to 10(3) CFU/g of feces). However, no gastrointestinal symptoms correlated with the presence of B. thuringiensis in the fecal samples.

Vibrio parahaemolyticus serovar O3:K6 as cause of unusually high incidence of food-borne disease outbreaks in Taiwan from 1996 to 1999

The occurrence of food-borne disease outbreaks in Taiwan increased dramatically in 1996, and the incidence has since remained elevated. This increase in outbreaks is correlated with a high rate of isolation of Vibrio parahaemolyticus, which caused between 61 and 71% of the total outbreaks for the period 1996 to 1999. By serotyping, 40 serovars were identified from 3743 V. parahaemolyticus isolates, of which O3:K6 was the most frequently detected. The O3:K6 serovar could have emerged in Taiwan as early as October 1995 and at that time accounted for only 0.6% of the V. parahaemolyticus infections. This level increased suddenly to 50.1% in 1996 and reached a peak (83.8%) in 1997. Comparison of the outbreak profiles for the etiology groups indicates that the high incidence of food-borne disease outbreaks during 1996 to 1999 can be attributed to the extraordinarily high O3:K6 infections. In 1999, the O3:K6 serovar was still prevalent, and accounted for 61.3% of all V. parahaemolyticus infections. Due to its extraordinarily high infection frequency and its capability to spread globally, this organism needs to be intensively monitored internationally.

Properties of Bacillus cereus and other bacilli contaminating biomaterial-based industrial processes

This paper is an overview on bacilli in industrial processes, with focus on food grade paper and paperboard production. Paperboards mainly contain sporeforming bacteria belonging to the genera Bacillus, Paenibacillus and Brevibacillus, usually found in quantities from < 50 to 250 cfu g(-1) homogenized paperboard. Of those frequently found, Bacillus cereus group, B. licheniformis, B. subtilis and Brevibacillus brevis are important for food hygiene because of their hydrolytic activities on food components and the ability of some strains to produce food poisoning toxins or to grow at refrigerated temperatures. We found that the phenotypic properties (lecithinase activity, nitrate reduction) used in standard methods (e.g., ISO, FDA, IDF) to recognize B. cereus, were unreliable for industrial isolates. Whole cell fatty acid composition of a group of the industrial isolates deviated so much from those in a widely used commercial database that the strains were not or only poorly recognized as B. cereus. Industrial isolates, including toxigenic ones, often missed one or more of these characters, even in cases where 100% 16S rDNA identity was found with B. cereus or with B. thuringiensis. 11-Methyldodecanoic acid and trans-9-hexadecenoic acid were found without exception in over 200 industrial B. cereus group isolates and in over 30 culture collection strains. The detection of these fatty acids is a secure method for the identification of B. cereus. Negative reaction for starch hydrolysis and for BCET-RPLA test and a specific ribotype were found in all B. cereus strains producing the emetic toxin.

Food-borne disease outbreaks due to bacteria in Taiwan, 1986 to 1995

Between 1986 and 1995, 852 outbreaks of food-borne disease involving 26,173 cases and 20 deaths were reported in Taiwan. About 80% of the outbreaks occurred in the warmer months, i.e., between April and October. Of the 852 reported outbreaks, 555 (65%) were caused by bacterial pathogens. The three most common bacteria involved were Vibrio parahaemolyticus (35%, 197 of 555 outbreaks), Staphylococcus aureus (30%, 169 of 555 outbreaks), and Bacillus cereus (18%, 104 of 555 outbreaks).

Enterotoxin-producing strains of Bacillus thuringiensis isolated from food

Strains of Bacillus thuringiensis were isolated from various food items (pasta, pitta bread and milk) and were found to belong to either H-serotype kurstaki or neoleonensis. The strains were bioassayed against Pieris brassicae and insecticidal activity of strains was found to correspond to the presence of the cry1A-gene. All strains, except one, were found to express cytotoxic effects on Vero cells as an indicator of enterotoxin activity. Further, the B. thuringiensis strains HD-1 (serotype kurstaki), NB-125 (serotype tenebrionis) and HD-567 (serotype israelensis ) which are used commercially for insect pest management, were also found to have cytotoxic effects on Vero cells.

Randomly amplified polymorphic DNA (RAPD) assay for genomic fingerprinting of Bacillus cereus isolates

Randomly amplified polymorphic DNA (RAPD) assay was used for epidemiological subtyping of B. cereus and B. lentus. Within 25 isolates of B. cereus up to 22 strain types could be determined when five primers were used. RAPD patterns, which were found in three B. lentus strains, clearly differed form those of B. cereus. The RAPD technique proved to be an effective tool for the characterization of B. cereus strains.

Bacillus cereus phage typing as an epidemiological tool in outbreaks of food poisoning

Bacillus cereus is responsible for an increasing number of food poisoning cases. By using 12 bacteriophages isolated from sewage, a typing scheme for B. cereus isolates from outbreaks or sporadic cases of food poisoning was developed. The phages belonged to three morphotypes. Ten phages with contractile tails and icosahedral heads were members of the Myoviridae family, and two phages with noncontractile tails belonged to the Siphoviridae family. Phage 11 represented a new species. It had an isometric head and a very long contractile tail with long wavy tail fibers and was one of the largest viruses known. The vast majority of 166 B. cereus strains (161, or 97%) isolated from food poisoning cases were typeable. Of 146 strains isolated from 18 outbreaks, 142 (97%) could be divided into 17 phage types. A good correlation, on the order of 80 to 100%, between phage types of strains isolated from suspected foods and those of strains isolated from stools of symptomatic patients was observed. Most Bacillus thuringiensis strains were also typeable, providing further evidence of the close relatedness of B. cereus and B. thuringiensis. This phage typing scheme can be a valuable epidemiological tool in tracing the origins of food poisoning caused by B. cereus.