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

Toxigenic diversity of Bacillus cereus isolated from fresh produce and effects of various factors on the growth and the cytotoxicity of B. cereus

This study analyzed the virulence, growth characteristics, and cytotoxicity of Bacillus cereus strains isolated from fresh produce, including romaine lettuce, sesame leaf, tomato, and cucumber grown by different methods. Polymerase chain reaction (PCR) was used to assess the toxigenic potential, and the cytotoxicity of B. cereus was estimated using cell-free supernatant in HEp-2 cells. The study found that hblD was the predominant diarrheal enterotoxin in the 59 isolated B. cereus strains, followed by nheB and hblC. The optimal temperatures for growth ranged from 42 to 44 °C, with the highest growth rates and shortest lag times. Cytotoxicity varied greatly depending on abiotic factors, including NaCl, pH, and medium, and was not always correlated with cell population. The study highlights the importance of establishing control measures to prevent B. cereus intoxication in fresh vegetables.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01330-0.

Prevalence, Toxin Genes, and Antibiotic Resistance Profiles of Bacillus cereus Isolates from Spices in Antalya and Isparta Provinces in Türkiye

Bacillus cereus is a pathogenic bacterium commonly found in nature and can produce toxins that cause food poisoning. This study aimed to detect the prevalence of B. cereus group bacteria in 50 unpackaged and 20 packaged spice samples frequently used as flavoring in Turkish cuisine, as well as investigate the presence of toxin genes and antibiotic resistance in the isolates. A total of 48 B. cereus group bacteria were isolated from 27 of 70 (38.57%) spice samples. The prevalence of B. cereus group bacteria in packaged (25%, 5/20) and unpackaged (44%, 22/50) spice samples did not differ significantly (P ˃ 0.05). All B. cereus group isolates were identified as B. cereus sensu stricto (B. cereus) using molecular methods. The hemolytic activity tests revealed that the most strains (44/48, 91.67%) are β-hemolytic. The distributions of toxin genes in isolates were investigated by PCR. It was determined that all isolates were identified to have 2-8 toxin genes, except B. cereus SBC3. The three most common toxin genes were found to be nheA (47/48, 97.92%), nheB (46/48, 95.83%), and entFM (46/48, 95.83%). All B. cereus isolates were susceptible to linezolid and vancomycin, while 35.42% (17/48) showed resistance to erythromycin. Multi-drug resistance (MDR) was detected in 8.3% (4/48) of B. cereus isolates, while 33.33% of the isolates showed multiple antibiotic resistance (MAR) index values higher than 0.2. The findings indicate that B. cereus may pose a health risk in packaged and unpackaged spices if present in high quantities. Therefore, the presence of B. cereus strains in both packaged and unpackaged spices should be monitored regarding consumer health and product safety.

Prevalence and characterization of toxigenic Bacillus cereus group isolated from low-moisture food products

The present study was conducted to determine the occurrence of B. cereus group members in low-moisture food products by phenotypic and genetic assessment and to evaluate the toxigenic potential of B. cereus group isolates. According to the results of their morphological shape, growth temperature range, strain-specific gene distribution, 79.5% and 20.5% among 112 isolates were identified as B. cereus sensu stricto (s.s.) and B. thuringiensis, respectively and other toxigenic B. cereus group members was not found. All B. cereus group isolates possessed nheABC, hblACD, cytK, entFM genes, and the most frequent gene was nheA. Only three B. cereus s. s. isolates exhibited as emetic toxin gene-harboring B. cereus group. Several B. cereus s.s. and B. thuringiensis isolates from a low-moisture food products were moderate biofilm formers and showed resistance to rifampicin, tetracycline, or clindamycin. The existence of B. cereus s.s. and B. thuringiensis in low-moisture food products indicates the possible risk of foodborne infections due to their virulence potential.

Prevalence, distribution, enterotoxin profiles, antimicrobial resistance, and genetic diversity of Bacillus cereus group isolates from lettuce farms in Korea

Lettuce wraps are popular in Korean cuisine for their high nutritional value and versatility as healthy additions to multiple dishes. Microbial contamination of lettuce is a major concern, as lettuce is consumed fresh without cooking. Among foodborne pathogens, the spore-forming, facultative anaerobic bacterium, Bacillus cereus is one of the frequently detected pathogen in lettuce in Korea. In this study, we investigated the prevalence and distribution of Bacillus cereus strains in lettuce production farms and further evaluated the enterotoxin gene profiles, antibiotic susceptibility, multidrug resistance pattern, and genetic differences among the B. cereus group isolates. Of the 140 samples isolated from 10 lettuce production farms, 30 samples (21.42%) were positive for B. cereus in which 19 (31.6%) and 10 (23.25%) were from soil and lettuce, respectively. The enterotoxin patterns A (hblCDA, nheABC, entFM, and cytK genes) and B (hblCDA, nheABC, and entFM genes) accounted for 50% and 20% of all the isolates, whereas the emetic gene cesB was not detected in any of the B. cereus group isolates. Antibiotic susceptibility testing of the B. cereus group isolates revealed that all the strains were predominantly resistant to β-lactam antibiotics except imipenem and generally susceptible to most of the non β-lactam antibiotics, including gentamycin, streptomycin, chloramphenicol, and tetracycline. ERIC-PCR and MLST analysis revealed high genetic diversity among the 30 B. cereus group isolates, which belonged to 26 different sequence types (STs) and seven new STs. Moreover, isolates with identical STs exhibited similar patterns of antibiotic resistance and enterotoxin profiles. Results of this study indicate a high prevalence of B. cereus group isolates in lettuce production farms in the Republic of Korea.

Phenotypic and genotypic characterization of the new Bacillus cereus phage SWEP1

A new Bacillus cereus phage, SWEP1, was isolated from black soil. The host lysis activity of phage SWEP1 has a relatively short latent time (20 min) and a small burst size of 83 PFU. The genome of SWEP1 consists of 162,461 bp with 37.77% G+C content. The phage encodes 278 predicted proteins, 103 of which were assigned functionally. No tRNA genes were found. Comparative genomics analysis indicated that SWEP1 is related to Bacillus phage B4 (86.91% identity, 90% query coverage). Phenotypic and genotypic characterization suggested that SWEP1 is a new member of a new species in the genus Bequatrovirus, family Herelleviridae.

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.

Enterotoxin Gene Distribution and Genotypes of Bacillus cereussensu lato Isolated from Cassava Starch

Bacillus cereus is a human pathogenic bacterium found in foods with the potential to cause emesis and diarrhea. This study estimated the presence, toxigenic and genomic diversity of B. cereus s.l. obtained from cassava starch samples collected in bakeries and powdered food companies in Medellín (Colombia). Bacillus cereuss.l. was found in 43 of 75 (57%) cassava starch samples and 98 isolates were obtained. The nheABC, hblCDAB, cytK2, entFM and cesB toxin genes were detected by multiplex PCR and the most frequent operon was nheABC, whereas cesB gene was not found. Twelve toxigenic profiles were determined by the detection of toxin genes, and the most frequent profiles harbored all enterotoxin genes. A broad genomic diversity was detected according to GTG5-PCR fingerprinting results with 76 B. cereus s.l. grouped in sixteen clusters and the 22 isolates clustering separately. No relationship was observed between genomic background and toxigenic profiles. In general, the results showed a high genomic and enterotoxigenic diversity in B. cereus s.l. found in cassava starch. These results should incentive future studies to understand the distribution of B. cereus s.l. isolated on raw materials in comparison with finished products.

Genetic and toxigenic diversity of Bacillus cereus group isolated from powdered foods

Bacillus cereus is a human pathogenic bacterium that produces emetic and diarrheal foodborne diseases. This study evaluated the genetic and toxigenic diversity in B. cereus group isolates from powdered foods collected in public educational institutions, bakeries and powdered food companies located in Medellín, Colombia. B. cereus was detected in 35 of 305 (11%) powdered food samples and 52 B. cereus were isolated. The presence of ten toxin genes, hblCDAB, nheABC, cytK2, entFM and cesB, was evaluated in the isolates by multiplex PCR. The nheABC operon was found in all isolates (100%), hblCDAB in 22 (42%), hblCDA in 8 (15%) and hblCD in 3 (6%); the cytK2 gene was detected in 32 isolates (62%) and entFM in 32 (62%). Notably, the cesB gene was not detected. According to the presence of toxin genes, fifteen profiles were identified. The predominant toxigenic profile contained all toxin genes but cesB. A large genetic diversity was observed by GTG₅ fingerprinting with 46 isolates grouped in seven clusters and the remaining six clustering individually. There was no relationship between toxigenic profiles and genetic clusters, but some genetic clusters seemed to be related to particular powdered food types. In general, the results evidenced high genetic and enterotoxigenic diversity among the B. cereus group isolates.

Prevalence, Enterotoxin Genes, and Antibiotic Resistance of Bacillus cereus Isolated from Raw Vegetables in Korea

Bacillus cereus has long been recognized as an important pathogen in foodborne poisoning worldwide. Fresh vegetables are often contaminated with enterotoxigenic B. cereus and have been implicated as a vehicle for the transmission of this bacterium. This study reports on the occurrence, virulence gene profile, and antibiotic resistance of B. cereus in fresh vegetables. Of 102 examined samples, 48 (47%) of the samples were contaminated with B. cereus (>1 log CFU/g) and 7 (6.8%) of the samples showed more than 3 log CFU/g. In total, 118 B. cereus isolates were examined for the virulence genes nheA, nheB, nheC, hblA, hblC, hblD, cytK, and entFM and for resistance to antibiotics. Of these B. cereus isolates, 70% harbored nheA, nheB, nheC, and cytK. Eighteen (80%) of 21 isolates from bell peppers possessed eight enterotoxin genes. B. cereus isolates were susceptible to imipenem, vancomycin, gentamicin, erythromycin, ciprofloxacin, and chloramphenicol, whereas 22.4% of isolates from garlic chives, 48.7% from perilla leaf, and 40.5% from romaine lettuce showed antibiotic resistance to rifampin and 6% of isolates from garlic chives exhibited resistance to tetracycline. Three isolates from garlic chives were resistant to both tetracycline and rifampin. Raw vegetables were revealed to be major sources of B. cereus containing multiple toxin genes and exhibiting antibiotic resistance. Therefore, the potential health risks of consuming these vegetables raw or undercooked should not be underestimated. This study provides basic information for monitoring the antibiotic resistance and toxigenicity of B. cereus in the food chain during vegetable distribution and for developing food safety management to reduce the contamination with and transmission of B. cereus.

Enhancing the antimicrobial activity of ginseng against Bacillus cereus and Staphylococcus aureus by heat treatment

This study evaluated the antimicrobial activities [diffusion inhibition zone, minimum inhibitory concentration (MIC), and minimum bactericidal concentration], of heated ginseng extracts (ethanol and methanol). The extract yields, ginsenoside compositions, growth inhibitory effects against Bacillus cereus and Staphylococcus aureus and bacterial cell membrane potential changes, were also investigated. Methanol extracts of heated ginseng, showed higher antimicrobial activity than ethanol extracts. B. cereus was more easily inhibited than S. aureus. Ginseng heated at 100 °C for 2 and 16 h, showed maximum antimicrobial activity against B. cereus and S. aureus, respectively. In the growth inhibitory test, S. aureus and B. cereus were completely inhibited after 2 and 8 h culture at the MIC. The cell membrane potential decreased with increasing concentration of extract, indicating cell metabolism disruption. Ginsenosides Rg₃, a potent antibacterial substance, which were absent in non-heated ginseng, were produced by heating ginseng at 100 °C for 4 and 8 h, respectively.

Isolation and Characterization of Bacillus cereus Bacteriophages from Foods and Soil

The aim of this study was to isolate and characterize Bacillus cereus bacteriophages of various origins. Twenty-seven bacteriophages against B. cereus were isolated from various Korean traditional fermented foods and soils. Plaque size, transmission electron microscopy, virulence profile, and in vitro lytic activity of bacteriophage isolates were examined. Transmission electron microscopy confirmed B. cereus bacteriophages belonging to the family Siphoviridae. Among B. cereus bacteriophages with broad host range, 18 isolates (66.7%) did not harbor any B. cereus virulence factors. Among them, bacteriophage strain CAU150036, CAU150038, CAU150058, CAU150064, CAU150065, and CAU150066 effectively inhibited B. cereus in vitro within 1 h. Therefore, they are considered potential candidates for controlling the contamination of B. cereus in food or other applications.

Molecular Characterization and Risk Assessment of Bacillus cereus Sensu Lato Isolated from Ultrahigh-Temperature and Pasteurized Milk Marketed in Rio de Janeiro, Brazil

The presence of Bacillus cereus in milk is a major concern in the dairy industry. In this study 27 Bacillus cereus sensu lato isolates from pasteurized and ultrahigh-temperature (UHT) milk (24 whole UHT and 4 pasteurized samples) collected at supermarket chains in Rio de Janeiro, Brazil, were evaluated to assess the potential risk for food poisoning. Toxigenic and virulence profiles were defined by gene-specific PCR. Affiliation to phylogenetic groups was assigned by panC sequencing. Microbiological analysis revealed the presence of B. cereus s.l. in eight (33.3%) brands (six brands of UHT and two brands of pasteurized milk). Twenty-seven isolates were recovered (13 B. cereus and 14 Bacillus thuringiensis ). Predominant toxigenic patterns were type I (contains all toxin genes except ces) and type II (does not contain cytK and ces), with seven (25.9%) isolates each. Predominant virulence patterns were type 2 (does not contain hlyII or shp) and type 3 (contains all virulence genes), with five (18.5%) isolates each. All isolates belonged to phylogenetic groups III and IV. Presence of hbl, piplc, and sph was associated with group IV isolates. Our results suggest that B. thuringiensis and B. cereus sensu stricto should be considered potential foodborne pathogens. Because the majority of the milk isolates studied have the potential to cause food poisoning because of the high prevalence of toxin and virulence genes and the specific phylogenetic group affiliations, these milk products can be potentially hazardous for human consumption.

Draft Genome Sequences of Enterotoxigenic Bacillus cereus Strains Obtained from Powdered Infant Formula

We introduce the draft genome sequences of five enterotoxigenic Bacillus cereus strains: Bc 12, Bc 67, Bc 111, Bc 112, and Bc 113, which were obtained from powdered infant formula. The genome sizes of the strains ranged from 5.5 to 5.8 Mb, and the G+C contents were ~35.2%.

Destruction of Bacillus cereus spores in a thick soy bean paste (doenjang) by continuous ohmic heating with five sequential electrodes

This study selected spores from Bacillus cereus FSP-2 strain (the isolate from a commercial doenjang processing line) as the test strain which showed significantly higher thermal resistance (P < 0·05) than B. cereus reference strain (ATCC 27348). The spores in doenjang were subjected to ohmic heating (OH) at 95, 105, 115 and 125°C for 30, 60 or 90 s using a five sequential electrode system (electrical field: 26·7 V cm(-1) ; alternating current frequency: 25 kHz). OH at 105°C for 30-90 s reduced the B. cereus spore count in doenjang samples to <4 log CFU g(-1) . Since OH treatment at 115 and 125°C caused a perceivable colour change in the product (>1·5 National Bureau of Standards units), treatment at 105°C for 60 s was selected and applied on a large scale (500 kg of product). Reliable and reproducible destruction of B. cereus spores occurred; the reductions achieved (to < 4 log CFU g(-1) ) met the Korean national standards. Scanning electron microscopy revealed microstructural alterations in the spores (shrinkage and a distorted outer spore coat). OH is an effective method for destroying B. cereus spores to ensure the microbiological quality and safety of a thick, highly viscous sauce.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that an ohmic heating (OH) using a five sequential electrode system can effectively destroy highly heat-resistant Bacillus cereus spores which have been frequently found in a commercial doenjang processing line without perceivable quality change in the product. In addition, it may demonstrate high potential of the unique OH system used in this study that will further contribute to ensure microbiological quality and safety of crude sauces containing high levels of electrolyte other than doenjang as well.

Occurrence of Toxigenic Bacillus cereus and Bacillus thuringiensis in Doenjang, a Korean Fermented Soybean Paste

This study determined the prevalence and toxin profile of Bacillus cereus and Bacillus thuringiensis in doenjang, a fermented soybean food, made using both traditional and commercial methods. The 51 doenjang samples tested were broadly contaminated with B. cereus; in contrast, only one sample was positive for B. thuringiensis. All B. cereus isolates from doenjang were positive for diarrheal toxin genes. The frequencies of nheABC and hblACD in traditional samples were 22.7 and 0%, respectively, whereas 5.1 and 5.1% of B. cereus isolates from commercial samples possessed nheABC and hblACD, respectively. The detection rate of ces gene was 10.8%. The predominant toxin profile among isolates from enterotoxigenic B. cereus in doenjang was profile 4 (entFM-bceT-cytK). The major enterotoxin genes in emetic B. cereus were cytK, entFM, and nheA genes. The B. thuringiensis isolate was of the diarrheagenic type. These results provide a better understanding of the epidemiology of the enterotoxigenic and emetic B. cereus groups in Korean fermented soybean products.

Inactivation of Bacillus cereus spores in a tsuyu sauce using continuous ohmic heating with five sequential elbow-type electrodes

AIMS

The effect of ohmic heating (OH) in a pilot plant system which had a zig-zag shaped (elbow-type) ohmic heater with five sequential voltage electrodes was investigated on Bacillus cereus spores in a commercial tsuyu sauce.

METHODS AND RESULTS

The electrical field was fixed at 26·7 V cm(-1) with an alternating current frequency of 25 kHz. Raw tsuyu sauce (50 l) inoculated with B. cereus spores was submitted in a 4 × 3 factorial design to the OH system and heated at 95, 105, 115, and 125°C each for 30, 60, and 90 s. Survival of B. cereus spores and colour change in the commercial tsuyu sauce were both measured before and after treatment. As the treatment temperature and time increased, the number of surviving B. cereus spores decreased. The OH treatment in a bath-type process at 105°C for more than 30 s resulted in the total inactivation of the inoculated B. cereus spores (average 5·4 log reductions to undetectable levels after treatment). The OH protocol of heating at 105°C for 60 s which ensure complete eradication of the inoculated spores without compromising product quality was chosen and investigated for its suitability for commercial application on bulk quantities of samples (500 l). Reliable and reproducible reductions in B. cereus spore counts of 4·7-5·5 log CFU ml(-1) (mean ± standard deviation = 5·1 ± 0·3 CFU ml(-1) ) were achieved by the selected protocol of the continuous OH treatment (105°C for 60 s).

CONCLUSION

This study suggests that OH treatment with five sequential elbow-type electrodes has great potential as an industrial sterilizing method for liquid food contaminated with B. cereus spores.

SIGNIFICANCE AND IMPACT OF THE STUDY

This procedure will enhance the microbiological quality of liquid foods while minimizing quality deterioration.

Toxin Profile, Biofilm Formation, and Molecular Characterization of Emetic Toxin-Producing Bacillus cereus Group Isolates from Human Stools

Emetic toxin-producing Bacillus cereus group species are an important problem, because the staple food for Korean is grains such as rice. In this study, we determined the prevalence (24 of 129 isolates) of emetic B. cereus in 36,745 stool samples from sporadic food-poisoning cases in Korea between 2007 and 2008. The toxin gene profile, toxin production, and biofilm-forming ability of the emetic B. cereus isolates were investigated. Repetitive element sequence polymorphism polymerase chain reaction fingerprints (rep-PCR) were also used to assess the intraspecific biodiversity of these isolates. Emetic B. cereus was present in 0.07% of the sporadic food-poisoning cases. The 24 emetic isolates identified all carried the nheABC and entFM genes and produced NHE enterotoxin. However, they did not have hemolysin BL toxin or related genes. A relationship between biofilm formation and toxin production was not observed in this study. The rep-PCR fingerprints of the B. cereus isolates were not influenced by the presence of toxin genes, or biofilm-forming ability. The rep-PCR assay discriminated emetic B. cereus isolates from nonemetic isolates, even if this assay did not perfectly discriminate these isolates. Further study on emetic isolates possessing a high degree of diversity may be necessary to evaluate the performance of the subtyping assay to discriminate emetic and nonemetic B. cereus isolates and could provide a more accurate indication of the risk from B. cereus strains.

Complete genome sequence and phylogenetic position of the Bacillus cereus group phage JBP901

Bacteriophage JBP901, isolated from fermented food, is specific for Bacillus cereus group species and exhibits a broad host spectrum among a large number of B. cereus isolates. Genome sequence analysis revealed a linear 159,492-bp genome with overall G+C content of 39.7 mol%, and 201 ORFs. The presence of a putative methylase, the large number of tRNAs, and the large number of nucleotide-metabolism- and replication-related genes in JBP901 reflects its broad lytic capacity. Most of the ORFs showed a high degree of similarity to Bcp1, Bc431v3 and BCP78, and various comparative genomics analyses also consistently clustered JBP901 with orphan (unclassified) Bacillus phages in the subfamily Spounavirinae of the family Myoviridae, supporting the presence of a distinguishable group in the subfamily.

Characterization and complete genome sequence of a virulent bacteriophage B4 infecting food-borne pathogenic Bacillus cereus

Bacillus cereus causes food poisoning, resulting in vomiting and diarrhea, due to production of enterotoxins. As a means of controlling this food-borne pathogen, the virulent bacteriophage B4 was isolated and characterized. Bacterial challenge assays showed that phage B4 effectively inhibited growth of members of the B. cereus group as well as B. subtilis, and growth inhibition persisted for over 20 h. One-step growth analysis also revealed the host lysis activity of phage B4, with relatively short eclipse/latent times (10/15 min) and a large burst size (>200 PFU). The complete genome of phage B4, containing a 162-kb DNA with 277 ORFs, was analyzed. The endolysin encoded by the phage B4 genome accounts for the cell lysis activity of this phage. These results suggest that phage B4 has potential as a biological agent to control B. cereus propagation.

Bacillus cereus infection outbreak in captive psittacines

This study reports an uncommon epizootic outbreak of Bacillus cereus that caused the sudden death of 12 psittacines belonging to the species Anodorhynchus hyacinthinus (1 individual), Diopsittaca nobilis (1 individual), Ara severa (1 individual) and Ara ararauna (9 individuals) in a Brazilian zoo. Post-mortem examination of the animals reveled extensive areas of lung hemorrhage, hepatic congestion, hemorrhagic enteritis and cardiac congestion. Histopathological examination of the organs showed the presence of multiple foci of vegetative cells of Gram-positive bacilli associated with discrete and moderate mononuclear inflammatory cell infiltrate. Seventeen B. cereus strains isolated from blood and sterile organs of nine A. ararauna were analyzed in order to investigate the genetic diversity (assessed by Rep-PCR) and toxigenic profiles (presence of hblA, hblC and hblD; nheA, nheB and nheC as well as cytK, ces and entFM genes) of such strains. Amplification of genomic DNA by Rep-PCR of B. cereus strains generated two closely related profiles (Rep-PCR types A and B) with three bands of difference. All strains were classified as belonging to the toxigenic profile I which contained HBL and NHE gene complexes, entFM and cytK genes. Altogether, microbiological and histopathological findings and the evidence provided by the success of the antibiotic prophylaxis, corroborate that B. cereus was the causative agent of the infection that killed the birds.

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.

Bacteriophages BCP1-1 and BCP8-2 require divalent cations for efficient control of Bacillus cereus in fermented foods

Bacillus cereus is a foodborne bacterial pathogen that causes diarrhea and vomiting. In this study, the usefulness of bacteriophages to eradicate B. cereus from fermented foods was investigated. A total of 13 phages were isolated from Korean fermented food products, and 2 (BCP1-1 and BCP8-2) were further characterized. Transmission electron microscopy (TEM), restriction enzyme digestion pattern analysis, and SDS-PAGE of the structural proteins suggest that both phages belong to the family Myoviridae, containing approximately 150 kbp-long genomes. The host ranges of both phages were limited to B. cereus group species (12/13), as they were not able to lyse other Gram-positive or negative strains including Bacillus subtilis. Purified phages were used to inhibit B. cereus growth in a model fermented food system, cheonggukjang, a fast-fermented soybean paste product. BCP1-1 and BCP8-2 were able to effectively eradicate B. cereus from the food only if divalent cations (Ca²⁺, Mg²⁺, or Mn²⁺) were added to the medium. Further studies reveal that divalent cations are essential for phage adsorption, while a monovalent cation (Na⁺) is required for the post-adsorption phase of phage infection. Taken together, our findings imply that a phage could be an ideal anti-bacterial agent for use in fermented food products that require the presence of beneficial microflora and, during phage application, optimization of phage reaction conditions is critical for the successful utilization of phage biocontrol.

Complete genome sequence of Bacillus cereus bacteriophage PBC1

Bacillus cereus is a ubiquitous, spore-forming bacterium associated with food poisoning cases. To develop an efficient biocontrol agent against B. cereus, we isolated lytic phage PBC1 and sequenced its genome. PBC1 showed a very low degree of homology to previously reported phages, implying that it is novel. Here we report the complete genome sequence of PBC1 and describe major findings from our analysis.

Characterization of LysB4, an endolysin from the Bacillus cereus-infecting bacteriophage B4

BACKGROUND

Bacillus cereus is a foodborne pathogen that causes emetic or diarrheal types of food poisoning. The incidence of B. cereus food poisoning has been gradually increasing over the past few years, therefore, biocontrol agents effective against B. cereus need to be developed. Endolysins are phage-encoded bacterial peptidoglycan hydrolases and have received considerable attention as promising antibacterial agents.

RESULTS

The endolysin from B. cereus phage B4, designated LysB4, was identified and characterized. In silico analysis revealed that this endolysin had the VanY domain at the N terminus as the catalytic domain, and the SH3_5 domain at the C terminus that appears to be the cell wall binding domain. Biochemical characterization of LysB4 enzymatic activity showed that it had optimal peptidoglycan hydrolase activity at pH 8.0-10.0 and 50°C. The lytic activity was dependent on divalent metal ions, especially Zn2+. The antimicrobial spectrum was relatively broad because LysB4 lysed Gram-positive bacteria such as B. cereus, Bacillus subtilis and Listeria monocytogenes and some Gram-negative bacteria when treated with EDTA. LC-MS analysis of the cell wall cleavage products showed that LysB4 was an L-alanoyl-D-glutamate endopeptidase, making LysB4 the first characterized endopeptidase of this type to target B. cereus.

CONCLUSIONS

LysB4 is believed to be the first reported L-alanoyl-D-glutamate endopeptidase from B. cereus-infecting bacteriophages. The properties of LysB4 showed that this endolysin has strong lytic activity against a broad range of pathogenic bacteria, which makes LysB4 a good candidate as a biocontrol agent against B. cereus and other pathogenic bacteria.

Molecular and toxigenic characterization of Bacillus cereus and Bacillus thuringiensis strains isolated from commercial ground roasted coffee

Thirty samples of roasted ground coffee beans from 10 different commercial brands were analyzed to investigate the occurrence and levels of Bacillus cereus and Bacillus thuringiensis strains. Strains were evaluated for their genetic diversity by repetitive element sequence polymorphism PCR (Rep-PCR) and for their toxigenic profiles, i.e., the presence of hblA, hblC, hblD, nheA, nheB, nheC, cytK, ces, and entFM. Survival and multiplication of B. cereus sensu lato in the ready-to-drink coffee was determined to evaluate this beverage as a possible vehicle for B. cereus infection. B. cereus was detected in 17 (56.7%) of the 30 samples, and B. thuringiensis was detected in 8 (26.7%) of the 30 samples. Five samples did not produce any characteristic growth. The most common gene, entFM, was detected in 23 strains (92%). The NHE complex (nheA, nheB, and nheC genes) was found in 19 strains (76%). The HBL complex (hblA, hblC, and hblD) was found in 16 strains (64%). All strains were negative for ces. The cytK gene was found in 16 strains (64%). The computer-assisted cluster analysis of Rep-PCR profiles using a clustering criterion of 80% similarity revealed four main clusters. Cluster 1 was the predominant and comprised three B. thuringiensis strains with 100% similarity, cluster 2 comprised two B. cereus strains (100% similarity), cluster 3 comprised two B. thuringiensis strains (90% similarity), and cluster 4 comprised one B. thuringiensis strain and one B. cereus strain (85% similarity). The cluster analysis of fingerprints generated by Rep-PCR revealed a high genetic diversity among the B. cereus strains, suggesting that the contamination could have originated from different sources. In our experiments, when sugar was added and the beverage was kept in thermic bottles there was a significant increase in B. cereus sensu lato levels, which may increase the risk of food poisoning. These results highlight the need for additional studies on this subject to better evaluate coffee as a food poisoning vehicle.

Complete genome sequence of Bacillus cereus bacteriophage BCP78

Bacillus cereus is generally found in soil habitats, and it contaminates a wide variety of foods, causing food poisoning with symptoms such as vomiting and diarrhea. To develop a novel biocontrol agent to inhibit this pathogen, bacteriophage BCP78 belonging to the Siphoviridae family was isolated from a fermented food sample. Here we announce the complete genome sequence of BCP78, which may be useful for understanding its inhibition mechanism against B. cereus, and describe major findings from the genome annotation.

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.

Genetic diversity, antimicrobial resistance and toxigenic profiles of Bacillus cereus isolated from food in Brazil over three decades

Bacillus cereus is an ever-present problem. It is widely distributed in several environments such as soil and plants and is commonly isolated from food and additives. In this study we analyzed 97 foodborne B. cereus sensu stricto strains isolated in Brazil in the 1980's, 1990's and 2000's in order to investigate the genetic diversity (assessed by Rep-PCR), antimicrobial resistance and toxigenic profiles (presence of hblA, hblC and hblD; nheA, nheB and nheC as well as cytK, ces and entFM genes) of such strains. The majority of the strains (79, 81.4%) were β-hemolytic. The NHE complex was found in 82 strains (84.5%) and HBL complex was found in 61 (62.9%) strains. All strains were negative to ces. The cytK-2 gene was found in 44 (45.4%) strains. The predominant toxigenic pattern was type I (32, 33%) which included strains positive for all toxin genes but ces. Computer assisted cluster analysis of Rep-PCR profiles showed a high genetic diversity. Seven major clusters comprising two or more strains were found and cluster 1 was predominant (ten strains, nine of them showing 100% similarity). This cluster included strains isolated in the 1980's and the 1990's. Cluster analysis of Rep-PCR profiles based on decade of isolation, source, hemolytic pattern, toxigenic and antibiotic resistance patterns revealed a similar clustering pattern as found in the analysis including all strains. The inability to observe a predominant band pattern when Rep-PCR cluster analysis was based on decade of isolation suggests that this diversity has been maintained over time. All strains were susceptible to gentamicin. We detected resistance to tetracycline (11 strains showing intermediate resistance and nine completely resistant strains), clindamycin (ten intermediate strains) and vancomycin (one strain). Clindamycin resistance showed statistical association with strains isolated in 2000's. The predominant resistance pattern was type A (72, 72.2%) which included strains susceptible to all drugs tested. Our results suggest that the majority of the strains present in several types of food in Brazil pose a potential risk to cause food poisoning due to the high prevalence of toxin genes found in these strains. However, additional studies involving cytotoxicity tests and affiliation of these strains to phylogenetic groups based on molecular data would be useful to better evaluate this potential and could provide a more accurate indication of the risk.