From soil to gut:Bacillus cereusand its food poisoning toxins

Assessment and molecular characterization of Bacillus cereus isolated from edible fungi in China

Background

Bacillus cereus is a foodborne pathogen commonly found in nature and food and can cause food spoilage and health issues. Although the prevalence of B. cereus in foods has been reported worldwide, the extent of contamination in edible fungi, which has become increasingly popular as traditional or functional food, is largely unknown. Here we investigated the prevalence, toxin genes’ distribution, antibiotic resistance, and genetic diversity of B. cereus isolated from edible fungi in China.

Results

Six hundred and ninety-nine edible fungi samples were collected across China, with 198 (28.3%) samples found to be contaminated by B. cereus, with an average contamination level of 55.4 most probable number (MPN)/g. Two hundred and forty-seven B. cereus strains were isolated from the contaminated samples. Seven enterotoxin genes and one cereulide synthetase gene were detected. The detection frequencies of all enterotoxin genes were ≥ 80%, whereas the positive rate of the cesB gene in B. cereus was 3%. Most isolates were resistant to penicillins, β-lactam/β-lactamase inhibitor combinations, cephems, and ansamycins, but were susceptible to penems, aminoglycosides, macrolides, ketolide, glycopeptides, quinolones, phenylpropanol, tetracyclines, lincosamides, streptogramins, and nitrofurans. Meanwhile, 99.6% of all isolates displayed multiple antimicrobial resistance to three or more classes of antimicrobials. Using genetic diversity analysis, all isolates were defined in 171 sequence types (STs), of which 83 isolates were assigned to 78 new STs.

Conclusions

This study provides large-scale insight into the prevalence and potential risk of B. cereus in edible fungi in China. Approximately one-third of the samples were contaminated with B. cereus, and almost all isolates showed multiple antimicrobial resistance. Detection frequencies of all seven enterotoxin genes were equal to or more than 80%. These new findings may indicate a need for proper pre-/post-processing of edible fungi to eliminate B. cereus, thereby preventing the potential risk to public health.

Technologically relevant Bacillus species and microbial safety of West African traditional alkaline fermented seed condiments

Fermented food condiments serve as a major source of nutrients to many homes in West Africa, especially among the rural poor who use these condiments as a cheap source of protein substitute for milk and other animal protein sources. Traditional fermented West African condiments are produced by spontaneous fermentation of legumes and protein-rich seeds of both cultivated and wild plant species. These fermented condiments are culturally accepted and widely produced in the West African sub-region, and rely on indigenous microbiota responsible for taste, texture, aroma development and the overall unique product characteristics. Detailed understanding of fermentation microbiota and their unique technological and functional properties are fundamental in developing products with enhanced quality and safety, as well as development of specific locally adapted starter cultures. Technologically relevant Bacillus spp., mainly Bacillus subtilis, are the predominant fermentative bacteria responsible for the natural fermentation of condiments across West Africa. Other species of Bacillus including B. amyloliquefaciens, B. licheniformis, B. pumilus, B. megaterium, B. sphaericus, B. cereus, B. badius and B. fusiformis are also frequently involved in the fermentation process. These bacterial species are responsible for flavor development, bio-conversion of complex food molecules, and production of antimicrobial compounds that impact shelf-life and safety, and in some instances, may confer host-beneficial health effects beyond basic nutrition. First, this review provides currently available information on the technologically relevant Bacillus species isolated from fermented food condiments in nine (9) West African countries. In addition, perspectives on harnessing the potentials of the technologically beneficial bacterial strains in fermented condiments in West Africa for enhanced food safety, quality and overall food security is presented.

Bacillus cereus Decreases NHE and CLO Exotoxin Synthesis to Maintain Appropriate Proteome Dynamics During Growth at Low Temperature

Cellular proteomes and exoproteomes are dynamic, allowing pathogens to respond to environmental conditions to sustain growth and virulence. Bacillus cereus is an important food-borne pathogen causing intoxication via emetic toxin and/or multiple protein exotoxins. Here, we compared the dynamics of the cellular proteome and exoproteome of emetic B. cereus cells grown at low (16 °C) and high (30 °C) temperature. Tandem mass spectrometry (MS/MS)-based shotgun proteomics analysis identified 2063 cellular proteins and 900 extracellular proteins. Hierarchical clustering following principal component analysis indicated that in B. cereus the abundance of a subset of these proteins—including cold-stress responders, and exotoxins non-hemolytic enterotoxin (NHE) and hemolysin I (cereolysin O (CLO))—decreased at low temperature, and that this subset governs the dynamics of the cellular proteome. NHE, and to a lesser extent CLO, also contributed significantly to exoproteome dynamics; with decreased abundances in the low-temperature exoproteome, especially in late growth stages. Our data therefore indicate that B. cereus may reduce its production of secreted protein toxins to maintain appropriate proteome dynamics, perhaps using catabolite repression to conserve energy for growth in cold-stress conditions, at the expense of virulence.

Quantitative bioluminescence assay for measuring Bacillus cereus nonhemolytic enterotoxin complex

Bacillus cereus is a foodborne pathogen causing emesis and diarrhea in those affected. It is assumed that the non-hemolytic enterotoxin (Nhe) plays a key role in B. cereus induced diarrhea. The ability to trace Nhe activity is important for food safety. While assays such as PCR and ELISA exist to detect Nhe, those methods cannot differentiate between active and inactive forms of Nhe. The existing rabbit ileal loop bioassay used to detect Nhe activity is ethically disfavored because it uses live experimental animals. Here we present a custom built low-cost CCD based luminometer and applied it in conjunction with a cell-based assay using Vero cells transduced to express the luciferase enzyme. The activity of Nhe was measured as its ability to inhibit synthesis of luciferase as quantified by reduction of light emission by the luciferase reaction. Emitted light intensity was observed to be inversely proportional to Nhe concentration over a range of 7 ng/ml to 125 ng/ml, with a limit of detection of 7 ng/ml Nhe.

Beyond Toxin Transport: Novel Role of ABC Transporter for Enzymatic Machinery of Cereulide NRPS Assembly Line

This study revealed a novel, potentially conserved mechanism involved in the biosynthesis of microbial natural products, exemplified by the mitochondrial active depsipeptide cereulide. Similar to other bioactive substances, such as the last-resort antibiotics vancomycin and daptomycin, the antitumor drug cryptophycin or the cholesterol-lowering agent lovastatin, cereulide is synthesized nonribosomally by multienzyme machinery, requiring the concerted actions of multiple proteins to ensure correct product assembly. Given the importance of microbial secondary metabolites in human and veterinary medicine, it is critical to understand how these processes are orchestrated within the host cells. By revealing that tethering of a biosynthetic enzyme to the cell membrane by an ABC transporter is essential for nonribosomal peptide production, our study provides novel insights into synthesis of microbial secondary metabolites, which could contribute to isolation of novel compounds from cryptic secondary metabolite clusters or improve the yield of produced pharmaceuticals.

Nonribosomal peptide synthetases (NRPSs) and polyketide synthetases (PKSs) play a pivotal role in the production of bioactive natural products, such as antibiotics and cytotoxins. Despite biomedical and pharmaceutical importance, the molecular mechanisms and architectures of these multimodular enzyme complexes are not fully understood. Here, we report on an ABC transporter that forms a vital part of the nonribosomal peptide biosynthetic machinery. Emetic Bacillus cereus produces the highly potent, mitochondrial active nonribosomal depsipeptide cereulide, synthesized by the NRPS Ces. The ces gene locus includes, next to the structural cesAB genes, a putative ABC transporter, designated cesCD. Our study demonstrates that tethering of CesAB synthetase to the cell membrane by CesCD is critical for peptide assembly. In vivo studies revealed that CesAB colocalizes with CesCD on the cell membrane, suggesting direct involvement of this ABC transporter in the biosynthesis of a nonribosomal peptide. Mutation of cesCD, disrupting the assembly of the CesCD complex, resulted in decreased interaction with CesAB and, as a consequence, negatively affected cereulide biosynthesis. Specific domains within CesAB synthetase interacting with CesC were identified. Furthermore, we demonstrated that the structurally similar BerAB transporter from Bacillus thuringiensis complements CesCD function in cereulide biosynthesis, suggesting that the direct involvement of ABC transporter in secondary metabolite biosynthesis could be a widespread mechanism. In summary, our study revealed a novel, noncanonical function for ABC transporter, which is essential for megaenzyme functionality of NRPS. The new insights into natural product biosynthesis gained may facilitate the discovery of new metabolites with bioactive potential.

Bacillus cereus: Epidemiology, Virulence Factors, and Host-Pathogen Interactions

The toxin-producing bacterium Bacillus cereus is an important and neglected human pathogen and a common cause of food poisoning. Several toxins have been implicated in disease, including the pore-forming toxins hemolysin BL (HBL) and nonhemolytic enterotoxin (NHE). Recent work revealed that HBL binds to the mammalian surface receptors LITAF and CDIP1 and that both HBL and NHE induce potassium efflux and activate the NLRP3 inflammasome, leading to pyroptosis. These mammalian receptors, in part, contribute to inflammation and pathology. Other putative virulence factors of B. cereus include cytotoxin K, cereulide, metalloproteases, sphingomyelinase, and phospholipases. In this review, we highlight the latest progress in our understanding of B. cereus biology, epidemiology, and pathogenesis, and discuss potential new directions for research in this field.

Bacterial diversity in six species of fresh edible seaweeds submitted to high pressure processing and long-term refrigerated storage

Seaweeds are highly perishable foods due to their richness in nutrients. High pressure processing (HPP) has been applied for extending the shelf life of fresh seaweeds but there is no information on the effect of HPP on the bacterial diversity of seaweeds. The culturable bacteria of six species of fresh edible seaweeds (green seaweeds Codium fragile and Ulva lactuca, brown seaweeds Himanthalia elongata, Laminaria ochroleuca and Undaria pinnatifida, and red seaweed Chondrus crispus) were investigated and compared to those of HPP-treated (400 and 600 MPa for 5 min) seaweeds, at the start and end of their refrigerated storage period. A total of 523 and 506 bacterial isolates were respectively retrieved from untreated and HPP-treated seaweeds. Isolates from untreated seaweeds belonged to 18 orders, 35 families, 71 genera and 135 species whereas isolates from HPP-treated seaweeds belonged to 13 orders, 23 families, 43 genera and 103 species. HPP treatment significantly reduced the number of isolates belonging to 6 families and greatly increased the number of Bacillaceae isolates. At the end of storage, decreases in bacterial diversity at the genus and species level were observed for untreated as well as for HPP-treated seaweeds.

No Assembly Required: Using BTyper3 to Assess the Congruency of a Proposed Taxonomic Framework for the Bacillus cereus Group With Historical Typing Methods

The Bacillus cereus group, also known as B. cereus sensu lato (s.l.), is a species complex comprising numerous closely related lineages, which vary in their ability to cause illness in humans and animals. The classification of B. cereus s.l. isolates into species-level taxonomic units is essential for facilitating communication between and among microbiologists, clinicians, public health officials, and industry professionals, but is not always straightforward. A recently proposed genomospecies-subspecies-biovar taxonomic framework aims to provide a standardized nomenclature for this species complex but relies heavily on whole-genome sequencing (WGS). It thus is unclear whether popular, low-cost typing methods (e.g., single- and multi-locus sequence typing) remain congruent with the proposed taxonomy. Here, we characterize 2,231 B. cereus s.l. genomes using a combination of in silico (i) average-nucleotide identity (ANI)-based genomospecies assignment, (ii) ANI-based subspecies assignment, (iii) seven-gene multi-locus sequence typing (MLST), (iv) single-locus panC group assignment, (v) rpoB allelic typing, and (vi) virulence factor detection. We show that sequence types (STs) assigned using MLST can be used for genomospecies assignment, and we provide a comprehensive list of ST/genomospecies associations. For panC group assignment, we show that an adjusted, eight-group framework is largely, albeit not perfectly, congruent with the proposed eight-genomospecies taxonomy, as panC alone may not distinguish (i) B. luti from Group II B. mosaicus and (ii) B. paramycoides from Group VI B. mycoides. We additionally provide a list of loci that capture the topology of the whole-genome B. cereus s.l. phylogeny that may be used in future sequence typing efforts. For researchers with access to WGS, MLST, and/or panC data, we showcase how our recently released software, BTyper3 (https://github.com/lmc297/BTyper3), can be used to assign B. cereus s.l. isolates to taxonomic units within this proposed framework with little-to-no user intervention or domain-specific knowledge of B. cereus s.l. taxonomy. We additionally outline a novel method for assigning B. cereus s.l. genomes to pseudo-gene flow units within proposed genomospecies. The results presented here highlight the backward-compatibility and accessibility of the recently proposed genomospecies-subspecies-biovar taxonomic framework and illustrate that WGS is not a necessity for microbiologists who want to use the proposed nomenclature effectively.

Repurposing Clinically Approved Drugs for the Treatment of Bacillus cereus, a Surrogate for Bacillus anthracis

Of the numerous infectious diseases afflicting humans, anthrax disease, caused by Bacillus anthracis, poses a major threat in its virulence and lack of effective treatment. The currently lacking standards of care, as well as the lengthy drug approval process, demonstrate the pressing demand for treatment for B. anthracis infections. The present study screened 1586 clinically approved drugs in an attempt to identify repurposable compounds against B. cereus, a relative strain that shares many physical and genetic characteristics with B. anthracis. Our study yielded five drugs that successfully inhibited B. cereus growth: dichlorophen, oxiconazole, suloctidil, bithionol, and hexestrol. These drugs exhibited varying levels of efficacy in broad-spectrum experiments against several Gram-positive and Gram-negative bacterial strains, with hexestrol showing the greatest inhibition across all tested strains. Through tests for the efficacy of each drug on B. cereus, bithionol was the single most potent compound on both solid and liquid media and exhibited even greater eradication of B. cereus in combination with suloctidil on solid agar. This multifaceted in vitro study of approved drugs demonstrates the potential to repurpose these drugs as treatments for anthrax disease in a time-efficient manner to address a global health need.

Cereulide Synthetase Acquisition and Loss Events within the Evolutionary History of Group III Bacillus cereus Sensu Lato Facilitate the Transition between Emetic and Diarrheal Foodborne Pathogens

Cereulide-producing members of Bacillus cereussensu lato group III (also known as emetic B. cereus) possess cereulide synthetase, a plasmid-encoded, nonribosomal peptide synthetase encoded by the ces gene cluster. Despite the documented risks that cereulide-producing strains pose to public health, the level of genomic diversity encompassed by emetic B. cereus has never been evaluated at a whole-genome scale. Here, we employ a phylogenomic approach to characterize group III B. cereussensu lato genomes which possess ces (ces positive) alongside their closely related, ces-negative counterparts (i) to assess the genomic diversity encompassed by emetic B. cereus and (ii) to identify potential ces loss and/or gain events within the evolutionary history of the high-risk and medically relevant sequence type (ST) 26 lineage often associated with emetic foodborne illness. Using all publicly available ces-positive group III B. cereussensu lato genomes and the ces-negative genomes interspersed among them (n = 159), we show that emetic B. cereus is not clonal; rather, multiple lineages within group III harbor cereulide-producing strains, all of which share an ancestor incapable of producing cereulide (posterior probability = 0.86 to 0.89). Members of ST 26 share an ancestor that existed circa 1748 (95% highest posterior density [HPD] interval = 1246.89 to 1915.64) and first acquired the ability to produce cereulide before 1876 (95% HPD = 1641.43 to 1946.70). Within ST 26 alone, two subsequent ces gain events were observed, as well as three ces loss events, including among isolates responsible for B. cereussensu lato toxicoinfection (i.e., "diarrheal" illness).IMPORTANCEB. cereus is responsible for thousands of cases of foodborne disease each year worldwide, causing two distinct forms of illness: (i) intoxication via cereulide (i.e., emetic syndrome) or (ii) toxicoinfection via multiple enterotoxins (i.e., diarrheal syndrome). Here, we show that emetic B. cereus is not a clonal, homogenous unit that resulted from a single cereulide synthetase gain event followed by subsequent proliferation; rather, cereulide synthetase acquisition and loss is a dynamic, ongoing process that occurs across lineages, allowing some group III B. cereussensu lato populations to oscillate between diarrheal and emetic foodborne pathogens over the course of their evolutionary histories. We also highlight the care that must be taken when selecting a reference genome for whole-genome sequencing-based investigation of emetic B. cereussensu lato outbreaks, since some reference genome selections can lead to a confounding loss of resolution and potentially hinder epidemiological investigations.

Groundwater promotes emergence of asporogenic mutants of emetic Bacillus cereus

Bacillus cereus is a ubiquitous endospore-forming bacterium, which mainly affects humans as a food-borne pathogen. Bacillus cereus can contaminate groundwater used to irrigate food crops. Here, we examined the ability of the emetic strain B. cereus F4810/72 to survive abiotic conditions encountered in groundwater. Our results showed that vegetative B. cereus cells rapidly evolved in a mixed population composed of endospores and asporogenic variants bearing spo0A mutations. One asporogenic variant, VAR-F48, was isolated and characterized. VAR-F48 can survive in sterilized groundwater over a long period in a vegetative form and has a competitive advantage compared to its parental strain. Proteomics analysis allowed us to quantify changes to cellular and exoproteins after 24 and 72 h incubation in groundwater, for VAR-F48 compared to its parental strain. The results revealed a significant re-routing of the metabolism in the absence of Spo0A. We concluded that VAR-F48 maximizes its energy use to deal with oligotrophy, and the emergence of spo0A-mutated variants may contribute to the persistence of emetic B. cereus in natural oligotrophic environments.

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.

Comparison of the antibiotic resistance between genetically diverse and toxigenic Bacillus cereus sensu lato from milk, pepper and natural habitats

AIMS

Bacillus cereus sensu lato is a complex group of closely related bacteria, which are commonly present in the natural environment and food products. These organisms may cause food poisoning and spoilage as well as opportunistic infections. Thus far, their resistance to selected antibiotics has been explored only in part, especially in the context of strain source. Therefore, our goal was to compare the resistance of B. cereus sl from milk (environment with the potential impact of antibiotics) with strains from soil and pepper (environment without contact with antibiotics) in relation to their origin, toxicity and phylogenetic relationships.

METHODS AND RESULTS

Antibiotic resistance of B. cereus sl was assessed by determining their minimal inhibitory concentrations (MICs) followed by statistical analyses. The phylogeny of the bacteria was investigated by multilocus sequence typing, and toxicity was determined with quantitative reverse-transcription real-time PCR. We found that the isolates from milk were more often multiresistant and exhibited a common resistance pattern to β-lactams but a varied sensitivity to the tested macrolides, clindamycin, tetracycline and vancomycin. Moreover they displayed often significantly higher average MICs; however, their resistance did not correlate with phylogeny, toxicity, or in most cases, with taxonomic affiliation.

CONCLUSION

We conclude that mainly food matrices may serve as an important reservoir of resistant isolates of B. cereus sl and that the use of antibiotics for the treatment of animal diseases must be carefully monitored as it strongly promotes natural selection for multiresistant strains, even among opportunist pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

The fact that compared to the isolates from natural habitats, nonpathogenic B. cereus sl isolated from food acquire antibiotic resistance faster, should increase producers and consumers awareness and result in protection of public health.

Potential of N2 Gas Flushing to Hinder Dairy-Associated Biofilm Formation and Extension

Worldwide, the dairy sector remains of vital importance for food production despite severe environmental constraints. The production and handling conditions of milk, a rich medium, promote inevitably the entrance of microbial contaminants, with notable impact on the quality and safety of raw milk and dairy products. Moreover, the persistence of high concentrations of microorganisms (especially bacteria and bacterial spores) in biofilms (BFs) present on dairy equipment or environments constitutes an additional major source of milk contamination from pre- to post-processing stages: in dairies, BFs represent a major concern regarding the risks of disease outbreaks and are often associated with significant economic losses. One consumption trend toward "raw or low-processed foods" combined with current trends in food production systems, which tend to have more automation and longer processing runs with simultaneously more stringent microbiological requirements, necessitate the implementation of new and obligatory sustainable strategies to respond to new challenges regarding food safety. Here, in light of studies, performed mainly with raw milk, that considered dominant "planktonic" conditions, we reexamine the changes triggered by cold storage alone or combined with nitrogen gas (N2) flushing on bacterial populations and discuss how the observed benefits of the treatment could also contribute to limiting BF formation in dairies.

Biofilm Production by Enterotoxigenic Strains of Bacillus cereus in Different Materials and under Different Environmental Conditions

Foodborne illnesses, such as infections or food poisoning, can be caused by bacterial biofilms present in food matrices or machinery. The production of biofilms by several strains of Bacillus cereus on different materials under different culture conditions was determined, as well as the relationship of biofilms with motility, in addition to the enterotoxigenic profile and candidate genes that participate in the production of biofilms. Biofilm production of B. cereus strains was determined on five materials: glass, polystyrene, polyethylene, polyvinylchloride (PVC), PVC/glass; in three culture media: Phenol red broth, tryptic soy broth, and brain heart infusion broth; in two different temperatures (37 °C and 25 °C), and in two different oxygen conditions (oxygen and CO₂ tension). Furthermore, the strains were molecularly characterized by end-point polymerase chain reaction. Motility was determined on semi-solid agar. The B. cereus strains in this study were mainly characterized as enterotoxigenic strains; statistically significant differences were found in the PVC material and biofilm production. Motility was positively associated with the production of biofilm in glass/PVC. The sipW and tasA genes were found in two strains. The results of this study are important in the food industry because the strains carry at least one enterotoxin gene and produce biofilms on different materials.

Characterization of Bacillus cereus in Dairy Products in China

Bacillus cereus is a common and ubiquitous foodborne pathogen with an increasing prevalence rate in dairy products in China. High and unmet demands for such products, particularly milk, raise the risk of B. cereus associated contamination. The presence of B. cereus and its virulence factors in dairy products may cause food poisoning and other illnesses. Thus, this review first summarizes the epidemiological characteristics and analytical assays of B. cereus from dairy products in China, providing insights into the implementation of intervention strategies. In addition, the recent achievements on the cytotoxicity and mechanisms of B. cereus are also presented to shed light on the therapeutic options for B. cereus associated infections.

Prevalence, Virulence Feature, Antibiotic Resistance and MLST Typing of Bacillus cereus Isolated From Retail Aquatic Products in China

Bacillus cereus is one of the most important foodborne pathogenic microorganisms, which can lead to gastrointestinal and non-gastrointestinal diseases. However, the potential risk of B. cereus in aquatic products in China has not been comprehensively evaluated yet. In this study, a total of 860 aquatic samples from three types of retail aquatic products were collected from 39 major cities in China from 2011 to 2016. The contamination, distribution of virulence genes, antibiotic resistance and genetic diversity of B. cereus isolates were measured and analyzed. Of all the samples, 219 (25.47%) were positive for B. cereus and 1.83% (4/219) of the samples had contamination levels of more than 1,100 most probable number (MPN)/g. Different isolates had virulence potential, within which 59.6% (164/275) contained all three kinds of enterotoxin genes (nhe, hbl, and cytK-2) and 5.1% (14/275) possessed cereulide encoding gene cesB. The antimicrobial resistance profiles revealed the universal antibiotic resistance to rifampin and most β-lactams, suggesting the necessity to continuously monitor the antibiotic resistance of B. cereus in aquatic products and to control drug use in aquaculture. In sum, our study indicates the potential hazards of B. cereus isolated from aquatic products to customers and may provide a reference for clinical treatment caused by B. cereus.

Identification and Pathogenic Potential of Bacillus cereus Strains Isolated from a Dairy Processing Plant Producing PDO Taleggio Cheese

Low levels of contamination by Bacillus cereus at the cheese farm is essential for reducing any opportunity for growth prior consumption. In this study, B. cereus distribution in a plant producing Protected Designation of Origin Taleggio cheese was investigated and the virulence potential of the isolates was evaluated. Seventy-four samples were collected from Food and Non Food Contact Surfaces (FCS, NFCS), saline curd, and Taleggio. The eleven isolates were identified, typified, and clustered. Strains were tested for the production of hemolysins, hemolysin BL (HBL), phosphatidylcholine-specific phospholipase C (PC-PLC), proteases, and biofilm, and for the presence of chromosomal toxin-encoding genes (sph, plcA, cytK, entFM, bcet, entS, nheA, nheB, nheC). B. cereus was detected on NFCS, FCS, and curd, but not in Taleggio. The isolates were grouped into six clusters, and all produced PC-PLC, hemolysins, and proteases, and most of them HBL (66.7%). All the clusters harbored the nheA, sph, plcA, entFM, and cytK genes, and some also nheB (83.3%), nheC (66.7%), bcet (50.0%), and entS (66.7%). All strains showed biofilm-forming ability. Our data reveal possible contamination of production plants and cheese curd by potentially virulent B. cereus, but bacterial absence in Taleggio highlights the efficacy of a proper management of the production phases in assuring consumer's protection.

Sequential CRISPR-Based Screens Identify LITAF and CDIP1 as the Bacillus cereus Hemolysin BL Toxin Host Receptors

Bacteria and their toxins are associated with significant human morbidity and mortality. While a few bacterial toxins are well characterized, the mechanism of action for most toxins has not been elucidated, thereby limiting therapeutic advances. One such example is the highly potent pore-forming toxin, hemolysin BL (HBL), produced by the gram-positive pathogen Bacillus cereus. However, how HBL exerts its effects and whether it requires any host factors is unknown. Here, we describe an unbiased genome-wide CRISPR-Cas9 knockout screen that identified LPS-induced TNF-α factor (LITAF) as the HBL receptor. Using LITAF-deficient cells, a second, subsequent whole-genome CRISPR-Cas9 screen identified the LITAF-like protein CDIP1 as a second, alternative receptor. We generated LITAF-deficient mice, which exhibit marked resistance to lethal HBL challenges. This work outlines and validates an approach to use iterative genome-wide CRISPR-Cas9 screens to identify the complement of host factors exploited by bacterial toxins to exert their myriad biological effects.

In Silico Analysis Highlights the Diversity and Novelty of Circular Bacteriocins in Sequenced Microbial Genomes

Consumer demand for “fresh food” with no chemical preservatives has prompted researchers to pay more attention to natural antimicrobial peptides such as bacteriocins. Nisin is currently the most widely used food biopreservative among the bacteriocins; however, its applications are restricted due to its low stability at neutral and alkaline pH values. Circular bacteriocins have potent antimicrobial activity against foodborne pathogens, show exceptional stability, and have great potential to be developed as biopreservatives. Here, we take advantage of the precursor peptides of 15 reported circular bacteriocins to devise an in silico approach to identify potential circular bacteriocins in sequenced microbial genomes. A total of nearly 7,000 putative precursor peptides were identified from 86 species of bacteria and further classified into 28 groups based on their amino acid similarity. Among the groups, 19 showed low similarity (less than 50%) to any known precursor peptide of circular bacteriocins. One novel circular bacteriocin in group 11, cerecyclin, showed the highest identity (34%) to the known circular bacteriocin enterocin NKR-5-3B and was selected for verification. Cerecyclin showed antimicrobial activity against several Gram-positive bacteria, inhibited the outgrowth of Bacillus cereus spores, and did not exhibit hemolysis activity. Moreover, it showed 4-fold- to 8-fold-higher antimicrobial activity against B. cereus and Listeria monocytogenes than nisin A. Cerecyclin also had increased stability compared to nisin A under neutral or alkaline conditions. This work not only identified a promising food biopreservative but also provided a rich source for novel circular bacteriocins.

IMPORTANCE Circular bacteriocins are promising biopreservatives, and it is important to identify more novel circular bacteriocins to enhance the current arsenal of antimicrobials. In this study, we used an in silico approach to identify a large number of novel circular bacteriocins and classified these bacteriocins into 28 groups rather than the 2 groups that were described in previous studies. Nineteen groups were novel and had low similarity (less than 50%) to any known precursor peptides of circular bacteriocins; this finding greatly expands the awareness of the novelty and diversity of circular bacteriocins. A novel circular bacteriocin which we named cerecyclin was identified in the B. cereus group; this circular bacteriocin had great antimicrobial activity against some foodborne pathogens and showed extreme stability. This study not only identified a promising food biopreservative but also provided a rich source for the identification of novel circular bacteriocins and the development of new biopreservatives.

Potential Enterotoxicity of Phylogenetically Diverse Bacillus cereus Sensu Lato Soil Isolates from Different Geographical Locations

Bacillus cereus sensu lato comprises Gram-positive spore-forming bacteria producing toxins associated with foodborne diseases. Three pore-forming enterotoxins, nonhemolytic enterotoxin (Nhe), hemolysin BL (Hbl), and cytotoxin K (CytK), are considered the primary factors in B. cereus sensu lato diarrhea. The aim of this study was to determine the potential risk of enterotoxicity among soil B. cereus sensu lato isolates representing diverse phylogroups and originated from different geographic locations with various climates (Burkina Faso, Kenya, Argentina, Kazakhstan, and Poland). While nheA- and hblA-positive isolates were present among all B. cereus sensu lato populations and distributed across all phylogenetic groups, cytK-2-positive strains predominated in geographic regions with an arid hot climate (Africa) and clustered together on a phylogenetic tree mainly within mesophilic groups III and IV. The highest in vitro cytotoxicity to Caco-2 and HeLa cells was demonstrated by the strains clustered within phylogroups II and IV. Overall, our results suggest that B. cereus sensu lato pathogenicity is a comprehensive process conditioned by many intracellular factors and diverse environmental conditions.IMPORTANCE This research offers a new route for a wider understanding of the dependency between pathogenicity and phylogeny of a natural bacterial population, specifically within Bacillus cereus sensu lato, that is widely distributed around the world and easily transferred into food products. Our study indicates differences in the phylogenetic and geographical distributions of potential enterotoxigenic B. cereus sensu lato strains. Hence, these bacilli possess a risk for human health, and rapid testing methods for their identification are greatly needed. In particular, the detection of the CytK enterotoxin should be a supporting strategy for the identification of pathogenic B. cereus sensu lato.

Bacillus cereus contamination of pasteurized human milk donations: frequency, origin, seasonal distribution, molecular typing of strains and proposed corrective/preventive actions

Objectives: An increase in pasteurized human milk contamination with Bacillus cereus was witnessed in milk donated to the Amiens-Picardie Human Milk Bank over the 2017-2018 period. To better understand the origin of such an increase, this study aimed to describe the frequency of Bacillus cereus contamination in anonymous and personalized human milk donations of Amiens Human Milk Bank in 2018, compare the genetic profiles of Bacillus cereus strains found in pasteurized human milk and set up corrective/preventive actions to reduce Bacillus cereus contamination.Study design: A retrospective cohort study of human milk donated from January to December 2018 was set. Data on the microbiological quality of donated human milk and genetic profiles of Bacillus cereus strains isolated from pasteurized donated human milk and the environment were collected.Results: The overall noncompliance rate related to the microbiological quality in the 1585 batches of analyzed human milk donations was of 27.3%. Post-Holder pasteurization, rejection rates were significantly higher for anonymous donations as compared to personalized ones. Bacillus cereus was the main cause of noncompliance. Bacillus cereus contaminations could not be attributed to a single strain spreading through Amiens human milk bank and Amiens hospital environment as the genetic profiles of the collected strains were different. Corrective actions led to a decrease in the noncompliance rate due to Bacillus cereus (37.7-9.7%) post-Holder pasteurization.Conclusion: Bacillus cereus was the primary cause of rejection for pasteurized human milk donations over the investigated period. These contaminations did not originate from the spread of a single strain. A first round of corrective actions enabled a fair decrease in Bacillus cereus contaminations.

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.

In ovo inoculation of duck embryos with different strains of Bacillus cereus to analyse their synergistic post-hatch anti-allergic potentialities

BACKGROUND

Bacillus cereus is a Gram-positive, facultative anaerobic bacteria with few strains reported to be used as probiotics for animals and birds in recent times if the doses are formulated properly.

OBJECTIVES

To analyse the synergistic anti-allergic potentiality of different Bacillus cereus strains on experimental in ovo and in vitro duck model, as probiotic immune stimulant.

MATERIALS AND METHODS

Different strains of Bacillus cereus from 29 isolates were identified through 16S rRNA gene sequencing from the milk samples of buffalo breeds of South Asia. The probiotic properties were tested in aspects of gram staining, catalase test, coagulase, test, bile salt tolerance, pH tolerance and phenol tolerance test. MIC₅₀ and MIC₉₀ levels were profiled using nine different antibiotics, and antimicrobial activity against eight different enteric pathogens was assessed. Finally, the test strains of Bacillus cereus (Colony Forming Unit [CFU] 30X10¹¹ ) were combined-infused at different concentrations in embryonated duck eggs to assess the post-hatch anti-allergic effects against histamine-induced allergic reaction and their immunoglobulin E (IgE) level was tested.

RESULTS

Molecular identification confirmed the test strains as B. cereus HKS 1-1, B. cereus LOCK 1,002 and B. cereus BF2, which were all motile, spore-forming, catalase-positive and rod-shaped. All were 0.3% bile salt, 0.4% phenol and pH tolerant. Two-way ANOVA test P values revealed that B. cereus BF2 was statistically significant (p < .0014) in bile salt tolerance test. B. cereus HKS 1-1 was significant in phenol and pH tolerance at p < .0002 and p < .0489, respectively. Besides, the test strains showed antibiotic sensitivity and antimicrobial activity to different enteric pathogens. In vivo model referred the test strains as effective in partial allergy reduction at same CFU but at different concentrations with p < .0001 among the groups.

CONCLUSION

The isolated and characterized strains of B. cereus showed partial immune-stimulating potentiality against experimentally induced allergic reaction.

Development of a selective and differential media for the isolation and enumeration of Bacillus cereus from food samples

AIM

Identification and enumeration of foodborne pathogens in food stuffs are valuable concerns. In the present study, starch-blood-egg yolk-polymyxin B-trimethoprim-ceftazidime (SBYPTC) agar was established to isolate and specify the number of Bacillus cereus in food products.

METHODS AND RESULTS

The effectiveness of the developed medium in selecting for B. cereus from pure cultures and food matrixes naturally contaminated by high levels of microbiota was estimated, and the results were compared with that of two commercially available MYPA and PMBA media. In pure cultures, there were no significant differences in the recoverability of B. cereus among the three media, however, SBYPTC agar showed a greater exclusivity. To examine SBYPTC performance in food, B. cereus were artificially inoculated into lettuce and potato samples with high background microbiota in two separated experiments. There were no significant differences between MYPA and PEMBA. However, SBYPTC manifested greater selectivity and exclusivity and made the differentiation easier by allowing growth of B. cereus in separated colonies and inhibiting competing microflora.

CONCLUSION

Our results showed that SBYPTC has high selective properties in comparison with MYPA and PEMBA. Thus, it can be considered as a useful tool to monitor the existence and the number of B. cereus in foods especially those contaminated with high levels of microflora.

SIGNIFICANCE AND IMPACT OF THE STUDY

In the food industry, SBYPTC can be employed for food quality assurance to monitor B. cereus in food products contaminated with high levels of microbiota.

Temperature-Dependent Growth Characteristics of Bacillus thuringiensis in a Ratatouille Food Model

ABSTRACT

In contrast to Bacillus cereus, the role of Bacillus thuringiensis in foodborne illness has been controversially discussed. As B. thuringiensis-based biopesticides containing a mixture of crystal toxins and viable spores are widely used, a current European Food Safety Authority opinion underlines the need for additional data to enable risk assessment. However, it is currently poorly understood if B. thuringiensis is able to multiply in food, which is crucial to sound risk assessment. Therefore, the aim of this study was to investigate growth of selected B. thuringiensis strains from food and insecticides in a ratatouille food model. To this end, the growth parameters of three B. thuringiensis strains were determined: insecticide strain ABTS-351 (CH_119, B. thuringiensis serovar kurstaki), insecticide strain ABTS-1857 (CH_121, B. thuringiensis serovar aizawai), and CH_48 (wild-type B. thuringiensis isolated from rosemary), producing extremely high levels of enterotoxins. After an initial drop in colony counts, we observed a statistically significant growth for the tested B. thuringiensis strains between 6 and 24 h at 22, 30, and 37°C, conditions mimicking prolonged holding times. We were also able to show that the enterotoxin overproducer CH_48 can grow up to 108 CFU/g in the ratatouille matrix within 24 h at 37°C. The two midlevel enterotoxin formers ABTS-351 (CH_119) and ABTS-1857 (CH_121) isolated from biopesticides exhibited growth between 6 and 24 h, with one of the strains growing to 107 CFU/g. To our knowledge, this is the first study providing evidence of B. thuringiensis growth in a food model with intact competitive flora. Our findings suggest strain-specific variation and stress the complexity of assessing the risk related to B. thuringiensis in food, indicating that some strains can represent a risk to consumer health when vegetable-based foods are stored under conditions of prolonged temperature abuse.

HIGHLIGHTS

Systematic review of descriptions of novel bacterial species: evaluation of the twenty-first century taxonomy through text mining

Although described bacterial species increased in the twenty-first century, they correspond to a tiny fraction of the actual number of species living on our planet. The volume of textual data of these descriptions constitutes valuable information for revealing trends that in turn could support strategies for improvement of bacterial taxonomy. In this study, a text mining approach was used to generate bibliometric data to verify the state-of-art of bacterial taxonomy. Around 9700 abstracts of bacterial classification containing the expression 'sp. nov.' and published between 2001 and 2018 were downloaded from PubMed and analysed. Most articles were from PR China and the Republic of Korea, and published in the International Journal of Systematic and Evolutionary Microbiology. From about 10 800 species names detected, 93.33 % were considered valid according to the rules of the Bacterial Code, and they corresponded to 82.98 % of the total number of species validated between 2001 and 2018. Streptomyces, Bacillus and Paenibacillus each had more than 200 species described in the period. However, almost 40 % of all species were from the phylum Proteobacteria. Most bacteria were Gram-stain-negative, bacilli and isolated from soil. Thirteen species and one genus homonyms were found. With respect to methodologies of bacterial characterization, the use of terms related to 16S rRNA and polar lipids increased along these years, and terms related to genome metrics only began to appear from 2009 onward, although at a relatively lower frequency. Bacterial taxonomy is known as a conservative discipline, but it gradually changed in terms of players and practices. With the advent of the mandatory use of genomic analyses for species description, we are probably witnessing a turning point in the evolution of bacterial taxonomy.

Proposal of a Taxonomic Nomenclature for the Bacillus cereus Group Which Reconciles Genomic Definitions of Bacterial Species with Clinical and Industrial Phenotypes

The Bacillus cereus group comprises numerous closely related species, including bioterrorism agent B. anthracis, foodborne pathogen B. cereus, and biopesticide B. thuringiensis Differentiating organisms capable of causing illness or death from those used in industry is essential for risk assessment and outbreak preparedness. However, current species definitions facilitate species-phenotype incongruences, particularly when horizontally acquired genes are responsible for a phenotype. Using all publicly available B. cereus group genomes (n = 2,231), we show that current species definitions lead to overlapping genomospecies clusters, in which 66.2% of genomes belong to multiple genomospecies at a conventional 95 average nucleotide identity (ANI) genomospecies threshold. A genomospecies threshold of ≈92.5 ANI is shown to reflect a natural gap in genome similarity for the B. cereus group, and medoid genomes identified at this threshold are shown to yield resolvable genomospecies clusters with minimal overlap (six of 2,231 genomes assigned to multiple genomospecies; 0.269%). We thus propose a nomenclatural framework for the B. cereus group which accounts for (i) genomospecies using resolvable genomospecies clusters obtained at ≈92.5 ANI, (ii) established lineages of medical importance using a formal collection of subspecies names, and (iii) heterogeneity of clinically and industrially important phenotypes using a formalized and extended collection of biovar terms. We anticipate that the proposed nomenclature will remain interpretable to clinicians, without sacrificing genomic species definitions, which can in turn aid in pathogen surveillance; early detection of emerging, high-risk genotypes; and outbreak preparedness.IMPORTANCE Historical species definitions for many prokaryotes, including pathogens, have relied on phenotypic characteristics that are inconsistent with genome evolution. This scenario forces microbiologists and clinicians to face a tradeoff between taxonomic rigor and clinical interpretability. Using the Bacillus cereus group as a model, a conceptual framework for the taxonomic delineation of prokaryotes which reconciles genomic definitions of species with clinically and industrially relevant phenotypes is presented. The nomenclatural framework outlined here serves as a model for genomics-based bacterial taxonomy that moves beyond arbitrarily set genomospecies thresholds while maintaining congruence with phenotypes and historically important species names.

A Review of Resistance Mechanisms of Synthetic Insecticides and Botanicals, Phytochemicals, and Essential Oils as Alternative Larvicidal Agents Against Mosquitoes

Mosquitoes are a serious threat to the society, acting as vector to several dreadful diseases. Mosquito management programes profoundly depend on the routine of chemical insecticides that subsequently lead to the expansion of resistance midst the vectors, along with other problems such as environmental pollution, bio magnification, and adversely affecting the quality of public and animal health, worldwide. The worldwide risk of insect vector transmitted diseases, with their associated illness and mortality, emphasizes the need for effective mosquitocides. Hence there is an immediate necessity to develop new eco-friendly pesticides. As a result, numerous investigators have worked on the development of eco-friendly effective mosquitocidal compounds of plant origin. These products have a cumulative advantage of being cost-effective, environmentally benign, biodegradable, and safe to non-target organisms. This review aims at describing the current state of research on behavioral, physiological, and biochemical effects of plant derived compounds with larvicidal effects on mosquitoes. The mode of physiological and biochemical action of known compounds derived from various plant families as well as the potential of plant secondary metabolites, plant extracts, and also the essential oils (EO), as mosquitocidal agents are discussed. This review clearly indicates that the application of vegetal-based compounds as mosquito control proxies can serve as alternative biocontrol methods in mosquito management programes.

Mammalian cell-free protein expression promotes the functional characterization of the tripartite non-hemolytic enterotoxin from Bacillus cereus

Bacillus cereus is increasingly recognized as an opportunistic pathogen causing local and systemic infections. The causative strains typically produce three pore-forming enterotoxins. This study focusses on the tripartite non-hemolytic enterotoxin (Nhe). Until today, studies have tried to elucidate the structure, complex formation and cell binding mechanisms of the tripartite Nhe toxin. Here, we demonstrate the synthesis of the functional tripartite Nhe toxin using eukaryotic cell-free systems. Single subunits, combinations of two Nhe subunits as well as the complete tripartite toxin were tested. Functional activity was determined by hemolytic activity on sheep blood agar plates, planar lipid bilayer measurements as well as cell viability assessment using the MTT assay. Our results demonstrate that cell-free protein synthesis based on translationally active eukaryotic lysates is a platform technology for the fast and efficient synthesis of functionally active, multicomponent toxins.

Bacillus cereus non-haemolytic enterotoxin activates the NLRP3 inflammasome

Inflammasomes are important for host defence against pathogens and homeostasis with commensal microbes. Here, we show non-haemolytic enterotoxin (NHE) from the neglected human foodborne pathogen Bacillus cereus is an activator of the NLRP3 inflammasome and pyroptosis. NHE is a non-redundant toxin to haemolysin BL (HBL) despite having a similar mechanism of action. Via a putative transmembrane region, subunit C of NHE initiates binding to the plasma membrane, leading to the recruitment of subunit B and subunit A, thus forming a tripartite lytic pore that is permissive to efflux of potassium. NHE mediates killing of cells from multiple lineages and hosts, highlighting a versatile functional repertoire in different host species. These data indicate that NHE and HBL operate synergistically to induce inflammation and show that multiple virulence factors from the same pathogen with conserved function and mechanism of action can be exploited for sensing by a single inflammasome.

Profiling of the viable bacterial and fungal microbiota in fermented feeds using single-molecule real-time sequencing

Fermented concentrated feed has been widely recognized as an ideal feed in the animal industry. In this study, we used a powerful method, coupling propidium monoazide (PMA) pretreatment with single-molecule real-time (SMRT) sequencing technology to compare the bacterial and fungal composition of feeds before and after fermentation with four added lactic acid bacteria (LAB) inoculants (one Lactobacillus casei strain and three L. plantarum strains). Five feed samples consisting of corn, soybean meal, and wheat bran were fermented with LAB additives for 3 d. Following anaerobic fermentation, the pH rapidly decreased, and the mean numbers of LAB increased from 106 to 109 colony-forming units (cfu)/g fresh matter. SMRT sequencing results showed that the abundance and diversity of bacteria and fungi in the feed were significantly higher before fermentation than after fermentation. Fifteen bacterial species and eight fungal genera were significantly altered following fermentation, and L. plantarum was the dominant species (relative abundance 88.94%) in the post-fermentation group. PMA treatment revealed that the bacteria Bacillus cereus, B. circulans, Alkaliphilus oremlandii, Cronobacter sakazakii, Paenibacillus barcinonensis, and P. amylolyticus (relative abundance >1%) were viable in the raw feed. After fermentation, their relative abundances decreased sharply to <0.2%; however, viable L. plantarum was still the dominant species post fermentation. We inferred that our LAB additives grew rapidly and inhibited harmful microorganisms and further improved feed quality. In addition, coupling PMA treatment with the Pacific Biosciences SMRT sequencing technology was a powerful tool for providing accurate live microbiota profiling data in this study.

Predominant Mycotoxins, Pathogenesis, Control Measures, and Detection Methods in Fermented Pastes

Fermented pastes are some of the most popular traditional products in China. Many studies reported a strong possibility that fermented pastes promote exposure to mycotoxins, including aflatoxins, ochratoxins, and cereulide, which were proven to be carcinogenic and neurotoxic to humans. The primary mechanism of pathogenicity is by inhibiting protein synthesis and inducing oxidative stress using cytochrome P450 (CYP) enzymes. The level of mycotoxin production is dependent on the pre-harvest or post-harvest stage. It is possible to implement methods to control mycotoxins by using appropriate antagonistic microorganisms, such as Aspergillus niger, Lactobacillus plantarum, and Saccharomyces cerevisiae isolated from ordinary foods. Also, drying products as soon as possible to avoid condensation or moisture absorption in order to reduce the water activity to lower than 0.82 during storage is also effective. Furthermore, organic acid treatment during the soaking process reduces toxins by more than 90%. Some novel detection technologies based on magnetic adsorption, aptamer probes, and molecular-based methods were applied to rapidly and accurately detect mycotoxins in fermented pastes.

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.

Toxins and mobile antimicrobial resistance genes in Bacillus probiotics constitute a potential risk for One Health

Probiotic microbes conferring health benefits to the hosts have attracted great attention. However, the safety of probiotics is not guaranteed, although the increasing widespread use of probiotics with excellent overall safety records. Here, we performed a systematic evaluation of the safety of commercial Bacillus probiotics intended for usage in humans, animals, plants, aquaculture and environment in China. Nearly half of the 65 isolated Bacillus spp. strains from these commercial probiotic products were capable of producing hazardous toxins. Infections with the representative isolates could cause sepsis, intestinal inflammation and liver injury in different mouse models. Additionally, these isolates harbor multiple antimicrobial resistance genes coupled with mobile genetic elements. Collectively, the capability for producing various toxins and harboring mobile antimicrobial resistance genes in Bacillus probiotics indicates a potential risk for One Health.

Prevalence of Virulence Determinants among Bacillus cereus Isolated from Milk Products with Potential Public Health Concern

BACKGROUND AND OBJECTIVE

Bacillus cereus is described as one of the public health pathogen causing severe food poisoning outbreaks worldwide. Accurate surveillance about B. cereus in Egypt is scanty. For this reason, the current study was conducted to determine the prevalence of B. cereus and its virulence genes among milk powder and Ras-cheese products.

MATERIALS AND METHODS

Two hundred samples (130 and 70) from milk powder and Ras-cheese, respectively were aseptically collected and cultured onto specific media. The obtained isolates were subjected to mPCR for screening of virulence genes (nhe, cytK, pc-plc, hblD, hbI and ces) among of B. cereus isolates that obtained from milk powder and Ras-cheese.

RESULTS

The result revealed that B. cereus was recovered with 6.9 and 8.5% from milk powder and Ras-cheese, respectively. The nhe gene was detected and dominated in all isolates 100% from both products. In milk powder, pc-plc was the most prevalent gene (100%). However, cytK, hblD, hbl and ces genes were prevalent with 55.5, 33.3, 33.3 and 22.2%, respectively. Regarding to Ras-cheese, the prevalence of cytK was (83.33%) while each of hbI, hblD, pc-plc and ces genes were recovered in 50% of tested isolates.

CONCLUSION

This result provided an important epidemiological view about the contamination rate and the most prevalent virulence genes of B. cereus in milk products in Egypt.

Population structure and toxin gene profiles of Bacillus cereus sensu lato isolated from flour products

Data on the occurrence, population structure and toxinogenic potential of Bacillus cereus sensu lato isolated from flour is essential to enable improved risk assessment. We aimed to provide data on the occurrence of B. cereus sensu lato in flour products at retail level. In addition, we screened the isolates for Bacillus thuringiensis and Bacillus cytotoxicus and determined population structure and toxin gene profiles. We screened 89 flour products for presence of B. cereus sensu lato, resulting in 75 positive samples (84%). We were able to show that the population structure of members of the B. cereus group isolated from flour is highly diverse. Isolates were assigned to panC types II (4%), III (21%), IV (39%) and V (36%). Production of parasporal crystals characteristic for Bacillus thuringiensis was detected in seven isolates assigned to panC type III, IV and V. No B. cytotoxicus were detected. Two of the isolates harbored ces encoding cereulide, which causes the emetic syndrome. Various enterotoxin genes were found, with all isolates harboring nhe, 75% of isolates harboring hbl and 51% of the isolates harboring cytK-2. Our findings suggest that toxinogenic B. cereus sensu lato are common in flour products at retail level.

Genomic and Toxigenic Heterogeneity of Bacillus cereus sensu lato Isolated from Ready-to-Eat Foods and Powdered Milk in Day Care Centers in Colombia

Bacillus cereus sensu lato (s.l.) is a group of bacteria commonly found in diverse environments, including foods, with potential to cause emesis and diarrhea. In Colombia, it is one of the main foodborne pathogens. The aim of this study was to determine the genomic and toxigenic heterogeneity of B. cereus s.l. isolated from ready-to-eat foods and powdered milk collected in day care centers of Medellin, Colombia. Of 112 B. cereus s.l. isolates obtained, 94% were β-hemolytic. Toxigenic heterogeneity was established by the presence of nheABC, hblCDAB, cytK2, entFM, and cesB toxigenic genes. The nheABC operon and entFM gene were most frequently detected in the isolates, whereas the cesB gene was not found. According to the toxin genes content, nine toxigenic profiles were identified. A 44% of isolates had profiles with all genes for nonhemolytic enterotoxin, hemolysin BL, and enterotoxin FM production (profiles II and IV). Pulsed-field gel electrophoresis analysis indicated a high genomic heterogeneity among the B. cereus s.l., with 68 isolates grouping into 16 clusters and 33 placed separately in the dendrogram. This study provides useful information on the safety of ready-to-eat foods and powdered milk in day care centers where children, a susceptible population, are exposed and it should incentive for more studies to understand the distribution of different toxin-encoding genes among B. cereus s.l. isolates, enabling detailed risk assessment.

Re-addressing the biosafety issues of plant growth promoting rhizobacteria

To promote agronomic sustainability, extensive research is being carried out globally, investigating biofertilizer development. Recently, it has been realized that some microorganisms used as biofertilizers behave as opportunistic pathogens and belong to the biosafety level 2 (BSL-2) classification. This poses serious risk to the environmental and human health. Evidence presented in various scientific forums is increasingly favoring the merits of using BSL-2 microorganisms as biofertilizers. In this review, we emphasize that partial characterization based on traditional microbiological approaches and small subunit rRNA gene sequences/conserved regions are insufficient for the characterization of biofertilizer strains. It is advised herein, that research and industrial laboratories developing biofertilizers for commercialization or environmental release must characterize microorganisms of interest using a multilateral polyphasic approach of microbial systematics. This will determine their risk group and biosafety characteristics before proceeding with formulation development and environmental application. It has also been suggested that microorganisms belonging to risk-group-1 and BSL-1 category should be used for formulation development and for field scale applications. While, BSL-2 microorganisms should be restricted for research using containment practices compliant with strict regulations.

Directed evolution by UV-C treatment of Bacillus cereus spores

Bacterial endospores are exposed to a broad variety of sublethal and lethal stresses in the food production chain. Generally, these stresses will not completely eliminate the existing spore populations, and thus constitute a selection pressure on the spores. One stress that is frequently used in the food production chains to disinfect (food) contact surfaces is UV-C. At a wavelength of 254 nm, UV-C has germicidal properties. The aim of this research is to investigate the impact of UV-C stress on the evolution of endospore recalcitrance and germination in B. cereus. A directed evolution experiment was set up in which B. cereus was repeatedly subjected to a cycle of sporulation, sporicidal UV-C treatment, germination and outgrowth. We show here that three independent lineages of UV-C cycled B. cereus spores reproducibly acquired a 30-fold or higher increase in UV-C resistance at 164 mJ/cm². Surprisingly, the UV-C resistant spores of the clones isolated from each of the lineages also became significantly more sensitive to wet heat as a normally non-lethal heat treatment at 70 °C for 15 min resulted in an average 1.8 log cfu/mL reduction. From time-lapse phase contrast microscopy analysis, UV-C resistant mutant spores also showed a distinctive heterogeneity in refractility and a severe germination defect compared to the wild type. However, UV-C resistance of the corresponding vegetative cells was not altered. In conclusion, this work shows that UV-C resistance of endospores is an adaptive trait that can readily be improved, although at an apparent cost for heat resistance and germination efficiency. As such, these results provide novel insights in the evolvability of, and correlation between, some endospore properties.

Risk presented to minimally processed chilled foods by psychrotrophic Bacillus cereus

BACKGROUND

Spores of psychrotrophic Bacillus cereus may survive the mild heat treatments given to minimally processed chilled foods. Subsequent germination and cell multiplication during refrigerated storage may lead to bacterial concentrations that are hazardous to health.

SCOPE AND APPROACH

This review is concerned with the characterisation of factors that prevent psychrotrophic B. cereus reaching hazardous concentrations in minimally processed chilled foods and associated foodborne illness. A risk assessment framework is used to quantify the risk associated with B. cereus and minimally processed chilled foods.

KEY FINDINGS AND CONCLUSIONS

Bacillus cereus is responsible for two types of food poisoning, diarrhoeal (an infection) and emetic (an intoxication); however, no reported outbreaks of food poisoning have been associated with B. cereus and correctly stored commercially-produced minimally processed chilled foods. In the UK alone, more than 1010 packs of these foods have been sold in recent years without reported illness, thus the risk presented is very low. Further quantification of the risk is merited, and this requires additional data. The lack of association between diarrhoeal food poisoning and correctly stored commercially-produced minimally processed chilled foods indicates that an infectious dose has not been reached. This may reflect low pathogenicity of psychrotrophic strains. The lack of reported association of psychrotrophic B. cereus with emetic illness and correctly stored commercially-produced minimally processed chilled foods indicates that a toxic dose of the emetic toxin has not been formed. Laboratory studies show that strains form very small quantities of emetic toxin at chilled temperatures.

A Cluster of Bacillus cereus Infections in the Neonatal Intensive Care Unit: Epidemiologic and Whole-genome Sequencing Analysis

Bacillus cereus isolates causing an outbreak in the neonatal intensive care unit were investigated using whole-genome sequencing. The outbreak coincided with construction work performed adjacent to the neonatal intensive care unit and ceased after strict sealing of the construction area. We found the outbreak to be polyclonal, however, the clonality did not correlate with the virulence in vivo. Genotypically similar isolates were associated with both lethal/severe infection and colonization/environmental contamination. Environmental bacterial load may be a major determinant of infection, especially in high-risk patients. Clinicians should be alert to unusual increase in B. cereus isolations from clinical cultures to facilitate early recognition and investigations of Bacillus outbreaks and pseudo-outbreaks. The integration of genomics into the classical infectious disease work can augment our understanding of pathogen transmission and virulence, and can rapidly assist our response to unusual disease trends.