Bacillus cereus Induces Severe Infections in Preterm Neonates: Implication at the Hospital and Human Milk Bank Level

Late-onset sepsis in newborns caused by Bacillus Cereus: a case report and literature review

Bacillus cereus is a bacterium capable of causing late-onset neonatal sepsis. By analyzing 11 cases, this study investigates the diagnosis, treatment, and prognosis of Bacillus cereus infections, aiming to provide insights into clinical diagnosis and therapy. The study scrutinized 11 instances of late-onset neonatal sepsis, including two fatalities attributable to Bacillus cereus, one accompanied by cerebral hemorrhage. An examination and analysis of these cases' symptoms, signs, laboratory tests, and treatment processes, along with a review of related literature from 2010 to 2020, revealed a high mortality rate of 41.38% in non-gastrointestinal infections caused by Bacillus cereus. Our findings underscore the critical importance of rapid diagnosis and effective antimicrobial therapy in reducing mortality rates. Once the source of infection is identified, implementing effective infection control measures is essential.

Psychological factors and barriers to donating and receiving milk from human milk banks: A review

Human milk banks (HMBs), established in the early 20th century, aimed to provide safe breast milk for infants with challenges obtaining it. The spread of infections since the 1980s resulted in strict regulations and screening in HMBs, to ensure the safety of donated milk. Several social and personal factors discourage mothers from practicing breastfeeding, making donated milk a viable alternative because of its protective and immunity-enhancing properties. However, psychological barriers can affect the decision to donate or receive donated milk. To identify psychological factors related to donating and receiving human milk from HMBs, we searched PubMed to identify studies reporting psychological factors in donating and receiving milk and excluding studies not reporting psychological factors. The search identified 28 articles meeting the inclusion criteria. Eligible studies from various countries spanned from 1995 to 2023 and focused on psychological factors influencing milk donation and receiving. Most studies were descriptive-qualitative. Factors facilitating or hindering milk donation and reception included perceptions, psychological aspects, and previous experiences. Positive factors for donors included the desire to help other mothers, support from health care professionals, and personal well-being. Negative factors included breast milk exclusivity and discomfort caused by health checks. For recipients, awareness of donated milk benefits was a positive factor, whereas fear regarding safety was negative. The altruistic motivation to help other mothers drove many women to donate. Proper awareness and support from health care professionals and families can help women understand the value of milk donation and support their personal and identity reintegration, especially in cases of the loss of a child.

Rapid Detection and Identification of Vancomycin-Sensitive Bacteria Using an Electrochemical Apta-Sensor

In order to combat the complex and diverse infections caused by bacteria, it is essential to develop efficient diagnostic tools. Current techniques for bacterial detection rely on laborious multistep procedures, with high costs and extended time of analysis. To overcome these limitations, we propose here a novel portable electrochemical biosensor for the rapid detection and identification of Gram-positive bacteria that leverages the recognition capabilities of vancomycin and aptamers. A vancomycin-modified screen-printed carbon electrode was used to selectively capture Gram-positive bacteria susceptible to this antibiotic. Electrochemical impedance spectroscopy and scanning electron microscopy demonstrated that capture was achieved in 10 min, with a limit of detection of only 2 CFU/mL. We then tested the device's potential for aptamer-based bacterial identification using Staphylococcus aureus and Bacillus cereus as the test strains. Specifically, electrodes with captured bacteria were exposed to species-specific aptamers, and the resulting changes in current intensity were analyzed using differential pulse voltammetry. When used directly in untreated milk or serum, the system was able to successfully identify a small amount of S. aureus and B. cereus (100 CFU/mL) in less than 45 min. This novel biosensor has the potential to serve as an invaluable tool that could be used, even by inexperienced staff, in a broad range of settings including clinical diagnostics, food safety analysis, environmental monitoring, and security applications.

Investigating environmental transmission to resolve a Bacillus cereus group outbreak in a neonatal intensive care unit using core genome multilocus sequence typing

BACKGROUND

We analyzed an outbreak of Bacillus cereus group (Bcg) at a single-center neonatal intensive care unit level IV by conducting comprehensive sampling of both patients and the environment.

METHODS

Between 06/2020 and 10/2021, all Bcg isolates identified by both regular colonization screening and additional sampling of the environment were subjected to whole-genome sequencing, followed by in vitro extraction of MLST ST, resistance genes and virulence factors. Using publicly available genome sequences, we defined an ad hoc core genome multilocus sequence typing (cgMLST) scheme comprising 2759 target genes for Bcg typing, which we applied to the detected isolates. We have compared the results with a stable cgMLST that was published in the meantime and completed the investigation with a SNP analysis.

RESULTS

We analyzed 28 Bcg isolates from patient and environmental samples using MLST and cgMLST. This revealed multiple sequence types, with ST127 being the most common (n = 13). Both cgMLST schemes grouped ten of the 13 ST127 isolates into a cluster, including two invasive isolates from two different patients and several environmental samples. SNP analysis postulated a screen from a ventilation machine as a possible reservoir.

CONCLUSION

In sensitive settings such as neonatal intensive care units, considering the environment in outbreak analyses is crucial, especially when investigating potential transmission routes through shared devices. When dealing with widespread bacteria such as Bcg, high-resolution typing techniques are necessary. In this study, we successfully resolved an outbreak of Bcg infections using a custom cgMLST scheme combined with a SNP analysis.

Exploring Disease Management and Control through Pathogen Diagnostics and One Health Initiative: A Concise Review

The "One Health" initiative is a critical strategy that recognizes the interconnectedness between human, animal, and environmental health in the spread and containment of infectious pathogens. With the ease of global transportation, transboundary disease outbreaks pose a significant threat to food safety and security, endangering public health and having a negative economic impact. Traditional diagnostic techniques based on genotypic and phenotypic analyses are expensive, time-consuming, and cannot be translated into point-of-care tools, hindering effective disease management and control. However, with advancements in molecular methods, biosensors, and new generation sequencing, rapid and reliable diagnostics are now available. This review provides a comprehensive insight into emergent viral and bacterial pathogens and antimicrobial resistance, highlighting the importance of "One Health" in connecting detection and effective treatment. By emphasizing the symbiotic relationship between human and animal health, this paper underscores the critical role of "One Health" initiatives in preventing and controlling infectious diseases.

Microbiological Screening of Donor Human Milk

Mother's own milk is recognized as the optimal feeding not only for term but also for preterm infants. In addition to risk reduction for sepsis, necrotizing enterocolitis, bronchopulmonary dysplasia, and retinopathy of prematurity in the early infancy, feeding preterm infants with mother's own milk is also associated with a better neurodevelopmental outcome; lower rates of otitis media, gastroenteritis, and respiratory infections; and a reduced risk of cardiovascular disease, obesity, and diabetes later in life. Donor human milk is the best alternative if mother's own milk is not available or with short supply. There is growing evidence that the benefits of human milk are mediated by the human milk microbiota and by human milk oligosaccharides through their influence on the infant's gut microbiota. Unfortunately, although human milk contains beneficial bacteria, it may also contain pathogenic bacteria. The antimicrobial properties of human milk protect those infants fed with their own mother's raw milk. In donor human milk, however, the antimicrobial activity is diminished due to storage and in particular by pasteurization, hereby lowering the resistance against bacterial infections. Subsequently, microbiological screening of donor human milk might enhance its safety for preterm infants. Up to date, a consensus on recommendations for the microbiological testing of donor human milk is lacking. Existing local and national guidelines for the microbiological screening vary significantly in terms of timing and frequency of testing as well as their specific acceptance and discard criteria. We reviewed the literature about microbiological testing of donor human milk to provide evidence-based recommendations for donor human milk.

High-Pressure Inactivation of Bacillus cereus in Human Breast Milk

Although Holder pasteurization is the recommended method for processing breast milk, it does affect some of its nutritional and biological properties and is ineffective at inactivating spores. The aim of this study was to find and validate an alternative methodology for processing breast milk to increase its availability for newborn babies and reduce the financial loss associated with discarding milk that has become microbiologically positive. We prepared two series of breast milk samples inoculated with the Bacillus cereus (B. cereus) strain to verify the effectiveness of two high-pressure treatments: (1) 350 MPa/5 min/38 °C in four cycles and (2) cumulative pressure of 350 MPa/20 min/38 °C. We found that the use of pressure in cycles was statistically more effective than cumulative pressure. It reduced the number of spores by three to four orders of magnitude. We verified that the method was reproducible. The routine use of this method could lead to an increased availability of milk for newborn babies, and at the same time, reduce the amount of wasted milk. In addition, high-pressure treatment preserves the nutritional quality of milk.

Development of peptide nucleic acid-based bead array technology for Bacillus cereus detection

Numerous novel methods to detect foodborne pathogens have been extensively developed to ensure food safety. Among the important foodborne bacteria, Bacillus cereus was identified as a pathogen of concern that causes various food illnesses, leading to interest in developing effective detection methods for this pathogen. Although a standard method based on culturing and biochemical confirmative test is available, it is time- and labor-intensive. Alternative PCR-based methods have been developed but lack high-throughput capacity and ease of use. This study, therefore, attempts to develop a robust method for B. cereus detection by leveraging the highly specific pyrrolidinyl peptide nucleic acids (PNAs) as probes for a bead array method with multiplex and high-throughput capacity. In this study, PNAs bearing prolyl-2-aminocyclopentanecarboxylic acid (ACPC) backbone with groEL, motB, and 16S rRNA sequences were covalently coupled with three sets of fluorescently barcoded beads to detect the three B. cereus genes. The developed acpcPNA-based bead array exhibited good selectivity where only signals were detectable in the presence of B. cereus, but not for other species. The sensitivity of this acpcPNA-based bead assay in detecting genomic DNA was found to be 0.038, 0.183 and 0.179 ng for groEL, motB and 16S rRNA, respectively. This performance was clearly superior to its DNA counterpart, hence confirming much stronger binding strength of acpcPNA over DNA. The robustness of the developed method was further demonstrated by testing artificially spiked milk and pickled mustard greens with minimal interference from food metrices. Hence, this proof-of-concept acpcPNA-based bead array method has been proven to serve as an effective alternative nucleic acid-based method for foodborne pathogens.

Retrospective surveillance of viable Bacillus cereus group contaminations in commercial food and feed vitamin B2 products sold on the Belgian market using whole-genome sequencing

Bacillus cereus is a spore-forming bacterium that occurs as a contaminant in food and feed, occasionally resulting in food poisoning through the production of various toxins. In this study, we retrospectively characterized viable B. cereus sensu lato (s.l.) isolates originating from commercial vitamin B₂ feed and food additives collected between 2016 and 2022 by the Belgian Federal Agency for the Safety of the Food Chain from products sold on the Belgian market. In total, 75 collected product samples were cultured on a general medium and, in case of bacterial growth, two isolates per product sample were collected and characterized using whole-genome sequencing (WGS) and subsequently characterized in terms of sequence type (ST), virulence gene profile, antimicrobial resistance (AMR) gene profile, plasmid content, and phylogenomic relationships. Viable B. cereus was identified in 18 of the 75 (24%) tested products, resulting in 36 WGS datasets, which were classified into eleven different STs, with ST165 (n = 10) and ST32 (n = 8) being the most common. All isolates carried multiple genes encoding virulence factors, including cytotoxin K-2 (52.78%) and cereulide (22.22%). Most isolates were predicted to be resistant to beta-lactam antibiotics (100%) and fosfomycin (88.89%), and a subset was predicted to be resistant to streptothricin (30.56%). Phylogenomic analysis revealed that some isolates obtained from different products were closely related or even identical indicating a likely common origin, whereas for some products the two isolates obtained did not show any close relationship to each other or other isolates found in other products. This study reveals that potentially pathogenic and drug-resistant B. cereus s.l. can be present in food and feed vitamin B₂ additives that are commercially available, and that more research is warranted to assess whether their presence in these types of products poses a threat to consumers.

Bacillus cereus strains from donor human milk and hospital environment: uncovering a putative common origin using comparative analysis of toxin and infra-red spectroscopy profiles

Bacillus cereus is reported as a common cause of toxin-induced food poisoning and of contamination in pasteurized human milk donations. As various toxins can be produced by B. cereus, the aim of this work was first to investigate the toxigenic potential and profiles of 63 B. cereus isolates from Amiens Picardie human milk bank. A comparison to the toxigenic profiles of 27 environmental B. cereus isolates harvested in the hospital in which this human milk bank is situated was performed. Toxin gene prevalences were the highest for nhe (ABC) and entFM followed by cytK and hbl(ACD). A 27% prevalence was found for ces human milk isolates, which is higher than previous works reporting on pasteurized milk and dairy products. No significant differences could be found between human milk and environmental isolates regarding toxin gene prevalences and/or toxin gene profiles. The second aim was to establish whether a B. cereus cross-contamination between human milk and the environment could occur. This was achieved with the help of Fourrier-transform infra-red spectroscopy which enabled the discrimination of 2 main clusters of 11 and 8 isolates, each containing human milk and Amiens Picardie human milk bank environmental isolates. For these two clusters, the time sequence showed that human milk isolates were the first to occur and might have contaminated the milk bank environment as well as other human milk donations. Routinely used on B. cereus isolates, Fourrier-transform infra-red spectroscopy could help in rapidly detecting such clusters and in limiting the spread of a B. cereus strain that might generate rejection of pasteurized donation by the human milk bank.

Region Met225 to Ile412 of Bacillus cereus Hemolysin II Is Capable to Agglutinate Red Blood Cells

Hemolysin II (HlyII) is one of the virulence factors of the opportunistic bacterium Bacillus cereus belonging to the group of β-pore-forming toxins. This work created a genetic construct encoding a large C-terminal fragment of the toxin (HlyIILCTD, M225-I412 according to the numbering of amino acid residues in HlyII). A soluble form of HlyIILCTD was obtained using the SlyD chaperone protein. HlyIILCTD was first shown to be capable of agglutinating rabbit erythrocytes. Monoclonal antibodies against HlyIILCTD were obtained by hybridoma technology. We also proposed a mode of rabbit erythrocyte agglutination by HlyIILCTD and selected three anti-HlyIILCTD monoclonal antibodies that inhibited the agglutination.

Plant Growth Promotion and Biocontrol of Leaf Blight Caused by Nigrospora sphaerica on Passion Fruit by Endophytic Bacillus subtilis Strain GUCC4

Passion fruit (Passiflora edulis Sims) is widely cultivated in tropic and sub-tropic regions for the production of fruit, flowers, cosmetics, and for pharmacological applications. Its high economic, nutritional, and medical values elicit the market demand, and the growing areas are rapidly increasing. Leaf blight caused by Nigrospora sphaerica is a new and emerging disease of passion fruit in Guizhou, in southwest China, where the unique karst mountainous landscape and climate conditions are considered potential areas of expansion for passion fruit production. Bacillus species are the most common biocontrol and plant-growth-promotion bacteria (PGPB) resources in agricultural systems. However, little is known about the endophytic existence of Bacillus spp. in the passion fruit phyllosphere as well as their potential as biocontrol agents and PGPB. In this study, 44 endophytic strains were isolated from 15 healthy passion fruit leaves, obtained from Guangxi province, China. Through purification and molecular identification, 42 of the isolates were ascribed to Bacillus species. Their inhibitory activity against N. sphaerica was tested in vitro. Eleven endophytic Bacillus spp. strains inhibited the pathogen by >65%. All of them produced biocontrol- and plant-growth-promotion-related metabolites, including indole-3-acetic acid (IAA), protease, cellulase, phosphatase, and solubilized phosphate. Furthermore, the plant growth promotion traits of the above 11 endophytic Bacillus strains were tested on passion fruit seedlings. One isolate, coded B. subtilis GUCC4, significantly increased passion fruit stem diameter, plant height, leaf length, leaf surface, fresh weight, and dry weight. In addition, B. subtilis GUCC4 reduced the proline content, which indicated its potential to positively regulate passion fruit biochemical properties and resulted in plant growth promotion effects. Finally, the biocontrol efficiencies of B. subtilis GUCC4 against N. sphaerica were determined in vivo under greenhouse conditions. Similarly to the fungicide mancozeb and to a commercial B. subtilis-based biofungicide, B. subtilis GUCC4 significantly reduced disease severity. These results suggest that B. subtilis GUCC4 has great potential as a biological control agent and as PGPB on passion fruit.

Factors Influencing Biofilm Formation by Salmonella enterica sv. Typhimurium, E. cloacae, E. hormaechei, Pantoea spp., and Bacillus spp. Isolated from Human Milk Determined by PCA Analysis

Bacteria enter milk during poor hygiene practices and can form a biofilm on surfaces that come into contact with human milk. The presence of a biofilm increases the risk of infections among newborns as bacteria protected by biofilm are resistant to washing and disinfection processes. The formation of the biofilm depends on the microbial species, environmental conditions, and the specific materials colonized. The aim of this study is to analyze the effects of factors such as temperature, incubation time, and initial cell concentration on biofilm formation by pathogenic bacteria isolated from human milk on model hydrophobic polystyrene surfaces. Model studies confirm that pathogenic bacteria appearing in human milk as a result of cross-contamination tend to form a biofilm. The majority of isolates formed biofilm at both 25 and 37 °C after 12 h at 1 × 10³ CFU/mL inoculum count. Multivariate principal component analysis (PCA) showed that at lower temperatures, biofilm formation by bacterial isolates was the main determinant of biofilm formation, other factors were less important; however, at 37 °C, time was a factor in biofilm formation. The model research performed underlines the importance of maintaining the proper hygiene of rooms, surfaces, and devices for expressing, storing, and preparing mothers' milk and powdered infant formula (PIF) in facilities responsible for feeding newborns and premature babies.

Characterization and Genetic Diversity of Bacillus cereus Strains Isolated from Baby Wipes

Bacillus cereus, a ubiquitous environmental microorganism known to cause foodborne illness, was isolated from samples taken from imported baby wipes from two different countries. These strains were characterized using a comprehensive molecular approach involving endpoint PCR, whole genome sequencing (WGS), comparative genomics, and biochemical analyses. A multiplex endpoint PCR assay was used to identify the enterotoxins: hemolysin BL, nonhemolytic enterotoxin, cytotoxin K, and enterotoxin FM toxin genes. Phylogenetically, the strains clustered into two major groups according to sequence type (ST) and singleton. We used the Center for Food Safety and Applied Nutrition (CFSAN) GalaxyTrakr BTyper computational tool to characterize the strains further. As an additional means of characterization, we investigated the possible role of carbohydrate transport systems and their role in nutrient uptake by performing a BLAST analysis of the 40 B. cereus genomes recovered from baby wipes. This study outlines a multifaceted workflow that uses the analysis of enterotoxigenic potential, bioinformatics, genomic diversity, genotype, phenotype, and carbohydrate utilization as a comprehensive strategy to characterize these B. cereus strains isolated from baby wipes and further our understanding of the phylogenetic relatedness of strains associated with baby wipe production facilities that could potentially pose an infection risk to a vulnerable infant population.

Bacillus cereus Invasive Infections in Preterm Neonates: an Up-to-Date Review of the Literature

Bacillus cereus group species are widespread, Gram-positive, spore-forming environmental bacteria. B. cereus sensu stricto is one of the major causes of food poisoning worldwide. In high-risk individuals, such as preterm neonates, B. cereus infections can cause fatal infections. It is important to note that the phenotypic identification methods commonly used in clinical microbiology laboratories make no distinction between B. cereus sensu stricto and the other members of the group (Bacillus anthracis excluded). As a result, all the invasive infections attributed to B. cereus are not necessarily due to B. cereus sensu stricto but likely to other closely related species of the B. cereus group. Next-generation sequencing (NGS) should be used to characterize the whole genome of the strains belonging to the B. cereus group. This could confirm whether the strains involved in previously reported B. cereus invasive infections preferentially belong to formerly known or emerging individual species. Moreover, infections related to B. cereus group species have probably been overlooked, since their isolation in human bacteriological samples has for a long time been regarded as an environmental contaminant of the cultures. Recent studies have questioned the emergence or reemergence of B. cereus invasive infections in preterm infants. This review reports our current understanding of B. cereus infections in neonates, including taxonomical updates, microbiological characteristics, bacterial identification, clinical features, host-pathogen interactions, environmental sources of contamination, and antimicrobial resistance.

Quantitative Risk Assessment of Bacillus cereus Growth during the Warming of Thawed Pasteurized Human Banked Milk Using a Predictive Mathematical Model

Bacillus cereus is relatively resistant to pasteurization. We assessed the risk of B. cereus growth during warming and subsequent storage of pasteurized banked milk (PBM) in the warmed state using a predictive mathematical model. Holder pasteurization followed by storage below −18 °C was used. Temperature maps, water activity values, and B. cereus growth in artificially inoculated PBM were obtained during a simulation of manipulation of PBM after its release from a Human Milk Bank. As a real risk level, we chose a B. cereus concentration of 100 CFU/mL; the risk was assessed for three cases: 1. For an immediate post-pasteurization B. cereus concentration below 1 CFU/mL (level of detection); 2. For a B. cereus concentration of 10 CFU/mL, which is allowed in some countries; 3. For a B. cereus concentration of 50 CFU/mL, which is approved for milk formulas. In the first and second cases, no risk was detected after 1 h of storage in the warmed state, while after 2 h of storage, B. cereus concentrations of 102 CFU/mL were occasionally encountered. In the third case, exceeding the B. cereus concentration of 102 CFU/mL could be regularly expected after 2 h of storage. Based on these results, we recommend that post-pasteurization bacteriological analysis be performed as recommended by the European Milk Bank Association (EMBA) and using warmed PBM within 1 h after warming (no exceptions).

Testing the effects of processing on donor human Milk: Analytical methods

Holder pasteurization is the current recommended method for donor human milk treatment. This method effectively eliminates most life-threatening contaminants in donor milk, but it also greatly reduces some of its biological properties. Consequently, there is a growing interest for developing novel processing methods that can ensure both microbial inactivation and a higher retention of the functional components of donor milk. Our aim was to offer a comprehensive overview of the analytical techniques available for the evaluation of such methods. To suggest an efficient workflow for the analysis of processed donor milk, a safety analytical panel as well as a nutritional value and functionality analytical panel are discussed, together with the principles, benefits, and drawbacks of the available techniques. Concluding on the suitability of a novel method requires a multifactorial approach which can be achieved by a combination of analytical targets and by using complementary assays to cross-validate the obtained results.

Breast Milk: A Meal Worth Having

A mother is gifted with breast milk, the natural source of nutrition for her infant. In addition to the wealth of macro and micro-nutrients, human milk also contains many microorganisms, few of which originate from the mother, while others are acquired from the mouth of the infant and the surroundings. Among these microbes, the most commonly residing bacteria are Staphylococci, Streptococci, Lactobacilli and Bifidobacteria. These microorganisms initiate and help the development of the milk microbiota as well as the microbiota of the gastrointestinal tract in infants, and contribute to developing immune regulatory factors such as cytokines, growth factors, lactoferrin among others. These factors play an important role in reducing the risk of developing chronic diseases like type 2 diabetes, asthma and others later in life. In this review, we will summarize the known benefits of breastfeeding and highlight the role of the breast milk microbiota and its cross-talk with the immune system in breastfed babies during the early years of life.

Identification of a New Pathogenicity Island Within the Large pAH187_270 Plasmid Involved in Bacillus cereus Virulence

Objectives

Bacillus cereus is responsible for food poisoning and rare but severe clinical infections. The pathogenicity of B. cereus strains varies from harmless to lethal strains. The objective of this study was to characterize three B. cereus isolates isolated from the same patient and identify their virulence potentials.

Methods

Three isolates of B. cereus were isolated from various blood samples from a patient who developed sepsis following a central venous catheter infection. The three isolates were compared by WGS, genotyping and SNP analysis. Furthermore, the isolates were compared by phenotypical analysis including bacterial growth, morphology, germination efficacy, toxin production, antibiotic susceptibility and virulence in an insect model of infection.

Results

According to WGS and genotyping, the 3 isolates were shown to be identical strains. However, the last recovered strain had lost the mega pAH187_270 plasmid. This last strain showed different phenotypes compared to the first isolated strain, such as germination delay, different antibiotic susceptibility and a decreased virulence capacity towards insects. A 50- kbp region of pAH187_270 plasmid was involved in the virulence potential and could thus be defined as a new pathogenicity island of B. cereus.

Conclusions

These new findings help in the understanding of B. cereus pathogenic potential and complexity and provide further hints into the role of large plasmids in the virulence of B. cereus strains. This may provide tools for a better assessment of the risks associated with B. cereus hospital contamination to improve hygiene procedure and patient health.

The pathogenic biomarker alcohol dehydrogenase protein is involved in Bacillus cereus virulence and survival against host innate defence

Bacillus cereus is a spore forming bacteria recognized among the leading agents responsible for foodborne outbreaks in Europe. B. cereus is also gaining notoriety as an opportunistic human pathogen inducing local and systemic infections. The real incidence of such infection is likely underestimated and information on genetic and phenotypic characteristics of the incriminated strains is generally scarce. We have recently analyzed a large strain collection of varying pathogenic potential. Screening for biomarkers to differentiate among clinical and non-clinical strains, a gene encoding an alcohol dehydrogenase-like protein was identified among the leading candidates. This family of proteins has been demonstrated to be involved in the virulence of several bacterial species. The relevant gene was knocked out to elucidate its function with regards to resistance to host innate immune response, both in vitro and in vivo. Our results demonstrate that the adhB gene plays a significant role in resistance to nitric oxide and oxidative stress in vitro, as well as its pathogenic ability with regards to in vivo toxicity. These properties may explain the pathogenic potential of strains carrying this newly identified virulence factor.

Bacillus cereus as a Major Cause of Discarded Pasteurized Human Banked Milk: A Single Human Milk Bank Experience

A systematic study, performed from 2017–2020 looked at the rate of positive post-pasteurization B. cereus findings, the quantity of B. cereus in pasteurized banked human milk (PBM), and the rate of B. cereus toxicogenic isolates from PBM. During the study period, 6815.71 L (30,943 tested bottles) of PBM were tested, with an average amount per year of 1703.93 L (7736 tested bottles). The PBM discard rate per year due to bacterial contamination varied between 8.7–10.0% and contamination with B. cereus was the most frequent reason. The total number of B. cereus positive tests was 2739 and the proportion of its positivity from all positive tests was between 56.7–66.6%. The prevalence of B. cereus positive tests rose significantly in the summer months. The production of enterotoxin was found in 3 of the 20 tested samples (15.0%). The B. cereus CFU-quantities in the PBM were below 10 CFU/mL in 80% of cases (16 of 20 samples tested). The quantitative data can be used in the risk assessment of cold storage of PBM at temperatures above zero and manipulation of PBM prior to its administration.

New genetic biomarkers to differentiate non-pathogenic from clinically relevant Bacillus cereus strains

OBJECTIVES

Bacillus cereus is responsible for food poisoning and rare but severe clinical infections. The pathogenicity of strains varies from harmless to lethal strains. However, there are currently no markers, either alone or in combination, to differentiate pathogenic from non-pathogenic strains. The objective of the study was to identify new genetic biomarkers to differentiate non-pathogenic from clinically relevant B. cereus strains.

METHODS

A first set of 15 B. cereus strains were compared by RNAseq. A logistic regression model with lasso penalty was applied to define combination of genes whose expression was associated with strain pathogenicity. The identified markers were checked for their presence/absence in a collection of 95 B. cereus strains with varying pathogenic potential (food-borne outbreaks, clinical and non-pathogenic). Receiver operating characteristic area under the curve (AUC) analysis was used to determine the combination of biomarkers, which best differentiate between the "disease" versus "non-disease" groups.

RESULTS

Seven genes were identified during the RNAseq analysis with a prediction to differentiate between pathogenic and non-pathogenic strains. The validation of the presence/absence of these genes in a larger collection of strains coupled with AUC prediction showed that a combination of four biomarkers was sufficient to accurately discern clinical strains from harmless strains, with an AUC of 0.955, sensitivity of 0.9 and specificity of 0.86.

CONCLUSIONS

These new findings help in the understanding of B. cereus pathogenic potential and complexity and may provide tools for a better assessment of the risks associated with B. cereus contamination to improve patient health and food safety.

Implication of a Key Region of Six Bacillus cereus Genes Involved in Siroheme Synthesis, Nitrite Reductase Production and Iron Cluster Repair in the Bacterial Response to Nitric Oxide Stress

Bacterial response to nitric oxide (NO) is of major importance for bacterial survival. NO stress is a main actor of the eukaryotic immune response and several pathogenic bacteria have developed means for detoxification and repair of the damages caused by NO. However, bacterial mechanisms of NO resistance by Gram-positive bacteria are poorly described. In the opportunistic foodborne pathogen Bacillus cereus, genome sequence analyses did not identify homologs to known NO reductases and transcriptional regulators, such as NsrR, which orchestrate the response to NO of other pathogenic or non-pathogenic bacteria. Using a transcriptomic approach, we investigated the adaptation of B. cereus to NO stress. A cluster of 6 genes was identified to be strongly up-regulated in the early phase of the response. This cluster contains an iron-sulfur cluster repair enzyme, a nitrite reductase and three enzymes involved in siroheme biosynthesis. The expression pattern and close genetic localization suggest a functional link between these genes, which may play a pivotal role in the resistance of B. cereus to NO stress during infection.