Evaluation of a real-time PCR assay for the detection and quantification of Bacillus cereus group spores in food

Flower-Shaped PCR Scaffold-Based Lateral Flow Bioassay for Bacillus cereus Endospores Detection

Bacillus cereus, a foodborne pathogen, produces resilient endospores that are challenging to detect with conventional methods. This study presents a novel Flower-Shaped PCR Scaffold-based Lateral Flow Biosensor (FSPCRS-LFB), which employs an aptamer-integrated PCR scaffold as capture probes, replacing the traditional streptavidin-biotin (SA-Bio) approach. The FSPCRS-LFB demonstrates high sensitivity and cost-efficiency in detecting B. cereus endospores, with a limit of detection (LOD) of 4.57 endospores/mL a visual LOD of 102 endospores/mL, and a LOD of 6.78 CFU/mL for endospore-cell mixtures. In chicken and tea samples, the platform achieved LODs of 74.5 and 52.8 endospores/mL, respectively, with recovery rates of 82.19% to 97.88%. Compared to existing methods, the FSPCRS-LFB offers a 3.7-fold increase in sensitivity while reducing costs by 26% over the SA-Bio strategy and 87.5% over rolling circle amplification (RCA). This biosensor provides a rapid, sensitive and cost-effective solution for point-of-care testing (POCT) of B. cereus endospores, expanding detection capabilities and offering novel approaches for pathogen detection.

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

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

Detection and quantification of Bacillus cereus and its spores in raw milk by qPCR, and distinguish Bacillus cereus from other bacteria of the genus Bacillus

Introduction

The raw milk is the basic raw material of dairy products, Bacillus cereus is a typical conditional pathogenic bacteria and cold-phagocytic spoilage bacteria in raw milk. This study established a qPCR method for detecting B. cereus in raw milk

Materials and Methods

In this study, a qPCR method for detecting B. cereus in raw milk was established. The specificity of the method was verified by using other Bacillus bacteria and pathogenic bacteria, the sensitivity of the method was evaluated by preparing recombinant plasmids and simulated contaminated samples, and the applicability of the method was verified by using pure spore DNA. The actual sample detection was completed by using the established qPCR method

Results

The qPCR established in this study can specifically detect B. cereus in raw milk. The LOD of the method was as low as 200 CFU/mL, and the LOQ ranged from 2 × 10 2 to 2 × 10 8 CFU/ml, the amplification efficiency of qPCR was 96.6%

Conclusins

The method established in this study can distinguish B. cereus from other Bacillus bacteria, and spore DNA can be used as the detection object. This method has the advantages of strong specificity, high sensitivity, wide application range and short detection time, which is expected to be applied in the dairy industry.

Evaluation of a Highly Efficient DNA Extraction Method for Bacillus anthracis Endospores

A variety of methods have been established in order to optimize the accessibility of DNA originating from Bacillusanthracis cells and endospores to facilitate highly sensitive molecular diagnostics. However, most endospore lysis techniques have not been evaluated in respect to their quantitative proficiencies. Here, we started by systematically assessing the efficiencies of 20 DNA extraction kits for vegetative B.anthracis cells. Of these, the Epicentre MasterPure kit gave the best DNA yields and quality suitable for further genomic analysis. Yet, none of the kits tested were able to extract reasonable quantities of DNA from cores of the endospores. Thus, we developed a mechanical endospore lysis protocol, facilitating the extraction of high-quality DNA. Transmission electron microscopy or the labelling of spores with the indicator dye propidium monoazide was utilized to assess lysis efficiency. Finally, the yield and quality of genomic spore DNA were quantified by PCR and they were found to be dependent on lysis matrix composition, instrumental parameters, and the method used for subsequent DNA purification. Our final standardized lysis and DNA extraction protocol allows for the quantitative detection of low levels (<50 CFU/mL) of B. anthracis endospores and it is suitable for direct quantification, even under resource-limited field conditions, where culturing is not an option.

Advanced Methods for Detection of Bacillus cereus and Its Pathogenic Factors

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

Food Sensing: Detection of Bacillus cereus Spores in Dairy Products

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

Food Targeting: A Real-Time PCR Assay Targeting 16S rDNA for Direct Quantification of Alicyclobacillus spp. Spores after Aptamer-Based Enrichment

Spore-forming Alicyclobacillus spp. are able to form metabolites that induce even in small amounts an antiseptical or medicinal off-flavor in fruit juices. Microbial contaminations could occur by endospores, which overcame the pasteurization process. The current detection method for Alicyclobacillus spp. can take up to 1 week because of microbiological enrichment. In a previous study, DNA aptamers were selected and characterized for an aptamer-driven rapid enrichment of Alicyclobacillus spp. spores from orange juice by magnetic separation. In the present work, a direct quantification assay for Alicyclobacillus spp. spores was developed to complete the two-step approach of enrichment and detection. After mechanical treatment of the spores, the isolated DNA was quantified in a real-time PCR-assay targeting 16S rDNA. The assay was evaluated by the performance requirements of the European Network of Genetically Modified Organisms Laboratories (ENGL). Hence, the presented method is applicable for direct spore detection from orange juice in connection with an enrichment step.

Compact Dry(R) X-BC for the enumeration of Bacillus cereus in food samples

We evaluated the effectiveness of using Compact Dry(R) X-BC (CD-XBC), a ready-to-use and self-diffusing dry medium sheet culture system based on a novel detection principle, for the detection and enumeration of Bacillus cereus. All 13 B. cereus strains, which were studied for the inclusivity study, grew as blue/green colonies on the CD-XBC. When 3 yeast strains and 103 bacterial strains other than B. cereus were tested for the exclusivity study, 5 strains formed white colonies, and 4 strains formed blue/green colonies, while 94 other strains failed to grow. The 4 strains that formed blue/green colonies were B. thuringiensis, which is known to have the same biochemical features as B. cereus. The CD-XBC method was compared with the MYP agar method (MYP) and the NGKG agar method (NGKG) in 130 artificially contaminated food samples. The correlation coefficients between CD-XBC and MYP, and CD-XBC and NGKG were 0.972 and 0.971, respectively.