Development of a rapid and sensitive immunomagnetic-bead based assay for detecting Bacillus cereus in milk

On-site detection of Sporothrix globosa using immunoglobulin Y, magnetic separation and loop-mediated isothermal amplification

BACKGROUND

Sporothrix globosa (S. globosa) is an agricultural activity-related but neglected pathogenic fungus responsible for sporotrichosis. Timely detection is crucial for managing and preventing its spread. However, due to the lack of efficient recognition elements for enriching S. globosa, the current approaches for detecting S. globosa are not simple and/or sensitive enough. This hinders their wider application of fast screening.

RESULTS

Herein, we successfully prepared immunoglobulin Y (IgY) targeting S. globosa, and developed a rapid and accurate detection method, improving upon current limited and inadequate detection approaches. Our method combined the use of IgY and loop-mediated isothermal amplification (LAMP) to enhance detection sensitivity and specificity simultaneously. The IgY was fabricated on magnetic beads to specifically concentrate S. globosa in samples, while LAMP amplified the captured target after simple boiling DNA extraction. By using our method, as low as 4.66 × 102 Cells mL-1S. globosa was accurately detected in soil and corn straw samples. We further integrated this assay into a portable toolbox for sample-to-result detection in resource-limited areas. By using this toolbox, we have colorimetrically detected soil and corn straw samples contaminated by S. globosa, suggesting the promising on-site detection potential.

SIGNIFICANCE AND NOVELTY

A new IgY recognizing S. globosa was prepared. Through the combination of IgY enrichment and LAMP amplification, the detection sensitivity and specificity were improved simultaneously. This method eliminated thermal cycling, simplified the operation, and reduced the analysis time. Compared to existing methods, our approach is more suitable for on-site detection and can significantly improve public health responses to sporotrichosis outbreaks.

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.

Carbohydrate Ligands on Magnetic Nanoparticles for Centrifuge-Free Extraction of Pathogenic Contaminants in Pasteurized Milk

Rapid detection of bacterial contamination in the food supply chain is critically important for food safety monitoring. Reliable extraction and concentration of bacteria from complex matrices is required to achieve high detection sensitivity, especially in situations of low contamination and infective dose. Carbohydrate ligands that attach to microbial cell-surface epitopes are promising economical and biocompatible substitutes for cell-targeting ligands and antibodies. Two different carbohydrate ligands immobilized onto magnetic nanoparticles (MNPs) were easily suspended in liquid food (milk) and allowed expedient extraction of microbes within minutes, without the need for centrifugation or loss in capture capacity. In this pilot study, 25-mL samples of undiluted milk were spiked with 5 mg of MNPs and artificially contaminated with bacteria at 3 to 5 log CFU/mL. MNPs and bacteria formed MNP-cell complexes, which were rapidly separated from the milk matrix with a simple magnet to allow supernatant removal. MNP-cell complexes were then concentrated by resuspension in 1 mL of fresh milk and plated per Bacteriological Analytical Manual procedures. Capture was carried out in vitamin D, 2% reduced fat, and fat-free milk spiked with Salmonella Enteritidis, Escherichia coli O157:H7, and Bacillus cereus for a combined total of 18 experiments (three replicates each). An additional eight experiments were conducted to investigate the effect of competitive bacteria on capture. All experiments were carried out over several months to account for environmental variations. Capture efficiency, on a log basis, for all combinations of milk and bacteria was 73 to 90%. Long-term exposure of the MNPs to milk did not markedly affect capture efficiency. These carbohydrate-functionalized MNPs have potential as nonspecific receptors for rapid extraction of bacteria from complex liquids, opening the door to discovery of biocompatible ligands that can reliably target pathogens in our food.

Modeling of Bacillus cereus growth in brown rice submitted to a combination of ultrasonication and slightly acidic electrolyzed water treatment

The combined effects of ultrasonication and slight acidic electrolyzed water were investigated to improve the microbial safety of brown rice against Bacillus cereus infection and to evaluate the growth kinetics of these bacteria during storage of untreated and treated rice at various temperatures (5, 10, 15, 20, 25, 30, and 35°C). The results indicate that this combination treatment was bactericidal against B. cereus, resulting in an approximately 3.29-log reduction. Although B. cereus can be efficiently reduced by treatment, temperature abuse during storage can allow B. cereus to recover and grow. A primary growth model (Baranyi and Roberts equation) was fitted to the raw growth data from untreated (control) and treated samples to estimate growth rate, lag time, and maximum population density, with a low standard error of the residuals (≤0.140) and high adjusted coefficient of determination (>0.990). The growth curves obtained from the Baranyi and Roberts model indicated that B. cereus grew more slowly on treated brown rice than on untreated brown rice. Secondary models predicting the square root of the maximum growth rate and the natural logarithm of the lag time as a function of temperature were satisfactory (bias factor = 0.993 to 1.013; accuracy factor = 1.290 to 1.352; standard error of prediction = 18.828 to 36.615%). Inactivation results and the model developed and validated in this study provided reliable and valuable growth kinetics information for quantitative microbiological risk assessment studies of B. cereus on brown rice.

Sensitive detection and quantification of gliadin contamination in gluten-free food with immunomagnetic beads based liposomal fluorescence immunoassay

Gliadin from wheat is a common food allergen that can induce baker's asthma, wheat-dependent exercise-induced anaphylaxis, atopic dermatitis, and celiac disease. This gliadin assay focuses on rapidly screen and check for gluten contamination in raw materials and in the gluten-free food production process, not only for wheat-sensitive patients but also for the industries producing gluten-free foodstuffs. The developed assay incorporates the use of anti-gliadin antibody-conjugated immunomagnetic beads (IMBs) to capture the gliadin in samples and fluorescent dyes-loaded immunoliposomal nanovesicles (IMLNs) to produce and enhance the detection signal. Hence, a sandwich complex is formed as "IMBs-gliadin-IMLNs". Experimental results indicate that this detection platform exhibits good sensitivity for gliadin with a detection limit as low as 0.6 μg mL(-1) of gliadin; as the polyclonal antibody showed slight cross-reactions with barley and rye. Excellent recovery rates were found ranging from 83.5 to 102.6% as testing the spiked samples. Moreover, the CV (%) of intra- and inter-assay of this developed assay are 4.8-10.6% and 3.5-9.9%, respectively. Based on a parallel analysis of twenty food samples, the results of this developed assay provide a good consistency with those of an AOAC-approved ELISA kit without any false-negative results. The proposed assay method is thus a highly promising alternative method for detecting the contamination of gliadin in the food industry.