Rapid and visual detection of Listeria monocytogenes by combining one-pot LAMP-CRISPR/Cas12b with lateral flow assay.

The VIDAS Listeria monocytogenes II (LMO2) method, which is an automated enzyme-linked fluorescent immunoassay (ELFA), was used for rapidly, specifically and sensitively detecting L. monocytogenes in food samples. All 31 L. monocytogenes strains examined gave positive results. The other bacterial species except Salmonella showed completely negative results, but it was suspected that Salmonella spp. had given a false-positive reaction to the assay. As the detectable limit of the assay was 10⁶ cfu/ml in a food suspension, food samples were required to be enriched in order to increase the number of the bacteria to the detectable limit. However, the ELFA was reconfirmed to be applied satisfactorily as a rapid and precise method for the detection of L. monocytogenes in various food samples, even if the culture had to be enriched for 12 h prior to the assay.

LAMP based electrochemical sensor for extraction-free detection of Listeria monocytogenes in food samples

Listeria monocytogenes is a major foodborne pathogen of global health concern. Herein, the rapid diagnosis of L. monocytogenes has been achieved using loop-mediated isothermal amplification (LAMP) based on the phosphatidylcholine-phospholipase C gene (plcB). Colorimetric detection was then performed through the formation of DNA concatemers and a gold nanoparticle/DNA probe complex (GNP/DNA probe). The overall detection process was accomplished within approximately 1 h with no need for complicated equipment. The limits of detection for L. monocytogenes in the forms of purified genomic DNA and pure culture were 800 fg and 2.82 CFU mL−1, respectively. No cross reactions were observed from closely related bacteria species. The LAMP-GNP/DNA probe assay was applied to the detection of 200 raw chicken meat samples and compared to routine standard methods. The data revealed that the specificity, sensitivity, and accuracy were 100, 90.20, and 97.50%, respectively. The present assay was 100% in conformity with LAMP-agarose gel electrophoresis assay. Five samples that were negative by both assays appeared to have the pathogen at below the level of detection. The assay can be applied as a rapid direct screening method for L. monocytogenes.

Integrating loop-mediated isothermal amplification with lateral flow assay to achieve a highly sensitive method for detecting Streptococcus suis Genome in raw pork

Background and Aim: Listeria monocytogenes remains a major foodborne pathogen globally, with mortality rates ranging from 20%–40%. The increasing incidence of listeriosis and the limitations of culture-based and polymerase chain reaction-based diagnostics highlight the need for rapid, cost-effective, and highly specific immunoassays. This study aimed to develop and validate a regionally adapted sandwich enzyme-linked immunosorbent assay (ELISA) based on monoclonal and polyclonal antibodies (pAbs) raised against a recombinant p60 antigen derived from a Kazakhstani L. monocytogenes field isolate. Materials and Methods: The p60 gene lacking its N-terminal signal peptide was amplified from a regional L. monocytogenes isolate, cloned into the pET28c(+) vector, and expressed in Escherichia coli arctic express (DE3). Recombinant p60 protein was purified by Ni2⁺-affinity chromatography and used to immunize BALB/c mice and Chinchilla rabbits for monoclonal antibodies and pAbs antibody production. Hybridoma clones were screened for specificity using indirect ELISA and Western blot. A sandwich ELISA was assembled using mAb 1H8 as the capture antibody and horseradish peroxidase-conjugated rabbit pAbs as detection antibodies. Analytical sensitivity and diagnostic performance were evaluated using serial dilutions of recombinant p60 and culture supernatants of L. monocytogenes isolates recovered from 507 food samples. Results: The recombinant p60 antigen (50.3 kDa) was successfully expressed and purified at 5.9 mg/L yield. Among seven stable hybridoma clones, mAb 1H8 exhibited the highest affinity (Ka = 2.5 × 1010 M⁻1) and specificity without cross-reactivity to non-Listeria bacteria. The optimized sandwich ELISA achieved a detection limit of 1.5 ng/mL, corresponding to approximately 103 colony-forming units/mL. All six L. monocytogenes field isolates tested positive in the assay, with results strongly correlating with viable cell counts (R2 = 0.89). The assay demonstrated comparable sensitivity to commercial kits while offering shorter assay time (2 h) and substantially lower production cost. Conclusion: The developed sandwich ELISA provides a sensitive, specific, rapid, and regionally tailored diagnostic platform for detecting pathogenic L. monocytogenes in food samples. By integrating locally produced recombinant antigens and immunoreagents, the assay offers a cost-effective alternative to imported kits, supporting national food safety programs and One Health surveillance initiatives. Keywords: food safety surveillance, foodborne pathogens, hybridoma technology, immunodiagnostics, Listeria monocytogenes, monoclonal antibodies, One Health, p60 antigen, polyclonal antibodies, recombinant protein, sandwich enzyme-linked immunosorbent assay.

The loop-mediated isothermal amplification (LAMP) detection method was applied to detect Listeria monocytogenes in food. The specificity and sensitivity of this method were evaluated through comparing it with Real-time PCR and conventional detection method. The LAMP primers were designed based on hly gene of Listeria monocytogenes. The LAMP method was applied to detect 88 Listeria monocytogenes, 1 reference strain ATCC 15313 of Listeria monocytogenes and 33 non-targets bacteria strains; base-material addition test and practical food samples detection were also conducted. Both of Real-time PCR and ISO 11290-1 methods were used as parallel detection method in addition to LAMP. The three kinds of methods were compared by specificity, sensitivity, detection limit and the detection result of practical food samples. Both detection results of LAMP and Real-time PCR for 89 Listeria monocytogenes were positive (100%, 89/89), 33 non-targets bacteria strains were negative (100%, 33/33). The sensitivity of LAMP was 2 × 10² CFU/ml, which was consistent with Real-time PCR method (2 × 10² CFU/ml) and better than ISO 11290-1 method (2 × 10² CFU/ml). Base-material addition test result showed that the detection limit of the three kinds of methods were 3 CFU/25 g samples. And the result of practical food samples displayed the same detection rate of 4% in the three methods (2/45). The LAMP method of Listeria monocytogenes established in this study has good specificity and sensitivity, which can be applied to the rapid detection of Listeria monocytogenes.

Detection of Listeria monocytogenes based on combined aptamers magnetic capture and loop-mediated isothermal amplification

Concentration of Listeria monocytogenes in skim milk and soft cheese through microplate immunocapture

Rapid Detection of Haptoglobin Gene Deletion in Alkaline-Denatured Blood by Loop-Mediated Isothermal Amplification Reaction

Cronobacter species previously known as Enterobacter sakazakii poses high risks to neonates and infants. In this work a rapid detection method was developed which combined loop-mediated isothermal amplification with lateral flow assay for detection of Cronobacter species in powdered infant formula. The fast amplification reaction without betaine was established and capable of performing DNA replication within 25 min. Based on the novel probe-free labeling methods, we established a lateral flow assay to capture the specific loop-mediated isothermal amplification amplicons which were labeled with fluorescein isothiocyanate and biotin. And the final detection time of this system was within 40 min. The false positive results of the lateral flow assay induced by primer dimer tagged with fluorescein isothiocyanate and biotin were eliminated by Taq single strand DNA binding protein (4 ng/μL). Simultaneously, the efficiency of the fast loop-mediated isothermal amplification assay was achieved. By injection of Taq SSB into the amplification assay as a replacement for betaine, the novel probe-free method could detect Cronobacter species with high specificity and sensitivity at the detection limit in PIF of 101 cfu/g. Our overall strategy has excellent potential in the rapid diagnosis of Cronobacter species label-free by integrating loop-mediated isothermal amplification and lateral flow assay.

Listeria monocytogenes represents serious danger for human health. Thus detection of this pathogen in food, which represents its main means of entry into the organism, is a topic of special importance. The original classic methods for the determination of Listeria monocytogenes are in general laborious and time-consuming procedures. In order to address this issue we developed a new rapid method for specific detection of Listeria monocytogenes in food samples. The method consists of three steps: i) enrichment of food microflora (16 h), ii) selective isolation of Listeria sp. exploiting immunomagnetic separation (2–3 h) followed by iii) precise identification of Listeria sp. and Listeria monocytogenes using duplex PCR. PCR primers specific to part of 16S rRNA were used in order to identify the members of Listeria genus. The specific identification of Listeria monocytogenes was accomplished exploiting a pair of primers specific to gene encoding invasion-associated protein – iap (4–5 h). Amplification products, 1003 bp and 593 bp respectively, were separated by electrophoresis and visualized by UV detection. The optimized IMS-PCR method was used to test the presence of Listeria sp. and Listeria monocytogenes in food samples (ground meat, low-fat milk and cheese [olomoucké tvarůžky]). A comparison of the efficiency of the bacteria enrichment step by IMS and centrifugation was also performed. The analysis time including enrichment is less than 24 h. The detection limit for Listeria monocytogenes was found between 101–102 cfu per 25 g of food sample.

The ability to rapidly detect pathogens in food is important from public health and food safety reasons. Traditional culture-based detection methods tend to be laborious, time consuming, technically demanding and may be limited due to their low sensitivity. Rapid detection methods for foodborne pathogens should be specific and sensitive to detect pathogens in low numbers. Sensitivity is important because a single pathogen present in food has the potential risk to cause infection. PCR and Real-time PCR are rapid, sensitive, and specific but require specific instruments and laboratory set-up. In the present study, a simple loop-mediated isothermal amplification (LAMP) assay was developed for rapid detection of Staphylococcus aureus. The LAMP assay was found to be ten times more sensitive than traditional end-point PCR with analytical sensitivity of 0.56 pg/μl and 5.6 pg/μl of DNA, respectively. In spiked chevon samples inoculated with S. aureus, the detection limit of LAMP and PCR assay was 3.3 × 105 CFU/g and 3.3 × 106 CFU/g, respectively, without enrichment. After enriching the samples for 6 h, the detection limit improved to 3.3 × 102 CFU/g and 3.3 × 104 CFU/g, respectively, indicating LAMP to be 100-fold more sensitive than PCR. The detection limit further improved to 3.3 CFU/g of meat after enrichment of 12 h. The developed LAMP was also found to be suitable when evaluated on field samples. The present study reports a simple LAMP assay for rapid visual detection of S. aureus which has potential for use in resource limited settings.

Sensitive and specific detection of Listeria monocytogenes in food samples using imprinted upconversion fluorescence probe prepared by emulsion polymerization method

A filtration-based real-time PCR method for the quantitative detection of viable Salmonella enterica and Listeria monocytogenes in food samples

BACKGROUNDFoodborne diseases are a major global public health concern. It is urgent to monitor foodborne pathogens from contaminated foods based on multi‐target detection.RESULTSIn this work, a self‐priming compartmentalization (SPC) microdevice made of poly(methyl methacrylate) (PMMA) was developed and integrated into a loop‐mediated isothermal amplification (LAMP) system for performing high‐throughput visual detection. The microfluidic chip is a self‐filling microwell array which can introduce reaction solution only through an access hole in a vacuum pumping system. The independent and closed wells can avoid cross‐contamination and ensure the accuracy of the results. The approach was able to perform the simultaneous identification of six foodborne pathogens (Salmonella typhimurium, Bacillus cereus, Staphylococcus aureus, Yersinia enterocolitica, Vibrio parahaemolyticus and Listeria monocytogenes) within 1 h. The results demonstrated that the method could specifically recognize the six foodborne pathogens.CONCLUSIONThe use of a LAMP‐based microdevice can be a faster alternative to conventional methods to detect pathogens in food samples, especially for those foods in which no pathogen is allowed (S. aureus), or foods for infant use. The simplicity and portability of the device can provide an alternative platform for foodborne pathogens where food safety needs accurate and timely detection confirmation. © 2020 Society of Chemical Industry