Rapid detection of Salmonella contamination in seafoods using multiplex PCR

Development of a multiplex PCR assay for detection of Riemerella anatipestifer serotype 1 and serotype 2 strains

Riemerella anatipestifer infection is one of the main infectious diseases that threaten the poultry industry at present. Serotypes 1 and 2 are the main serotypes causing global outbreaks of R. anatipestifer. In this study, we designed the primers specific for R. anatipestifer serotypes 1 and serotype 2 strains, and for R. anatipestifer 16S rRNA (for the species identification) to establish a multiplex PCR assay for rapid detection of the serotype 1 and serotype 2 strains. The specificity test showed that a 505 bp fragment was amplified from serotype 1 strains, and a 1125 bp fragment was amplified from serotype 2 strains. A 843 bp fragment of 16S rRNA was amplified from R. anatipestifer strains with different serotypes. No amplification band was shown for other species of bacterial pathogens, including Escherichia coli, Salmonella, Pasteurella multocida, Mycoplasma gallisepticum and Mycoplasma synoviae. The sensitivity test showed a detection limit of 102 CFU of the multiplex PCR assay. Furthermore, a total of 60 R. anatipestifer clinical isolates were tested for identification of the serotypes, and the results showed that a 843 bp 16S rRNA fragment was amplified from all 60 isolates, confirming they are R. anatipestifer strains. Moreover, a 505 bp serotype 1 fragment was amplified from 9 isolates, and a 1125 bp serotype 2 fragment was amplified from 28 isolates. R. anatipestifer serotype 1 and 2 strains accounted for 61.67 % of the isolates. The results were further validated by slide agglutination test, which showed 100 % consistency with the multiplex PCR.

The Unique Capability of Endolysin to Tackle Antibiotic Resistance: Cracking the Barrier

The lack of new antibacterial medicines and the rapid rise in bacterial resistance to antibiotics pose a major threat to individuals and healthcare systems. Despite the availability of various antibiotics, bacterial resistance has emerged for almost every antibiotic discovered to date. The increasing prevalence of multidrug-resistant bacterial strains has rendered some infections nearly untreatable, posing severe challenges to health care. Thus, the development of alternatives to conventional antibiotics is critical for the treatment of both humans and food-producing animals. Endolysins, which are peptidoglycan hydrolases encoded by bacteriophages, represent a promising new class of antimicrobials. Preliminary research suggests that endolysins are more effective against Gram-positive bacteria than Gram-negative bacteria when administered exogenously, although they can still damage the cell wall of Gram-negative bacteria. Numerous endolysins have a modular domain structure that divides their binding and catalytic activity into distinct subunits, which helps maximize their bioengineering and potential drug development. Endolysins and endolysin-derived antimicrobials offer several advantages as antibiotic substitutes. They have a unique mechanism of action and efficacy against bacterial persisters (without requiring an active host metabolism); subsequently, they target both Gram-positive and Gram-negative bacteria (including antibiotic-resistant strains), and mycobacteria. Furthermore, there has been limited evidence of endolysin being resistant. Because these enzymes target highly conserved links, resistance may develop more slowly compared to traditional antibiotics. This review provides an overview and insight of the potential applications of endolysins as novel antimicrobials.

Clinical detection of four emerging canine diarrhea-associated viruses and evolutionary analysis of canine kobuvirus

In this study, a multiplex PCR method was developed for the detection of four diarrhea-associated viruses of canines, including canine bocavirus (CBoV), canine circovirus (CCV), torque teno canis virus (TTCV), and canine kobuvirus (CKV). Four pairs of compatible primers, one specific for each virus, were designed based on conserved sequences. After optimization of parameters such as primer concentration and annealing temperature in single and multiple amplifications, four specific fragments were amplified simultaneously with high sensitivity and specificity in one PCR reaction. The fragments amplified were 165 bp (CBoV), 345 bp (CCV), 506 bp (TTCV), and 666 bp (CKV) in length. The sensitivity of this one-step multiplex PCR is about 10 times lower than that of regular singleplex PCR. There was no cross-reaction with the canine pathogens canine parvovirus (CPV), canine distemper virus (CDV), or canine coronavirus (CCoV). Testing of canine fecal samples from China using the multiplex PCR assay revealed the presence of CBoV, CCV, TTCV, and CKV in 10.1%, 6.2%, 2.8%, and 1.7% of the samples, respectively. The results of multiplex PCR agreed with the singleplex PCR results with a coincidence rate of 100%. In addition, the complete genome sequences of the viruses in three CKV-positive samples were determined and found to be 95.7 - 96.6% identical to the reference strain US-PC0082 and genetically more distant from other animal kobuvirus. The multiplex PCR method established in this study is convenient, with high specificity and sensitivity, which will be helpful for the rapid differential diagnosis of CBoV, CCV, TTCV, and CKV infections.

Research progress of loop-mediated isothermal amplification in the detection of Salmonella for food safety applications

Salmonella, the prevailing zoonotic pathogen within the Enterobacteriaceae family, holds the foremost position in global bacterial poisoning incidents, thereby signifying its paramount importance in public health. Consequently, the imperative for expeditious and uncomplicated detection techniques for Salmonella in food is underscored. After more than two decades of development, loop-mediated isothermal amplification (LAMP) has emerged as a potent adjunct to the polymerase chain reaction, demonstrating significant advantages in the realm of isothermal amplification. Its growing prominence is evident in the increasing number of reports on its application in the rapid detection of Salmonella. This paper provides a systematic exposition of the technical principles and characteristics of LAMP, along with an overview of the research progress made in the rapid detection of Salmonella using LAMP and its derivatives. Additionally, the target genes reported in various levels, including Salmonella genus, species, serogroup, and serotype, are summarized, aiming to offer a valuable reference for the advancement of LAMP application in Salmonella detection. Finally, we look forward to the development direction of LAMP and expect more competitive methods to provide strong support for food safety applications.

Establishment and application of multiplex PCR for rapid detection of three mink diarrhea-associated viruses

In this report, a multiplex PCR method was developed for the detection of three diarrhea-associated viruses in mink, including circovirus (MCV), bocavirus (MBoV), and enteritis virus (MEV). Three compatible sets of primers specific for each virus were designed respectively based on their conserved sequences. After optimization of the crucial factors such as primer concentration and annealing temperature in single and multiple amplification, three specific fragments were simultaneously amplified with the highest sensitivity and specificity in one PCR reaction. The fragments amplified were 259 bp (MCV)，455 bp (MBoV) and 671 bp (MEV). The sensibility of this one-step multiplex PCR is about 10 times lower than that of regular singleplex PCR. There were no cross-reactions with some relevant pathogens like mink coronavirus, canine distemper virus, and aleutian mink disease virus. In our study we analyzed viral DNA in mink fecal samples by multiplex PCR assay from China, which revealed the occurrence of MCV, MBoV, and MEV as 3.1 %, 5.7 %, and 9.8 %, respectively. The testing results of multiplex PCR agreed with the singleplex PCR results with a coincidence rate of 100 %. These results indicated that the method could provide technical support for rapid detection of the three diarrhea-associated viruses, and epidemiological investigation of mink viral diarrhea.

A dual RPA-LFD assay for the simultaneous detection of Salmonella typhimurium and Salmonella enteritidis

Introduction: Salmonella was one of the most common bacteria that caused foodborne illness, with S. typhimurium (Salmonella typhimurium) and S. enteritidis (Salmonella enteritidis) infections accounting for more than 75% of human salmonella infections. Methods: In this study, we developed a method of dual recombinase polymerase amplification (RPA) combined with a lateral flow dipstick for the rapid detection of S. typhimurium and S. enteritidis in clinical specimens (stool). Results: The entire reaction process, including amplification and result reading, could be completed within 65 min. The detection limits of S. typhimurium and S. enteritidis in pure culture samples were 5.23 × 101 CFU/mL and 3.59 × 101 CFU/mL, respectively. The detection limits of S. typhimurium and S. enteritidis in artificially contaminated samples were 8.30 × 101 CFU/mL and 2.70 × 102 CFU/mL, respectively. In addition, the method had no cross-reaction with other pathogenic microorganisms. The results in clinical samples were fully consistent with those obtained using Bacterial Analysis Manual, with sensitivity and specificity were 100% (8/8) and 100% (17/17) for S. typhimurium and 100% (4/4) and 100% (21/21) for S. enteritidis, respectively. Discussion: The detection limits of S. typhimurium and S. enteritidis in artificially contaminated samples were higher than those in pure culture samples, which might be attributed to the inherent complex composition of artificially contaminated samples. In addition, the detection limits of S. typhimurium and S. enteritidis in the same sample were also different, which might be attributed to different amplification efficiency of two target genes in the same reaction system. Conclusion: This assay had potential application outdoors, as it could be performed within 1 h at 38°C without a complex instrument, and the results could be observed with the naked eye. In conclusion, the dual RPA-LFD assay established in this study had practical significance for the rapid detection of S. typhimurium and S. enteritidis in the future.

Salmonella detection with LAMP and qPCR and identification of serovars of interest by multiplex qPCR in poultry carcasses

Salmonella is present in the poultry production chain and is a major challenge in terms of food safety and animal health. The early Salmonella detection is one of the main tools to control and prevent the transmission of this pathogen. Microbiological isolation and serotyping to identify and differentiate Salmonella serovars are laborious processes, time-consuming, and expensive. Therefore, molecular diagnostic methods can be rapid and efficient alternatives to the detection of this pathogen. Thus, the aim herein was to standardize and evaluate the use of loop-mediated isothermal amplification (LAMP) in comparison with real-time PCR (qPCR) for detection of Salmonella associated with a multiplex qPCR for simultaneous identification and differentiation of S. Enteritidis, S. Typhimurium, S. Pullorum, and S. Gallinarum. The LAMP, qPCR, and multiplex qPCR assays were comparable in specificity. The three techniques were evaluated for specificity for 16 different serovars of Salmonella and for 37 strains of the serovars of interest. The limit of detection and the efficiency of the LAMP, qPCR, and multiplex qPCR reactions were determined. The techniques were applied to 33 samples of chicken carcasses and compared to the results of conventional microbiology for validation. As results, LAMP was specific in the detection of different Salmonella serovars but presented lower limit of detection ranging from 101 to 104 CFU/reaction. In comparison, qPCR could detect less cells (100 to 102 CFU/reaction), reaching equal specificity and better repeatability in the assays. The qPCR multiplexing for identification of the different serovars also showed good specificity, with the detection threshold between entre 101 and 102 CFU/reaction. The results obtained in the analyses on poultry carcasses suggested a correspondence between the results obtained in molecular methods and in conventional microbiology. Thus, the proposed assays are promising for the diagnosis of Salmonella in poultry carcasses, already proved to be faster and more efficient than conventional diagnostics techniques, being of great interest for poultry production, animal, and public health.

A Comprehensive Review for the Surveillance of Human Pathogenic Microorganisms in Shellfish

Bivalve molluscan shellfish have been consumed for centuries. Being filter feeders, they may bioaccumulate some microorganisms present in coastal water, either naturally or through the discharge of human or animal sewage. Despite regulations set up to avoid microbiological contamination in shellfish, human outbreaks still occur. After providing an overview showing their implication in disease, this review aims to highlight the diversity of the bacteria or enteric viruses detected in shellfish species, including emerging pathogens. After a critical discussion of the available methods and their limitations, we address the interest of technological developments using genomics to anticipate the emergence of pathogens. In the coming years, further research needs to be performed and methods need to be developed in order to design the future of surveillance and to help risk assessment studies, with the ultimate objective of protecting consumers and enhancing the microbial safety of bivalve molluscan shellfish as a healthy food.

Development and Application of Real-Time PCR Assay for Detection of Salmonella Abortusequi

Salmonella enterica subsp. enterica serovar Abortusequi is a major pathogen in horse and donkey herds, causing abortion in pregnant equids and resulting in enormous economic losses. A rapid and reliable method is urgently needed to detect S. Abortusequi in herds where the disease is suspected. To achieve this goal, a TaqMan-based real-time PCR assay targeting the gene for the flagellin protein phase 2 antigen FljB was developed. This real-time PCR assay had high specificity, sensitivity, and reproducibility. The detection limit of the assay was 30 copies/μL of standard plasmid and 10 CFU/μL of bacterial DNA. Furthermore, 540 clinical samples, including 162 tissue, 192 plasma, and 186 vaginal swab samples collected between 2018 and 2021 in China, were tested to assess the performance of the developed assay. Compared to the gold standard method of bacterial isolation, the real-time PCR assay exhibited 100% positive agreement for all tissue, plasma and vaginal swab tests. Additionally, this assay detected DNA from S. Abortusequi from 56.7% (34/60) culture-negative tissue and 22.9% (41/179) culture-negative vaginal swab samples from infected equids. Receiver operating characteristic analysis demonstrated that the results of the developed real-time PCR assays were in significant agreement with those of the culture method. The real-time PCR assay can be completed within 45 min of extraction of DNA from samples. Our results show that this assay could serve as a reliable tool for the rapid detection of S. Abortusequi in tissue, plasma, and vaginal swab clinical samples.

Graphene oxide-assisted optimized narrow-thermal-cycling amplification for accurate detection of Salmonella spp

Salmonella is a rod-shaped, Gram-negative zoonotic pathogen that poses a serious global socioeconomic and public health threat. Rapid and accurate detection of Salmonella spp. is critical for effective control of its infection. In this study, an accurate, sensitive and specific graphene oxide-assisted accelerated strand exchange amplification (GO-ASEA) method for rapid detection of Salmonella spp. was developed and validated. The detection limit of the GO-ASEA method was 8.6 × 10¹ fg μL^-1 of Salmonella genomic DNA or 1 × 10¹ CFU g^-1 of Salmonella in spiked chicken faeces free of pre-enrichment. And the GO-ASEA method could specifically detect Salmonella spp. without cross-reactivity with other enteric pathogens. In addition, the novel method achieved Salmonella detection within 30 min and was validated using 209 clinical samples, showing its good clinical applicability. Therefore, the GO-ASEA method is a new optional tool for the rapid detection of pathogenic microorganisms, which is ideal for food safety monitoring and high-throughput detection.

Advances in multiplex molecular detection technologies for harmful algae

As the eutrophication of natural water bodies becomes more and more serious, the frequency of outbreaks of harmful algal blooms (HABs) mainly formed by harmful algae also increases. HABs have become a global ecological problem that poses a serious threat to human health and food safety. Therefore, it is extremely important to establish methods that can rapidly detect harmful algal species for early warning of HABs. The traditional morphology-based identification method is inefficient and inaccurate. In recent years, the rapid development of molecular biology techniques has provided new ideas for the detection of harmful algae and has become a research hotspot. The current molecular detection methods for harmful algal species mainly include fluorescence in situ hybridization, sandwich hybridization, and quantitative PCR (qPCR), but all of these methods can only detect single harmful algal species at a time. The establishment of methods for the simultaneous detection of multiple harmful algal species has become a new trend in the development of molecular detection technology because various harmful algal species may coexist in the natural water environment. The established molecular techniques for multiple detections of harmful algae mainly include gene chip, multiplex PCR, multiplex qPCR, massively parallel sequencing, antibody chip, and multiple isothermal amplification. This review mainly focuses on the principles, advantages and disadvantages, application progress, and application prospects of these multiple detection technologies, aiming at providing effective references not only for the fisheries but also for economic activities, environment, and human health.

Multiplex PCR assay based on the citE2 gene and intergenic sequence for the rapid detection of Salmonella Pullorum in chickens

Salmonella is one of the most common Gram-negative pathogens and seriously threatens chicken farms and food safety. This study aimed to establish a multiplex polymerase chain reaction (PCR) approach for the identification of different Salmonella enterica subsp. enterica. The citE2 gene and interval sequence of SPS4_00301–SPS4_00311 existed in all S. enterica subsp. enterica serovars by genomic comparison. By contrast, a 76 bp deletion in citE2 was found only in Salmonella Pullorum. Two pairs of special primers designed from citE2 and interval sequence were used to establish the multiplex PCR system. The optimized multiplex PCR system could distinguish Salmonella Pullorum and non-Salmonella Pullorum. The sensitivity of the optimized multiplex PCR system could be as low as 6.25 pg/μL and 10⁴ colony-forming units (CFU)/mL for genomic DNA and Salmonella Pullorum cells, respectively. The developed multiplex PCR assay distinguished Salmonella Pullorum from 33 different Salmonella enterica subsp. enterica serotypes and 13 non-target species. The detection of egg samples artificially contaminated with Salmonella Pullorum, Salmonella Enteritidis, and naturally contaminated 69 anal swab samples showed that results were consistent with the culture method. These features indicated that the developed multiplex PCR system had high sensitivity and specificity and could be used for the accurate detection of Salmonella Pullorum in clinical samples.

Multiplex PCR method for the detection of human norovirus, Salmonella spp., Shigella spp., and shiga toxin producing Escherichia coli in blackberry, coriander, lettuce and strawberry

A multiplex PCR method was developed for the simultaneous detection of murine norovirus (MNV-1) as a surrogate for human norovirus (HuNoV) GI and GII, Salmonella spp., Shigella spp., and Shiga toxin producing Escherichia coli (STEC) in fresh produce. The toxicity of the glycine buffer on bacterial pathogens viability was evaluated. The growth of each of the three pathogens (previously stressed) was evaluated at 35 and 41.5 °C in modified buffered peptone water (mBPW) and trypticase soy broth (TSB), supplemented with vancomycin, novobiocin and brilliant green at two concentration levels. The selected conditions for simultaneous enrichment were: 41.5 °C/mBPW/supplemented with 8 ppm vancomycin, 0.6 ppm novobiocin and 0.2 ppm brilliant green. The pathogens and aerobic plate count (APC) growth was evaluated in the enrichment of lettuce, coriander, strawberry and blackberry under the best enrichment conditions. Starting from 1 to 10 CFU/mL, Salmonella reached from 7.63 to 8.91, Shigella 6.81 to 7.76 and STEC 7.43 to 9.27 log CFU/mL. The population reached for the APC was 5.11-6.56 log CFU/mL. Simultaneous detection by PCR was done using designed primers targeting invA, ipaH, stx1 and stx2 genes, and MNV-1. The detection sensitivity was 10-100 PFU for the MNV-1 and 1-10 CFU for each pathogenic bacteria. This protocol takes 6 h for MNV-1 and 24 h for Salmonella spp., Shigella spp., and STEC detection from the same food portion. In total, 200 samples were analyzed from retail markets from Queretaro, Mexico. Two strawberry samples were positive for HuNoV GI and one lettuce sample was positive for STEC. In conclusion, the method developed in this study is capable of detecting HuNoV GI and GII, Salmonella spp., Shigella spp and STEC from the same fresh produce sample.

Capture and identification of bacteria from fish muscle based on immunomagnetic beads and MALDI-TOF MS

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A protocol for the bacterial analysis in fish muscle was developed.

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Anti-bacterial antibodies modified magnetic beads (MBs) were used to capture bacteria.

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The bacterial identification accuracy from different complex food matrices was good.

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The presence of 10 CFU/mL E. coli is still detectable.

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It is promising to be applied in bacterial analysis to ensure muscle food safety.

In the present study, E. coli was taken as a model bacterium, anti-E. coli functionalized magnetic beads were constructed and used to capture E. coli from aqueous extracts of fish sarcoplasmic protein (FSP) and fish muscle protein of sablefish. The excellency of the reproducibility of the present protocol was demonstrated by capturing E. coli from sablefish FSP extracts. The presence of 10 CFU/mL E. coli is still detectable. A microbial safety test on the surface of fish muscle was successfully performed. The bacterial identification accuracy from samples with different matrices was found to be excellent with RSD = 3%. High specific detection of target bacteria in complex biological samples was testified by spiking Staphylococcus aureus and Klebsiella pneumoniae in samples as interference. Ten biomarker ions were discovered for E. coli’s recognition. It is promising to apply the present protocol in bacterial analysis in muscle food samples to ensure their safety.