Rapid detection of Salmonella from hydrodynamic pressure-treated poultry using molecular beacon real-time PCR

Susceptibility of the Different Oxygen-Sensing Probes to Interferences in Respirometric Bacterial Assays with Complex Media

Respirometric microbial assays are gaining popularity, but their uptake is limited by the availability of optimal O2 sensing materials and the challenge of validating assays with complex real samples. We conducted a comparative evaluation of four different O2-sensing probes based on Pt-porphyrin phosphors in respirometric bacterial assays performed on standard time-resolved fluorescence reader. The macromolecular MitoXpress, nanoparticle NanO2 and small molecule PtGlc4 and PtPEG4 probes were assessed with E. coli cells in five growth media: nutrient broth (NB), McConkey (MC), Rapid Coliform ChromoSelect (RCC), M-Lauryl lauryl sulfate (MLS), and Minerals-Modified Glutamate (MMG) media. Respiration profiles of the cells were recorded and analyzed, along with densitometry profiles and quenching studies of individual media components. This revealed several limiting factors and interferences impacting assay performance, which include probe quenched lifetime, instrument temporal resolution, inner filter effects (mainly by indicator dyes), probe binding to lipophilic components, and dynamic and static quenching by media components. The study allowed for the ranking of the probes based on their ruggedness, resilience to interferences and overall performance in respirometric bacterial assays. The 'shielded' probe NanO2 outperformed the established MitoXpress probe and the small molecule probes PtGlc4 and PtPEG4.

Advanced diagnostic methods for identification of bacterial foodborne pathogens: contemporary and upcoming challenges

It is a public health imperative to have safe food and water across the population. Foodborne infections are one of the primary causes of sickness and mortality in both developed and developing countries. An estimated 100 million foodborne diseases and 120 000 foodborne illness-related fatalities occur each year in India. Several factors affect foodborne illness, such as improper farming methods, poor sanitary and hygienic conditions at all levels of the food supply chain, the lack of preventative measures in the food processing industry, the misuse of food additives, as well as improper storage and handling. In addition, chemical and microbiological combinations also play a key role in disease development. But recent disease outbreaks indicated that microbial pathogens played a major role in the development of foodborne diseases. Therefore, prompt, rapid, and accurate detection of high-risk food pathogens is extremely vital to warrant the safety of the food items. Conventional approaches for identifying foodborne pathogens are labor-intensive and cumbersome. As a result, a range of technologies for the rapid detection of foodborne bacterial pathogens have been developed. Presently, many methods are available for the instantaneous detection, identification, and monitoring of foodborne pathogens, such as nucleic acid-based methods, biosensor-based methods, and immunological-based methods. The goal of this review is to provide a complete evaluation of several existing and emerging strategies for detecting food-borne pathogens. Furthermore, this review outlines innovative methodologies and their uses in food testing, along with their existing limits and future possibilities in the detection of live pathogens in food.

Listeria monocytogenes in foods-From culture identification to whole-genome characteristics

Listeria monocytogenes is an important foodborne pathogen, which is able to persist in the food production environments. The presence of these bacteria in different niches makes them a potential threat for public health. In the present review, the current information on the classical and alternative methods used for isolation and identification of L. monocytogenes in food have been described. Although these techniques are usually simple, standardized, inexpensive, and are routinely used in many food testing laboratories, several alternative molecular-based approaches for the bacteria detection in food and food production environments have been developed. They are characterized by the high sample throughput, a short time of analysis, and cost-effectiveness. However, these methods are important for the routine testing toward the presence and number of L. monocytogenes, but are not suitable for characteristics and typing of the bacterial isolates, which are crucial in the study of listeriosis infections. For these purposes, novel approaches, with a high discriminatory power to genetically distinguish the strains during epidemiological studies, have been developed, e.g., whole-genome sequence-based techniques such as NGS which provide an opportunity to perform comparison between strains of the same species. In the present review, we have shown a short description of the principles of microbiological, alternative, and modern methods of detection of L. monocytogenes in foods and characterization of the isolates for epidemiological purposes. According to our knowledge, similar comprehensive papers on such subject have not been recently published, and we hope that the current review may be interesting for research communities.

Recent advances in gold nanoparticles-based biosensors for food safety detection

Food safety issue remains a challenge worldwide. Common substances in food can pose a great threat to human health including but not limited to food borne-pathogens, heavy metals, mycotoxins, pesticides, herbicides, veterinary drugs, allergens and illegal additives. To develop rapid, low-cost, portable and on-site detection methods of those contaminants and allergens to ensure food safety, gold nanoparticles (AuNPs) of versatile shapes and morphologies such as nanorods, nanoclusters, nanoflowers, nanostars, nanocages, nanobipyramids and nanowires have been employed as probes because they possess extraordinary properties that can be used to design biosensors enabling detecting various contaminants and allergens. By means of surface modification, AuNPs can directly or indirectly sense specific targets based on different mechanisms, such as hydrogen bonds, nucleic acid hybridization, aptamer-target binding, antigen-antibody recognition, enzyme inhibition, and enzyme-mimicking activity. AuNPs can induce a distinct color change from red to blue when they transform from a monodispersed state to an aggregated state in liquid solution, which can be observed by naked eyes. If Raman molecules are functionalized on AuNPs, their aggregation will alter the interparticle distance and induce the surface-enhanced Raman scattering that can be employed for highly sensitive detection. Ultra-small AuNPs such as Au nanoclusters also feature in fluorescence that enable a fluorescent readout. The formats of AuNPs for food safety detection in real world range broadly including but not limited to films, fibers, liquid solutions, tapes, chips and lateral flow strips. In this review, recent applications of AuNPs-based biosensors for food safety detection will be discussed, mainly in the aspect of different contaminants and allergens encountered in food samples.

Point-of-Need DNA Testing for Detection of Foodborne Pathogenic Bacteria

Foodborne pathogenic bacteria present a crucial food safety issue. Conventional diagnostic methods are time-consuming and can be only performed on previously produced food. The advancing field of point-of-need diagnostic devices integrating molecular methods, biosensors, microfluidics, and nanomaterials offers new avenues for swift, low-cost detection of pathogens with high sensitivity and specificity. These analyses and screening of food items can be performed during all phases of production. This review presents major developments achieved in recent years in point-of-need diagnostics in land-based sector and sheds light on current challenges in achieving wider acceptance of portable devices in the food industry. Particular emphasis is placed on methods for testing nucleic acids, protocols for portable nucleic acid extraction and amplification, as well as on the means for low-cost detection and read-out signal amplification.

Comparison of turn-on and ratiometric fluorescent G-quadruplex aptasensor approaches for the detection of ATP

Two fluorescent aptasensor methods were developed for the detection of ATP in biochemical systems. The first method consisted of a label-free fluorescent "turn-on" approach using a guanine-rich ATP aptamer sequence and the DNA-binding agent berberine complex. In the presence of ATP, the ATP preferentially binds with its aptamer and conformationally changes into a G-quadruplex structure. The association of berberine with the G-quadruplex results in the enhancement of the fluorescence signal of the former. The detection limit of ATP was found to be 3.5 μM. Fluorescence, circular dichroism and melting temperature (T_m) experiments were carried out to confirm the binding specificity and structural changes. The second method employs the ratiometric fluorescent approach based on the Forster resonance energy transfer (FRET) for the detection of ATP using berberine along with a quencher (AuNRs, AgNPs) and a fluorophore (red quantum dots (RQDs), carbon dots (CDs)) labeled at 5' and 3' termini of the ATP-binding aptamer sequence. Upon addition of ATP and berberine, ATP specifically binds with its aptamer leading to the formation of G-quadruplex, and similarly, berberine also binds to the G-quadruplex. This leads to an enhancement of fluorescence of berberine while that of RQD and CDs were significantly quenched via FRET. The respective detection limits calculated were 3.6 μM and 3.8 μM, indicating these fluorescent aptasensor methods may be used for a wide variety of small molecules. Graphical abstract.

Label-free aptasensors based on fluorescent screening assays for the detection of Salmonella typhimurium

We report two label-free fluorescent aptasensor methods for the detection of S. typhimurium. In the first method, we have used a ''turn off'' approach in which the aptamer is first intercalated with SYBR Green I (SG), leading to a greatly enhanced fluorescence signal. The addition of S. typhimurium (approximately 1530-96938 CFU/mL), which specifically binds with its aptamer and releases SG, leads to a linear decrease in fluorescence intensity. The lowest detection limit achieved with this approach was in the range of 733 CFU/mL. In the second method, a ''turn on'' approach was designed for S. typhimurium through the Förster resonance energy transfer (FRET) between Rhodamine B (RB) and gold nanoparticles (AuNPs). When the aptamer and AuNPs were mixed with RB, the fluorescence of RB was significantly quenched via FRET. The aptamer adsorbs to the AuNP surface to protect them from salt-induced aggregation, which leads to the fluorescence quenching of RB in presence of AuNPs. Upon the addition of S. typhimurium, S. typhimurium specifically binds with its aptamer and loses the capability to stabilize AuNPs. Thus, the salt easily induces the aggregation of AuNPs, resulting in the fluorescence recovery of the quenched RB. S. typhimurium concentrations ranging from 1530 to 96938 CFU/mL with the detection limit of 464 CFU/mL was achieved with this methodology. Given these data, some insights into the molecular interactions between the aptamer and the bacterial target are provided. These aptasensor methods also may be adapted for the detection of a wide variety of targets.

A new phosphothreonine lyase electrochemical immunosensor for detecting Salmonella based on horseradish peroxidase/GNPs-thionine/chitosan

In the current study, a novel double-layer gold nanoparticles- electrochemical immunosensor electrode (DGN-EIE) immobilized with Salmonella plasmid virulence C (SpvC) antibody was developed. To increase the fixed quantity of antibodies and electrochemical signal, an electrochemical biosensing signal amplification system was utilized with gold nanoparticles-thionine-chitosan absorbing horseradish peroxidase (HRP). In addition, the SpvC monoclonal antibodies (derived from Balb/c mice) were prepared and screened with a high affinity to SpvC. To evaluate the quality of DGN-EIE, the amperometric I-t curve method was applied to determine Salmonella in PBS. The results showed that the response current had a good linear correlation with the bacterial quantity ranged from 1.0 × 10¹-5.0 × 10⁴ cfu/mL. The lowest detection limit was found at 5 cfu/mL. Furthermore, the proposed immunosensor has been demonstrated with high sensitivity, good selectivity and reproducibility. Apparently, DGN-EIE may be a very useful tool for monitoring the bacteria.

A novel aptasensor for the colorimetric detection of S. typhimurium based on gold nanoparticles

A simple, fast and convenient colorimetric aptasensor was fabricated for the detection of Salmonella typhimurium (S. typhimurium) which was based on the color change effect of gold nanoparticles (GNPs). S. typhimurium is one of the most common causes of food-associated disease. Aptamers with specific recognition toward S. typhimurium was modified to the surface of prepared GNPs. They play a role for the protection of GNPs from aggregation toward high concentrations of NaCl. With the addition of S. typhimurium, aptamers preferably combined to S. typhimurium and the protection effect was broken. With more S. typhimurium, more aptamers detached from GNPs. In such a situation, the exposed GNPs would aggregated to some extent with the addition of NaCl. The color changed from red, purple to blue which could be characterized by UV-Vis spectrophotometer. The absorbance spectra of GNPs redshifted constantly and the intensity ratio of A700/A521 changed regularly. This could be calculated for the basis of quantitative detection of S. typhimurium from 10²cfu/mL to 10⁷cfu/mL. The obtained linear correlation equation was y=0.1946x-0.2800 (R²=0.9939) with a detection limit as low as 56cfu/mL. This method is simple and rapid, results in high sensitivity and specificity, and can be used to detect actual samples.

Simultaneous detection of Staphylococcus aureus and Salmonella typhimurium using multicolor time-resolved fluorescence nanoparticles as labels

Foodborne illnesses caused by Staphylococcus aureus and Salmonella typhimurium are common public health issues worldwide, affecting both developing and developed countries. In this study, aptamers labeled with multicolor lanthanide-doped time-resolved fluorescence (TRFL) nanoparticles were used as signal probes, and immobilized by Fe₃O₄ magnetic nanoparticles were used as the capture probes. The signal probes were bonded onto the captured bacteria by the recognition of aptamer to form the sandwich-type complex. Under the optimal conditions, TRFL intensity at 544nm was used to quantify S. typhimurium (y=10,213×-12,208.92, R²=0.9922) and TRFL intensity at 615nm for S. aureus (y=4803.20×-1933.87, R²=0.9982) in the range of 10²-10⁵CFU/ml. Due to the magnetic separation and concentration of Fe₃O₄ nanoparticles, detection limits of the developed method were found to be 15, 20CFU/ml for S. typhimurium and S. aureus, respectively. The application of this bioassay in milk was also investigated, and results were consistent with those of plate-counting method. Therefore, this simple and rapid method owns a great potential in the application for the multiplex analysis in food safety.

Recombinant plasmid-based quantitative Real-Time PCR analysis of Salmonella enterica serotypes and its application to milk samples

The aim of the current study was to develop, a new, rapid, sensitive and quantitative Salmonella detection method using a Real-Time PCR technique based on an inexpensive, easy to produce, convenient and standardized recombinant plasmid positive control. To achieve this, two recombinant plasmids were constructed as reference molecules by cloning the two most commonly used Salmonella-specific target gene regions, invA and ttrRSBC. The more rapid detection enabled by the developed method (21 h) compared to the traditional culture method (90 h) allows the quantitative evaluation of Salmonella (quantification limits of 10(1)CFU/ml and 10(0)CFU/ml for the invA target and the ttrRSBC target, respectively), as illustrated using milk samples. Three advantages illustrated by the current study demonstrate the potential of the newly developed method to be used in routine analyses in the medical, veterinary, food and water/environmental sectors: I--The method provides fast analyses including the simultaneous detection and determination of correct pathogen counts; II--The method is applicable to challenging samples, such as milk; III--The method's positive controls (recombinant plasmids) are reproducible in large quantities without the need to construct new calibration curves.

Gold nanoparticles enhanced SERS aptasensor for the simultaneous detection of Salmonella typhimurium and Staphylococcus aureus

Salmonella typhimurium and Staphylococcus aureus are most common causes of food-associated disease. A Raman based biosensor was developed for S. typhimurium and S. aureus detection simultaneously. The biosensor was based on nanoparticles enhanced Raman intensity and the specific recognition of aptamer. The Raman signal probe and the capture probe are built. Gold nanoparticles (GNPs) modified with Raman molecules (Mercaptobenzoic acid and 5,5'-Dithiobis(2-nitrobenzoic acid)) and aptamer are used as the signal probe for S. typhimurium and S. aureus, respectively. Fe3O4 magnetic gold nanoparticles (MGNPs) immobilized with both aptamer of S. typhimurium and S. aureus are used as the capture probe. When S. typhimurium and S. aureus are added in the reaction system, the capture probe will capture the target bacteria through the specific binding effect of aptamer. And then the signal probe will be connected to the bacteria also by the effect of aptamer to form the sandwich like detection structure. The Raman intensified spectrum was measured to quantify S. typhimurium and S. aureus. Under optimal conditions, the SERS intensity of MBA at 1582 cm(-1) are used to measure S. typhimurium (y=186.4762+704.8571x, R(2)=0.9921) and the SERS intensity of DNTB at 1333 cm(-1) are used to measure S. aureus (y=135.2381+211.4286x, R(2)=0.9946) in the range of 10(2)-10(7) cfu mL(-1). The LOD is 35 cfu mL(-1) for S. aureus and 15 cfu mL(-1) for S. typhimurium. This method is simple and rapid, results in high sensitivity and specificity, and can be used to detect actual samples.

Rapid methods for the detection of foodborne bacterial pathogens: principles, applications, advantages and limitations

The incidence of foodborne diseases has increased over the years and resulted in major public health problem globally. Foodborne pathogens can be found in various foods and it is important to detect foodborne pathogens to provide safe food supply and to prevent foodborne diseases. The conventional methods used to detect foodborne pathogen are time consuming and laborious. Hence, a variety of methods have been developed for rapid detection of foodborne pathogens as it is required in many food analyses. Rapid detection methods can be categorized into nucleic acid-based, biosensor-based and immunological-based methods. This review emphasizes on the principles and application of recent rapid methods for the detection of foodborne bacterial pathogens. Detection methods included are simple polymerase chain reaction (PCR), multiplex PCR, real-time PCR, nucleic acid sequence-based amplification (NASBA), loop-mediated isothermal amplification (LAMP) and oligonucleotide DNA microarray which classified as nucleic acid-based methods; optical, electrochemical and mass-based biosensors which classified as biosensor-based methods; enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay which classified as immunological-based methods. In general, rapid detection methods are generally time-efficient, sensitive, specific and labor-saving. The developments of rapid detection methods are vital in prevention and treatment of foodborne diseases.

Rapid methods for the detection of foodborne bacterial pathogens: principles, applications, advantages and limitations

The incidence of foodborne diseases has increased over the years and resulted in major public health problem globally. Foodborne pathogens can be found in various foods and it is important to detect foodborne pathogens to provide safe food supply and to prevent foodborne diseases. The conventional methods used to detect foodborne pathogen are time consuming and laborious. Hence, a variety of methods have been developed for rapid detection of foodborne pathogens as it is required in many food analyses. Rapid detection methods can be categorized into nucleic acid-based, biosensor-based and immunological-based methods. This review emphasizes on the principles and application of recent rapid methods for the detection of foodborne bacterial pathogens. Detection methods included are simple polymerase chain reaction (PCR), multiplex PCR, real-time PCR, nucleic acid sequence-based amplification (NASBA), loop-mediated isothermal amplification (LAMP) and oligonucleotide DNA microarray which classified as nucleic acid-based methods; optical, electrochemical and mass-based biosensors which classified as biosensor-based methods; enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay which classified as immunological-based methods. In general, rapid detection methods are generally time-efficient, sensitive, specific and labor-saving. The developments of rapid detection methods are vital in prevention and treatment of foodborne diseases.

Development of ssDNA aptamers for the sensitive detection of Salmonella typhimurium and Salmonella enteritidis

Salmonella enterica subsp. enterica ser. enteritidis and Salmonella enterica subsp. enterica ser. typhimurium are the most common and severe food-borne pathogens responsible for causing salmonellosis in humans and animals. The development of an early and ultra-sensitive detection system is the first critical step in controlling this disease. To accomplish this, we used the cell systematic evolution of ligands by exponential enrichment (Cell-SELEX) technique to identify single-stranded DNA (ssDNA) aptamers to be used as detection probes that can specifically bind to S. enteritidis and S. typhimurium. A total of 12 target-specific ssDNA aptamers were obtained through ten rounds of Cell-SELEX under stringent selection conditions, and negative selection further enhanced the selectivity among these aptamers. Aptamer specificity was investigated using the gram-negative bacteria E. coli and P. aeruginosa and was found to be much higher towards S. enteritidis and S. typhimurium. Importantly, three candidate aptamers demonstrated higher binding affinities and the dissociation constants (Kd) were found to be in the range of nanomolar to submicromolar levels. Furthermore, individual aptamers were conjugated onto polyvalent directed aptamer polymer, which led to 100-fold increase in binding affinity compared to the individual aptamers alone. Taken together, this study reports the identification of higher affinity and specificity ssDNA aptamers (30mer), which may be useful as capture and detection probes in biosensor-based detection systems for salmonellosis.

Detection of Salmonella in chicken meat by insulated isothermal PCR

Consumption of Salmonella-contaminated foods, such as poultry and fresh eggs, is known to be one of the main causes of salmonellosis. Conventional PCR methods, including real-time PCR for rapid detection of Salmonella, in general require skilled technicians and costly instruments. A recently developed novel convective PCR, insulated isothermal PCR (iiPCR), is carried out in polycarbonate capillary tubes. In this study, we designed TaqMan probes and PCR primers based on the yrfH gene encoding a heat shock protein for the iiPCR detection of Salmonella in chicken meat samples. The TaqMan probe was labeled with 6-carboxyfluorescein and 6-carboxytetramethylrhodamine at the 5' and 3' ends, respectively. The PCR amplicon was 133 bp. A typical run of this iiPCR assay was completed within 1 h. Specific PCR products were obtained for 148 strains representing 49 serotypes of Salmonella tested. Under the same conditions, false-positive results were not obtained for 98 non-Salmonella strains tested, including strains of Enterobacteriaceae closely related to Salmonella. For chicken meat samples, with a 5-h enrichment step Salmonella at as low as 10⁰ CFU/g of poultry meat could be detected. Because the amplification signals from the probes are detectable at 520 nm, identification of the PCR products by gel electrophoresis is not required. Compared with conventional PCR, the iiPCR system requires less expertise and provides an economical, reliable, and rapid tool for result interpretation. Detection results can be obtained within 8 h, including the enrichment and DNA extraction steps.

Application of Molecular Beacons in Real-Time PCR

Real-time PCR or quantitative PCR (QPCR) is a powerful technique that allows measurement of PCR product while the amplification reaction proceeds. It incorporates the fluorescent element into conventional PCR as the calculation standard to provide a quantitative result. In this sense, fluorescent chemistry is the key component in QPCR. Till now, two types of fluorescent chemistries have been adopted in the QPCR systems: one is nonspecific probe and the other is specific. As a brilliant invention by Kramer et al. in 1996, molecular beacon is naturally suited as the reporting element in real-time PCR and has been adapted for many molecular biology applications. In this chapter, we briefly introduce the working principle of QPCR and overview different fluorescent chemistries, and then we focus on the applications of molecular beacons-like gene expression study, single-nucleotide polymorphisms and mutation detection, and pathogenic detection.

New developments in shockwave technology intended for meat tenderization: Opportunities and challenges. A review

Meat tenderness is an important quality parameter determining consumer acceptance and price. Meat tenderness is difficult to ensure in the global meat chain because the production systems are not always aiming at this purpose (ex.: cattle derived from milk production) and by the existence within the carcass of "tough" primals. Different methods can be used by the meat industry to improve meat tenderness each with its advantages and drawbacks. The application of hydrodynamic pressure or shockwaves has showed outstanding improvements by reducing the Warner Bratzler Shear Force by 25% or more. However, the technology has not penetrated into the market as first systems were based on the use of explosives and further developments seemed to lack the robustness to fulfill industrial requirements. The present paper describes the main challenges to construct a prototype for the continuous treatment of meat by shockwaves based on electrical discharges under water. Finally, improvements on the tenderness of meat by using the novel prototype are presented.

Detection of Salmonella enterica serovar Enteritidis using real time PCR, immunocapture assay, PNA FISH and standard culture methods in different types of food samples

Several methods for the rapid and specific detection of Salmonella in food samples have been described. Here, we compare 4 of those methods in terms of assay time, procedure complexity, detection limit, sensitivity, specificity and accuracy. Milk, eggs and mayonnaise samples were artificially contaminated with Salmonella enterica serovar Enteritidis cell concentrations ranging from 1×10(-2) to 1×10(2) CFU per 25 g or ml of food. Samples were then pre-enriched and analyzed by either: i) real-time PCR, using the iQ-Check Salmonella kit; ii) immunocapture, using the RapidChek SELECT Salmonella; iii) a peptide nucleic acid fluorescence in situ hybridization (PNA FISH) method and iv) the traditional bacteriological method ISO 6579:2002. All methods were able to detect Salmonella in the different types of food matrixes and presented a similar detection level of 1CFU per 25 g or ml of food sample. The immunocapture and the PNA FISH methods proved to be very reliable, as their results were 100% in agreement with the ISO method. However, real-time PCR presented a significant number of false positives, which resulted in a specificity of 55.6% (CI 95%, 31.3-77.6) and an accuracy of 82.2% (CI 95%, 63.2-91.4) for this method. Sensitivity was 100% since no false negative results were observed. In conclusion, the implementation of these molecular techniques, mainly the immunocapture and PNA-FISH methods, provides a reliable and less time-consuming alternative for the detection of Salmonella spp. in food samples.

Salmonella detection in poultry meat and meat products by the Vitek immunodiagnostic assay system easy Salmonella method, a LightCycler polymerase chain reaction system, and the International Organization for Standardization method 6579

This study was conducted to evaluate the capability of the Vitek immunodiagnostic assay system easy Salmonella (VIDAS ESLM) method and a specific real-time PCR system (LightCycler, LCPCR) to complement the International Organization for Standardization Method 6579 (ISO) in detecting Salmonella from a total of 105 naturally contaminated samples comprised of poultry meat and poultry meat products. The detection limit of ISO and LCPCR was 9 cfu/mL for both poultry meat and poultry meat products, whereas that of VIDAS ESLM with both sample types was determined to be 90 cfu/mL. Twelve (33.33%), 11 (30.55%), and 18 (50.00%) out of 36 poultry meat samples were positive for Salmonella by ISO, VIDAS ESLM, and LCPCR, respectively. Salmonella detection rates from poultry meat products were 5.80% for ISO and 8.69% for LCPCR, whereas none of these products tested positive by VIDAS ESLM. In poultry meat samples, VIDAS ESLM and LCPCR detection results were in substantial agreement with ISO, with the relative accuracy, sensitivity, and specificity rates of 97.2, 91.7, and 100%, respectively, for VIDAS ESLM and 83.3, 100, and 75%, respectively, for LCPCR. This is the first report on the evaluation of both VIDAS ESLM and LCPCR to complement ISO for the rapid detection of Salmonella in poultry meat and meat products. We determined that both VIDAS ESLM and LCPCR have the potential to complement the ISO standard culture method in the rapid screening of Salmonella from naturally contaminated poultry meats. For the poultry meat products, VIDAS ESLM and LCPCR can be used for rapid primary screening, and they should be complemented absolutely by ISO. Although LCPCR can preferentially be used for initial screening poultry meat products, the results should definitely be confirmed by ISO. Also, the VIDAS ESLM did not seem to be a suitable method for detecting Salmonella in poultry meat products.

Accuracy and sensitivity of commercial PCR-based methods for detection of Salmonella enterica in feed

The present study compared the performance of commercial PCR-based Salmonella enterica detection methods (BAX System Q7, the iQ-Check Salmonella II kit, and the TaqMan Salmonella enterica detection kit) with culture-based methods (modified semisolid Rappaport-Vassiliadis [MSRV] and NMKL71) in spiked and naturally contaminated samples of feed mill scrapings (FMS), palm kernel meal (PKM), pelleted feed (PF), rape seed meal (RSM), soybean meal (SM), and wheat grain (WG). When results from the various feeds were compared, the number of Salmonella enterica CFU/25 g required to produce a positive were as follows: PKM > FMS = WG > RSM = SM = PF. These data are similar to those developed in earlier studies with culture-based Salmonella detection methods. PCR-based methods were performed similarly to culture-based methods, with respect to sensitivity and specificity. However, many PCR positives could not be confirmed by Salmonella isolation and for that reason the evaluated methods were found to be suitable only when rapid results were paramount. Nevertheless, PCR-based methods cannot presently replace culture-based methods when typing information is required for tracing studies or epidemiological investigations. The observed difference in detection levels is a potential problem when prevalence data are compared as well as when feed ingredients are tested for conformance with microbiological criteria. This paper also presents a statistical model that describes the detection probability when different levels (CFU) of Salmonella contamination are present in feed materials.

Real-time fluorescent quantitative immuno-PCR method for determination of fluoranthene in water samples with a molecular beacon

A reliable and sensitive competitive real-time fluorescent quantitative immuno-PCR (RTFQ-IPCR) assay using a molecular beacon was developed for the determination of trace fluoranthene (FL) in the environment. Under optimized assay conditions, FL can be determined in the concentration range from 1 fg/mL to 100 ng/mL, withy = 0.194x + 7.859, and a correlation coefficient of 0.967 was identified, with a detection limit of 0.6 fg/mL. Environmental water samples were successfully analyzed, recovery was between 90% and 116%, with intra-day relative standard deviation (RSD) of 6.7%-12.8% and inter-day RSD of 8.4%-15.2%. The results obtained from RTFQ-IPCR were confirmed by ELISA, showing good accuracy and suitability to analyze FL in field samples. As a highly sensitive method, the molecular beacon-based RTFQ-IPCR is acceptable and promising for providing reliable test results to make environmental decisions.

Detection of trace anthracene in soil samples with real-time fluorescence quantitative immuno-PCR using a molecular beacon probe

We developed a highly sensitive and robust real-time fluorescence quantitative immuno-PCR (RTFQ-IPCR) method which uses molecular beacon (MB) probe to detect trace anthracene in the environment. This method was performed on serial dilutions of known anthracene concentrations equivalent to 10-fold dilutions of 10fg/mL to 100pg/mL. We obtained a linear relationship between 10fg/mL and 100pg/mL, with y=0.684x+13.221. A correlation coefficient of 0.994 was also identified, with a detection limit of 4.5fg/mL. After investigating the presence of anthracene in soil samples via RTFQ-IPCR, the obtained concentrations were confirmed by ELISA to be correct and believable, with the recovery ratio ranging from 82% to 112.5%. Based on its sensitivity and reproducibility, MB-based RTFQ-IPCR was found to be acceptable for use in on-site field tests to provide rapid, quantitative, and reliable test results for making environmental decisions.

Molecular beacon-based real-time PCR detection of primary isolates of Salmonella Typhimurium and Salmonella Enteritidis in environmental and clinical samples

Background

A fast and simple two-step multiplex real-time PCR assay has been developed to replace the traditional, laborious Salmonella serotyping procedure. Molecular beacons were incorporated into the assay as probes for target DNA. Target sequences were regions of the invA, prot6E and fliC genes specific for Salmonella spp. Salmonella Enteritidis and Salmonella Typhimurium, respectively, the two most clinically relevant serotypes. An internal amplification positive control was included in the experiment to ensure the optimal functioning of the PCR and detect possible PCR inhibition. Three sets of primers were used for the amplification of the target sequences. The results were compared to those of the Kauffmann-White antigenic classification scheme.

Results

The assay was 100% sensitive and specific, correctly identifying all 44 Salmonella strains, all 21 samples of S. Enteritidis and all 17 samples of S. Typhimurium tested in this work. Therefore, the entire experiment had specificity and sensitivity of 100%. The detection limit was down to 10 copies of DNA target per 25 μl reaction.

Conclusion

The assay can amplify and analyse a large number of samples in approximately 8 hours, compared to the 4 to 5 days conventional identification takes, and is thus considered a very promising method for detecting the two major serotypes of Salmonella quickly and accurately from clinical and environmental samples.

Validation of a same-day real-time PCR method for screening of meat and carcass swabs for Salmonella

BACKGROUND

One of the major sources of human Salmonella infections is meat. Therefore, efficient and rapid monitoring of Salmonella in the meat production chain is necessary. Validation of alternative methods is needed to prove that the performance is equal to established methods. Very few of the published PCR methods for Salmonella have been validated in collaborative studies. This study describes a validation including comparative and collaborative trials, based on the recommendations from the Nordic organization for validation of alternative microbiological methods (NordVal) of a same-day, non-commercial real-time PCR method for detection of Salmonella in meat and carcass swabs.

RESULTS

The comparative trial was performed against a reference method (NMKL-71:5, 1999) using artificially and naturally contaminated samples (60 minced veal and pork meat samples, 60 poultry neck-skins, and 120 pig carcass swabs). The relative accuracy was 99%, relative detection level 100%, relative sensitivity 103% and relative specificity 100%. The collaborative trial included six laboratories testing minced meat, poultry neck-skins, and carcass swabs as un-inoculated samples and samples artificially contaminated with 1-10 CFU/25 g, and 10-100 CFU/25 g. Valid results were obtained from five of the laboratories and used for the statistical analysis. Apart from one of the non-inoculated samples being false positive with PCR for one of the laboratories, no false positive or false negative results were reported. Partly based on results obtained in this study, the method has obtained NordVal approval for analysis of Salmonella in meat and carcass swabs. The PCR method was transferred to a production laboratory and the performance was compared with the BAX Salmonella test on 39 pork samples artificially contaminated with Salmonella. There was no significant difference in the results obtained by the two methods.

CONCLUSION

The real-time PCR method for detection of Salmonella in meat and carcass swabs was validated in comparative and collaborative trials according to NordVal recommendations. The PCR method was found to perform well. The test is currently being implemented for screening of several hundred thousand samples per year at a number of major Danish slaughterhouses to shorten the post-slaughter storage time and facilitate the swift export of fresh meat.

Rapid quantification of Salmonella typhimurium inoculated to meat products by real-time PCR

The objective of this study was to use a 5'-nuclease (TaqMan) real-time PCR method with primers and probe specific to the spaQ gene as a rapid approach to quantitatively determine Salmonella Typhimurium. The result showed that the correlation coefficient between real-time PCR estimates and bovine serum albumin (BSA) plate counts of S. Typhimurium was 0.99, independently of 10(5)-fold numbers of bystander Escherichia coli O157:H7 or total viable counts. The sensitivity of the real-time quantitative PCR assay was 10 CFU/mL for pure S. Typhimurium culture without enrichment. A known number of S. Typhimurium target cells were inoculated to dumpling fillings and chicken nuggets and DNA was extracted for real-time PCR analysis. The sensitivity was 60 CFU/g for S. Typhimurium inoculated to the food samples without any preceding procedure of enrichment. The duration of the entire experiment from DNA isolation and purification to PCR amplification was less than 12 h. This study demonstrated that real-time PCR is a rapid and reliable technique for quantifying S. Typhimurium possessing the spaQ gene in pure culture and in meat products.

Rapid real-time PCR assay for detecting Salmonella in raw and ready-to-eat meats

A real-time PCR assay was evaluated for the rapid detection (10 h) of Salmonella in meats using molecular beacon probes available as a commercial kit (iQ-Check, Bio-Rad laboratories). Raw (chicken, pork) and ready-to-eat (RTE) meats were artificially contaminated with Salmonella enterica serovar Typhimurium at the estimated level of 2 to 4 cells per 25 g. After 8 h of pre-enrichment in buffered peptone water, a molecular beacon-based PCR assay was performed to detect contamination in raw and RTE meats. The sensitivity and accuracy of the assay were compared with the conventional USDA microbiological procedure. Comparative evaluation of the USDA procedure with the rapid PCR assay for meat samples (n = 63) revealed 1 false negative pork sample with the PCR assay. All uninoculated controls (n = 34) but one sample were negative by both the 10-h PCR assay and the USDA procedure. Developing rapid pathogen detection methods with shorter pre-enrichment times (8-h) and real-time data monitoring capabilities will benefit the industry in preventing recall of contaminated meats by stopping the contaminated products from being introduced into the marketplace.

Detection of naphthalene by real-time immuno-PCR using molecular beacon

A rapid and quantitative technique is urgently needed in detecting toxicological and carcinogenic polycyclic aromatic hydrocarbons (PAHs) in the environment. Using a molecular beacon (MB), this study aimed at detecting the presence of naphthalene through an assay developed via a highly sensitive and robust, real-time fluorescent quantitative immuno-PCR (FQ-IPCR), which was then performed on serial dilutions of known naphthalene concentrations equivalent to 10-fold dilutions of 1-10(4) fg/mL. A correlation coefficient of 0.996 was identified, and a linear relationship between 1 fg/mL and 10 pg/mL, with y = 1.392x + 11.188, was obtained. A trace amount (1 fg/mL) of naphthalene congeners could be detected using this method. Five water samples were then used for validation, the results of which were further confirmed through a conventional enzyme-linked immuno sorbent assay (ELISA). Based on sensitivity and reproduction, the MB-based FQ-IPCR technique is a promising tool for monitoring environmental endocrine disruptors.

Detection of Salmonella species in foodstuffs

Conventional methods to detect Salmonella spp. in foodstuffs may take up to 1 wk. Methods for pathogen detection are required. Real-time detection of Salmonella spp. will broaden our ability to screen large number of samples in a short time. This chapter describes a step-by-step procedure using an oligonucleotide probe that becomes fluorescent upon hybridization to the target DNA (Molecular Beacon; MB) in a real-time polymerase chain reaction (PCR) assay. The capability of the assay to detect Salmonella species from artificially inoculated fresh- and fresh-cut produce as well as ready-to-eat meats is demonstrated. The method uses internal positive and negative controls which enable researchers to detect false-negative PCR results. The procedure uses the buffered peptone water for the enrichment of Salmonella spp. and successfully detects the pathogen at low level of contamination (2-4 cells/25 g) in <24 h.

Development of real-time PCR methods for the rapid detection of low concentrations of Gluconobacter and Gluconacetobacter species in an electrolyte replacement drink

AIMS

To develop a rapid real-time polymerase chain reaction (PCR) method to detect Gluconobacter and Gluconacetobacter species in electrolyte replacement drinks.

METHODS AND RESULTS

Samples of electrolyte replacement drinks were artificially contaminated with Gluconobacter species and then filtered to collect cells. DNA was extracted from the filters and analysed by real-time PCR on the ABI Prism 7000 system, using commercial detection kits for lactic and acetic acid bacteria. In addition, specific primers and Taqman probe were designed and used for the detection of seven Gluconobacter and Gluconacetobacter species. All the assays tested demonstrated a linear range of quantification over four orders of magnitude, suggesting detection levels down to 1 CFU ml(-1) in the original drink.

CONCLUSIONS

A real-time PCR method was developed to detect low concentrations of Gluconobacter and Gluconacetobacter sp. in an electrolyte replacement drink.

SIGNIFICANCE AND IMPACT OF THE STUDY

Real-time PCR methods allow a rapid, high throughput and automated procedure for the detection of food spoilage organisms. The real-time PCR assay described is as sensitive as the conventional method that involves pre-enrichment, enumeration on a selective agar (typically malt extract agar) and identification with a differential medium (typically Wallerstein nutrient agar). The real-time PCR assay also provides a more rapid rate of detection, with results in less than 24 h following enrichment for Gluconobacter and Gluconacetobacter species.