Rapid detection of stressed Salmonella spp. in dairy and egg products using immunomagnetic separation and PCR

Use of uncoated magnetic beads to capture Mycobacterium smegmatis and Mycobacterium avium paratuberculosis prior detection by mycobacteriophage D29 and real-time-PCR

Uncoated tosyl-activated magnetic beads were evaluated to capture Mycobacterium smegmatis and Mycobacterium avium subspecies paratuberculosis (MAP) from spiked feces, milk, and urine. Centrifugation and uncoated magnetic beads recovered more than 99% and 93%, respectively, of 1.68 × 10⁷ CFU/mL, 1.68 × 10⁶ CFU/mL and 1.68 × 10⁵ CFU/mL M. smegmatis cells resuspended in phosphate buffer saline. The use of magnetic beads was more efficient to concentrate cells from 1.68 × 10⁴ CFU/mL of M. smegmatis than centrifugation. Likewise, the F57-qPCR detection of MAP cells was different whether they were recovered by beads or centrifugation; cycle threshold (Ct) was lower (p < 0.05) for the detection of MAP cells recovered by beads than centrifugation, indicative of greater recovery. Magnetic separation of MAP cells from milk, urine, and feces specimens was demonstrated by detection of F57 and IS900 sequences. Beads captured no less than 10⁹ CFU/mL from feces and no less than 10⁴ CFU/mL from milk and urine suspensions. In another detection strategy, M. smegmatis coupled to magnetic beads were infected by mycobacteriophage D29. Plaque forming units were observed after 24 h of incubation from urine samples containing 2 × 10⁵ and 2 × 10³ CFU/mL M. smegmatis. The results of this study provide a promising tool for diagnosis of tuberculosis and Johne's disease.

Preparation of immunomagnetic beads coupled with a rhodamine hydrazine immunosensor for the detection of Mycobacterium avium subspecies paratuberculosis in bovine feces, milk, and colostrum

The aim of this study was to develop and evaluate a method for detecting Mycobacterium avium ssp. paratuberculosis (MAP) bacteria in bovine fecal, milk, and colostrum samples using immunomagnetic beads (IMB) and a rhodamine hydrazone immunosensor. Immunomagnetic beads were prepared by using purified antibodies from hyperimmunized sera that were coupled to Fe nanoparticles with diethylene triamine pentaacetic acid (DTPA) or ethyl (dimethyl aminopropyl) carbodiimide (EDC)-N-hydroxy succinimide (NHS) as linkers. Rhodamine hydrazone particles were synthesized and coupled to IgY anti-MAP antibodies using DTPA or EDC-NHS linkers. Separation efficiency of the IMB was tested on bovine fecal, milk, and colostrum samples experimentally contaminated with MAP. The studied methods were evaluated on their ability to detect MAP and separate bacteria in complex mediums. The ELISA results indicated 95% efficacy in antibody coupling to IMB, with the DTPA-IMB method being more efficient than the EDC-NHS-IMB method. By using the DTPA-IMB method, MAP bacteria were successfully recovered from fecal, milk, and colostrum samples. The DTPA-IMB method used in combination with the rhodamine hydrazone immunosensor had a limit of detection equal to 30 and 30,000 MAP cells/mL using chromogenic and fluorescent properties, respectively. Combining the DTPA-IMB separation method with the rhodamine hydrazone immunosensor provides a fast, sensitive, and cost-beneficial method for detecting MAP in bovine feces, milk, and colostrum.

Phage Amplification Assay for Detection of Mycobacterial Infection: A Review

An important prerequisite for the effective control, timely diagnosis, and successful treatment of mycobacterial infections in both humans and animals is a rapid, specific, and sensitive detection technique. Culture is still considered the gold standard in the detection of viable mycobacteria; however, mycobacteria are extremely fastidious and slow-growing microorganisms, and therefore cultivation requires a very long incubation period to obtain results. Polymerase Chain Reaction (PCR) methods are also frequently used in the diagnosis of mycobacterial infections, providing faster and more accurate results, but are unable to distinguish between a viable and non-viable microorganism, which results in an inability to determine the success of tuberculosis patient treatment or to differentiate between an active and passive infection of animals. One suitable technique that overcomes these shortcomings mentioned is the phage amplification assay (PA). PA specifically detects viable mycobacteria present in a sample within 48 h using a lytic bacteriophage isolated from the environment. Nowadays, an alternative approach to PA, a commercial kit called Actiphage™, is also employed, providing the result within 6–8 h. In this approach, the bacteriophage is used to lyse mycobacterial cells present in the sample, and the released DNA is subsequently detected by PCR. The objective of this review is to summarize information based on the PA used for detection of mycobacteria significant in both human and veterinary medicine from various kinds of matrices.

Impedimetric Biosensor Based on a Hechtia argentea Lectin for the Detection of Salmonella spp

A sensitive electrochemical detection method for Salmonella spp. was described, based on the use of Hechtia argentea lectin immobilised on a screen-printed gold electrode. The lectin was extracted from Hechtia argentea, a plant belonging to the Bromeliaceae family. The lectin with molecular weight near 27.4 kDa showed selectivity towards D-mannose, contained on the lipopolysaccharide cell wall of Salmonella spp. Carbohydrate selectivity of the lectin was measured as a change in impedance with respect to concentration. The binding of the bacteria to the biosensor surface increased impedance with increasing concentrations of Salmonella spp., achieving a linear range of detection of 15–2.57 × 107 CFU mL−1, with a limit of detection of 5 CFU mL−1. Increases in impedance were measured using electrochemical impedance spectroscopy and analysed using Nyquist plots. The biosensor was applied in analysis of hen egg samples, and the results were consistent with those obtained using the official analysis methodology.

Detection of Salmonella Typhimurium in Romaine Lettuce Using a Surface Plasmon Resonance Biosensor

Leafy vegetables have been associated with high-profile outbreaks causing severe illnesses. Timely and accurate identification of potential contamination is essential to ensure food safety. A surface plasmon resonance (SPR) assay has been developed for the detection of Salmonella Typhimurium in leafy vegetables. The assay utilizes a pair of well characterized monoclonal antibodies specific to the flagellin of S. Typhimurium. Samples of romaine lettuce contaminated with S. Typhimurium at different levels (between 0.9 and 5.9 log cfu/g) were pre-enriched in buffered peptone water. Three SPR assay formats, direct assay, sequential two-step sandwich assay, and pre-incubation one-step sandwich assay were evaluated. All three assay formats detect well even at a low level of contamination (0.9 log cfu/g). The SPR assay showed a high specificity for the detection of S. Typhimurium in the presence of other commensal bacteria in the romaine lettuce samples. The results also suggested that further purification of flagellin from the sample preparation using immunomagnetic separation did not improve the detection sensitivity of the SPR assay. The functional protocol developed in this study can be readily used for the detection of S. Typhimurium in leafy vegetables with high sensitivity and specificity.

Microbial separation from a complex matrix by a hand-held microfluidic device

Through a simple chemical activation of biomolecules present in the outer structures of microbial cells, microorganisms can be rapidly isolated on gold-coated surfaces in a microfluidic device with over 99% capture efficiency. Bacterial and fungal cells can be selectively captured, concentrated and retrieved for further analysis.

Magnetic Separation Methods for the Detection of Mycobacterium avium subsp. paratuberculosis in Various Types of Matrices: A Review

The main reasons to improve the detection of Mycobacterium avium subsp. paratuberculosis (MAP) are animal health and monitoring of MAP entering the food chain via meat, milk, and/or dairy products. Different approaches can be used for the detection of MAP, but the use of magnetic separation especially in conjunction with PCR as an end-point detection method has risen in past years. However, the extraction of DNA which is a crucial step prior to PCR detection can be complicated due to the presence of inhibitory substances. Magnetic separation methods involving either antibodies or peptides represent a powerful tool for selective separation of target bacteria from other nontarget microorganisms and inhibitory sample components. These methods enable the concentration of pathogens present in the initial matrix into smaller volume and facilitate the isolation of sufficient quantities of pure DNA. The purpose of this review was to summarize the methods based on the magnetic separation approach that are currently available for the detection of MAP in a broad range of matrices.

Generation and characterization of nucleic acid aptamers targeting the capsid P domain of a human norovirus GII.4 strain

Human noroviruses (NoV) are the leading cause of acute viral gastroenteritis worldwide. Significant antigenic diversity of NoV strains has limited the availability of broadly reactive ligands for design of detection assays. The purpose of this work was to produce and characterize single stranded (ss)DNA aptamers with binding specificity to human NoV using an easily produced NoV target-the P domain protein. Aptamer selection was done using SELEX (Systematic Evolution of Ligands by EXponential enrichment) directed against an Escherichia coli-expressed and purified epidemic NoV GII.4 strain P domain. Two of six unique aptamers (designated M1 and M6-2) were chosen for characterization. Inclusivity testing using an enzyme-linked aptamer sorbent assay (ELASA) against a panel of 14 virus-like particles (VLPs) showed these aptamers had broad reactivity and exhibited strong binding to GI.7, GII.2, two GII.4 strains, and GII.7 VLPs. Aptamer M6-2 exhibited at least low to moderate binding to all VLPs tested. Aptamers significantly (p<0.05) bound virus in partially purified GII.4 New Orleans outbreak stool specimens as demonstrated by ELASA and aptamer magnetic capture (AMC) followed by RT-qPCR. This is the first demonstration of human NoV P domain protein as a functional target for the selection of nucleic acid aptamers that specifically bind and broadly recognize diverse human NoV strains.

Enumeration of salmonellae in table eggs, pasteurized egg products, and egg-containing dishes by using quantitative real-time PCR

Salmonellae are a major cause of food-borne outbreaks in Europe, with eggs and egg products being identified as major sources. Due to the low levels of salmonellae in eggs and egg products, direct quantification is difficult. In the present study, enrichment quantitative real-time PCR (qPCR) was employed for enumeration of salmonellae in different matrices: table eggs, pasteurized egg products, and egg-containing dishes. Salmonella enterica serovar Enteritidis and S. enterica serovar Tennessee were used to artificially contaminate these matrices. The results showed a linear regression between the numbers of salmonellae and the quantification cycle (Cq) values for all matrices used, with the exception of pasteurized egg white. Standard curves were constructed by using both stationary-phase cells and heat-stressed cells, with similar results. Finally, this method was used to evaluate the fate of salmonellae in two egg-containing dishes, long egg and tiramisu, at abused refrigeration temperatures, and results indicated the growth of bacteria over a 1-week period. In conclusion, enrichment qPCR was shown to be reliable for enumeration of salmonellae in different egg products.

Maximizing capture efficiency and specificity of magnetic separation for Mycobacterium avium subsp. paratuberculosis cells

In order to introduce specificity for Mycobacterium avium subsp. paratuberculosis prior to a phage amplification assay, various magnetic-separation approaches, involving either antibodies or peptides, were evaluated in terms of the efficiency of capture (expressed as a percentage) of M. avium subsp. paratuberculosis cells and the percentage of nonspecific binding by other Mycobacterium spp. A 50:50 mixture of MyOne Tosylactivated Dynabeads coated with the chemically synthesized M. avium subsp. paratuberculosis-specific peptides biotinylated aMp3 and biotinylated aMptD (i.e., peptide-mediated magnetic separation [PMS]) proved to be the best magnetic-separation approach for achieving 85 to 100% capture of M. avium subsp. paratuberculosis and minimal (<1%) nonspecific recovery of other Mycobacterium spp. (particularly if beads were blocked with 1% skim milk before use) from broth samples containing 10(3) to 10(4) CFU/ml. When PMS was coupled with a recently optimized phage amplification assay and used to detect M. avium subsp. paratuberculosis in 50-ml volumes of spiked milk, the mean 50% limit of detection (LOD(50)) was 14.4 PFU/50 ml of milk (equivalent to 0.3 PFU/ml). This PMS-phage assay represents a novel, rapid method for the detection and enumeration of viable M. avium subsp. paratuberculosis organisms in milk, and potentially other sample matrices, with results available within 48 h.

Preparation of cellulose magnetic microspheres with "the smallest critical size" and their application for microbial immunocapture

The goal of this paper is to introduce a universal method for quantitative control of the particle size of magnetic cellulose microspheres (MCMS) and to produce an optimal antibody absorption capability as an aid in the research of new applications of MCMS in immunomagnetic capture. In this study, "the smallest critical size theory" (TSCS) was proposed, tested, and confirmed by IgG-carrying capability measurements, magnetic response analysis, immunomagnetic capture, and PCR identification of bacteria. A Gaussian expression was proposed and used to guide the preparation of MCMS of the smallest critical size (SCS). The results showed that the diameter of the SCS of MCMS in this study was 5.82 mum, while the IgG absorption capability of the MCMS with SCS was 186.8 mg/mL. In addition, its high sensitivity and the efficiency of immunomagnetic capture of Salmonella bacteria exhibited another new application for MCMS.

Real-Time Reverse Transcriptase PCR for the Rapid and Sensitive Detection of Salmonella Typhimurium from Pork

Reverse transcriptase PCR (RT-PCR) detects the presence of mRNA and has a greater potential for detecting viable pathogens than do DNA-based PCR assays, with improved speed and sensitivity compared with traditional methods. Our objective was to rapidly and sensitively detect Salmonella Typhimurium from pork within two 8-h work shifts using a SYBR Green I real-time RT-PCR (rt-RT-PCR) assay. Pork chop and sausage samples (25 g) were inoculated with 108 to 100 CFU of Salmonella Typhimurium and stomached in 225 ml of tetrathionate broth. Serial dilutions were spread plated on xylose lysine Tergitol 4 agar either immediately or after 10 h of selective preenrichment or preenrichment followed by 12 h of selective enrichment (for stressed cells) at 37°C for standard cultural enumeration. RNA was extracted using the TRIzol method. The rt-RT-PCR assay was carried out in a Bio-Rad iCycler using a SYBR Green I one-step RT-PCR kit and Salmonella specific invA gene primers with an internal amplification control (IAC). The PCR was followed by melting temperature (Tm) analysis to determine specific Salmonella invA (Tm = 87.5°C) and IAC (Tm = 82°C) products. Improved Salmonella detection up to 101 CFU/25 g of pork and 100 CFU/25 g of sausages was obtained after 10 h of enrichment within approximately 24 h. Even without enrichment, Salmonella could be detected from both pork chop and sausage at 106 CFU/25 g within 1 day. This robust rt-RT-PCR detects and confirms Salmonella in pork within approximately 24 h and thus is significantly faster than traditional methods that take ≥1 week. This assay shows promise for routine testing and monitoring of Salmonella by the pork industry.

Rapid detection of Salmonella in milk by combined immunomagnetic separation-polymerase chain reaction assay

During the past few years, milk has presented a risk of Salmonella contamination; it has been implicated as the cause in several outbreaks of salmonellosis. Because conventional detection methods require 5 to 7 d for completion and involve several subcultivation stages followed by biochemical and serological tests, rapid and sensitive methods have been sought, mainly at the DNA level. Therefore, a study including milk samples was conducted to evaluate the performance of a combination of 2 techniques--immunomagnetic separation and polymerase chain reaction (PCR)--for the detection of Salmonella. The 16-, 14-, 12-, 10-, and 8-h nonselective pre-enrichment steps before immunomagnetic separation and the high-pure DNA preparation method before PCR were used in a combined assay. Milk samples, which were found to be Salmonella-negative by a reference method, were first inoculated with Salmonella Enteritidis. Next, the shortest pre-enrichment time that is required for detection of 1 or 10 cfu of Salmonella/mL by combined immunomagnetic separation-PCR assay was found by using 16-, 14-, 12-, 10-, and 8-h incubation periods. The detection limit using a 16-, 14-, or 12-h nonselective pre-enrichment was 1 to 10 cfu/mL. However, the sensitivity decreased to 10(1) and 10(2) cfu/mL, respectively, when 10- and 8-h pre-enrichments were used. This assay, in conjunction with a 12-h pre-enrichment, proved to be rapid (overall 16 h) and sensitive (1-10 cfu/mL) for the detection of Salmonella in milk samples and promising for routine use in the detection of Salmonella in milk.

Selection, characterization, and application of DNA aptamers for the capture and detection of Salmonella enterica serovars

Sensitive and specific pre-analytical sample processing methods are needed to enhance our ability to detect and quantify food borne pathogens from complex food and environmental samples. In this study, DNA aptamers were selected and evaluated for the capture and detection of Salmonella enterica serovar. Typhimurium. A total of 66 candidate sequences were enriched against S. Typhimurium outer membrane proteins (OMPs) with counter-selection against Escherichia coli OMPs and lipopolysaccharides (LPS). Specificity of the selected aptamers was evaluated by gel-shift analysis against S. Typhimurium OMP. Five Salmonella-specific aptamer candidates were selected for further characterization. A dilution-to-extinction capture protocol using pure cultures of S. Typhimurium further narrowed the field to two candidates (aptamers 33 and 45) which showed low-end detection limits of 10-40CFU. DNase protection assays applied to these aptamers confirmed sequence-specific binding to S. Typhimurium OMP preparations, while South-Western blot analysis combined with mass spectrometry identified putative membrane proteins as targets for aptamer binding. Aptamer 33 was bound to magnetic beads and used for the capture of S. Typhimurium seeded into whole carcass chicken rinse samples, followed by detection using quantitative real-time RT-PCR. In a pull-down assay format, detection limits were 10(1)-10(2)CFU S. Typhimurium/9mL rinsate, while in a recirculation format, detection limits were 10(2)-10(3)CFU/25mL rinsate. Reproducible detection at <10(1)S. typhimurium CFU/g was also achieved in spike-and-recovery experiments using bovine feces. The pull-down analysis using aptamer 33 was validated on 3 naturally infected chicken litter samples confirming their applicability in the field. This study demonstrates the applicability of Salmonella specific aptamers for pre-analytical sample processing as applied to food and environmental sample matrices.

Immunomagnetic separation combined with real-time reverse transcriptase PCR assays for detection of norovirus in contaminated food

We developed an immunomagnetic separation (IMS) technique combined with real-time TaqMan reverse transcriptase PCR (RT-PCR), which allowed detection of norovirus at a level as low as 3 to 7 RT-PCR units from artificially contaminated strawberries. The inoculum recovery rate ranged from 14 to 30%. The data demonstrate that IMS combined with real-time RT-PCR will be useful as a rapid and sensitive method for detecting food-borne microbial contaminants.

Biosensors and bio-based methods for the separation and detection of foodborne pathogens

The safety of our food supply is always a major concern to consumers, food producers, and regulatory agencies. A safer food supply improves consumer confidence and brings economic stability. The safety of foods from farm-to-fork through the supply chain continuum must be established to protect consumers from debilitating, sometimes fatal episodes of pathogen outbreaks. The implementation of preventive strategies like hazard analysis critical control points (HACCP) assures safety but its full utility will not be realized unless supportive tools are fully developed. Rapid, sensitive, and accurate detection methods are such essential tools that, when integrated with HACCP, will improve safety of products. Traditional microbiological methods are powerful, error-proof, and dependable but these lengthy, cumbersome methods are often ineffective because they are not compatible with the speed at which the products are manufactured and the short shelf life of products. Automation in detection methods is highly desirable, but is not achievable with traditional methods. Therefore, biosensor-based tools offer the most promising solutions and address some of the modern-day needs for fast and sensitive detection of pathogens in real time or near real time. The application of several biosensor tools belonging to the categories of optical, electrochemical, and mass-based tools for detection of foodborne pathogens is reviewed in this chapter. Ironically, geometric growth in biosensor technology is fueled by the imminent threat of bioterrorism through food, water, and air and by the funding through various governmental agencies.

Rapid detection of Salmonella sp. in pork samples using fluorescent in situ hybridization: a comparison with VIDAS®-SLM system and ISO 6579 cultural method

This study reports the use of the fluorescent in situ hybridization (FISH) with Sal3 probe for Salmonella detection in swine carcasses inner surface (swab); and in the correspondent samples of ileum, ileocolic, and mandibular lymph nodes; and tonsils, after dilution (1:10) in buffered peptone water and a pre-enrichment step (37(0)C, 18h). In order to evaluate the efficiency of FISH, 235 naturally contaminated samples were simultaneously tested by the cultural method (ISO 6579) and by the Vitek Immuno Diagnostic Assay System (VIDAS®) - Salmonella (SLM) system. The cultural method identified 39 positive samples. From these, VIDAS®- SLM only detected 23. FISH identified 115 positive samples. This difference was highly significant (P<0.001). From positive samples, 32 were also confirmed by the cultural method. The results indicate FISH as a promising tool for rapid Salmonella detection in samples of pork and swine carcasses.

Evaluation of an immunomagnetic separation-real-time PCR assay for the rapid detection of Salmonella in meat

The aim of this study was the comparison of an immunomagnetic separation (IMS)-real-time PCR assay for the detection of Salmonella with the cultural reference method according to and 35 of the German Law on Food and Commodities (LMBG, L 00.00.20:1998). The IMS-real-time PCR assay includes a nonselective preenrichment step, an IMS, DNA extraction, as well as DNA purification followed by hybridization probe-based real-time PCR analysis. An accurate comparability was achieved, because both methods analyzed the same preenrichment. The evaluation was carried out using both artificially and naturally contaminated meat samples. The IMS-real-time PCR assay provides a result after 12 to 13 h. Compared with the reference method and regarding artificially contaminated meat samples, the IMS-real-time PCR assay achieved a specificity of 80% (false-positive rate of 20%) and a sensitivity of 100% (false-negative rate of 0%). The relative accuracy was 94%. The detection limit of both methods was 10 CFU/25 g. The concordance index kappa, which defines the statistical accordance, was 0.85 and indicated the agreement of both methods on statistical criteria. Compared to the reference method and analyzing naturally contaminated meat samples (n = 491), the IMS-real-time PCR assay showed a specificity of 99.3% (false-positive rate of 0.7%) and a sensitivity of 83.7% (false-negative rate of 16.3%). The relative accuracy was 98%. The concordance index kappa had a value of 0.87 and highlighted the statistical agreement of both methods. In conclusion, the IMS-real-time PCR assay is suitable as specific, sensitive, and rapid screening method for the detection of Salmonella from meat.

Preliminary evaluation of flow-through immunocapture followed by real-time PCR for the detection of Salmonella serovars on tomato surfaces within 8 hours

This study reports a preliminary evaluation of flow-through immunocapture (FTI) followed by real-time PCR (FTI-PCR) for the detection of Salmonella serovars on tomato surfaces within 8 h. The FTI-PCR method was compared with real-time PCR, direct plating of FTI beads on xylose lysine desoxycholate (XLD), and the conventional culture method for Salmonella found in the U.S. Food and Drug Administration's (FDA) Bacteriological Analytical Manual (BAM). Unwaxed green tomatoes were spot inoculated with a five-serovar Salmonella cocktail on smooth surfaces at levels of 10(0) to 10(4) CFU per tomato and washed in lactose broth (LB) using a shake-rub method. The resulting LB rinse was incubated at 37 degrees C for 4 h prior to analysis by FTI-XLD, real-time PCR, or FTI-PCR and for 24 h as the first step in the BAM Salmonella culture method. For FTI-XLD, the observed lowest detection level (LDL) was 4.6 x 10(1) CFU per tomato. There was no significant difference in performance between the FTI-XLD method and the BAM Salmonella culture method (P > 0.05); however, the FTI-XLD method reduced the overall assay time by 48 h. For real-time PCR and FTI-PCR, the observed LDLs were 4.6 x 10(1) and 9.2 x 10(0) CFU per tomato, respectively. The FTI-PCR method was superior to the BAM Salmonella culture method (P < 0.05) for the detection of Salmonella serovars on tomato surfaces and was completed within 8 h.

Combination of immunomagnetic separation with flow cytometry for detection of Listeria monocytogenes

Listeria monocytogenes can grow at the low temperature commonly used in the storage and transportation of food, and the number of cases of food poisoning caused by L. monocytogenes has increased recently in the US and Europe. Several methods of detecting L. monocytogenes cells have been proposed; however, all existing methods require approximately 48 h incubation. In this study, we attempted rapid detection of L. monocytogenes using flow cytometry (FCM). The method is based on measuring the number of L. monocytogenes cells by using a combination of FCM and immunomagnetic separation (IMS). First, polyclonal antibodies (anti-L. monocytogenes rabbit IgG-FITC) conjugated with fluorescein isothiocyanate (FITC) were reacted with L. monocytogenes cells, and then FCM was applied. The cell numbers were determined by FCM using a traditional colony-counting method in the range of 10(4)-10(8) cells ml(-1). Tetrameric antibody complexes (TAC) were used because they can recognize both magnetic and FITC molecules on the FITC-conjugated antibodies. FITC-labeled L. monocytogenes cells were reacted with a secondary antibody (TAC) bound to magnetic beads. Then, IMS was used. The method is suitable for detection in the range of 10(2)-10(8)cells ml(-1). The FCM assay enumerated the cells within 1 min and the total assay time, including sample preparation, was less than 2 h.

Cultural and Immunological Detection Methods for Salmonella spp. in Animal Feeds - A Review

Food-borne salmonellosis continues to be a major public health concern, and contamination with Salmonella spp. in pre-harvest animal production is considered a primary contributor to this problem. Animal feeds can easily become contaminated during primary production, feed mixing and processing as well as during feeding. Consequently, monitoring and surveillance of feeds and feed ingredients for Salmonella spp. contamination may be useful or necessary in the prevention and control of this organism. Cultural and immunological detection methods for salmonellae have been used or suggested as possible approaches for use in animal feeds. Cultural methods remain advantageous owing to their ability to detect viable bacterial cells, while immunological methods have the capability of detecting nonculturable bacterial cells. Advancements and improvements in both methodologies offer opportunities for eventual routine use of these detection technologies in animal feed assays.

Current and developing technologies for monitoring agents of bioterrorism and biowarfare

Recent events have made public health officials acutely aware of the importance of rapidly and accurately detecting acts of bioterrorism. Because bioterrorism is difficult to predict or prevent, reliable platforms to rapidly detect and identify biothreat agents are important to minimize the spread of these agents and to protect the public health. These platforms must not only be sensitive and specific, but must also be able to accurately detect a variety of pathogens, including modified or previously uncharacterized agents, directly from complex sample matrices. Various commercial tests utilizing biochemical, immunological, nucleic acid, and bioluminescence procedures are currently available to identify biological threat agents. Newer tests have also been developed to identify such agents using aptamers, biochips, evanescent wave biosensors, cantilevers, living cells, and other innovative technologies. This review describes these current and developing technologies and considers challenges to rapid, accurate detection of biothreat agents. Although there is no ideal platform, many of these technologies have proved invaluable for the detection and identification of biothreat agents.

Ferrite supports for isolation of DNA from complex samples and polymerase chain reaction amplification

The influence of cobalt ferrite particles, with non-modified or modified surface, on the course of polymerase chain reaction (PCR) was investigated. DNA isolated from bacterial cells of Bifidobacterium bifidum was used in PCR evaluation of magnetic microspheres. The presence of cobalt ferrite particles inhibits PCR amplification. The effect is not dependent on the functional groups of the modifying reagents used (none, amino, carboxyl). Amplification was improved after the magnetic separation of magnetic particles. Proposed indirect method enabled verification of the suitability of designed particles for their application in PCR assays. Magnetic particles coated with alginic acid under high PEG and sodium chloride concentration were used for the isolation of PCR-ready bacterial DNA from various dairy products. DNA was isolated from crude bacterial cell lysates without phenol extraction of samples. Bifidobacterium and Lactobacillus DNAs were identified in dairy products using PCR.

Combination of immunomagnetic separation with real-time PCR for rapid detection of Salmonella in milk, ground beef, and alfalfa sprouts

A rapid, specific, and sensitive method for detecting Salmonella spp. in pasteurized milk, ground beef, and alfalfa sprouts was developed. The method combined immunomagnetic separation with a real-time PCR assay based on the double-stranded DNA binding dye SYBR Green I. The primers used produced a product with a melting temperature of 87+/-0.5 degrees C during the PCR assay by amplifying a 284-bp sequence from the invasive gene (invA) of Salmonella. The method was successful in detecting 20 Salmonella strains, but the expected PCR product was not formed by any of 11 other bacterial strains. To test this combined method for the monitoring of Salmonella, Salmonella enterica serotype Newport was inoculated into 52 samples each of pasteurized milk, ground beef, and alfalfa sprouts. Following a 10-h nonselective enrichment step in buffered peptone water, cells were removed by immunomagnetic separation and DNA extracted using the High Pure PCR template preparation kit. The DNA produced was used as a template in the real-time PCR assay. When spiked pasteurized milk, ground beef, and alfalfa sprout samples were analyzed by this protocol, an initial inoculum of 1 CFU/ml, 25 CFU/25 g, and 1.5 CFU/25 g, respectively, was detectable within 13 h. These results indicate that the combination of immunomagnetic separation and real-time PCR assay was a highly specific and sensitive method for the rapid detection of Salmonella.

Application of a molecular beacon—real-time PCR technology to detect Salmonella species contaminating fruits and vegetables

An oligonucleotide probe that becomes fluorescent upon hybridization to the target DNA (molecular beacon; MB) was evaluated in a real-time polymerase chain reaction (PCR) assay to detect the presence of Salmonella species. As few as 1-4 colony-forming units (CFU) per PCR reaction could be detected. The capability of the assay to detect Salmonella species from artificially inoculated fresh-cut produce such as cantaloupe, mixed-salad, cilantro, and alfalfa sprouts was demonstrated. A comparison of two commercially available kits utilizing MB-PCR (iQ-Check, Bio-Rad Laboratories) and conventional Association of Official Analytical Chemists (AOAC)-approved PCR (BAX, Dupont Qualicon) was performed on artificially inoculated produce. As few as 4 CFU/25 g of produce were detected after 16 h of enrichment in buffered peptone broth. These assays could be carried out entirely in sealed PCR tubes, enabling a rapid and high-throughput detection of Salmonella species in a large number of food and environmental samples. This is the first report of the application of MB probe being used for real-time detection of Salmonella species in whole and fresh-cut fruits and vegetables.

Magnetic hydrophilic methacrylate-based polymer microspheres designed for polymerase chain reactions applications

Magnetic hydrophilic non-porous P(HEMA-co-EDMA), P(HEMA-co-GMA) and PGMA microspheres were prepared by dispersion (co)polymerization of 2-hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (EDMA) or glycidyl methacrylate (GMA) in the presence of several kinds of magnetite. It was found that some components used in the preparation of magnetic carriers interfered with polymerase chain reaction (PCR). Influence of non-magnetic and magnetic microspheres, including magnetite nanoparticles and various components used in their synthesis, on the PCR course was thus investigated. DNA isolated from bacterial cells of Bifidobacterium longum was used in PCR evaluation of non-interfering magnetic microspheres. The method enabled verification of the incorporation of magnetite nanoparticles in the particular methacrylate-based polymer microspheres and evaluation of suitability of their application in PCR. Preferably, electrostatically stabilized colloidal magnetite (ferrofluid) should be used in the design of new magnetic methacrylate-based microspheres by dispersion polymerization.

Rapid, specific detection of Salmonella Enteritidis in pooled eggs by real-time PCR

An assay was developed for the specific detection of Salmonella Enteritidis in eggs with the use of an application of the fluorogenic 5' nuclease assay (TaqMan). In this assay, a segment of the gene sefA specific to Salmonella group D strains such as Salmonella Enteritidis was used. The amplification of the target gene products was monitored in real-time by incorporating a fluorescent dye-labeled gene-specific probe in the PCR reaction. This method correctly detected and distinguished Salmonella Enteritidis from nearly 50 of non-group D Salmonella and other non-Salmonella strains. Detection of the sefA gene was linear for DNA extracted from approximately 10(2) to 10(9) CFU/ml in phosphate-buffered saline and 10(3) to 10(8) CFU/ml in raw egg. In two trials, when applied to detection of Salmonella Enteritidis in homogenized egg pools and compared with conventional culture methods, the newly developed PCR method yielded a 100% correlation with results obtained by a conventional culture method. However, the PCR method required only 2 days, compared to the 5 days required by the culture method. The sensitivity of this assay was approximately less than 1 CFU/600 g of egg pool. The real-time PCR assay proved to be a rapid, highly sensitive test for detection and quantification of low concentrations of Salmonella Enteritidis in egg samples.

Immunomagnetic separation and detection of Salmonella cells using newly designed carriers

Magnetic nonporous poly(HEMA-co-EDMA) and poly(HEMA-co-GMA) microspheres were prepared by dispersion copolymerisation of 2-hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (EDMA) or glycidyl methacrylate (GMA) in the presence of magnetite. They were functionalized by polyclonal Salmonella antibodies via the trichlorotriazine method. Salmonella cells were then successfully identified using cultural and polymerase chain reaction (PCR) methods after their immunomagnetic separation. The PCR sensitivity of target cell detection was negatively influenced by the presence of some compounds used in the process of particle preparation. In some cases, magnetic poly(HEMA-co-EDMA) microspheres with immobilized proteinase K were used for degradation of intracellular inhibitors present in Salmonella cells.