RapidChek SELECT Salmonella enteritidis test system for the detection of Salmonella enteritidis in poultry house drag swabs, shell egg pools, and chicken carcass rinsates

The RapidChek SELECT Salmonella Enteritidis Test System was validated for the detection of Salmonella Enteritidis (SE) in poultry house drag swabs, shell egg pools, and chicken carcass rinsates. The method utilizes RapidChek SELECT Salmonella (AOAC PTM License No. 080601) proprietary primary and secondary enrichment media. Following enrichment, an immunochromatographic test strip is inserted into the tube containing the secondary enrichment broth, developed for 10 min, and interpreted. Salmonella Enteritidis-inoculated samples (1-5 CFU SE/analytical unit) were tested by the test method as well as the appropriate cultural reference method U.S. Food and Drug Administration-Bacteriological Analytical Manual (drag swabs and egg pools) or U.S. Department of Agriculture-Food Safety and Inspection Service (chicken carcass rinsates). A total of 80 samples were tested by both methods in the study. Fifty-two samples were positive by the RapidChek SELECT Salmonella Enteritidis method and 38 were found positive by the respective reference method. The sensitivity of the method was 100% and the specificity was 100%. The accuracy of the test method was 137%, indicating that the method was more sensitive than the reference method. The RapidChek SELECT Salmonella Enteritidis method was tested with 82 Salmonella Group D1 strains including 63 Salmonella Enteritidis strains as well as 32 non-Salmonella Group D1 strains representing 10 bacteria genera. The test method detected all 82 Group D1 strains (100% sensitivity). None of the non-Salmonella Group D1 or other genera of bacteria were detected, indicating a specificity of 100%. The method was shown to be highly robust and stable under control and accelerated stability conditions.     

Reveal Salmonella 2.0 test for detection of Salmonella spp. in foods and environmental samples. Performance Tested Method 960801

Reveal Salmonella 2.0 is an improved version of the original Reveal Salmonella lateral flow immunoassay and is applicable to the detection of Salmonella enterica serogroups A-E in a variety of food and environmental samples. A Performance Tested Method validation study was conducted to compare performance of the Reveal 2.0 method with that of the U.S. Department of Agriculture-Food Safety and Inspection Service or U.S. Food and Drug Administration/Bacteriological Analytical Manual reference culture methods for detection of Salmonella spp. in chicken carcass rinse, raw ground turkey, raw ground beef, hot dogs, raw shrimp, a ready-to-eat meal product, dry pet food, ice cream, spinach, cantaloupe, peanut butter, stainless steel surface, and sprout irrigation water. In a total of 17 trials performed internally and four trials performed in an independent laboratory, there were no statistically significant differences in performance of the Reveal 2.0 and reference culture procedures as determined by Chi-square analysis, with the exception of one trial with stainless steel surface and one trial with sprout irrigation water where there were significantly more positive results by the Reveal 2.0 method. Considering all data generated in testing food samples using enrichment procedures specifically designed for the Reveal method, overall sensitivity of the Reveal method relative to the reference culture methods was 99%. In testing environmental samples, sensitivity of the Reveal method relative to the reference culture method was 164%. For select foods, use of the Reveal test in conjunction with reference method enrichment resulted in overall sensitivity of 92%. There were no unconfirmed positive results on uninoculated control samples in any trials for specificity of 100%. In inclusivity testing, 102 different Salmonella serovars belonging to serogroups A-E were tested and 99 were consistently positive in the Reveal test. In exclusivity testing of 33 strains of non-salmonellae representing 14 genera, 32 were negative when tested with Reveal following nonselective enrichment, and the remaining strain was found to be substantially inhibited by the enrichment media used with the Reveal method. Results of ruggedness testing showed that the Reveal test produces accurate results even with substantial deviation in sample volume or device development time.     

Reveal Listeria 2.0 test for detection of Listeria spp. in foods and environmental samples

A Performance Tested Method validation study was conducted for a new lateral flow immunoassay (Reveal Listeria 2.0) for detection of Listeria spp. in foods and environmental samples. Results of inclusivity testing showed that the test detects all species of Listeria, with the exception of L. grayi. In exclusivity testing conducted under nonselective growth conditions, all non-listeriae tested produced negative Reveal assay results, except for three strains of Lactobacillus spp. However, these lactobacilli are inhibited by the selective Listeria Enrichment Single Step broth enrichment medium used with the Reveal method. Six foods were tested in parallel by the Reveal method and the U.S. Food and Drug Administration/Bacteriological Analytical Manual (FDA/BAM) reference culture procedure. Considering data from both internal and independent laboratory trials, overall sensitivity of the Reveal method relative to that of the FDA/BAM procedure was 101%. Four foods were tested in parallel by the Reveal method and the U.S. Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) reference culture procedure. Overall sensitivity of the Reveal method relative to that of the USDA-FSIS procedure was 98.2%. There were no statistically significant differences in the number of positives obtained by the Reveal and reference culture procedures in any food trials. In testing of swab or sponge samples from four types of environmental surfaces, sensitivity of Reveal relative to that of the USDA-FSIS reference culture procedure was 127%. For two surface types, differences in the number of positives obtained by the Reveal and reference methods were statistically significant, with more positives by the Reveal method in both cases. Specificity of the Reveal assay was 100%, as there were no unconfirmed positive results obtained in any phase of the testing. Results of ruggedness experiments showed that the Reveal assay is tolerant of modest deviations in test sample volume and device incubation time.     

Reveal E. coli 2.0 method for detection of Escherichia coli O157:H7 in raw beef

Reveal E. coli 2.0 is a new lateral-flow immunodiagnostic test for detection of E. coli O157:H7 and O157:NM in raw beef trim and ground beef. Compared with the original Reveal E. coli O157:H7 assay, the new test utilizes a unique antibody combination resulting in improved test specificity. The device architecture and test procedure have also been modified, and a single enrichment protocol was developed which allows the test to be performed at any point during an enrichment period of 12 to 20 h. Results of inclusivity and exclusivity testing showed that the test is specific for E. coli serotypes O157:H7 and O157:NM, with the exception of two strains of O157:H38 and one strain of O157:H43 which produced positive reactions. In internal and independent laboratory trials comparing the Reveal 2.0 method to the U.S. Department of Agriculture-Food Safety and Inspection Service reference culture procedure for detection of E. coli O157:H7 in 65 and 375 g raw beef trim and ground beef samples, there were no statistically significant differences in method performance with the exception of a single internal trial with 375 g ground beef samples in which the Reveal method produced significantly more positive results. There were no unconfirmed positive results by the Reveal assay, for specificity of 100%. Results of ruggedness testing showed that the Reveal test produces accurate results even with substantial deviation in sample volume or device incubation time or temperature. However, addition of the promoter reagent to the test sample prior to introducing the test device is essential to proper test performance.     

Precollaborative study of the GeneQuence Salmonella assay using 24-hour enrichment protocols for detection of Salmonella spp. in select foods

New enrichment protocols are described for use with a DNA hybridization (DNAH) method for detection of Salmonella spp. in select foods. GeneQuence Salmonella, in its original version, utilized a 3-stage enrichment of minimum 42 h duration. New 2-stage procedures of 24-28 h duration are described for raw poultry, raw beef, pasteurized egg products, milk chocolate, and dry pet food. In the validation study described here, a total of 345 samples were tested by the abbreviated DNAH method in parallel with either the U.S. Food and Drug Administration's Bacteriological Analytical Manual (FDA/BAM) or U.S. Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) reference culture procedures. Results showed an overall sensitivity for the DNAH method of 97.1% (false-negative rate 2.9%). There were no false-positive results by the DNAH method; therefore the specificity was 100%. Overall agreement between the DNAH and reference culture methods was 98.5%. There were no significant differences in performance between the DNAH and reference methods for any of the foods tested as determined by Chi-square analysis. It is recommended that the DNAH method be subjected to AOAC collaborative study.     

SDIX RapidChek Listeria F.A.S.T. environmental test system for the detection of Listeria species on environmental surfaces

The SDIX RapidChek Listeria F.A.S.T. test system was validated against the U.S. Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) cultural reference method for the detection of Listeria species on stainless steel, plastic, rubber, and painted concrete. The SDIX method uses a proprietary RapidChek Listeria enrichment media for a one-step, 24-40 h enrichment at 30 degrees C, and detects Listeria on an immunochromatographic lateral flow device in 10 min. Different Listeria species were used to spike each of the environmental surfaces. Environmental surfaces were spiked at levels ranging from 50 to 400 CFU/surface (1 in.2 swabs for painted concrete, 4 in.(2) for sponge). A total of 120 spiked samples were tested by the SDIX method at 24 and 40 h and the cultural reference method. Total confirmed positives were 49, 54, and 48 for the SDIX 24 h method, the SDIX 40 h method, and the USDA-FSIS cultural reference method, respectively. Nonspiked samples from all environmental surfaces were reported as negative for Listeria spp. by all methods. The overall Chi square was 0.017 (P = 0.104) and 0.611 (P= 0.566) after a 24 and 40 h enrichment, respectively, indicating that the test method was equivalent in performance to the reference method at both enrichment times. The SDIX method was evaluated for the detection of 50 Listeria and 35 non-Listeria bacterial strains. All 50 Listeria strains were detected by the method (100% sensitivity). Five out of 35 non-Listeria species gave light test signals when grown in nonselective broth culture and tested undiluted. However, when grown in the RapidChek Listeria F.A.S.T. proprietary media, only one bacterial strain (Staphylococcus aureus) was detected, giving a very low test signal (97% specificity). The method was shown to be robust toward several alterations in testing and storage conditions.     

Clonal structure and variation in virulence of Salmonella enteritidis isolated from mice, chickens, and humans

The clonal analysis of a diverse collection of Salmonella Enteritidis indicates that most strains belong to a single multilocus genotype (i.e., ET-3) regardless of phage type, geographic origin, or time of isolation that spanned over 2 decades (1978 to 2004). Attachment and invasion assays, however, indicate that, among ET-3 isolates, there is a distinct invasive bacterial subpopulation that is more readily recovered from eggs and clinical cases in humans than from chicken cecal samples. These observations support the hypothesis that the specialized ability of S. Enteritidis to infect the avian reproductive tract and contaminate eggs has been critical in its emergence as a frequent cause of human illness.     

Salmonella in foods: new enrichment procedure for TECRA Salmonella Visual Immunoassay using a single rv(R10) only, TT only, or dual rv(R10) and TT selective enrichment broths (AOAC official method 998.09): collaborative study

A collaborative study was conducted to compare a new enrichment procedure for the TECRA Salmonella Visual Immunoassay (TSVIA) with the reference method given in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (7th Ed.). Three food types (milk powder, pepper, and soy flour) were analyzed in Australia and 3 food types (milk chocolate, dried egg, and raw turkey) were analyzed in the United States. Thirty-eight collaborators participated in the study. The TECRA method was evaluated using both Rappaport-Vassiliadis R10 (RV(R10)) and tetrathionate (TT) broths for selective enrichment. M broth cultures arising from each of the 2 selective enrichment broths were tested in the TSVIA using 2 individual wells, one for each selective broth, and a single well to test the pooled selective enrichment broths. The results for the pooled enrichment broths were reported elsewhere. This study presents the results for the use of single enrichment broths, i.e., RV(R10) only or TT only, with the TSVIA. No significant differences (p > 0.05) were observed for the pairwise comparison of the proportion of positive samples for either RV(R10) or TT used as a single enrichment broth for the TSVIA with that for the reference method.     

Multicenter validation of PCR-based method for detection of Salmonella in chicken and pig samples

As part of a standardization project, an interlaboratory trial including 15 laboratories from 13 European countries was conducted to evaluate the performance of a noproprietary polymerase chain reaction (PCR)-based method for the detection of Salmonella on artificially contaminated chicken rinse and pig swab samples. The 3 levels were 1-10, 10-100, and 100-1000 colony-forming units (CFU)/100 mL. Sample preparations, including inoculation and pre-enrichment in buffered peptone water (BPW), were performed centrally in a German laboratory; the pre-PCR sample preparation (by a resin-based method) and PCR assay (gel electrophoresis detection) were performed by the receiving laboratories. Aliquots of BPW enrichment cultures were sent to the participants, who analyzed them using a thermal lysis procedure followed by a validated Salmonella-specific PCR assay. The results were reported as negative or positive. Outlier results caused, for example, by gross departures from the experimental protocol, were omitted from the analysis. For both the chicken rinse and the pig swab samples, the diagnostic sensitivity was 100%, with 100% accordance (repeatability) and concordance (reproducibility). The diagnostic specificity was 80.1% (with 85.7% accordance and 67.5% concordance) for chicken rinse, and 91.7% (with 100% accordance and 83.3% concordance) for pig swab. Thus, the interlaboratory variation due to personnel, reagents, thermal cyclers, etc., did not affect the performance of the method, which will be proposed as part of a developing international PCR standard.     

Detection of Salmonella in meat: comparative and interlaboratory validation of a noncomplex and cost-effective pre-PCR protocol

Cost-effective and rapid monitoring of Salmonella in the meat production chain can contribute to food safety. The objective of this study was to validate an easy-to-use pre-PCR sample preparation method based on a simple boiling protocol for screening of Salmonella in meat and carcass swab samples using a real-time PCR method. The protocol included incubation in buffered peptone water, centrifugation of an aliquot, and a boiling procedure. The validation study included comparative and interlaboratory trials recommended by the Nordic Organization for Validation of Alternative Microbiological Methods (NordVal). The comparative trial was performed against a reference method (NMKL 187, 2007) and a PCR method previously approved by NordVal with a semiautomated magnetic bead-based DNA extraction step using 122 artificially contaminated samples. The LOD was found to be 3.0, 3.2, and 3.4 CFU/sample for the boiling, magnetic bead-based, and NMKL 187 methods, respectively. When comparing the boiling method with the magnetic beads, the relative accuracy (AC), relative sensitivity (SE), and relative specificity (SP) were 98, 102, and 98%, respectively (Cohen's kappa index 0.95). When comparing results obtained by the boiling to the culture-based method, the AC, SE, and SP were found to be 98, 102, and 98%, respectively (kappa index 0.93). In the interlaboratory trial including valid results from 11 laboratories, apart from two false-positive samples by the boiling method combined with PCR, no deviating results were obtained (SP, SE, and AC were 100, 95, and 97%, respectively). This test is under implementation by the Danish meat industry, and can be useful for screening of large number of samples in the meat production, especially for fast release of minced meat with a short shelf life.     

Evaluation of the GeneQuence DNA hybridization method in conjunction with 24-hour enrichment protocols for detection of Salmonella spp. in select foods: collaborative study

A multilaboratory study was conducted to compare performance of the GeneQuence DNA hybridization (DNAH) method incorporating new 24 h enrichment protocols and reference culture procedures for detection of Salmonella spp. in select foods. Six food types (raw ground turkey, raw ground beef, dried whole egg, milk chocolate, walnuts, and dry pet food) were tested by the DNAH method and by the culture methods of either the U.S. Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) or the U.S. Food and Drug Administration's Bacteriological Analytical Manual (FDA/BAM). Fifteen laboratories participated in the study. Four of the foods tested (raw ground turkey, dried whole egg, milk chocolate, and dry pet food), showed no statistically significant differences in performance between the DNAH method and the reference procedure as determined by Chi square analysis. Sensitivity rates for the DNAH method ranged from 92 to 100%. The DNAH method, with the specific enrichment protocol evaluated, was found to be ineffective for detection of Salmonella spp. in walnuts. For raw ground beef, results from one trial showed a statistically significant difference in performance, with more positives obtained by the reference method. However, evidence suggests that the difference in the number of positives was likely due to lack of homogeneity of the test samples rather than to DNAH method performance.     

Comparison of the Reveal 20-hour method and the BAM culture method for the detection of Escherichia coli O157:H7 in selected foods and environmental swabs: collaborative study.

Four different food types along with environmental swabs were analyzed by the Reveal for E. coli O157:H7 test (Reveal) and the Bacteriological Analytical Manual (BAM) culture method for the presence of Escherichia coli O157:H7. Twenty-seven laboratories representing academia and private industry in the United States and Canada participated. Sample types were inoculated with E. coli O157:H7 at 2 different levels. Of the 1,095 samples and controls analyzed and confirmed, 459 were positive and 557 were negative by both methods. No statistical differences (p <0.05) were observed between the Reveal and BAM methods.     

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.     

Evaluation of VIDAS Salmonella (SLM) easy Salmonella method for the detection of Salmonella in a variety of foods: collaborative study

The VIDAS Salmonella (SLM) Easy Salmonella method is a specific enzyme-linked fluorescent immunoassay performed in the automated VIDAS instrument. The VIDAS Easy Salmonella method is a simple 2-step enrichment procedure, using pre-enrichment followed by selective enrichment in a newly formulated broth, SX2 broth. This new method was compared in a multilaboratory collaborative study to the U.S. Food and Drug Administration's Bacteriological Analytical Manual, Chapter 5 method for five food matrixes (liquid egg, vanilla ice cream, spinach, raw shrimp, and peanut butter) and the U.S. Department of Agriculture's Microbiology Laboratory Guidebook 4.04 method for deli turkey. Each food type was artificially contaminated with Salmonella at three inoculation levels. A total of 15 laboratories representing government, academia, and industry, throughout the United States, participated. In this study, 1583 samples were analyzed, of which 792 were paired replicates and 791 were unpaired replicates. Of the 792 paired replicates, 285 were positive by both the VIDAS and reference methods. Of the 791 unpaired replicates, 341 were positive by the VIDAS method and 325 were positive by the cultural reference method. A Chi-square analysis of each of the six food types was performed at the three inoculation levels tested. For all foods evaluated, the VIDAS Easy SLM method demonstrated results comparable to those of the reference methods for the detection of Salmonella.     

Salmonella in foods--a new enrichment procedure for use with the TECRA Salmonella visual immunoassay: collaborative study.

A collaborative study was conducted to compare a new enrichment procedure for the TECRA Salmonella Visual Immunoassay with the reference method given in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM 7th Ed.). Three food types (milk powder, black pepper, and soy flour) were analyzed in Australia, and 3 food types (milk chocolate, dried egg, and raw turkey) were analyzed in the United States. Thirty-eight collaborators participated in the study. No significant differences (p > 0.05) were observed for the pairwise comparison of the proportion of positive samples for the TECRA method with that for the reference method. The new enrichment procedure for the TECRA method has been adopted First Action by AOAC INTERNATIONAL.     

Reveal for Salmonella test system.

The Reveal for Salmonella (RSS) test system is a presumptive qualitative test that detects the presence of Salmonella organisms in foods within 21 h total testing time, allowing the user to release negative products 24 h earlier than when using other rapid test kits. Foods are enriched with a proprietary resuscitation medium called Revive and then selectively enriched with either Selenite Cystine or Rappaport-Vassiliadis selective media. The enriched culture is used to inoculate the RSS detection device, which initiates a lateral flow through a reagent zone containing anti-Salmonella antibodies conjugated to colloidal gold particles that capture antigens present in the culture. The antigen-antibody complex migrates farther and is captured by an additional anti-Salmonella antibody, causing the colloidal gold to precipitate and form a visual line, indicating a positive result. A procedural control line also will form regardless of the presence of Salmonella organisms to indicate the test is working properly. Existing AOAC Official Methods for Salmonella organisms require a 48 h enrichment before testing. Hence, a food product has to be held before release, adding extra cost to the company and the consumer. The RSS test system was evaluated by quantitative spiking studies. Although AOAC encourages inclusion of naturally contaminated foods, almost all microbiological AOAC validation studies have been performed with artificially contaminated foods for absolute control over the study. The RSS test system is designed to test many food types for Salmonella organisms and has a limit of detection of 5-10 colony-forming units (cfu)/25 g with a false-negative rate of < 1% and a false-positive rate of < 5.0%. It showed an 81% overall agreement with the traditional procedure of the U.S. Department of Agriculture's Food Safety Inspection Service.     

Simultaneous Determination of Cadmium,Mercury, Lead,Arsenic, Copper,and Zinc in Human Breast Milk by ICP‐MS/Microwave Digestion

Abstract

An analytical method using microwave digestion and inductively coupled argon plasma-mass spectrometry (ICP‐MS) analysis was developed for the measurement of Cd, Hg, Pb, As, Cu, and Zn in human breast milk. We applied external calibration, internal calibration, and standard addition for reference material and pooled milk analysis. Method performances were defined in terms of detection limits, accuracy, and precision. Accuracy varied between 93% and 105% and precision between 3% and 8%. External calibration and background interferences were checked through a calibrator addition procedure. Our method has shown high accuracy, precision, and sensitivity, as well as linearity within a wide range of values. Our methodology, developed by treatment of reference material and pooled milk samples, was applied for determination of Cu, Zn, As, Cd, Hg, and Pb in 120 human breast milk samples.     

Validation of a microwell DNA probe assay for detection of Listeria spp. in foods Performance-tested method 010403

A new DNA hybridization assay in microwell format for detection of Listeria spp. in foods and environmental samples was developed. This assay uses Listeria-specific oligonucleotide probes labeled with horseradish peroxidase and a photometrically determined end point. Validation studies with 15 different food commodities and a variety of environmental sample types were conducted to compare the performance of this alternative test versus reference methods. Meats, seafood, dairy products, and vegetables comprised the categories of food tested. Food samples were inoculated at 2 levels and refrigerated or frozen for at least 72 h. Uninoculated (negative) control samples were included in each trial. Samples were enriched according to the procedure recommended by either the U.S. Food and Drug Administration (FDA) or the U.S. Department of Agriculture (USDA), Food Safety and Inspection Service (FSIS). Samples enriched for 24 h were transferred to Oxford agar plates and incubated for 24 h. The surface of the plates was then swabbed and any growth present was transferred to phosphate buffer solution for the performance of the DNA assay. A standard confirmation procedure was used to compare the number of positive samples obtained with the DNA method versus reference methods. Statistical analyses of the results indicate that the proposed alternative method performs equally to cultural reference methods. The DNA assay is able to detect as low as 1 colony-forming unit of Listeria in a 25 g food sample, with results available as early as 48 h after the start of sample enrichment.     

Optimized procedure for the determination of antimony in lipid-rich environmental matrices by flow injection hydride generation atomic absorption spectrometry

An analytical procedure for the reliable determination of Sb in digests of lipid-rich environmental matrices in the low ng l-1-range based on flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) has been developed. Prior to HG-AAS, aliquots (250 to 320 mg) of dry samples were mineralized with 3 ml nitric acid and 0.5 ml of each sulfuric and perchloric acids in open digestion vessels made of glassy carbon in a heating block. Procedure detection and quantification limits of a previously developed procedure for the determination of Sb in plant materials by FI-HG-AAS were decreased with respect to the lower Sb concentrations in animal tissues, the sensitivity of the instrumental response was increased, and the composition of the acid digestion mixture was re-optimized for lipid-rich samples. The accuracy and precision of the developed procedure was evaluated by the analysis of the two reference materials Bovine Liver 1577a and Pig Kidney CRM 186. These reference materials have been additionally spiked with appropriate amounts of Sb to obtain recovery data. The solution detection limit (3 sigma) in digested samples was 0.021 microgram l-1, the detection limit for the whole procedure based on the dry powders was 7 pg g-1, the method quantification limit for a reliable determination of Sb was 23 pg g-1. The reproducibility of repetitive measurements was 6.0% at 0.1 microgram Sb l-1 and 2.2% at 0.5 microgram Sb l-1. Calibration curves were linear from 0.05 to 3 micrograms Sb l-1. To demonstrate the suitability of the developed method, concentrations of Sb have been determined in pigeon eggs (approximately 2 ng Sb g-1), as well as in bream livers (approximately 4 ng g-1) and in deer livers (approximately 5 to 8 ng g-1) from animals living in remote and urban-industrialized areas of Germany, respectively.     

Development of a filtration-based SERS mapping platform for specific screening of Salmonella enterica serovar Enteritidis

The presence of Salmonella in natural freshwater and drinking water is a leading cause of intestinal illness all over the world; thus, the detection of Salmonella in water is of great importance to public health. The objective of this study is to develop a rapid screening method for the detection of Salmonella enterica serovar Enteritidis in water involving surface-enhanced Raman spectroscopy (SERS), aptamers, and filtration. SERS offers a great alternative to traditional methods of pathogen detection, with a simplified detection assay and shortened detection time. The specific capturing and labeling of Salmonella Enteritidis are realized by a specific single-stranded DNA aptamer, which is modified with an additional chain of adenine and fluorescein (FAM) and used as presence/absence indicator of Salmonella Enteritidis. By incorporating a vacuum filtration system, bacterial cells recognized by the specific aptamer are concentrated onto a membrane. With additional filtration of gold nanoparticles, the aptamer signals were captured and used to construct a SERS mapping indicating the presence and absence of target bacterial strains with potential quantitative capability. The specificity of the method was validated by using other strains of bacteria such as Escherichia coli and Listeria monocytogenes. The sensitivity of the method goes down to 10³ CFU/mL for 1 mL of sample with a total detection and analyzing time within 3 h. This study demonstrates the capability of the filtration-based SERS platform for detecting Salmonella Enteritidis in various aqueous matrices such as distilled water and rinsing water from fresh produce with high selectivity and sensitivity.

Graphical abstract