Evaluation of VIDAS Listeria species Xpress (LSX) immunoassay method for the detection of Listeria species in foods: collaborative study

In a multilaboratory study, the effectiveness of an alternative method for rapid screening of Listeria species compared to traditional reference methods was demonstrated in a variety of food products. A collaborative study was conducted to compare the VIDAS Listeria species Xpress (LSX) method and the standard cultural methods for the detection of Listeria species in foods. Six food types were tested: vanilla ice cream, cheddar cheese, raw ground beef, frozen green beans, deli turkey, and cooked shrimp. Each food, inoculated with a different Listeria strain at two levels and uninoculated test portions, was analyzed by each method. A total of 15 laboratories representing government and industry participated. In this study 1134 tests were analyzed in the statistical analysis. There were 490 positives by the VIDAS LSX method using the sample boiling step, 483 positives by the VIDAS LSX method using the Heat and Go system, and 439 positives by the standard culture methods. Overall, the Chi-square result for the VIDAS LSX method with boiling for all foods was 7.25, indicating a significant statistical difference between the VIDAS method and the standard methods at the 5% confidence. For the VIDAS LSX method with the Heat and Go system, the Chi-square result for all foods was 5.37, indicating a significant statistical difference between the VIDAS LSX assay with the Heat and Go system and the standard methods at the 5% level of significance. In both cases, the VIDAS method was more sensitive than the standard methods. The LSX method detects Listeria species in foods with negative or presumptive positive results in a minimum of 30 h compared to at least 5 days for the cultural methods. Based on the results of this collaborative study, it is recommended that the VIDAS LSX method be adopted as an AOAC Official Method for the detection of Listeria species in dairy products, vegetables, seafood, raw meats and poultry, and processed meats and poultry.     

Evaluation of the VIDAS staph enterotoxin II (SET 2) immunoassay method for the detection of staphylococcal enterotoxins in selected foods: collaborative study

A multilaboratory study was conducted to determine the limit of detection (LOD) of Staphylococcal enterotoxins (SET) in 5 foods. Cooked chicken, ham, potato salad, pasteurized liquid whole milk, and canned mushrooms were each spiked with a different enterotoxin (A, B, C1, D, or E), and tested at 0.25 and 0.5 ng/g SET levels to determine the LOD of the assay for those foods in a collaborative study. Unspiked controls were also included. A total of 19 laboratories representing government and industry participated. In this study, 1674 test portions were analyzed, of which 1638 were used in the statistical analysis. Of the 1638 test portions used in the statistical analysis, 1104 were spiked test portions, of which 1073 were positive by the VIDAS Staph enterotoxin II (SET 2) method. The detection rates at the 0.25 ng/mL level were cooked chicken, 98.2%; ham, 99.0%; potato salad, 99.1%; liquid whole milk, 85.2%; and canned mushrooms, 100%. The detection rates at the 0.5 ng/mL level were cooked chicken, 97.4%; ham, 98.1%; potato salad, 100%; liquid whole milk, 99.0%; and canned mushrooms, 100%. The data indicate that the SET 2 method is capable of detecting SET at 0.25 ng/g in cooked chicken, ham, potato salad, and canned mushrooms and at 0.5 ng/g in pasteurized liquid whole milk.     

VIDAS enzyme-linked immunoflourescent assay for detection of Listeria in foods: collaborative study

The VIDAS LIS method and the traditional culture methods for detection of Listeria species in food were evaluated in a multilaboratory comparative study. The 6 foods tested were either naturally contaminated or inoculated with 3 different concentrations of Listeria. Results for each food and each contamination level with the VIDAS LIS method were as good as or better than those obtained with the traditional culture method. Of 1558 samples tested, 935 were positive: 839 by the VIDAS method and 809 by standard culture methods. Overall false negative rates were 10.3 and 13.5% for the VIDAS LIS and culture methods, respectively. The false positive rate for the VIDAS LIS assay was 1.4% based on 9 VIDAS LIS positive assays that did not confirm positive by isolation of Listeria. The agreement between the VIDAS LIS and culture methods for all samples tested was 86%.     

Evaluation of VIDAS Salmonella (SLM) immunoassay method with Rappaport-Vassiliadis (RV) medium for detection of Salmonella in foods: collaborative study

A collaborative study was conducted to compare the VIDAS Salmonella (SLM) with Rappaport-Vassiliadis (RV) method for detection of Salmonella in foods to the current standard method presented in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) and the culture method presented in AOAC's Official Methods of Analysis. The VIDAS SLM with RV method uses tetrathionate broth in combination with RV medium in place of selenite cystine broth for selective enrichment, thereby eliminating the hazardous waste issue for laboratories. Twenty five laboratories participated in the evaluation, each testing one or more of 8 test products: nonfat dry milk, dried egg, soy flour, lactic casein, milk chocolate, raw ground pork, raw ground turkey, and raw peeled shrimp. Results of the study showed no significant differences in the numbers of confirmed positive samples with the VIDAS SLM with RV procedure and the BAM/AOAC culture procedure. The VIDAS SLM with RV method was effective for rapid detection of Salmonella in foods. It is recommended that AOAC INTERNATIONAL modify the VIDAS Salmonella SLM procedure to include the RV method.     

Evaluation of VIDAS Immuno-Concentration Salmonella (ICS)/VIDAS Salmonella (SLM) immunoassay method for detection of Salmonella in selected foods (Method Modification 2001.09): collaborative study

A new method for detection of Salmonella in foods in a minimum of 24 h was adopted as an AOAC Official First Action Method for selected foods (2001.09) using both the VIDAS Immuno-Concentration Salmonella (ICS) and VIDAS Salmonella (SLM) methods.     

Evaluation of the BAX system for detection of Listeria monocytogenes in foods: collaborative study

A multilaboratory study was conducted to compare the automated BAX system and the standard cultural methods for detection of Listeria monocytogenes in foods. Six food types (frankfurters, soft cheese, smoked salmon, raw, ground beef, fresh radishes, and frozen peas) were analyzed by each method. For each food type, 3 inoculation levels were tested: high (average of 2 CFU/g), low (average of 0.2 CFU/g) and uninoculated controls. A total of 25 laboratories representing government and industry participated. Of the 2335 samples analyzed, 1109 were positive by the BAX system and 1115 were positive by the standard method. A Chi square analysis of each of the 6 food types, at the 3 inoculation levels tested, was performed. For all foods, except radishes, the BAX system performed as well as or better than the standard reference methods based on the Chi square results.     

Evaluation of VIDas immuno-concentration Salmonella/VIDAS salmonella immunoassay method for detection of Salmonella in selected foods: collaborative study

The VIDAS Immuno-concentration Salmonella ICS)/VIDAS Salmonella (SLM) immunoassay method for the detection of Salmonella was compared to the Bacteriological Analytical Manual (BAM)/AOAC culture method in a collaborative study. Thirty-two laboratories participated in the evaluation. Each laboratory tested one or more of the 6 test products: milk chocolate, nonfat dry milk, dried whole egg, soy flour, ground black pepper, and ground raw turkey. The 2 methods were in agreement for 1,266 of the 1,440 samples. Of the 174 samples not in agreement, 69 were VIDAS CS/SLM-positive and BAM/AOAC-negative and 105 were VIDAS ICS/SLM-negative and BAM/AOAC-positive.     

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.     

Evaluation of the VIDAS Listeria (LIS) immunoassay for the detection of Listeria in foods using demi-Fraser and Fraser enrichment broths, as modification of AOAC Official Method 999.06 (AOAC Official Method 2004.06)

A multilaboratory study was conducted to compare the VIDAS LIS immunoassay with the standard cultural methods for the detection of Listeria in foods using an enrichment modification of AOAC Official Method 999.06. The modified enrichment protocol was implemented to harmonize the VIDAS LIS assay with the VIDAS LMO2 assay. Five food types--brie cheese, vanilla ice cream, frozen green beans, frozen raw tilapia fish, and cooked roast beef--at 3 inoculation levels, were analyzed by each method. A total of 15 laboratories representing government and industry participated. In this study, 1206 test portions were tested, of which 1170 were used in the statistical analysis. There were 433 positive by the VIDAS LIS assay and 396 positive by the standard culture methods. A Chi-square analysis of each of the 5 food types, at the 3 inoculation levels tested, was performed. The resulting average Chi square analysis, 0.42, indicated that, overall, there are no statistical differences between the VIDAS LIS assay and the standard methods at the 5% level of significance.     

Evaluation of VIDAS Immuno-Concentration Salmonella (ICS) plus selective plate method (Hektoen enteric, bismuth sulfite, Salmonella identification) for detection of Salmonella in selected foods (Method Modification 2001.07): collaborative study

A new method for detection of Salmonella in foods in 48 h has been granted AOAC First Action approval in selected foods (Official Method 2001.07) using both the VIDAS Immuno-Concentration Salmonella (ICS) method and a combination of 3 selective plates: Hektoen enteric (HE), bismuth sulfite (BS), and Salmonella Identification (SMID).     

Evaluation of VIDAS Immuno-Concentration Salmonella (ICS) plus selective plate method (Hektoen enteric, bismuth sulfite, xylose lysine desoxycholate) for detection of Salmonella in selected foods (Method Modification 2001.08): collaborative study

A new method for detection of Salmonella in foods in 48 h has been granted AOAC First Action approval in selected foods (Official Method 2001.08) using both the VIDAS Immuno-Concentration Salmonella (ICS) method and a combination of 3 selective plates: Hektoen enteric (HE), bismuth sulfite (BS), and xylose lysine desoxycholate (XLD).     

Evaluation of the BAX system for detection of Salmonella in selected foods: collaborative study

A multilaboratory study was conducted to compare the automated BAX System to the standard cultural methods for detection of Salmonella in selected foods. Five food types--frankfurters, raw ground beef, mozzarella cheese, raw frozen tilapia fish, and orange juice--at 3 inoculation levels, were analyzed by each method. A sixth food type, raw ground chicken, was tested using 3 naturally contaminated lots. A total of 16 laboratories representing government and industry participated. In this study, 1386 samples were analyzed, of which 1188 were paired samples and 198 were unpaired samples. Of the 1188 paired samples, 461 were positive by both methods and 404 were negative by both methods. Thirty-seven samples were positive by the BAX System but negative by the standard reference method, and 11 samples were positive by standard cultural method and negative by the BAX System. Of the 198 unpaired samples, 106 were positive by the BAX System and 60 were positive by the standard cultural method. A Chi square analysis of each of the 6 food types, at the 3 inoculation levels tested, was performed. For all foods, the BAX System demonstrated results comparable to those of the standard reference methods based on the Chi square results.     

Method extension study to validate applicability of AOAC Official Method 996.14 Assurance polyclonal enzyme immunoassay for detection of Listeria monocytogenes and related Listeria spp. from environmental surfaces: collaborative study

Test portions from 3 environmental surface types, representative of typical surfaces found in a food production facility, were analyzed by the Assurance Listeria Polyclonal Enzyme Immunoassay (EIA) and the U.S. Department of Agriculture/Food Safety and Inspection Service (USDA/FSIS) culture method for Listeria monocytogenes and related Listeria species. In all cases, naturally contaminated environmental test samples were collected from an actual food production facility by sponge or swab. Test samples from concrete surfaces were collected by both swab and sponge; sponge test samples were collected from rubber surfaces, and swabs were used to sample steel surfaces. Test portions from each surface type were simultaneously analyzed by both methods. A total of 23 collaborators, representing government agencies, as well as private industry in both the United States and Canada, participated in the study. During this study, a total of 550 test portions and controls was analyzed and confirmed, of which 207 were positive and 336 were negative by both methods. Six test portions were positive by culture, but negative by the EIA. Three test portions were negative by culture, but positive by the EIA. Two test portions were negative by EIA and by culture, but confirmed positive when EIA enrichment broths were subcultured to selective agars. The data reported here indicate that the Assurance Listeria EIA method and the USDA/FSIS culture method are statistically equivalent for detection of L. monocytogenes and related Listeria species from environmental surfaces taken by sponges or swabs.     

Salmonella in selected foods by VIDAS immuno-concentration Salmonella plus selective plate method (Hektoen enteric,xylose lysine desoxycholate,bismuth sulfite): collaborative study

The VIDAS Immuno-concentration Salmonella (ICS) plus selective plate method (Hektoen enteric, xylose lysine desoxycholate, bismuth sulfite) method for the detection of Salmonella was compared to the Bacteriological Analytical Manual (BAM)/AOAC culture method in a collaborative study. Thirty-two laboratories participated in the evaluation. Each laboratory tested one or more of the 6 test products: milk chocolate, nonfat dry milk, dried whole egg, soy flour, ground black pepper, and ground raw turkey. The 2 methods were in agreement for 1,297 of the 1,455 samples. Of the 158 samples not in agreement, 82 were VIDAS ICS plus selective plate-positive and BAM/AOAC-negative, and 76 were VIDAS ICS plus selective plate-negative and BAM/AOAC-positive.     

Evaluation of a chromogenic medium for identification and differentiation of Listeria monocytogenes in selected foods

Listeria monocytogenes continues to be a threat to food safety in the United States despite a "zero tolerance" policy. When Listeria species are identified by standard cultural methods, confirmation of L. monocytogenes takes days to complete. RAPID'L.Mono agar, developed by Bio-Rad Laboratories, is a chromogenic medium that differentiates L. monocytogenes from other species of Listeria by a simple color change reaction. Differentiation is based on the specific detection of phosphatidylinositol phospholipase C activity, resulting in a blue colony, and the inability of L. monocytogenes to metabolize xylose, resulting in the absence of a yellow halo. Detection principles of standard method agars, Oxford and PALCAM, are based on the ability of all species of Listeria to hydrolyze esculin. Thus, all species of Listeria have similar colony morphology on these agars, making differentiation of pathogenic L. monocytogenes from other nonhuman pathogens difficult. RAPID'L.Mono agar has been validated with surimi, mixed salad, brie, and processed deli turkey because of the prevalence of L. monocytogenes in these foods. Sensitivity and specificity for this medium was determined to be 99.4 and 100%, respectively. Overall method agreement of RAPID'L.Mono with standard culture methods (U.S. Department of Agriculture/Food Safety and Inspection Service; U.S. Food and Drug Administration/Bacteriological Analytical Manual; and AOAC INTERNATIONAL) was excellent, with enrichment protocols 24 h shorter than those of standard methods.     

Evaluation of VIDAs Immuno-concentration Salmonella assay Plus selective plate method (Hektoen enteric,bismuth sulfite,Salmonella identification) for detection of Salmonella in selected foods: collaborative study

The VIDAS Immuno-concentration Salmonella (ICS) plus selective plate method (Hektoen enteric, bismuth sulfite, Salmonella identification) method for the detection of Salmonella was compared to the Bacteriological Analytical Manual (BAM)/AOAC culture method in a collaborative study. Thirty-two laboratories participated in the evaluation. Each laboratory tested one or more of the 6 test products: milk chocolate, nonfat dry milk, dried whole egg, soy flour, ground black pepper, and ground raw turkey. The 2 methods were in agreement for 1,283 of the 1,440 test samples. Of the 157 test samples not in agreement, 82 were VIDAS ICS plus selective plate-positive and BAM/AOAC-negative, and 75 were VIDAS ICS plus selective plate-negative and BAM/AOAC-positive.     

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.     

Equivalence of Visual Immunoprecipitate Assay (VIP) for Salmonella for the detection of motile and nonmotile Salmonella in all foods to AOAC culture method: collaborative study

Six foods representative of a wide variety of processed, dried powder processed, and raw food types were analyzed by the Visual Immunoprecipitate Assay (VIP) for Salmonella and AOAC INTERNATIONAL culture method. Paired samples of each food type were simultaneously analyzed; one sample by the VIP method and one by the AOAC culture method. A total of 24 laboratories representing federal government agencies and private industry, in the United States and Canada, participated in this collaborative study. Food types were inoculated with species of Salmonella with the exception of raw ground chicken, which was naturally contaminated. No statistical differences (p < 0.05) were observed between VIP for Salmonella interpretation and the AOAC culture method for any inoculation level of any food type or naturally contaminated food. The method was adopted Official First Action status by AOAC INTERNATIONAL.     

Method extension study to validate applicability of AOAC Official Method 997.03 visual immunoprecipitate assay (VIP) for Listeria monocytogenes and related Listeria spp. from environmental surfaces: collaborative study

Test portions from 3 environmental surface types, representative of typical surfaces found in a food production facility, were analyzed by the Visual Immunoprecipitate assay (VIP) and the U.S. Department of Agriculture/Food Safety and Inspection Service (USDA/FSIS) culture method for Listeria monocytogenes and related Listeria species. In all cases, naturally contaminated environmental test samples were collected from an actual food production facility by sponge or swab. Test samples from concrete surfaces were collected by both swab and sponge; sponge test samples were collected from rubber surfaces, and swabs were used to sample steel surfaces. Test portions from each surface type were simultaneously analyzed by both methods. A total of 27 laboratories, representing government agencies as well as private industry in both the United States and Canada, participated in the study. During this study, a total of 615 test portions and controls was analyzed and confirmed, of which 227 were positive and 378 were negative by both methods. Nine test portions were positive by culture, but negative by the VIP. Five test portions were negative by culture, but positive by the VIP. Four test portions were negative by VIP and by culture, but confirmed positive when VIP enrichment broths were subcultured to selective agars. The data reported here indicate that the VIP method and the USDA/FSIS culture method are statistically equivalent for detection of L. monocytogenes and related Listeria species from environmental surfaces taken by sponges or swabs.     

Modification of enrichment protocols for TECRA Listeria Visual Immunoassay method 995.22: collaborative study

A collaborative study was conducted to validate new enrichment methods for the TECRA Listeria Visual Immunoassay (TLVIA). These new methods incorporate a newly formulated medium, TECRA Listeria Enrichrment Broth, which does not contain the highly toxic antifungal agent, cycloheximide. The new procedures will provide an alternative to the enrichment procedures described in AOAC Method 995.22. Three food types (raw ground beef, lettuce, and ice cream) were analyzed in the United States, and 2 food types (cooked turkey and cooked fish fillets) were analyzed in Australasia. Thirty collaborators participated in the study, 16 in Australasia and 14 in the United States. With the exception of one batch of ground beef, comparison of the proportion of positive test portions (p > or = 0.05) showed no significant difference between the TLVIA and the reference method for the 5 foods at 3 inoculation levels. For the one batch of naturally contaminated raw ground beef, the TLVIA gave significantly more confirmed positive results than the reference method.