Evaluation of rapid «Salmonella» immunoassays and characterization of bacterial isolates that cause false-negative and false-positive in the tests
Bibliographic record
Abstract
Salmonella spp. is a widely distributed Gram-negative foodborne pathogen that is a major cause of foodborne outbreaks in North America. The Public Health Agency of Canada (PHAC) estimates that approximately 88,000 Canadians are affected by foodborne Salmonellosis annually. In recent years, contaminated fresh produce has emerged as an important source of salmonellosis. Standardized culture methods for Salmonella spp. are considered as the "gold standard" in food diagnostics and are still in use today; however, they are laborious, time-consuming and must be confirmed by secondary biochemical tests. Immunoassays are the most commonly used rapid methods for the detection of Salmonella in food, and presumptive results are available within 8 to 24 hours. However, a common issue observed using immunoassays to test fresh produce for the presence of Salmonella, is a high percentage of false-positive test results due to the misidentification of closely related, non-Salmonella bacteria such as Citrobacter spp., Hafnia spp. and Proteus spp. In addition, there is also the chance of false-negative test results, due to high variation in surface antigens of Salmonella enterica. In this study, two commercially available immunoassays, the VIDAS UP Salmonella Phage Technology (SPT) Assay (BioMérieux, Saint-Laurent, Quebec, Canada, Inc.) and an antibody-based lateral-flow test, the Reveal 2.0 Salmonella Assay (Neogen Corporation, Lansing, Michigan, United States) were evaluated for their accuracy in detecting Salmonella. VIDAS UP Salmonella (SPT) assay correctly identified 52/54 (96.3%) of the Salmonella isolates that were tested. The Reveal 2.0 Salmonella Assay identified 43/54 (79.63%) of the Salmonella isolates correctly. However, both assays failed to identify one isolate each of Salmonella enterica serovars Hull and Duesseldorf. Several VIDAS UP Salmonella (SPT) enrichment samples were obtained from a fresh produce grower. These enrichments had previously tested presumptive positive for Salmonella, however, confirmatory tests did not indicate the presence of Salmonella. The enrichments were analyzed in order to obtain pure isolates of bacteria from the enrichment mixture that were responsible for the false positive test results. Three bacterial isolates that caused false-positive VIDAS UP Salmonella (SPT) reactions were isolated and subjected to whole genome sequencing and bioinformatic analysis. Blast analysis of the three false-positive isolates identified Citrobacter amalonaticus as the likeliest organism. The two isolates (one each) of S. Hull and S. Duesseldorf that produced false-negative results were analyzed in order to identify surface exposed components that are used as diagnostic targets in Salmonella immunoassays. Analysis of S. Duesseldorf showed that the flagella genes fljB and fliC differed significantly from other Salmonella isolates that tested positive, and the three C.amalonaticus isolates that caused false-positive test results. Analysis of the S. Hull genome identified a gene encoding a putative repression of phase I flagellin, which was located on a cryptic incomplete prophage. Both of these observations are likely responses for the lack of complete flagella on the surface of the S. Duesseldorf and S. Hull isolates, which may be responsible for the false-negative test results. The results of this work have identified the potential basis for false-positive and false-negative test results in rapid Salmonella immunoassays. The development of more selective immunoassays based on more specific monoclonal antibodies, identification of new antigens that are more specific to Salmonella and development of more selective enrichment media will lead to improved fresh produce testing and enhanced food safety in Canada.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.006 | 0.007 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".