A comparison of enrichment and direct-plating methods for isolation of <i>Listeria monocytogenes</i> from surface water
Bibliographic record
Abstract
Listeria monocytogenes is a facultative intracellular pathogen distributed in the environment. Reference isolation methods include an enrichment step. We compared 2 protocols: one based on enrichment and the other on direct plating, with respect to the efficiency of isolation of L. monocytogenes from surface water samples. From March to May 2006, 126 surface water samples were collected biweekly from 24 discrete sampling sites located in the South Nation River basin (Ontario). Presumptive Listeria spp. were isolated using the 2 methods, and L. monocytogenes isolates were confirmed based on colony morphology and amplification of 3 pathogenicity genes: iap, inlA, and hlyA. Listeria monocytogenes was detected in 31 water samples using the enrichment approach and in 27 using the direct-plating approach, with only 13 samples positive using both approaches. No correlation was observed between the ability of the enrichment procedure to fail in the detection of the pathogenic bacterium and the abundance of several indicator bacteria. The proportion of samples carrying isolates from serovar groups 1/2a, 3a; 1/2b, 3b, 7; 4b, 4d, 4e; and Listeria spp. was significantly different between the 2 approaches. This data indicate that a direct-plating approach would be suitable for the detection of L. monocytogenes in water samples, but that enrichment and direct-plating protocols both have specific biases.
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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 | 0.003 | 0.005 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| 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".