Freeze-thaw effect on selected fecal indicator bacteria : Escherichia coli and Enterococcus faecalis / by Nicole A. Hawdon.
Bibliographic record
Abstract
The survival of two selected fecal indicator organisms, two strains of Escherichia coli, a Gram-negative bacterium, and two strains of Enterococcus faecalis, a Gram-positive bacterium, after freezing and thawing successively for five cycles was determined using a drop plating method. It was found that all bacterial strains, when an initial concentration of 1.0 x E +08 was used, showed significant decreases in their ability to be cultured (p < 0.05) when frozen and thawed at -15C, compared to three other freezing temperatures, -7, -30 and -80C, when all four were frozen for 24 hours. In addition, the number of culturable cells at -7, -30, or -80C were not significantly different from each other (p > 0.05). The differences in cell inactivation between the two strains of each species of bacteria tested at all temperatures was not significantly different after five freeze-thaw cycles; while the difference between species was shown to be significant, depending on the temperature and condition tested (p < 0.05). When comparing small sample volume sizes (100l) to larger sample volume sizes (100ml) the observed differences were that Escherichia coli strains showed a decrease in cell culturability at both -7C and -15C when cycled in the larger volume; whereas, Enterococcus faecalis strains showed a decrease in cell culturability at -7C and an increase in cell culturability at -15C when cycled at the larger volume. \nAdditional studies investigating culturability, cell wall integrity, and membrane damage of the bacterial strains were conducted using 100ml samples, cycled at -7, -15, and -30?C, and evaluated by three microbiological methods: drop plating, epi-fluorescent microscopy, and flow cytometry, respectively. In all instances, the plate counting method \nindicated that there was a decrease in cells that were culturable. Results from flow cytometry indicated a smaller decrease in cell culturability, followed, lastly, by results using the epi-fluorescent microscope. Thus, these studies would suggest that the most damage that occurs to frozen and thawed cells, when cycled five times at -7,-15 or -30?C, would be due to damages occurring at the cellular level, rather than damages occurring \non the cell envelope, since less cells were able to uptake nutrients from the culture plates.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
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".