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.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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 teacher head, 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".