Rapid and spontaneous loss of phthiocerol dimycocerosate (PDIM) from Mycobacterium tuberculosis grown in vitro: implications for virulence studies
Bibliographic record
Abstract
Isolated in vitro more than half a century ago, the H37Rv strain of Mycobacterium tuberculosis still remains the strain of choice for the majority of laboratories conducting in vivo studies of TB pathogenesis. In this report we reveal that H37Rv is highly prone to losing the ability to synthesize the cell wall lipid phthiocerol dimycocerosate (PDIM) during extended periods of in vitro culture. In addition, H37Rv stocks that have been held in vitro for even a short length of time should be thought of as a heterogeneous population of PDIM-positive and PDIM-negative cell types. We demonstrate that after weekly subculture of PDIM-positive isolates over a period of 20 weeks, the proportion of PDIM-negative cells rises above 30 %. That PDIM biosynthesis is negatively selected in vitro is evident from the broad range of mutation types we observe within cultures originating from a single PDIM-positive parental clone. Moreover, the appearance of these multiple mutation types coupled with an enhanced growth rate of PDIM-negative bacteria ensures that 'PDIM-less' clones rapidly dominate in vitro cultures. It has been known for almost a decade that strains of M. tuberculosis that lack PDIM are severely attenuated during in vivo infection. Therefore, the loss of PDIM raises a very serious issue in regard to the interpretation of putative virulence factors where heterogeneous parental cultures are potentially being compared in vivo to recombinant clones isolated within a PDIM-negative background. It is essential that researchers undertaking in vivo virulence studies confirm the presence of PDIM within all recombinant clones and the parental strains they are derived from.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 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".