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Appearance of mouse-lethal toxin in liquid cultures of Bordetella pertussis
Abstract:
The mouse-lethal toxin present in liquid cultures of most smooth strains of Bordetella pertussis is known to originate in the cytoplasm of the organism but to be most lethal for mice when released into the supernatant fluid. It is also recognized that cell degeneration and lysis occur in liquid cultures during the stationary and decline phases of growth. For these reasons, it is generally believed that most of the toxicity demonstrable in liquid cultures at the time of harvest is released during the later stages of cultivation, when high alkalinity and aging of cells favor lysis. However, the results reported here have indicated that high levels of mouse-lethal toxicity arise during very early log phase and that the peak of toxicity is reached before the end of the log phase. No further increase in toxicity was observed during stationary and decline phases. The very early appearance of toxicity could not be explained by the presence in the inoculum of a proportion of dead and degenerating cells, and it is concluded that the toxin is produced mainly by actively growing cells. This was confirmed by tests on organisms growing in continuous culture. Electron-microscopic examination of cells from a very early log-phase culture revealed the presence of large numbers of small vesicles on the cell walls of about 5% of the population. It is suggested that these vesicles may be associated with the releases of toxin from living cells. It is concluded that no useful reduction in the toxicity of cultures would result from harvesting before the end of the log phase of growth.
Insights
Toxicity from Bordetella pertussis arises early in bacterial growth, peaking before the log phase ends. Harvesting cultures later does not increase mouse-lethal toxin levels.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Toxinology
Background:
- Bordetella pertussis mouse-lethal toxin is typically found in the cytoplasm but exerts maximum toxicity when extracellular.
- Bacterial lysis and cell degeneration in liquid cultures are associated with toxin release during later growth phases.
Purpose of the Study:
- To investigate the temporal production and release of mouse-lethal toxin during Bordetella pertussis cultivation.
- To determine the optimal harvest time for bacterial cultures to manage toxin levels.
Main Methods:
- Cultivation of Bordetella pertussis under varying conditions, including continuous culture.
- Assessing mouse-lethal toxicity at different growth phases (log, stationary, decline).
- Electron microscopy to examine bacterial cell morphology.
Main Results:
- High levels of mouse-lethal toxicity were detected during the early log phase of growth.
- Toxicity peaked before the end of the log phase, with no significant increase in later stages.
- Electron microscopy revealed vesicles on bacterial cell walls in early log-phase cultures, potentially linked to toxin release.
Conclusions:
- Bordetella pertussis toxin is primarily produced by actively growing cells, not solely during lysis.
- Harvesting cultures before the end of the log phase does not reduce overall toxicity.
- Vesicle formation on cell walls may indicate a mechanism for toxin release from living bacteria.