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Effects of in vitro growth phase on the pathogenesis of Salmonella typhimurium in mice
Abstract:
The growth phase of a bacterial (Salmonella typhimurium) culture was shown to have pronounced effects on the pathogenic properties of the harvested bacteria. Salmonellae obtained from a culture in primary (exponential) growth phase (PP) were more readily cleared from the blood and more readily killed by phagocytes than were salmonellae obtained from a more slowly growing secondary growth phase (SP) culture. PP salmonellae were observed to cause death of mice sooner than SP salmonellae. This appeared to be because the more rapid growth of PP, as compared to SP, salmonellae continued in the liver and spleen for several hours following intravenous injection, and more than compensated for their high in vivo death rate. As a result, within 4 h there were approximately 10-fold more live salmonellae in the spleens and livers of mice that had received PP, as compared to SP, salmonellae. This 10-fold difference was maintained until the death of the mice, indicating that after the first 4 h post-inoculation, the net in vivo growth of the salmonellae was the same regardless of their growth phase in the inoculating culture. This transition between PP and SP salmonellae occurred long before a dense stationary phase culture was obtained. Salmonellae grown in minimal media exhibited the biological properties of SP salmonellae and never entered as rapid a growth phase as did salmonellae in complete media.
Insights
Bacterial growth phase significantly impacts Salmonella typhimurium virulence. Primary phase bacteria are cleared faster but cause quicker death in mice due to rapid initial multiplication in organs. Secondary phase bacteria show slower growth but are more resistant to immune clearance.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Immunology
Background:
- Bacterial culture conditions can influence virulence.
- Understanding Salmonella typhimurium growth dynamics is crucial for infection control.
Purpose of the Study:
- To investigate the impact of bacterial growth phase on Salmonella typhimurium pathogenicity.
- To compare the in vivo behavior of bacteria from primary (PP) and secondary (SP) growth phases.
Main Methods:
- Culturing Salmonella typhimurium in different growth phases (PP and SP).
- Inoculating mice intravenously with PP and SP Salmonella typhimurium.
- Monitoring bacterial clearance, phagocytosis, survival rates, and organ colonization in mice.
Main Results:
- PP Salmonella typhimurium were cleared more rapidly by phagocytes but caused faster mortality in mice.
- PP bacteria exhibited rapid initial multiplication in liver and spleen, compensating for higher death rates.
- A 10-fold difference in bacterial load was observed within 4 hours and maintained until death.
- Minimal media-grown Salmonella exhibited SP characteristics.
Conclusions:
- Bacterial growth phase is a critical determinant of Salmonella typhimurium virulence.
- The rapid in vivo proliferation of PP bacteria outweighs their increased susceptibility to host defenses in the early stages of infection.
- Bacterial culture media composition influences growth rate and subsequent pathogenicity.