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Updated: Jul 14, 2026
Intratracheal Inoculation of Fischer 344 Rats with Francisella tularensis
Published on: September 30, 2017
Francisella tularensis has a significant extracellular phase in infected mice
Colin A Forestal1, Meenakshi Malik, Sally V Catlett
1Center for Infectious Diseases, Stony Brook University, Stony Brook, NY 11794, USA.
Abstract:
The ability of Francisella tularensis to replicate in macrophages has led many investigators to assume that it resides primarily intracellularly in the blood of mammalian hosts. We have found this supposition to be untrue. In almost all cases, the majority of F. tularensis recovered from the blood of infected mice was in plasma rather than leukocytes. This distribution was observed irrespective of size of inoculum, route of inoculation, time after inoculation, or virulence of the infecting strain. Our findings yield new insight into the pathogenesis of tularemia and may have important ramifications in the search for anti-Francisella therapies.
Insights
Francisella tularensis, the bacterium causing tularemia, is primarily found in plasma, not inside cells, in the blood of infected mammals. This challenges the long-held belief about its intracellular location and impacts treatment strategies.
Area of Science:
- Microbiology
- Immunology
- Pathogenesis
Background:
- Francisella tularensis is known to replicate within host macrophages.
- This intracellular replication has led to the assumption that F. tularensis resides primarily within leukocytes in the bloodstream.
Purpose of the Study:
- To investigate the in vivo distribution of Francisella tularensis in the blood of infected mammalian hosts.
- To determine whether F. tularensis is predominantly intracellular (within leukocytes) or extracellular (in plasma).
Main Methods:
- Infected mice were analyzed for the location of F. tularensis in blood.
- Quantification of F. tularensis in plasma versus leukocytes was performed.
Main Results:
- The majority of recovered F. tularensis was found in plasma, not leukocytes.
- This extracellular distribution was consistent across different inoculum sizes, routes, time points, and bacterial strains.
Conclusions:
- The common assumption of Francisella tularensis residing intracellularly in blood is incorrect.
- Findings suggest an extracellular role in the bloodstream, offering new insights into tularemia pathogenesis and anti-Francisella therapy development.
