Published in:
01-04-2008 | Brief Report
The presence of infectious extracellular Francisella tularensis subsp. novicida in murine plasma after pulmonary challenge
Authors:
J.-J. Yu, E. K. Raulie, A. K. Murthy, M. N. Guentzel, K. E. Klose, B. P. Arulanandam
Published in:
European Journal of Clinical Microbiology & Infectious Diseases
|
Issue 4/2008
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Excerpt
Francisella tularensis is a gram-negative, facultative intracellular bacterium and is the causative agent of the zoonotic disease tularemia [
1].
F. tularensis has been considered a potential biological weapon due to its low infectious dose and high mortality rate [
2].
F. tularensis can be classified into several subspecies, including those relevant to human disease:
F. tularensis subsp.
tularensis (type A) and
F. tularensis subsp.
holarctica (type B);
F. novicida and
F. mediasiatica [
3]. However, most of our knowledge about the pathogenesis of
Francisella and the immune responses to the infection have come from studies of
F. tularensis LVS (derived from
holartica) and
F. novicida [
4‐
6]. Both organisms are attenuated in humans, while retaining virulence in mice. It is well established that
Francisella enters and replicates within host cells, and a strong research focus has been on deciphering the mechanisms for intramacrophage growth. However, little is known about the extracellular phase of
Francisella.
F. tularensis has been cultured from blood of infected animals and humans, although the reported cases have been rare [
7,
8]. Specifically, Long et al. [
8] demonstrated that LVS could be recovered from plasma prepared from mice 72 h after intravenous infection. These extracellular bacteria accounted for less than 1% of total LVS within the blood. However, a recent study by Forestal et al. [
9] indicated a much higher percentage (>50%) of extracelluar
Francisella (type A SCHU S4 and LVS) within plasma of mice infected intradermally or intranasally. Here, independently, we confirm the presence of extracellular
Francisella in plasma after intranasal
F. novicida challenge in a murine model of pulmonary tularemia [
6]. Moreover, we demonstrate that the extracellular
Francisella in plasma is highly infectious and that this phase may contribute to the rapid dissemination of the bacterium from lungs to the liver after pulmonary infection. …
